Photosynthetic responses to heat treatments at different temperatures and following recovery in grapevine (Vitis amurensis L.) leaves

Background

The electron transport chain, Rubisco and stomatal conductance are important in photosynthesis. Little is known about their combined responses to heat treatment at different temperatures and following recovery in grapevines (Vitis spp.) which are often grown in climates with high temperatures.

Methodology/Findings

The electron transport function of photosystem II, the activation state of Rubisco and the influence of stomatal behavior were investigated in grapevine leaves during heat treatments and following recovery. High temperature treatments included 35, 40 and 45°C, with 25°C as the control and recovery temperature. Heat treatment at 35°C did not significantly (P>0.05) inhibit net photosynthetic rate (P _n). However, with treatments at 40 and 45°C, P _n was decreased, accompanied by an increase in substomatal CO₂ concentration (C _i), decreases in stomatal conductance (g _s) and the activation state of Rubisco, and inhibition of the donor side and the reaction center of PSII. The acceptor side of PSII was inhibited at 45°C but not at 40°C. When grape leaves recovered following heat treatment, P _n, g_s and the activation state of Rubisco also increased, and the donor side and the reaction center of PSII recovered. The increase in P _n during the recovery period following the second 45°C stress was slower than that following the 40°C stress, and these increases corresponded to the donor side of PSII and the activation state of Rubisco.

Conclusions

Heat treatment at 35°C did not significantly (P>0.05) influence photosynthesis. The decrease of P _n in grape leaves exposed to more severe heat stress (40 or 45°C) was mainly attributed to three factors: the activation state of Rubisco, the donor side and the reaction center of PSII. However, the increase of P _n in grape leaves following heat stress was also associated with a stomatal response. The acceptor side of PSII in grape leaves was responsive but less sensitive to heat stress.     

Is the rate of photosynthesis under blue light altered in the 7B-1 tomato mutant?

Changes of photosynthesis under blue light were examined in the ABA-overproducing 7B-1 mutant in tomato. Net photosynthetic rate (P _N), stomatal conductance (g _s), intrinsic water-use efficiency (WUE_i) and chlorophyll (a+b) [Chl (a+b)] content in leaves of different insertion (1^st, 4^th and 9^th ones) were measured in 5-, 7- and 9-week-old plants. P _N, g _s, and Chl (a+b) content were mostly similar in young leaves of 7B-1 and wild type (WT) plants. With the aging of leaves, a blue-light-induced increase in P _N and g _s to steady-state was delayed and steady-state values of P _N and g _s were lower in 7B-1 plants compared with WT. Steady-state values of WUE_i were increased in 4^th and 9^th leaves of 7B-1 plants compared with WT. The results can be explained by the higher endogenous level of ABA in 7B-1 plants and their lower sensitivity to ABA in earlier growth stage.     

Effects of fertilization on leaf photosynthetic characteristics and grain yield in tartary buckwheat Yunqiao1

Tartary buckwheat (Fagopyrum tataricum Gaertn) has been praised as one of green foods for humans in the 21_st century. Effects of fertilization on leaf photosynthetic characteristics and grain yield of tartary buckwheat has not been yet reported in detail. Our experiment was set as a split-plot factorial. The main plots and subplots were designed by fertilizer ratio and rate as: NPK 1:1:1 (A1), NPK 1:4:2 (A2), NPK 1:2:3 (A3), and 300 (B1), 450 (B2), and 600 (B3) kg (NPK) ha^–1. Our results showed that the grain yield was significantly and positively correlated with the net photosynthetic rate (P _N), stomatal conductance (g _s), transpiration rate (E), PAR, stomatal limitation value (L_s), chlorophyll content (SPAD value), and leaf area index (LAI), while significantly and negatively correlated with intercellular CO₂ concentration (C _i) and water-use efficiency (WUE). The grain yield, P _N, g _s, E, PAR, L_s, SPAD, and LAI increased and then decreased with enhanced fertilization, and their maximum values appeared in the A2B2 treatment. The C _i and WUE decreased and then increased with enhanced fertilization, and their minimum values appeared in the A2B2 treatment. Our results suggested that fertilization had significant effects on the leaf photosynthetic capacity and grain yield of tartary buckwheat Yunqiao 1, and the best fertilization strategy was 450 kg ha^–1 with NPK 1:4:2.     

Mapping Intercellular CO2 Mole Fraction (Ci) in Rosa rubiginosa Leaves Fed with Abscisic Acid by Using Chlorophyll Fluorescence Imaging : Significance of Ci Estimated from Leaf Gas Exchange

Imaging of photochemical yield of photosystem II (PSII) computed from leaf chlorophyll fluorescence images and gas-exchange measurements were performed on Rosa rubiginosa leaflets during abscisic acid (ABA) addition. In air ABA induced a decrease of both the net CO₂ assimilation (A_n) and the stomatal water vapor conductance (g_s). After ABA treatment, imaging in transient nonphotorespiratory conditions (0.1% O₂) revealed a heterogeneous decrease of PSII photochemical yield. This decline was fully reversed by a transient high CO₂ concentration (7400 μmol mol⁻¹) in the leaf atmosphere. It was concluded that ABA primarily affected A_n by decreasing the CO₂ supply at ribulose-1,5-bisphosphate carboxylase/oxygenase. Therefore, the A_n versus intercellular mole fraction (C_i) relationship was assumed not to be affected by ABA, and images of C_i and g_s were constructed from images of PSII photochemical yield under nonphotorespiratory conditions. The distribution of g_s remained unimodal following ABA treatment. A comparison of calculations of C_i from images and gas exchange in ABA-treated leaves showed that the overestimation of C_i estimated from gas exchange was only partly due to heterogeneity. This overestimation was also attributed to the cuticular transpiration, which largely affects the calculation of the leaf conductance to CO₂, when leaf conductance to water is low.     

Low sink-induced stomatal closure alters photosynthetic rates of source leaves in beans as dependent on H2O2 and ABA accumulation in guard cells

Low sink demand provided by pod removal and stem girdling of beans (Vicia faba, cv. Daqingshan) (-Sink) induced a significantly lower net photosynthetic rate (P _n), stomatal conductance (g _s), internal CO₂ concentration (C _i), and transpiration rate (E) compared with pod and root sink retention (CK). This depression in P _n was due to stomatal limitation. Low sink demand of -Sink plants resulted in a higher leaf sucrose content, but a lower sucrose content in guard cells. Moreover, the significant accumulation of H₂O₂ and ABA were observed in both leaves and guard cells of -Sink plants. The most intensive electron dense deposit of cerium perhydroxides, produced by H₂O₂ reaction with cerium chloride, was present in the cell walls, especially the dorsal walls of guard cells. Immunogold electron-microscopy localization of ABA showed that ABA was distributed in ventral walls of guard cells and the intercellular space of mesophyll cells of -Sink leaves in contrast to CK plants. Application of exogenous sucrose to isolated bean leaves increased H₂O₂ and ABA contents. H₂O₂ and ABA in leaves was likely generated by two independently regulated pathways, each affected by the high sucrose concentration induced by low sink demand. Increased sucrose in leaves in response to low sink demand may have caused the increase of H₂O₂ and ABA, and their accumulation in mesophyll cells and guard cells was likely the primary cause for stomatal closure under low sink demand.     

Effect of Water Stress on Photosynthesis and Growth in Two Teak Phenotypes

Two teak (Tectona grandis L.f.) phenotypes differing in their leaf length/breadth ratios were subjected to water stress by withholding water supply for three weeks. Growth rates of whole plants, developing leaves (1^st and 2^nd from shoot apices), and 2^nd and 3^rd internodes were higher in broad leaved (BL) phenotype than in narrow leaved (NL) phenotype before and after imposing water stress treatment. However, the effect of water stress on these parameters was higher in the BL phenotype than in the NL one. Diurnal course of net photosynthetic rate (P _N) of 3^rd or 4^th leaves from shoot apices measured under well-watered conditions was higher for the NL than BL phenotype. P _N, stomatal conductance (g _s), and transpiration rate (E) in both phenotypes were negatively affected by water stress and their decline under water stress was significantly higher in the BL than NL plants.     

Effects of the interaction between ozone and carbon dioxide on gas exchange,photosystem II and antioxidants in rice leaves

To understand the interactive effects of O₃ and CO₂ on rice leaves; gas exchange, chlorophyll (Chl) fluorescence, ascorbic acid and glutathione were examined under acute (5 h), combined exposures of O₃ (0, 0.1, or 0.3 cm³ m⁻³, expressed as O₀, O_0.1, or O_0.3, respectively), and CO₂ (400 or 800 cm³ m⁻³, expressed as C⁴⁰⁰ or C⁸⁰⁰, respectively) in natural-light gas-exposure chambers. The net photosynthetic rate (P _N), maximum (F_v/F_m) and operating (F_q′/F_m′) quantum efficiencies of photosystem II (PSII) in young (8^th) leaves decreased during O₃ exposure. However, these were ameliorated by C⁸⁰⁰ and fully recovered within 3 d in clean air (O⁰ + C⁴⁰⁰) except for the O^0.3 + C⁴⁰⁰ plants. The maximum PSII efficiency at 1,500 μmol m⁻² s⁻¹ PPFD (F_v′/F_m′) for the O^0.3 + C₄₀₀ plants decreased for all measurement times, likely because leaves with severely inhibited P _N also had a severely damaged PSII. The P _N of the flag (16^th) leaves at heading decreased under O₃ exposure, but the decline was smaller and the recovery was faster than that of the 8^th leaves. The F_q′/F_m′ of the flag leaves in the O^0.3 + C⁴⁰⁰ and O^0.3 + C⁸⁰⁰ plants decreased just after gas exposure, but the F_v/F_m was not affected. These effects indicate that elevated CO₂ interactively ameliorated the inhibition of photosynthesis induced by O₃ exposure. However, changes in antioxidant levels did not explain the above interaction.     

Photosynthetic response of Podophyllum hexandrum Royle from different altitudes in Himalayan ranges

Plants of Podophyllum hexandrum, collected from lower, mid, and upper distribution limits in alpine Himalaya were studied under greenhouse conditions to evaluate the photosynthetic response. Net photosynthetic rates (P _N), stomatal conductance (g _s), and efficiency of carbon uptake increased with altitude. The maximum P _N and g _s were measured in the considered population during the 3–6^th week of development. P _N and g _s decreased on an average by 58 and 48 % from maximum rates reached around 4^th week to the 10^th week of growth, respectively. The photosynthetic response in the three ecotypes appeared to be genetically controlled.     

Limitation factors for photosynthesis in ‘Bluecrop’ highbush blueberry (Vaccinium corymbosum) leaves in response to moderate water stress

The levels of stomatal, mesophyll and biochemical limitations in CO₂ assimilation of ‘Bluecrop’ highbush blueberry leaves were compared at two different levels of leaf water potential. The leaf water potentials were ?1.49 and ?1.94 MPa in daily-irrigated (DI) and non-irrigated (NI) shrubs, respectively. The NI shrubs represented plants under moderate water stress. Mesophyll conductance (g _m) and chloroplastic CO₂ concentration (C _c) were estimated by combined measurements of gas exchange and chlorophyll fluorescence under various intercellular CO₂ concentrations (C _i). Net CO₂ assimilation rates (A _n) as a function of C _c were used for calculating maximum carboxylation efficiency (α _cmax) at the real sites of CO₂ assimilation. Maximum A _n (A _nmax) from the light response curves at 400 μmol mol^?1 air of ambient CO₂ concentration (C _a) were lower in the leaves of NI shrubs than in those of DI ones. However, electron transport rates were higher in the leaves of NI shrubs than in those of DI ones. The decrease in CO₂ assimilation following water stress may be caused by a decrease in g _m rather than a decrease in stomatal conductance (g _s) according to limitation analysis. Limitation rates by g _s, calculated at 400 μmol mol^?1 air of C _a in A _n-C _i curves, were not significantly different between the leaves of DI and NI shrubs. However, limitation rates by g _m from A _n-C _c curves were significantly higher in the leaves of NI shrubs than in those of DI ones. Maximum carboxylation efficiency (α _cmax) values calculated from the A _n-C _c curve, contrary to those calculated from the A _n-C _i curve, were higher in the leaves of NI shrubs than in those of DI ones. Consequently, mesophyll limitation than stomatal and biochemical limitations mainly down-regulated the photosynthesis in the leaves of ‘Bluecrop’ blueberry shrubs during moderate water stress.     

Ozone sensitivity of four Pakchoi cultivars with different leaf colors: physiological and biochemical mechanisms

Ozone (O₃) is important air pollutant inducing severe losses of horticultural production. Cultivars of the same species, but with different leaf colors, may differ in their ozone sensitivity. However, it has not been clarified yet if different leaf coloration influences such a sensitivity. In this study, two purple-leafed and two green-leafed cultivars of Pakchoi were selected for ozone fumigation (240 ± 20 nmol mol^–1, 09:00–16:00 h). Elevated O₃ decreased chlorophyll content, increased anthocyanin (Ant) content, damaged cell membrane integrity, enhanced antioxidative enzyme activities, depressed photosynthetic rate (P _N) and stomatal conductance (g _s), inhibited maximal quantum yield (F_v/F_m) and effective quantum yield [Y_II] of PSII photochemistry, and caused visible injury. Purple-leafed cultivars with higher Ant contents were more tolerant than green-leafed cultivars as indicated by lower relative enhancement in malondialdehyde content and lower relative losses in P _N, g _s, F_v/F_m, and Y_II. The higher ability to synthesize Ant in the purple-leafed cultivars contributed to their higher photoprotective ability.     

Causes of decreased photosynthetic rate and metabolic capacity in water-deficient leaf cells: a critical evaluation of mechanisms and integration of processes

Background

Water deficit (WD) decreases photosynthetic rate (A) via decreased stomatal conductance to CO₂ (g_s) and photosynthetic metabolic potential (A_pot). The relative importance of g_s and A_pot, and how they are affected by WD, are reviewed with respect to light intensity and to experimental approaches.

Scope and Conclusions

With progressive WD, A decreases as g_s falls. Under low light during growth and WD, A is stimulated by elevated CO₂, showing that metabolism (A_pot) is not impaired, but at high light A is not stimulated, showing inhibition. At a given intercellular CO₂ concentration (C_i) A decreases, showing impaired metabolism (A_pot). The C_i and probably chloroplast CO₂ concentration (C_c), decreases and then increases, together with the equilibrium CO₂ concentration, with greater WD. Estimation of C_c and internal (mesophyll) conductance (g_i) is considered uncertain. Photosystem activity is unaffected until very severe WD, maintaining electron (e⁻) transport (ET) and reductant content. Low A, together with photorespiration (PR), which is maintained or decreased, provides a smaller sink for e⁻_, causing over-energization of energy transduction. Despite increased non-photochemical quenching (NPQ), excess energy and e⁻ result in generation of reactive oxygen species (ROS). Evidence is considered that ROS damages ATP synthase so that ATP content decreases progressively with WD. Decreased ATP limits RuBP production by the Calvin cycle and thus A_pot. Rubisco activity is unlikely to determine A_pot. Sucrose synthesis is limited by lack of substrate and impaired enzyme regulation. With WD, PR decreases relative to light respiration (R_L), and mitochondria consume reductant and synthesise ATP. With progressing WD at low A, R_L increases C_i and C_c. This review emphasises the effects of light intensity, considers techniques, and develops a qualitative model of photosynthetic metabolism under WD that explains many observations: testable hypotheses are suggested.Key words: Water stress, photosynthesis, photorespiration, stomata, ATP synthase, ATP, photoinhibition, electron transport, Rubisco, fluorescence, sucrose, mesophyll conductance     

Assessment of photosynthetic potential of indoor plants under cold stress

Photosynthetic parameters including net photosynthetic rate (P_N), transpiration rate (E), water-use efficiency (WUE), and stomatal conductance (g_s) were studied in indoor C₃ plants Philodendron domesticum (Pd), Dracaena fragans (Df), Peperomia obtussifolia (Po), Chlorophytum comosum (Cc), and in a CAM plant, Sansevieria trifasciata (St), exposed to various low temperatures (0, 5, 10, 15, 20, and 25°C). All studied plants survived up to 0°C, but only St and Cc endured, while other plants wilted, when the temperature increased back to room temperature (25°C). The P_N declined rapidly with the decrease of temperature in all studied plants. St showed the maximum P_N of 11.9 μmol m^?2 s^?1 at 25°C followed by Cc, Po, Pd, and Df. E also followed a trend almost similar to that of P_N. St showed minimum E (0.1 mmol m^?2 s^?1) as compared to other studied C₃ plants at 25°C. The E decreased up to ≈4-fold at 5 and 0°C. Furthermore, a considerable decline in WUE was observed under cold stress in all C₃ plants, while St showed maximum WUE. Similarly, the g_s also declined gradually with the decrease in the temperature in all plants. Among C₃ plants, Pd and Po showed the maximum g_s of 0.07 mol m^?2 s^?1 at 25°C followed by Df and Cc. However, St showed the minimum g_s that further decreased up to ～4-fold at 0°C. In addition, the content of photosynthetic pigments [chlorophyll a, b, (a+b), and carotenoids] was varying in all studied plants at 0°C. Our findings clearly indicated the best photosynthetic potential of St compared to other studied plants. This species might be recommended for improving air quality in high-altitude closed environments.     

Interactions of Elevated CO2 Concentration and Drought Stress on Photosynthesis in Eucalyptus Cladocalyx F. Muell

Response of net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (c _i), and photosynthetic efficiency (F_v/F_m) of photosystem 2 (PS2) was assessed in Eucalyptus cladocalyx grown for long duration at 800 (C₈₀₀) or 380 (C₃₈₀) µmol mol^-1 CO₂ concentration under sufficient water supply or under water stress. The well-watered plants at C₈₀₀ showed a 2.2 fold enhancement of P _N without any change in g _s. Under both C₈₀₀ and C₃₈₀, water stress decreased P _N and g _s significantly without any substantial reduction of c _i, suggesting that both stomatal and non-stomatal factors regulated P _N. However, the photosynthetic efficiency of PS2 was not altered.     

小麦和玉米叶片光合-蒸腾日变化耦合机理

植物叶片光合-蒸腾耦合是陆地生态系统碳-水耦合的基础.已有研究将叶片光合-蒸腾耦合笼统归因于气孔的共同控制作用,缺乏对其耦合机理的全面分析.选择华北地区大田作物冬小麦(C3)和夏玉米(C4)为研究对象,分别在小麦开花期和玉米拔节期选择典型晴天进行叶片光合蒸腾日变化观测(8:00-18:00).结果发现:1)光合速率(An)、蒸腾速率(Tr)以及光合有效辐射(PAR)、叶片表面温度(T)和气孔导度(gs)均表现出单峰日变化特征,峰值出现在正午前后;2)An-Tr具有极显著线性正相关关系(小麦和玉米的相关系数分别为0.75**和0.92**,回归直线斜率分别为1.99和3.62);3)PAR、T和gs与An和Tr有线性正相关关系;4)PAR-An与PAR-Tr、T-An与T-Tr、gs-An与gs-Tr的回归直线形态非常相似.分析认为:1)在光合-蒸腾耦合特征方面,C3作物小麦和C4作物玉米叶片光合-蒸腾都有明显的线性耦合关系,但两者的耦合关系特征存在明显差异,玉米的An-Tr线性回归斜率要明显大于小麦;2)在光合-蒸腾耦合机理方面,日变化中PAR、T和gs同时受太阳辐射调控与An、Tr发生趋向相同、形态相似且近似同步的变化,因此PAR-An与PAR-Tr、T-An与T-Tr、gs-An与gs-Tr具有形态相似的线性关系,这保证了在PAR、T和gs等调控因子发生较大变化的日变化过程中光合-蒸腾保持良好的线性耦合关系.     

Rearrangement of leaf traits with changing source-sink relationship in blueberry (Vaccinium corymbosum L.) leaves

The source-sink relationship is one of major determinants of plant performance. The influence of reproductive sink demand on light-saturated photosynthesis (P_max), dark respiration (R_D), stomatal conductance (g_s), intrinsic water-use efficiency (WUE_i), contents of soluble sugar (SSC), nitrogen, carbon, and photosynthetic pigments was examined in blueberry (Vaccinium corymbosum L. cv. ‘Brigitta’) during the final stage of rapid fruit growth. Measurements were performed three times per day on developed, sun-exposed leaves of girdled shoots with 0.1, 1, and 10 fruit per leaf (0.1F:L, 1F:L, and 10F:L, respectively) and nongirdled shoots bearing one fruit per leaf (NG). Girdling and lower fruit amount induced lower P_max, g_s, N, and total chlorophyll (Chl) and higher WUE_i, SSC, R_D, Chl a/b ratio and carotenoids-to-chlorophylls ratio (Car/Chl) for the 1F:L and 0.1F:L treatments. The impact of girdling was counterbalanced by 10F:L, with NG and 10F:L having similar values. Variables other than P_max, R_D, g_s, WUE_i, and SSC were unaffected throughout the course of the day. P_max and g_s decreased during the course of the day, but g_s decreased more than P_max in the afternoon, while WUE_i was increasing in almost all treatments. SSC increased from the morning until afternoon, whereas R_D peaked at noon regardless of the treatment. Generally, P_max was closely and negatively correlated to SSC, indicating that sugar-sensing mechanisms played an important role in regulation of blueberry leaf photosynthesis. With respect to treatments, P_max and N content were positively related, while R_D was not associated to substrate availability. The enhanced Car/Chl ratio showed a higher photoprotection under the lower sink demand. Changes in the source-sink relationship in ‘Brigitta’ blueberry led to a rearrangement of physiological and structural leaf traits which allowed adjusting the daily balance between carbon assimilation and absorbed light energy.     

Diurnal changes in needle gas exchange in alpine Pinus pumila during snow-melting and summer seasons

Pinus pumila (Pallas) Regel. is a dominant dwarf tree in alpine regions of Japan. The possible factors limiting the net photosynthetic rate (P_n) of the needles of P. pumila were examined in the snow-melting (May) and the summer (August) seasons. In August, in situ maximum P_n was 20 mol kg^–1 needle s^–1 in the current-year needles and 25 mol kg^–1 needle s^–1 in the 1-year-old needles. Diurnal trends of P_n in August were positively related to fluctuations in photosynthetic photon flux density (PPFD) and no midday depression of P_n was found, indicating that a decrease in PPFD rather than an increase in needle-to-air vapor pressure deficit (W) might cause the reduction of P_n. Both stomatal conductance (g_s) and P_n were lower in May than in August. In May, P_n and g_s were almost zero in the morning, but gradually increased with decreasing W, reaching maximum P_n values (4 mol kg^–1 needle s^–1) and g_s (60 mmol kg^–1 needle s^–1) at 16.00 hours. The daytime P_n in May was positively related to g_s. Relative water content in the exposed needles above the snow in May was 83%, which was far above the lethal level. This indicates that the water flow from stems or soils to needles was enough to compensate for a small amount of water loss due to the low g_s in May, although the water supplied to needles would be impeded by the low temperatures. Thus, the reduced g_s in May would be important for avoiding needle desiccation, and would result in a reduced P_n.     

Photosynthetic characteristics of the leaves of 'Golden Delicious' appletrees

Abstract Using an open-system leaf chamber, gas exchange measurements on attached leaves of 3-4-year-old Golden Delicious apple trees, made through two seasons, provided data from which the parameters of a leaf photosynthesis model could be derived. The equation is: where C₁ is internal CO₂ concentration and Q_p is the incident quantum flux. There was considerable leaf to leaf variation in the values of the parameters but no clear seasonal trends were established. The initial slope (a) had an average value of about 2.5 × 10^?3 mg μmol^?1? (i.e. quantum yield ～ 0.057); the mesophyll conductance (g_m) was about 3.5 mm s^?1 in extension leaves of trees carrying fruit and 2.5 mm s^?1 in extension leaves of defruited trees. Differences between the values of g_m for spur leaves with and without subtending fruits were not significant; 2.5 mm s^?1 may be used. Dark respiration (R_d, mg m^?2 s^?1) increased exponentially with temperature (T°C); R_d～ 0.006 exp (0.09 T). At saturating photon flux density P_n was linearly related to C_i, up to C_i～ 250 mg m^?3. Optimum temperatures for P_n were slightly different in the two years and were in the range 16-26°C.     

Decorrelating source and sink determinism of nitrogen remobilization during grain filling in wheat

Background and Aims

Nitrogen (N) remobilization is the major source of N for grain filling in wheat, the other being N uptake after anthesis (N_up); however, variations in remobilization efficiency are not fully understood. It is hard to tell whether the source or the sink effects predominate, because N in the culm at anthesis (N_ant) correlates strongly with both N remobilization (N_rem) and grain number (G_n), respectively the main source and the main sink.

Methods

A pot experiment was thus designed to assess the relative contributions of the source and sink to N_rem regulation. Using two cultivars of winter wheat (Triticum aestivum, ‘Apache’ and ‘Autan’), three pre-anthesis and two post-anthesis N fertilization levels were applied in order to vary the N sources, while ear trimming at anthesis reduced sink size.

Key Results

Unlike results observed at a scale of m², the equation binding N_ant to N_rem exhibited a negative intercept, challenging the concept of nitrogen remobilization efficiency. Before ear trimming, G_n fitted well to N_ant, with a slope dependent on genotype. To obtain a sink variable that was less correlated with N_ant, the difference δG_n was calculated between actual grain number and that which could be predicted from culm N before trimming. A multiple regression then predicted N_rem (r² = 0·95) from N_ant, N_up and δG_n, with fitting unbiased by fertilization treatment, trimming or genotype.

Conclusions

In untrimmed culms, δG_n had a negligible effect, so that N_rem could be fitted to N_ant and N_up only: grain N filling appeared to be determined by sources only (N_ant and N_up), not by sink, and the reduction of N_rem by N_up was quantified. In these ‘normal’ cases, the regulation of N_rem should thus be located within the N sources themselves. In contrast, ear-trimming needs to be considered with caution as it introduced a sink limitation on N_rem; moreover one with an important genotype effect.Key words: Triticum aestivum, winter wheat, source/sink, grain filling, nitrogen uptake, grain number, nitrogen harvest index, nitrogen remobilization efficiency, genotype × environment     

Comparison of the effects of Enterococcus faecium and aromatic oils from sage and oregano on growth performance and diarrhoeal diseases of weaned pigs

The influence of a probiotic additive and aromatic oils from medicinal and spicy plants on the basic production parameters and on the incidence of intestinal disorders of weaned pigs (weaning at the age of 30–32 days) was compared in two trials in a commercial pig fattening farm (Michalovce, Slovakia). In the first trial, an experimental (n _ex = 38) and a control group (n _co = 32) were used. A commercial probiotic additive containing Enterococcus faecium M-74 (6 × 10⁸ CFU/g) and IgY antibodies (920 mg/g dried activated egg matter) against pig Rotavirus and different strains of Escherichia coli (K88, K99, 987P, F18) were added to feed mixture of the experimental group from 30^th to 40^th day (12 × 10⁸ CFU/g) and subsequently from 40^th to 50^th day (6 × 10⁸ CFU/g) of age. The second trial was performed with three groups of pigs (n _ex1 = 28, n _ex2 = 24, n _co = 28). Aromatic oils isolated from sage (Salvia officinalis L., Labiateae) or oregano (Origanum vulgare L., Lamiaceae) were added to feed mixtures of the 1^st (90 mL/100 kg) and 2^nd experimental group (35 mL/100 kg), respectively, from 32^th to 53^th day of age. A statisticaly non-significant decrease of the incidence of diarrhoeal diseases was observed in the experimental groups of both trials as follows: in the 1^st trial by 43.41%, whereas in the 2^nd trial by 20.03% (1^st exp. group) and 6.72% (2^nd exp. group) in comparison with the control groups. The daily weight gains increased in the 1^st trial by 42.95 g/day, while in the 2^nd trial by 69.52 g/day (1^st exp. group) and 105.23 g/day (2^nd exp. group; p < 0.05) compared with controls. Presented at the Second Probiotic Conference, Košice, 15–19 September 2004, Slovakia.     

Photosynthetic characteristics of diploid honeysuckle (<Emphasis Type="Italic">Lonicera japonica</Emphasis> Thunb.) and its autotetraploid cultivar subjected to elevated ozone exposure

In order to investigate the effect of chromosome doubling on ozone tolerance, we compared the physiological responses of a diploid honeysuckle (Lonicera japonica Thunb.) and its autotetraploid cultivar to elevated ozone (O₃) exposure (70 ng g⁻¹, 7 h d⁻¹ for 31 d). Net photosynthetic rate (P _N) of both cultivars were drastically (P<0.01) impaired by O₃. Although there were significantly positive correlation between P _N and stomatal conductance (g _s) in both cultivars under each treatment, the decreased g _s in O₃ might be the result rather than the cause of decreased P _N as indicated by stable or increasing the ratio of intercellular to ambient CO₂ concentration(C _i/C _a). P _N under saturating CO₂ concentration (P _Nsat) and carboxylation efficiency (CE) significantly decreased under O₃ fumigation, which indicated the Calvin cycle was impaired. O₃ also inhibited the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (F_v/F_m), actual quantum yield of PSII photochemistry (Φ_PSII), electron transport rate (ETR), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), the maximum in vivo rate of Rubisco carboxylation (V_cmax) and the maximal photosynthetic electron transport rate (J_max) which demonstrated that the decrease in P _N of the honeysuckle exposed to elevated O₃ was probably not only due to impairment of Calvin cycle but also with respect to the light-harvesting and electron transport processes. Compared to the diploid, the tetraploid had higher relative loss in transpiration rate (E), (g _s), (P _Nsat), V_cmax and J_max. This result indicated that the Calvin cycle and electron transport in tetraploid was damaged more seriously than in diploid. A barely nonsignificant (P=0.086) interaction between O₃ and cultivar on P _N suggested a higher photosynthetic sensitivity of the tetraploid cultivar.