Photosynthesis parameters and activities of enzymes of oxidative stress in two young ‘Chemlali’ and ‘Chetoui’ olive trees under water deficit

The effects of water deficit on photochemical parameters and activities of superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase were investigated in two olive cultivars differing in drought tolerance — ‘Chemlali’ and ‘Chetoui’. After 30 days without irrigation, leaf water potential fell to −5.5 MPa that was accompanied by a marked decrease in net photosynthesis in ‘Chetoui’ olive cultivar. Maximal efficiency of PSII photochemistry (F_v/F_m) decreased slightly in ‘Chemlali’ (28 %) and substantially in ‘Chétoui’ (47 %). Both cultivars showed a similar decline (about 25 %) in the photochemical quenching coefficient, but only the drought-sensitive olive cultivar exhibited an enhancement (31 %) of non-photochemical fluorescence quenching under water deficit conditions. The quantum yield of electron transport decreased in both olive cultivars. ‘Chemlali’ showed a higher protection against oxidative stress, as judged from the lower levels of the malondialdehyde production. Catalase activity was higher in ‘Chetoui’. Glutathione reductase activity was increased similarly in both olive cultivars under water stress. Ascorbate peroxidase activity was enhanced in ‘Chemlali’ under water stress, but was unaffected in ‘Chetoui’. While, superoxide dismutase activity was inhibited in both cultivars under water stress, but higher activity was detected in ‘Chemlali’. Thus, the ability to increase ascorbate peroxidase and a higher superoxide dismutase activity might be an important attribute linked to the drought tolerance in ‘Chemlali’ olive cultivar.     

Osmoregulation and osmoprotection in the leaf cells of two olive cultivars subjected to severe water deficit

In this study, we compared the efficacy of defense mechanisms against severe water deficit in the leaves of two olive (Olea europaea L.) cultivars, ‘Chemlali’ and ‘Meski’, reputed drought resistant and drought sensitive, respectively. Two-year old plants growing in sand filled 10-dm³ pots were not watered for 2 months. Changes in chlorophyll fluorescence parameters and malondialdehyde content as leaf relative water content (RWC) decreased showed that ‘Chemlali’ was able to maintain functional and structural cell integrity longer than ‘Meski’. Mannitol started to accumulate later in the leaves of ‘Chemlali’ but reached higher levels than in the leaves of ‘Meski’. The latter accumulated several soluble sugars at lower dehydration. ‘Chemlali’ leaves also accumulated larger quantities of phenolic compounds which can improve its antioxidant response. Furthermore, the activity of three antioxidant enzymes catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) increased as leaf RWC decreased. However, differences were observed between the two cultivars for CAT and POD but not for APX. The activity of the first two enzymes increased earlier in ‘Meski’, but reached higher levels in ‘Chemlali’. At low leaf hydration levels, ‘Chemlali’ leaves accumulated mannitol and phenolic compounds and had increased CAT and POD activities. These observations suggest that ‘Chemlali’ was more capable of maintaining its leaf cell integrity under severe water stress because of more efficient osmoprotection and antioxidation mechanisms.     

Effects of the planting density on water relations and production of ‘Chemlali’ olive trees (Olea europaea L.)

Water relations are a key factor limiting olive production. In this study, effects of plating density on physiological aspects and productivity of ‘Chemlali’ olive trees were analyzed under rain-fed conditions in four planting densities (156, 100, 69 and 51 trees ha⁻¹), in an experimental olive orchard located in the center of Tunisia. Seasonal changes in leaf relative water content (RWC), leaf water potential, stomatal conductance (g _s), CO₂ assimilation rate and tree production were studied. Accompanying the changes in leaf water status, all the monitored trees reduced leaf stomatal conductance (g _s) and photosynthetic rate (A) throughout the summer drought, mirroring the increase in soil moisture deficit and vapor pressure deficit. However, the decrease in gas exchange was much more pronounced in high planting densities than in low ones. Our results confirm that the increase of tree-to-tree water competition with planting density was significant in the dry climate of Tunisia. Thus, planting density is critical when planting new olive orchards in arid regions.     

Physiological and anatomical changes induced by drought in two olive cultivars (cv Zalmati and Chemlali)

Photosynthetic gas exchange, vegetative growth, water relations and fluorescence parameters as well as leaf anatomical characteristics were investigated on young plants of two Olea europaea L. cultivars (Chemlali and Zalmati), submitted to contrasting water availability regimes. Two-year-old olive trees, grown in pots in greenhouse, were not watered for 2 months. Relative growth rate (RGR), leaf water potential (Ψ_LW) and the leaf relative water content (LWC) of the two cultivars decreased with increasing water stress. Zalmati showed higher values of RGR and LWC and lower decreased values of Ψ_LW than Chemlali, in response to water deficit, particularly during severe drought stress. Water stress also caused a marked decline on photosynthetic capacity and chlorophyll fluorescence. The net photosynthetic rate, stomatal conductance, transpiration rate, the maximal photochemical efficiency of PSII (F _v/F _m) and the intrinsic efficiency of open PSII reaction centres (F′ _v/F′ _m) decreased as drought stress developed. In addition, drought conditions, reduced leaf chlorophyll and carotenoids contents especially at severe water stress. However, Zalmati plants were the less affected when compared with Chemlali. In both cultivars, stomatal control was the major factor affecting photosynthesis under moderate drought stress. At severe drought-stress levels, the non-stomatal component of photosynthesis is inhibited and inactivation of the photosystem II occurs. Leaf anatomical parameters show that drought stress resulted in an increase of the upper epidermis and palisade mesophyll thickness as well as an increase of the stomata and trichomes density. These changes were more characteristic in cv. ‘Zalmati’. Zalmati leaves also revealed lower specific leaf area and had higher density of foliar tissue. From the behaviour of Zalmati plants, with a smaller reduction in relative growth rate, net assimilation rate and chlorophyll fluorescence parameters, and with a thicker palisade parenchyma, and a higher stomatal and trichome density, we consider this cultivar more drought-tolerant than cv. Chemlali and therefore, very promising for cultivation in arid areas.     

Relationship between osmotic stress-induced abscisic acid accumulation,biomass production and plant growth in drought-tolerant and -sensitive wheat cultivars

The effects of increasing osmotic stress induced by 100–400 mOsm (−0.976 MPa) polyethylene glycol (PEG 6000) were investigated in a drought-tolerant (Triticum aestivum L. cv. Mv Emese) and drought-sensitive (cv. GK élet) wheat cultivar at the three-leaf stage. During osmotic stress, the decline of the water potential (ψ _w) was more significant in the leaves, while the abscisic acid (ABA) levels of the roots increased earlier and remained higher in the sensitive than in the tolerant variety. There was an increasing gradient of ABA content toward the youngest leaves in the drought-sensitive GK élet, while more ABA accumulated in the fully developed, older leaves of the tolerant cultivar Mv Emese. In accordance with the rapid and significant accumulation of ABA, the stomatal conductance decreased earlier in the tolerant cultivar. The effect of water stress on the PSII photochemistry was pronounced only 1 week after the exposure to PEG, as indicated by the earlier decrease of the net CO₂ fixation, the effective quantum yield (Φ_PSII) and the photochemical quenching (q _P) in light-adapted samples of the tolerant variety in 400 mOsm PEG 6000. The stress treatment caused more significant reductions in these parameters toward the end of the experiment in the sensitive cultivar. In spite of small differences in the photosynthetic characteristics, the net biomass production was not significantly altered by this osmotic stress. The accumulation of ABA controlled the distribution of the biomass between the shoot and root systems under osmotic stress, and contributed to the development of stronger and deeper roots in the drought-sensitive cultivar GK élet. However, the root elongation did not correlate with the drought sensitivity of these cultivars on the basis of crop yield.     

Contributions of apoplasmic cadmium accumulation,antioxidative enzymes and induction of phytochelatins in cadmium tolerance of the cadmium-accumulating cultivar of black oat (<Emphasis Type="Italic">Avena strigosa</Emphasis> Schreb.)

The contributions of cadmium (Cd) accumulation in cell walls, antioxidative enzymes and induction of phytochelatins (PCs) to Cd tolerance were investigated in two distinctive genotypes of black oat (Avena strigosa Schreb.). One cultivar of black oat ‘New oat’ accumulated Cd in the leaves at the highest concentration compared to another black oat cultivar ‘Soil saver’ and other major graminaceous crops. The shoot:root Cd ratio also demonstrated that ‘New oat’ was the high Cd-accumulating cultivar, whereas ‘Soil saver’ was the low Cd-accumulating cultivar. Varied levels of Cd exposure demonstrated the strong Cd tolerance of ‘New oat’. By contrast, low Cd-accumulating cultivar ‘Soil saver’ suffered Cd toxicity such as growth defects and increased lipid peroxidation, even though it accumulated less Cd in shoots than ‘New oat’. Higher activities of ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1. 15. 1. 1) were observed in the leaves of ‘New oat’ than in ‘Soil saver’. No advantage of ‘New oat’ in PCs induction was observed in comparison to Cd-sensitive cultivar ‘Soil saver’, although Cd exposure increased the concentration of total PCs in both cultivars. Higher and increased Cd accumulation in cell wall fraction was observed in shoots of ‘New oat’. On the other hand, in ‘Soil saver’, apoplasmic Cd accumulation showed saturation under higher Cd exposure. Overall, the present results suggest that cell wall Cd accumulation and antioxidative activities function in the tolerance against Cd stress possibly in combination with vacuolar Cd compartmentation.     

Understanding osmotic stress tolerance in leaves and nodules of two <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> cultivars with contrasting drought tolerance

Drought and salinity are environmental constraints that affect crop yields worldwide. In nature, both stresses are multifaceted problems that are usually associated with other adverse circumstances which limit plant performance such as water shortage and nutrient deficits. In order to assess common features of both stresses, the effects of mannitol-induced osmotic stress were monitored using two Phaseolus vulgaris cultivars, Cv. ‘Flamingo’ (tolerant) and Cv. ‘Coco Blanc’ (sensitive) which differed in their drought and salinity tolerance. Growth, water relations, organic and inorganic compound accumulation and soluble protein contents were measured in leaves and nodules of these N₂-fixing plants. The aim of the present study was to check whether osmotic stress tolerance is associated with accumulation of some of these compounds either in leaves, nodules or both organs. At the whole-plant level, Cv. ‘Flamingo’ showed a better maintenance of plant biomass and shoot water status. At the cell level, this was related to a better osmotic adjustment ability both in leaves and nodules and also to a better adjustment of the cell wall elasticity. At the metabolic level, the contrasting accumulation of the different amino acids in nodules of each cultivar suggested that amino acids pathways can be regulated to different degrees under stress conditions. At the metabolic level, it seems that symbiosis in the sink organ (the nodule) plays a crucial role in conferring drought and salinity tolerance in the common bean.     

干旱胁迫下不同抗旱性小麦叶片内源激素含量的变化与抗旱力强弱的关系

以抗旱性强的小麦品种昌乐5号和抗旱性弱的鲁麦5号的幼苗为材料,研究了随着干旱胁迫的加剧,小麦叶片相对含水量、气孔导度和内源激素水平的变化．结果表明,叶片的气孔导度和细胞激动素与脱落酸含量的比值（CTKs/ABA）呈较强的线性正相关关系而与叶片RWC的相关关系较弱,说明气孔导度受CTKs/ABA调控,而不是受叶片RWC的调控．在不同强度的干旱胁迫下我们可以利用CTKs/ABA的变化判断品种抗旱性大小：①抗旱力强的小麦品种叶片的平均CTKs/ABA值较高,而弱者较低,说明强者内源促进型激素含量相对较高,从而在干旱胁迫下保持较高的生活力．②抗旱力强的小麦品种叶片CTKs/ABA与干旱处理天数呈二次负相关关系,而弱者是线性负相关关系,说明强者具有较强的抗逆缓冲能力．③抗旱力强的小麦品种成熟叶（第二叶）CTKs／ABA下降快,新叶（第三叶）下降慢,而弱者反之,说明抗旱性强者可能存在着较强的从成熟叶向新叶的物质运输从而具有自我保护性调节机制．     

ABA and proline accumulation in leaves and roots of wild (<Emphasis Type="Italic">Hordeum spontaneum</Emphasis>) and cultivated (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> ‘Maresi’) barley genotypes under water deficit conditions

The purpose of the study was to examine water stress-induced changes in the ABA and proline contents in roots and leaves of a potentially more resistant wild accession of Hordeum spontaneum and the modern cultivar Maresi (Hordeum vulgare). Leaves of H. spontaneum had higher contents of constitutive ABA and proline in comparison to those of ‘Maresi’. A moderate water deficit resulted only in root dehydration, which was higher in ‘Maresi’. Increases of water deficit in roots coincided with an increase of ABA content in roots, followed by that in leaves. The level of proline increased only in leaves and only in the case of H. spontaneum. Under conditions of severe water stress, the root dehydration levels were similar in the both genotypes, whereas leaf dehydration was higher in ‘Maresi’. H. spontaneum, as compared to ‘Maresi’ showed an earlier increase of ABA content in the roots and accumulated more ABA in the leaves. Free proline levels in the roots increased in both genotypes but H. spontaneum exhibited a 2-fold higher proline accumulation than ‘Maresi’. In H. spontaneum the accumulation of proline in the leaves occurred noticeably earlier and to a higher extent than in ‘Maresi’. A possible connection of these modifications with water stress resistance of the investigated genotypes is discussed in this paper.     

Influence of Exogenous Glycine Betaine and Abscisic Acid on Papaya in Responses to Water-deficit Stress

The effects of exogenous foliar glycine betaine (GB) and abscisic acid (ABA) on papaya responses to water stress were investigated under distinct water regimes. Papaya seedlings (Carica papaya L. cultivar “BH-65”) were pretreated with GB or ABA and subsequently subjected to consecutive periods of drought, rehydration, and a second period of drought conditions. Results indicated that water stress induced ABA, jasmonic acid (JA), and proline accumulation but did not modify malondialdehyde (MDA) concentration. In addition, water deprivation reduced photosynthetic rate, stomatal conductance, relative water content (RWC), leaf fresh weight, and increased leaf abscission. GB applied prior to drought imposition decreased the impact of water stress on ABA, JA, proline accumulation, leaf water status, growth, and photosynthetic performance. However, ABA-pretreated plants did not show alteration of most of these parameters under water stress conditions when compared with non-pretreated plants except a clear induction of JA accumulation. Taken together, the data suggest that GB may modulate ABA, JA, and proline accumulation through the control of stomatal movement and the high availability of compatible solutes, leading to improvement of leaf water status, growth, and photosynthetic machinery function. In contrast, exogenous ABA did not stimulate papaya physiological responses under drought, but interestingly ABA in combination with drought could induce progressive JA synthesis, unlike drought alone, which induces a transitory JA increase and may trigger endogenous ABA accumulation. The data also suggest that irrespective of the pretreatments, papaya did not suffer oxidative damage.     

The effect of NaCl stress and relief on gas exchange properties of two olive cultivars differing in tolerance to salinity

Young olive plants (Olea europaea L.) were grown either in hydroponic or soil culture in a glasshouse over two growing seasons. Plants were exposed to NaCl concentrations between 0 and 200 mM for 34–35 days followed by 30–34 days of relief from stress to determine the effect of salinity on gas exchange of two cultivars ('Frantoio' and 'Leccino') differing in salt-exclusion capacity. Salinity stress brought about a reduction in net CO₂ assimilation and stomatal conductance in both cultivars, but the effect was more pronounced in the salt tolerant 'Frantoio' than in the salt-sensitive 'Leccino' cultivar. Therefore, gas exchange parameters may be misleading if used to evaluate the salt tolerance of olive genotypes. Recovery in gas exchange parameters during relief from stress was slower in the salt sensitive cultivar. In general, the decline in assimilation reflected the salt-induced reduction in stomatal conductance, but a marked effect on carboxylation efficiency and CO₂ compensation point was measured in plants treated with 200 mM NaCl for four weeks. The cultivar 'Frantoio' showed a 50% reduction in assimilation and stomatal conductance at 146 and 78 mM leaf Na+ concentration (tissue water molar basis) respectively, whereas the corresponding 50% thresholds for the cultivar 'Leccino' were at 275 and 264 mM, respectively.     

The Effects of Drought Stress and Leaf Ageing on Leaf Photosynthesis and Electron Transport in Photosystem 2 in Sweet Potato (Ipomoea batatas Lam.) Cultivars

Of the four tested sweet potato cultivars having different features in growth and yield, cv. Koganesengan (KOG) was sustainable in photosynthetic activity through young to aged leaves under drought. One of the causes for this phenomenon may be stomatal conductance (g _s) of this cultivar that was relatively high in both aged and drought-imposed leaves. In these leaves the non-photochemical quenching (NPQ) was low and the quantum yield of photosystem 2 (Φ_e) was high, compared to those of the other cultivars. This helps to prevent excessive accumulation of chemical energy in leaves and a decrease in photoinhibition damage to the photosynthetic function, by which KOG sustains a relatively high photosynthetic activity under the drought and alleviates functional deterioration caused by leaf age. This revised version was published online in August 2006 with corrections to the Cover Date.     

Gas exchange,chlorophyll fluorescence,and osmotic adjustment in two mango cultivars under drought stress

The responses of photosynthetic gas exchange, chlorophyll fluorescence, content of pigments, main osmolytes, and malondialdehyde (MDA) to water-withholding for 15 days and re-hydration in seedlings of two mango cultivars (Mangifera indica L. var. “Choke Anand’ and var. “Khieo Sawoei”) under 50% sunlight and full sunlight were investigated. For both cultivars, the water-witholding resulted in progressively decreases in leaf relative water content, net photosynthesis (P _n), stomatal conductance (g _s), and increases in the conversion of xanthophyll cycle pigments estimated by an index of leaf spectral reflectance (ΔPRI), carotenoid to chlorophyll ratio, non-photochemical quenching (NPQ), the contents of malondialdehyde (MDA) and compatible solutes (total soluble sugar and proline). The effect of the water stress was more pronounced in full sunlight than 50% sunlight. The maximum photochemistry efficiency measured at dawn was fairly constant during the period of the treatment for both cultivars under both light regimes. The water stress caused less pronounced inhibition of photosynthesis in “Choke Anand” than in “Khieo Sawoei” cultivar under both light regimes. After re-hydration, the recovery was relatively quicker in “Choke Anand” than in “Khieo Sawoei” cultivar. Both cultivars in both 50% and full sunlight showed complete recovery in photochemistry after 5 days of re-watering but photosynthesis did not show a complete recovery as indicated by gas exchange rates. As the results of lower NPQ, ΔPRI and osmotic adjustment in the cultivar “Khieo Sawoei” compared to the cultivar “Choke Anand”, the former cultivar was less tolerant to drought than the latter. Our study further showed that partial shading (e.g., 50% of sunlight) significantly alleviated the harmful effect of drought stress on mango cultivars but in fact stomata of seedlings grown in partial shade was more responsive to water deficit than in full light.     

Changes in lipid composition, water relations and gas exchange in leaves of two young ‘Chemlali’ and ‘Chetoui’ olive trees in response to water stress

The comparative responses of two young olive trees (Olea europaea L. ‘Chemlali’ and ‘Chetoui’) to drought stress were investigated during 1 month. Three-month-old own-rooted plants were subjected to two irrigation treatments: WW (well watered plants that were irrigated with fresh water to maintain a soil water content close to field capacity), and WS (water stressed plants by withholding water). Leaf water potential, gas exchange and leaf lipid composition were studied. ‘Chemlali’ was able to maintain higher leaf CO₂ assimilation rate and leaf stomatal conductance throughout the drought cycle compared to ‘Chetoui’. Water stress induced a larger decrease in the total lipid content in ‘Chetoui’ than in ‘Chemlali’. Interestingly, the constitution of different lipid classes was highly altered in ‘Chetoui’. Lipid changes in Chemlali, a drought tolerant cultivar, revealed more stability of its cellular membranes to drought stress as compared to the drought susceptible olive cultivar, Chétoui. Furthermore, in comparison to the controls, drought stressed plants showed an increase in the degree of unsaturation of leaf lipids in the two olive cultivars. Moreover, the results observed in Chemlali showed that besides changes in lipids composition this cultivar may have an efficient defence strategy which can be related on antioxidative production against oxidative stress.     

Evaluation of physiological traits for improving drought tolerance in faba bean (<Emphasis Type="Italic">Vicia faba</Emphasis> L.)

Among grain legumes, faba bean is becoming increasingly popular in European agriculture due to recent economic and environmental interests. Faba bean can be a highly productive crop, but it is sensitive to drought stress and yields can vary considerably from season to season. Understanding the physiological basis of drought tolerance would indicate traits that can be used as indirect selection criteria for the development of cultivars adapted to drought conditions. To assess genotypic variation in physiological traits associated with drought tolerance in faba bean and to determine relationships among these attributes, two pot experiments were established in a growth chamber using genetic materials that had previously been screened for drought response in the field. Nine inbred lines of diverse genetic backgrounds were tested under adequate water supply and limited water conditions. The genotypes showed substantial variation in shoot dry matter, water use, stomatal conductance, leaf temperature, transpiration efficiency, carbon isotope discrimination (Δ¹³C), relative water content (RWC) and osmotic potential, determined at pre-flowering vegetative stage. Moisture deficits decreased water usage and consequently shoot dry matter production. RWC, osmotic potential, stomatal conductance and Δ¹³C were lower, whereas leaf temperature and transpiration efficiency were higher in stressed plants, probably due to restricted transpirational cooling induced by stomatal closure. Furthermore, differences in stomatal conductance, leaf temperature, Δ¹³C and transpiration efficiency characterized genotypes that were physiologically more adapted to water deficit conditions. Correlation analysis also showed relatively strong relationships among these variables under well watered conditions. The drought tolerant genotypes, ILB-938/2 and Melodie showed lower stomatal conductance associated with warmer leaves, whereas higher stomatal conductance and cooler leaves were observed in sensitive lines (332/2/91/015/1 and Aurora/1). The lower value of Δ¹³C coupled with higher transpiration efficiency in ILB-938/2, relative to sensitive lines (Aurora/1 and Condor/3), is indeed a desirable characteristic for water-limited environments. Finally, the results showed that stomatal conductance, leaf temperature and Δ¹³C are promising physiological indicators for drought tolerance in faba bean. These variables could be measured in pot-grown plants at adequate water supply and may serve as indirect selection criteria to pre-screen genotypes.     

Abscisic Acid Accumulation in Detached Leaves of Rice (Oryza sativa L.) in Response to Water Stress: A Correlation with Leaf Size

When water stress was imposed on detached leaves of two rice(Oryza sativa L.) cultivars, more ABA per unit fresh weightaccumulated in IR20, a small-leaved cultivar, than in 63–83,a large-leaved cultivar; the difference being up to threefold.In an F₂ population of a cross between the two cultivars ABAaccumulation was found to be significantly negatively correlatedwith leaf fresh weight. This correlation persisted in the F₃generation. Such a correlation was not evident, however, whena number of rice cultivars, which varied widely in leaf size,were examined. The difference in ABA accumulation between IR20 and 63–83was not accounted for by different spatial patterns of waterloss or ABA accumulation within a leaf, and cultivar differencesin ABA content were maintained both across, and at various positionsalong the leaf. No major differences in leaf anatomy were observed between thetwo cultivars. Differences found in leaf water relations characteristicswere few and generally minor. It therefore seems unlikely thatthese properties account for the difference between the cultivarsin the ability to accumulate ABA or for the correlation withleaf size. Oryza sativa L, rice, water stress, abscisic acid, leaf size     

Effects of ethylene and 1-MCP (1-methylcyclopropene) on bud and flower drop in mini <Emphasis Type="Italic">Phalaenopsis</Emphasis> cultivars

Phalaenopsis frequently exhibits bud drop during production and in response to adverse postharvest conditions. The effect of exogenous ethylene on bud drop of mini Phalaenopsis was studied and ethylene sensitivity of four cultivars was compared. Water content, membrane permeability and ABA (abscisic acid) content in floral buds and flowers were determined after ethylene treatment. Exogenous ethylene induced flower bud drop in all tested Phalaenopsis cultivars and the different cultivars showed distinct differences in ethylene sensitivity. The cultivar Sogo ‘Vivien’ exhibited the highest bud drop, water loss and change in membrane permeability in floral petals, while Sogo ‘Berry’ showed the lowest sensitivity. The ethylene inhibitor 1-MCP (1-methylcyclopropene) reduced ethylene-induced floral bud drop in the cultivar Sogo ‘Yenlin’. ABA content in floral buds was increased in response to ethylene and 1-MCP pretreatment inhibited the ethylene-induced increase in ABA levels efficiently. This finding suggests that the observed increase in ABA content during bud drop was mediated by ethylene. The interaction between ABA and ethylene is discussed.     

Biochemical responses to drought stress in mulberry (<Emphasis Type="Italic">Morus alba</Emphasis> L.): evaluation of proline,glycine betaine and abscisic acid accumulation in five cultivars

Five popularly grown mulberry cultivars (K-2, MR-2, TR-10, BC2-59 and S-13) were subjected to drought stress by withholding irrigation, to obtain leaf water potentials (Ψ_w) ranging from −0.75, −1.50 and −2.25 MPa. Accumulation of proline, glycine betaine and abscisic acid (ABA) were quantified in control and water stressed mulberry leaves. The activities of enzymes involved in proline accumulation including glutamate dehydrogenase (EC1.4.1.2-4), pyrroline-5-carboxylate synthetase (EC 1.2.1.41), pyrroline-5-carboxylate reductase (EC1.5.1.2), ornithine transaminase (EC 2.6.1.13) were significantly enhanced in the leaves of all the cultivars with decreasing leaf water potentials, while the activities of proline dehydrogenase (EC 1.5.1.2) were reduced with progressive increase in water stress. Accumulation of proline, glycine betaine and abscisic acid was relatively higher in S-13 and BC2-59 compared to K-2, MR-2 and TR-10 under water deficit conditions. Our results demonstrate that S-13 and BC2-59 have superior osmoprotectant mechanisms under water-limited growth regimes.     

Characterization of a wilty sunflower (Helianthus annuus L.) mutant: III. Phenotypic interaction in reciprocal grafts from wilty mutant and wild-type plants

The present study was conducted to evaluate phenotypic interactionin reciprocal grafts between wilty (w-1) sunflower mutant andnormal (W-1) plants. The w-1 genotype is a ‘leaky’ABA-deficient mutant, characterized by high stomatal conductance,in both light and dark conditions, and high transpiration rate. In well-watered conditions, mutant scions grafted on to normalrootstock (w-1/W-1) showed higher leaf relative water content,leaf water potential and ABA levels than those of control grafts(w-1/w-1). In addition, detached leaves of w-1/W-1 exhibitedlower water loss than w-1/w-1 grafts, while mutant rootstockdid not affect the transpiration rate of detached W-1 leaves.When drought stress was imposed to potted plants by withholdingwater, the mutant scions grafted on to normal roots showed apartial phenotypic reversion. A rapid stomatal closure and arise in ABA levels in response to a small decrease in leaf waterpotential was observed. By contrast, in w-1/w-1 grafts significantreductions in stomatal conductance and ABA accumulation weredetected only in conjunction with a severe water deficit. W-1scions on mutant stocks (W-1/w-1) maintained the normal phenotypeof control wild-type grafts (W1/W-1). Key words: ABA, grafting, Helianthus annuus, stomatal conductance, water relations, wilty mutant     

Free proline accumulation in drought-stressed plants under laboratory conditions

Summary Free proline accumulation was measured in leaves of intact sorghum (Sorghum bicolor L. cv. Pioneer 846) and soybean (Glycine max. L. cv. Calland) grown in growth chambers and subjected to ‘normal’ drought stress. Stomatal diffusive resistance and leaf water potential were used to determine the degree of stress at the time of proline analysis. Free proline did not accumulate markedly in either species until each was severely stressed, indicating that proline is not a sensitive indicator of drought stress. Free proline accumulated under less stress in soybean than in sorghum. Since soybean is less drought resistant than sorghum, proline accumulation may be an indicator of drought resistance or susceptibility. re]19731003