Effect of long-term drought stress on leaf gas exchange and fluorescence parameters in C<Subscript>3</Subscript> and C<Subscript>4</Subscript> plants

A field study was performed on triticale, field bean, maize and amaranth, to find differences between studied species in physiological alterations resulting from progressive response as injuries and/or acclimation to long-term soil drought during various stages of plant development. The measurements of leaf water potential, electrolyte leakage, chlorophyll a fluorescence, leaf gas exchange and yield analysis were done. A special emphasis was given to the measurements of the blue, green, red and far-red fluorescence. Beside, different ratios of the four fluorescence bands (red/far-red: F ₆₉₀/F ₇₄₀, blue/red: F ₄₄₀/F ₆₉₀, blue/far-red: F ₄₄₀/F ₇₄₀ and blue/green: F ₄₄₀/F ₅₂₀) were calculated. Based on both yield analysis and measurements of physiological processes it can be suggested that field bean and maize responded with better tolerance to the water deficit in soil due to the activation of photoprotective mechanism probably connected with synthesis of the phenolic compounds, which can play a role of photoprotectors in different stages of plant development. The photosynthetic apparatus of those two species scattered the excess of excitation energy more effectively, partially through its transfer to PS I. In this way, plants avoided irreversible and/or deep injuries to PS II. The observed changes in the red fluorescence emission and in the F _v/F _m for triticale and amaranth could have occurred due to serious and irreversible photoinhibitory injuries. Probably, field bean and maize acclimatized more effectively to soil drought through the development of effective mechanisms for utilising excitation energy in the photosynthetic conversion of light accompanied by the mechanism protecting the photosynthetic apparatus against the excess of this energy.     

Interspecific differences in root architecture among maize and triticale genotypes grown under drought,waterlogging and soil compaction

Environmental stresses (soil compaction, drought, waterlogging) cause changes in plants’ root system structure, also affecting the growth of above-ground parts. The aim of this study was to estimate phenotypic variation among maize and triticale genotypes in root penetration ability through petrolatum-wax-layer (RPA). Also, the effect of shortage or excess of soil water on dry matter of shoots and roots and morphological changes in root system structure in sensitive and resistant maize and triticale genotypes grown in low or high soil compaction level was evaluated. To estimate RPA index, the petrolatum-wax-layer method (PWL) was used. The strength of three petrolatum-wax concentrations 60, 50 and 40 % was 0.52, 1.07 and 1.58 MPa, respectively. High coefficients of variation (CV) were observed in 0.52 and 1.07 MPa and for maize were 19.2 and 21.7 %, and for triticale, 12.5 and 18.3 %, respectively. The data indicate that the use of PWL technique is an effective screening method, and makes it possible to divide the genotypes into resistant and sensitive groups. The second part of this study investigated a multistress effect of soil compaction combined with drought or waterlogging on root and shoot growth and morphological changes in root system structure of maize and triticale genotypes differing in susceptibility to environmental stresses. Seedlings were grown for 4 weeks in root-boxes under conditions of low (LSC 1.1 g cm^?3) or severe (SSC 1.6 g cm^?3) soil compaction. Drought or waterlogging stresses were applied for 2 weeks from 14th to 28th day. In comparison to LSC treatment, in SSC treatment the decrease in dry matter of shoots and roots was greater for sensitive genotypes of maize and triticale (Ancora, CHD-147). Soil drought or waterlogging caused greater decrease of dry matter of shoots and roots in seedlings grown in SSC in comparison to LSC. The root penetration index (RPI) was estimated as a ratio of root dry matter in 15–40 cm root-box layer to total root dry matter. On the basis of RPI it was possible to group the genotypes according to their ability to distribute roots in soil profile. In comparison to LSC, SSC exerted a strong influence on the length of seminal and seminal adventitious roots, as well as the number and length of L- and S-type lateral roots developed on seminal and nodal roots. In both species the restriction effect of soil compaction on number and length of roots was more severe in sensitive (Ankora, CHD-147) than in resistant (Tina, CHD-247) genotypes. The restriction in roots propagation was greater in triticale than in maize. Exposure to drought or waterlogging in the case of genotypes grown in LSC and SSC treatments caused a decrease in number and length of particular components of root system structure. In both species the decrease of root number and length in plants grown under waterlogging was greater than under drought. The observed changes in root system were greater in sensitive (Ankora, CHD147) than in resistant (Tina, CHD-247) genotypes. Statistically significant correlations were found between RPA and RPI and also between these indexes and soil compaction, drought and waterlogging susceptibility indexes. This indicates that genotypes resistant to soil compaction were resistant to drought or waterlogging and also that genotypes resistant to drought were resistant to waterlogging.     

Multicolour Fluorescence Imaging of Sugar Beet Leaves with Different Nitrogen Status by Flash Lamp UV-Excitation

Fluorescence images of leaves of sugar beet plants (Beta vulgaris L. cv. Patricia) grown on an experimental field with different fertilisation doses of nitrogen [0, 3, 6, 9, 12, 15 g(N) m^–2] were taken, applying a new multicolour flash-lamp fluorescence imaging system (FL-FIS). Fluorescence was excited by the UV-range (280–400 nm, _max = 340 nm) of a pulsed Xenon lamp. The images were acquired successively in the four fluorescence bands of leaves near 440, 520, 690, and 740 nm (F₄₄₀, F₅₂₀, F₆₉₀, F₇₄₀) by means of a CCD-camera. Parallel measurements were performed to characterise the physiological state of the leaves (nitrogen content, invert-sugars, chlorophylls and carotenoids as well as chlorophyll fluorescence induction kinetics and beet yield). The fluorescence images indicated a differential local patchiness across the leaf blade for the four fluorescence bands. The blue (F₄₄₀) and green fluorescence (F₅₂₀) were high in the leaf veins, whereas the red (F₆₉₀) and far-red (F₇₄₀) chlorophyll (Chl) fluorescences were more pronounced in the intercostal leaf areas. Sugar beet plants with high N supply could be distinguished from beet plants with low N supply by lower values of F₄₄₀/F₆₉₀ and F₄₄₀/F₇₄₀. Both the blue-green fluorescence and the Chl fluorescence rose at a higher N application. This increase was more pronounced for the Chl fluorescence than for the blue-green one. The results demonstrate that fluorescence ratio imaging of leaves can be applied for a non-destructive monitoring of differences in nitrogen supply. The FL-FIS is a valuable diagnostic tool for screening site-specific differences in N-availability which is required for precision farming.     

Changes of leaf water potential and gas exchange during and after drought in triticale and maize genotypes differing in drought tolerance

Influence of drought (D) on changes of leaf water potential (Ψ) and parameters of gas exchange in D-resistant and D-sensitive genotypes of triticale and maize was compared. Soil D (from −0.01 to −2.45 MPa) was simulated by mannitol solutions. At −0.013 MPa significant differences in Ψ, net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and internal CO₂ concentration (C _i) of D-resistant and D-sensitive triticale and maize genotypes were not found. Together with the increase in concentration of the mannitol solution the impact of D on E and g _s for D-sensitive genotypes (CHD-12, Ankora) became lower than for the D-resistant ones (CHD-247, Tina). Inversely, impact of D on Ψ was higher in D-sensitive than D-resistant genotypes. From 1 to 3 d of D, a higher decrease in P _N was observed in D-resistant genotypes than in the D-sensitive ones. Under prolonged D (5–14 d) and simultaneous more severe D the decrease in P _N was lower in D-resistant than in D-sensitive genotypes. Changes in Ψ, P _N, E, and g _s caused by D in genotypes differing in the drought susceptibility were similar for triticale and maize. Compared to control plants, increase of C _i was different for triticale and maize genotypes. Hence one of the physiological reasons of different susceptibility to D between sensitive and resistant genotypes is more efficient protection of tissue water status in resistant genotypes reflected in higher decrease in g _s and limiting E compared to the sensitive ones. Other reason, observed in D-resistant genotypes during the recovery from D-stress, was more efficient removal of detrimental effects of D.     

The relationship between seedling growth and grain yield under drought conditions in maize and triticale genotypes

The effects of drought stress on seedlings?? growth and grain yield of 13 single cross maize hybrids and 11 breeding lines and cultivars of spring triticale were studied in greenhouse and field experiments. In the field experiment, the drought susceptibility index (DSI_GY) was calculated by determining the change in grain yield (GY) in conditions with two soil moisture levels (IR, irrigated; D, drought). In the greenhouse experiment the response to soil drought was evaluated using DSI_DW, by determining changes in the dry weight (DW) of vegetative plant parts. Marked variations in GY and DW were observed among the studied genotypes. In control conditions, the GY and DW in drought-sensitive genotypes were higher compared to the drought-resistant ones; but in drought conditions, the decreases in GY and DW in resistant genotypes were smaller than in drought-sensitive ones. DSI_GY and DSI_DW revealed variations in the degree of drought tolerance among the examined maize and triticale genotypes. The values of DSI_GY in the field experiment and DSI_DW in the greenhouse experiment enabled a division of the studied genotypes into drought-resistant or -sensitive groups. A close correlation between DSI_GY and DSI_DW was found. The positive linear correlation and determination coefficients between DSI_GY and DSI_DW were statistically significant (P?=?0.05), being equal to R ²?=?0.614 (maize) and R ²?=?0.535 (triticale). The ranking of the studied genotypes based on DSI_GY was in most cases consistent with the ranking based on DSI_DW, which indicates that genetically conditioned drought tolerance is similar for plants in the seedling and reproductive growth stages or may at least partly have a common genetic background.     

Changes in response to drought stress of triticale and maize genotypes differing in drought tolerance

Direct effects and after-effects of soil drought for 7 and 14 d were examined on seedling dry matter, leaf water potential (ψ), leaf injury index (LI), and chlorophyll (Chl) content of drought (D) resistant and sensitive triticale and maize genotypes. D caused higher decrease in number of developed leaves and dry matter of shoots and roots in the sensitive genotypes than in the resistant ones. Soil D caused lower decrease of ψ in the triticale than maize leaves. Influence of D on the Chl b content was considerably lower than on the Chl a content. In triticale the most harmful D impact was observed for physiologically younger leaves, in maize for the older ones. A period of 7-d-long recovery was too short for a complete removal of an adverse influence of D.     

The relations between drought susceptibility index based on grain yield (DSIGY) and key physiological seedling traits in maize and triticale genotypes

The physiological reasons for the differences in sensitivity of C₃ and C₄ plant species to environmental stresses have not been thoroughly explained. In this study the effects of drought stress on the growth and selected physiological traits were examined in the seedlings of 13 single cross maize (C₄ plant) hybrids and 11 spring triticale (C₃ plant) breeding lines and varieties differing in drought sensitivity. For plants in the seedling stage the results demonstrated a genetic variation in dry matter accumulation of shoots and roots (DW_S, DW_R), number (N) and length (L) of particular components (seminal, seminal adventitious, nodal) of the root system, membrane injury by soil drought (LI_D), osmotic and high temperature stress (LI_OS, LI_HT), water potential (ψ), water loss (WL), grain germination in osmotic stress (FG, PI), and seedling survival (SS). Seedlings grown under moderate soil drought showed a decrease in dry matter of the top parts and roots and a decrease in the length of seminal, seminal adventitious and nodal roots in comparison to seedlings grown in control conditions. The observed harmful effects of drought stress were more distinct in drought sensitive genotypes. Used in this paper drought susceptibility indexes (DSI_GY) were calculated in other experiment by determining the changes in grain yield (GY) under two soil moisture levels (irrigated and drought). The variation of DSI_GY for maize ranges from 0.381 to 0.650 and for triticale from 0.354 to 0.578. The correlations between DSI_GY and laboratory tests (LI, FG, SS) confirmed that they are good indicators of drought tolerance in plants. The highest values of genetic variation were observed in LI, DW_S, SS and WL and the lowest in the measurements of ψ FG, PI, L_S, L_SA and L_N. The correlation coefficients between LI_OS and LI_HT tests were, in most of the considered cases, statistically significant, which indicates that in maize and triticale the mechanisms of membrane injury caused by simulated drought or high temperature are physiologically similar. It can be concluded that an approach to the breeding of maize and triticale for drought tolerance using these tests can be implemented on the basis of separate selection for each trait or for all of them simultaneously. In that case, it would be necessary to determine the importance of the trait in relation to growth phase, drought timing and level, as well as its associations with morphological traits contributing to drought tolerance. The obtained values of the correlation coefficient between laboratory tests suggest that the same physiological traits may be applied as selection criteria in drought tolerance of maize and triticale genotypes.     

Physiological markers of stress susceptibility in maize and triticale under different soil compactions and/or soil water contents

Differences between two maize and two triticale genotypes grown in low soil compaction (LSC), moderate soil compaction (MSC) and severe soil compaction (SSC) and with a limited (D) or excess (W) soil water content were observed as a decrease in shoot (S) and root (R) biomass, leaf greening (SPAD) and increase in membrane injury (LI), root and leaf water potential (ψ), photosynthesis (Pn), transpiration (E) and stomata conductance (g_S). Close correlations between ψ_L and ψ_R, and between differences ψ_L and ψ_R (Δψ) were found. Drought or waterlogging with LSC conditions in both maize genotypes resulted in higher WUE than in control plants (LSC C), but under the SSC WUE declined. However, for triticale differences in WUE, between treatments were small and insignificant. In general, changes in markers were greater for genotypes sensitive to the soil compaction (Ankora, CHD-12) than in resistant ones (Tina, CHD-247) and were higher in seedlings grown under SSC conditions.

Abbreviations: ψ_R, ψ_L: root and leaf water potential; C: control; D: drought; E: transpiration rate; FWC: field water capacity; g_S: stomatal conductance; LSC, MSC, SSC: low, moderate and severe soil compaction; P_n: photosynthesis rate; W: waterlogging     

Physio-morphological traits and osmoregulation strategies of hybrid maize (Zea mays) at the seedling stage in response to water-deficit stress

Drought has been identified as a major factor restricting maize productivity worldwide, especially in the rainfed areas. The objective of the present study was to investigate the physiological adaptation strategies and sugar-related gene expression levels in three maize (Zea mays L.) genotypes with different drought tolerance abilities (Suwan4452, drought tolerant as a positive check; S7328, drought susceptible as a negative check; Pac339, drought susceptible) at the seedling stage. Ten-day old seedlings of maize genotypes were subjected to (i) well-watered (WW) or control and (ii) water-deficit (WD) conditions. Leaf osmotic potential of cv. S7328 under WD was significantly decreased by 1.35–1.45 folds compared with cv. Pac339 under WW, whereas it was retained in cv. Suwan4452, which utilized total soluble sugars as the major osmolytes for maintaining leaf greenness, F_v/F_m, Φ_PSII, and stomatal function (P_n, net photosynthetic rate; g_s, stomatal conductance; and E, transpiration rate). Interestingly, sucrose degradation (65% over the control) in cv. Pac339 under WD was evident in relation to the downregulation of the ZmSPS1 level, whereas glucose enrichment (1.65 folds over the control) was observed in relation to the upregulation of ZmSPS1 and ZmSUS1. Moreover, CWSI (crop water stress index), calculated from leaf temperature of stressed plants, was negatively correlated with E, g_s, and P_n. Overall, growth characteristics, aboveground and belowground parts, in the drought-susceptible cv. Pac339 and cv. S7328, were significantly decreased (> 25% over the control), whereas these parameters in the drought-tolerant cv. Suwan4452 were unaffected. The study validates the use of leaf temperature, CWSI, P_n, g_s, and E as sensitive parameters and overall growth characters as effective indices for drought tolerance screening in maize genotypes at the seedling stage. However, further experiments are required to validate the results observed in this study under field conditions.

     

Silicon Alleviates Drought Stress of Rice Plants by Improving Plant Water Status,Photosynthesis and Mineral Nutrient Absorption

Drought is a major constraint for rice production in the rainfed lowlands in China. Silicon (Si) has been verified to play an important role in enhancing plant resistance to environmental stress. Two near-isogenic lines of rice (Oryza sativa L.), w-14 (drought susceptible) and w-20 (drought resistant), were selected to study the effects of exogenous Si application on the physiological traits and nutritional status of rice under drought stress. In wet conditions, Si supply had no effects on growth and physiological parameters of rice plants. Drought stress was found to reduce dry weight, root traits, water potential, photosynthetic parameters, basal quantum yield (F _v/F ₀), and maximum quantum efficiency of PSII photochemistry (F _v/F _m) in rice plants, while Si application significantly increased photosynthetic rate (Pr), transpiration rate (Tr), F _v/F ₀, and F _v/F _m of rice plants under drought stress. In addition, water stress increased K, Na, Ca, Mg, Fe content of rice plants, but Si treatment significantly reduced these nutrient level. These results suggested that silicon application was useful to increase drought resistance of rice through the enhancement of photochemical efficiency and adjustment of the mineral nutrient absorption in rice plants.     

Leaf optical properties during and after drought stress in triticale and maize genotypes differing in drought tolerance

The effect of a short (7 days) and prolonged (14 days) soil drought (D) on leaf optical properties (R reflectance, T transmittance and A absorbance) in PAR and NIR range of irradiation, and on changes in leaf water potential (ψ), leaf injury index (LI), leaf thickness (LT) and chlorophyll (a + b) content (Chl) was studied for maize and triticale genotypes differing in drought tolerance. Under control conditions (C) leaves of maize in comparison to triticale were better hydrated, were thicker and had higher content of chlorophyll (a + b). In non-stressed plants, small differences were observed in measurements of R, T and A. In the range from 500 to 600 nm, the differences between D-resistant and D-sensitive were observed only in transmittance (T) and in range from 700 to 1,100 nm in absorbance (A). In genotypes belonging to the group of D-sensitive T in PAR range and A in NIR range were two times higher than in D-resistant ones. However, in NIR range R for D-sensitive genotypes was lower than for D-resistant ones. The drought stress caused the decrease in ψ, Chl, LT and the increase in leaf injury index (LI). Soil drought applied within 14 days caused larger changes in these physiological characters in comparison to 7 days drought. The observed harmful influence of drought was more visible for maize than triticale. Moreover for genotypes belonging to D-sensitive ones, changes were larger than for D-resistant ones. Similar to changes in ψ, LT and LI drought stress caused changes in leaf optical properties parameters R, A and T. In the PAR range, the highest changes were observed in R, whereas changes in T and A, which were not considerable. Both in maize and triticale, increase in R was higher in plants subjected to 14 days drought than in plants exposed to drought for 7 days. In maize, increase in R was larger for D-sensitive genotype. For both species, changes in T and A of PAR range were small. In NIR range, an increase in R and A, and decrease in T were observed. After 7 days of recovery in plants subjected to shorter period of drought significant differences were still visible in most cases. The same was observed for ψ, LT, LI and Chl parameters. It shows that the period of 7 days rehydration is too short to remove the injuries caused by drought stress. This results indicate that measurements of R, T and A might be useful in practical application for the estimation of the drought tolerance level. Some limitations in the practical application for plant breeding may be caused by relatively high cost of necessary equipment.     

Application of photochemical parameters and several indices based on phenotypical traits to assess intraspecific variation of oat (<Emphasis Type="Italic">Avena sativa</Emphasis> L.) tolerance to drought

Functionality of the photosynthetic system under water stress is of major importance in drought tolerance. Oat (Avena sativa L.) doubled haploid (DH) lines obtained by pollination of F ₁ oat crosses with maize were used to assess the differences in plant genotypic response to soil drought. The investigations were based on the measurements of gas exchange and chlorophyll a fluorescence kinetics. Drought was applied to 17-day-old seedlings by withholding water for 14 days and subsequent plant recovery. Non-stressed optimally watered plants served as controls. Yield components were determined when plants reached full maturity. It was shown differences among the oat lines with respect to drought stress susceptibility (SI) and stress tolerance index mean productivity and drought susceptibility index. Sensitivity to drought of individual DH lines was significantly different, as demonstrated by the correlation between drought susceptibility index and yield components, such as dry weight (GW) or grain number (GN) of the harvested plants. GW and GN were lower in drought-sensitive genotypes exposed to drought stress compared to those resistant to drought. The principal component analysis allow to separate three groups of lines differing in their sensitivity to drought stress and indicated that tolerance to drought in oat has a common genetic background.     

Differences in the physiological state between triticale and maize plants during drought stress and followed rehydration expressed by the leaf gas exchange and spectrofluorimetric methods

The studies were carried out in order to estimate differences in the physiological state between triticale and maize plants subjected to drought stress followed by rehydration. The physiological state of the plants was evaluated by measurements of leaf water potential, net photosynthesis, transpiration and stomatal conductance. Spectrofluorimetric methods for the study of blue, green and red fluorescence were applied. We observed that the soil drought induced a greater water loss in triticale leaves than in maize and consequently caused greater injuries to the photosynthetic apparatus. Moreover, triticale plant recovery was slower than in maize plants during the rehydration phase. The effect was probably connected with the higher functional and structural disorganisation of the photosynthetic apparatus observed during drought stress in triticale. Water stress is responsible for damages to photosystem PS II. The worst light utilisation in photosynthetic light conversion was recorded as an increase in the intensity of red fluorescence. Drought stress induced a strong increase in the intensity of blue and green fluorescence in the studied species and it was still high in maize plants during the first day of rehydration. Increase in the intensity of blue and green fluorescence in maize seems to be the effect of the photoprotection mechanism which prevents damage to PS II through utilisation of excess energy.     

Effect of drought stress on leaf optical properties in drought-resistant and drought-sensitive maize and triticale genotypes

The effect of a short (7 d), prolonged (14 d) soil drought (D) and (7 d) recovery (DR) on the leaf optical properties — reflectance (R), transmittance (T) and absorptance (A) in photosynthetically active radiation (PAR) and near infrared radiation (NIR) range of irradiation (750–1100 nm) was studied for maize and triticale genotypes differing in drought tolerance. The drought stress caused the changes in leaf optical properties parameters in comparison with non-drought plants. The observed harmful influence of drought was more visible for maize than triticale.     

Physiological and biochemical adaptations in lentil genotypes under drought stress

Drought is a major restrictive factor for declining grain yield in lentil globally. Present investigation was conducted by taking microsperma (HUL-57) and macrosperma (IPL-406) genotypes of lentil (Lens culinaris Medik.) as information regarding physiological and biochemical basis of differences in drought resistance in macrosperma (bold-seeded) and microsperma (small-seeded) are not well understood. Pot grown plants were exposed to drought stress at specific phenophase viz. mid-vegetative, flower initiation and pod formation stage by withholding irrigation till the plants experienced one cycle of permanent wilting (PWP). Genotypes exhibited substantial differences for most of the measured traits under drought irrespective of the phenophase of stress imposed. Under drought HUL-57 had lower CMI, higher CSI, lower values of Δ¹³C, maintained higher SLN, accumulated more N and efficiently remobilized accumulated N to developing seeds. Higher chlorophyll content, increased accumulation of osmotically active solutes viz. soluble sugars and proline under drought stress was evident in HUL-57. Drought induced H₂O₂ accumulation and lipid peroxidation in both genotypes, but increments were of lesser magnitudes in HUL-57. Drought stress of pod formation stage followed by flower initiation stage was most damaging than the stress imposed at mid-vegetative stage in both genotypes. HUL-57 showed a better drought resistance capacity than IPL-406. Drought indices viz. DSI, STI and MP are proposed as criterion to identify and breed lentil genotypes for drought conditions.     

Salicylic Acid Application Mitigates Oxidative Damage and Improves the Growth Performance of Barley under Drought Stress

Drought is a severe environmental constraint, causing a significant reduction in crop productivity across the world. Salicylic acid (SA) is an important plant growth regulator that helps plants cope with the adverse effects induced by various abiotic stresses. The current study investigated the potential effects of SA on drought tolerance efficacy in two barley (Hordeum vulgare) genotypes, namely BARI barley 5 and BARI barley 7. Ten-day-old barley seedlings were exposed to drought stress by maintaining 7.5% soil moisture content in the absence or presence of 0.5, 1.0 and 1.5 mM SA. Drought exposure led to severe damage to both genotypes, as indicated by phenotypic aberrations and reduction of dry biomass. On the other hand, the application of SA to drought-stressed plants protected both barley genotypes from the adverse effects of drought, which was reflected in the improvement of phenotypes and biomass production. SA supplementation improved relative water content and proline levels in drought-stressed barley genotypes, indicating the osmotic adjustment functions of SA under water-deficit conditions. Drought stress induced the accumulation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide (O₂ ^•− ), and the lipid peroxidation product malondialdehyde (MDA) in the leaves of barley plants. Exogenous supply of SA reduced oxidative damage by restricting the accumulation of ROS through the stimulation of the activities of key antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX). Among the three-applied concentrations of SA, 0.5 mM SA exhibited better mitigating effects against drought stress considering the phenotypic performance and biochemical data. Furthermore, BARI barley 5 showed better performance under drought stress than BARI barley 7 in the presence of SA application. Collectively, our results suggest that SA played a crucial role in improving water status and antioxidant defense strategy to protect barley plants from the deleterious effects of water deficiency.     

Chlorophyll fluorescence imaging of photosynthetic activity with the flash-lamp fluorescence imaging system

A flash-lamp chlorophyll (Chl) fluorescence imaging system (FL-FIS) is described that allows to screen and image the photosynthetic activity of several thousand leaf points (pixels) of intact leaves in a non-destructive way within a few seconds. This includes also the registration of several thousand leaf point images of the four natural fluorescence bands of plants in the blue (440 nm) and green (520 nm) regions as well as the red (near 690 nm) and far-red (near 740 nm) Chl fluorescence. The latest components of this Karlsruhe FL-FIS are presented as well as its advantage as compared to the classical single leaf point measurements where only the fluorescence information of one leaf point is sensed per each measurement. Moreover, using the conventional He-Ne-laser induced two-wavelengths Chl fluorometer LITWaF, we demonstrated that the photosynthetic activity of leaves can be determined measuring the Chl fluorescence decrease ratio, R_Fd (defined as Chl fluorescence decrease F_d from maximum to steady state fluorescence F_s:F_d/F_s), that is determined by the Chl fluorescence induction kinetics (Kautsky effect). The height of the values of the Chl fluorescence decrease ratio R_Fd is linearly correlated to the net photosynthetic CO₂ fixation rate P _N as is indicated here for sun and shade leaves of various trees that considerably differ in their P _N. Imaging the R_Fd-ratio of intact leaves permitted the detection of considerable gradients in photosynthetic capacity across the leaf area as well as the spatial heterogeneity and patchiness of photosynthetic quantum conversion within the control leaf and the stressed plants. The higher photosynthetic capacity of sun versus shade leaves was screened by Chl fluorescence imaging. Profile analysis of fluoresence signals (along a line across the leaf area) and histograms (the signal frequency distribution of the fluorescence information of all measured leaf pixels) of Chl fluorescence yield and Chl fluorescence ratios allow, with a high statistical significance, the quantification of the differences in photosynthetic activity between various areas of the leaf as well as between control leaves and water stressed leaves. The progressive uptake and transfer of the herbicide diuron via the petiole into the leaf of an intact plant and the concomitant loss of photosynthetic quantum conversion was followed with high precision by imaging the increase of the red Chl fluorescence F₆₉₀. Differences in the availability and absorption of soil nitrogen of crop plants can be documented via this flash-lamp fluorescence imaging technique by imaging the blue/red ratio image F₄₄₀/F₆₉₀, whereas differences in Chl content are detected by collecting images of the fluorescence ratio red/far-red, F₆₉₀/F₇₄₀.     

Evaluation of physiological screening tests for breeding drought resistant triticale (x <Emphasis Type="Italic">Triticosecale</Emphasis> wittmack)

Effects of soil drought on crop yield of 4 strains and 7 cultivars of spring triticale was investigated under field condition. The Drought Susceptibility Index (DSI) was evaluated in a two year experiment by the determination of grain loss in conditions of two soil moisture levels (drought-D and irrigated-IR). In the experiment response to drought was evaluated by different screening tests (leaf gaseous exchange, leaf water potential, chlorophyll content and fluorescence, leaf injury by drought and by simulated drought and heat temperature and water loss by excited leaf. The DSI values and the results of screening tests showed the genetic variation in the degree of drought tolerance. The values of DSI enabled the ranking of the tested triticale genotypes with respect to their drought tolerance and allow to divide them into three groups of drought susceptibility. Large differences among studied forms were observed also in changes of leaf water potential, fluorescence and leaf injury. For plants in vegetative stage of growth the tested breeding forms were easily separated into groups of different drought tolerance. Changes of ψ, Fv/Fm and LI as a screening tests were the most suitable techniques for estimation of degree of drought tolerance for triticale. Laboratory screening tests (leaf injury by simulated drought (LI_DS) and high temperature (LI_HT) and water loss (WL) of excited leaf conducted for nonstressed plants in most cases were significantly correlated with DSI. The statistically significant correlation between leaf water potential (ψ) was observed only with leaf fluorescence (Fv/Fm). Changes of Fv/Fm were significantly correlated with ψ, LI and LI_HT for 50 °C. Index of leaf injury (LI) by soil drought were significantly correlated with Fv/Fm, LI_DS (−1.0, −1.5 MPa), LI_HT (45 and 50°C) and water loss (WL). The correlation coefficient between the tests LI_DS and LI_HT were most of the considered cases statistically significant which indicate that the mechanism of membranes injury resulted from simulated drought or high temperature were similar in triticale. Water loss (WL) of excited leaves was the most suitable test for screening drought tolerance in triticale population. Changes of gaseous exchange parameters were not useful as screening test in this research.     

The influence of ABA on water relation, photosynthesis parameters, and chlorophyll fluorescence under drought conditions in two maize hybrids with contrasting drought resistance

Drought is a major limitation of maize cultivation in Brazil. Agronomic and physiological practices have been considered to overcome this stress and consequently, increase grain production. The present study investigated the role of abscisic acid (ABA) application in some physiological parameters, in two hybrids with contrasting drought resistance (DKB 390 and BRS 1030 resistant and sensitive, respectively). Contrasting resistance to drought in these genotypes was determined in previous studies. Water deficit was imposed for 10 days at flowering stage, in association with the application of 100 μM abscisic acid on plant canopy. Evaluations of gas exchange, chlorophyll fluorescence, relative water content (RWC), and endogenous ABA content were performed during stress period and also at water recovery (recovery irrigation). A significant functional relationship was observed between RWC and the parameters of gas exchange and fluorescence. During water recovery, no differences were observed among the treatments. DKB 390 presented higher photosynthesis rate (P _n) and electron transport rate (ETR) under water stress, while BRS 1030 presented higher intercellular CO₂ concentration (C _i) and lower photochemical quenching (qP), non-photochemical quenching (NPQ), and lower F _v/F _m ratio. DBK 390 was more responsive to ABA application than BRS 1030, presenting higher endogenous ABA content in the first day of stress. DBK 390 with ABA application reduced the effect of water stress through maintenance of water status, an increase of photosynthetic parameters, and a decrease of decline in the functions of photosystem II during stress.     

The impact of different soil moisture and soil compaction on the growth of triticale root system

Effects of different soil moisture (soil drought and waterlogging) and soil compaction (1.33 and 1.50 g·cm⁻³) on the growth and morphological traits of the root system were studied in four breeding forms and seven cultivars of triticale. Morphological changes, including the restriction of root extension, expansion and proliferation of laterals roots, occur in plants grown in different soil moisture and in compact soil. The investigations comprised quantitative and qualitative analyses of a developed plant root system through determining the number, length and dry matter of the particular components of the root system. Obtained results have demonstrated a relatively broad variation in the habit of the triticale root system. Plants grown under compact soil and low or high soil water content showed a smaller number and less dry matter of lateral branching than plants grown in control conditions. The harmful effects of compact soil and drought conditions on the growth of roots was greater when compared with that of plants exposed to waterlogging. The observed effects of all treatments were more distinct in a drought sensitive strains. The drought resistant forms were a more characterize with extensive rooting and by smaller alterations in the root morphology under the stress conditions compared with drought sensitive one. Results confirm that the breeding forms (CHD-12 and CHD-173) of a high drought susceptibility was found to be also more sensitive to periodical soil water excess. A more efficient water use and a lower shoot to root (S/R) ratio were found to be major reasons for a higher stress resistance of the breeding forms (CHD-220 and CHD-247). The reasons for a different response of the examined breeding forms and cultivars to the conditions of drought or waterlogging may be a more economical water balance and more favourable relations between the shoot and root dimensions in the drought resistant forms and cultivars. The results suggest that the morphological traits of the triticale root system may be used in practice as direct or indirect selection criteria in maize breeding.