Regulation of some biochemical attributes in drought-stressed cauliflower (Brassica oleracea L.) by seed pre-treatment with ascorbic acid

Cauliflower (Brassica oleracea L. var. botrytis) is widely used as a vegetable in many countries; however, productivity is adversely affected in areas affected by drought. To investigate the role of exogenously applied ascorbic acid (AsA) in mitigating the negative effects of drought on cauliflower, a pot experiment was performed using two cultivars of cauliflower ‘Local’ and ‘S-78’. Seeds of both cultivars were soaked in 75 mg l^–1, or in 150 mg l^–1 AsA, or in water (control) for 16 h. Water-deficit stress suppressed plant growth, reduced leaf chlorophyll concentrations, relative water contents (RWC), shoot and root P and K⁺ ion concentrations, and total soluble protein concentrations, significantly. However, significant drought-induced increases were observed in relative membrane permeability (RMP), the accumulation of total phenolic compounds, leaf free proline, glycinebetaine (GB), endogenous AsA, and hydrogen peroxide concentrations, and in the activity of superoxide dismutase (SOD). Seed treatment with 75 or 150 mg l^–1 AsA resulted in lower accumulations of H₂O₂, while increasing shoot and root fresh weights and dry weights, RWC, total phenolic compound, free proline, GB, and endogenous AsA concentrations, and the activities of SOD and catalase (CAT). No changes were observed in leaf chlorophyll concentrations or in peroxidase (POD) activities, RMP, shoot and root P and K⁺ ion accumulation, or in total soluble protein concentrations under water stress or non-stress conditions following seed treatment with AsA. ‘Local’ had higher proline concentrations and SOD activities; however, ‘S-78’ had higher RWC values, GB, and AsA concentrations. Overall, a pre-sowing treatment of cauliflower seed with 75 or 150 mg l^–1 AsA improved seedling tolerance to drought stress in both cultivars, which could be attributed to AsA-induced decreases in RMP and H₂O₂ concentrations, increases in the activities of CAT and SOD, increased RWC, and higher total phenolic compound, proline, GB, and AsA concentrations. The exogenous application of AsA therefore offers an effective strategy to minimise the adverse effects of drought stress on vegetable crops, including cauliflower.     

Abscisic acid alleviates the deleterious effects of cold stress on ‘Sultana’ grapevine (Vitis vinifera L.) plants by improving the anti-oxidant activity and photosynthetic capacity of leaves

The effects of exogenous application of abscisic acid (ABA) on anti-oxidant enzyme activities and photosynthetic capacity in ‘Sultana’ grapevine (Vitis vinifera L.) were investigated under cold stress. When vines had an average of 15 leaves, 0 (control), 50, 100, or 200 µM ABA was sprayed to run-off on all leaves of each plant. Twenty-four hours after foliar spraying with ABA, half (n = 5) of the water-only control vines and half (n = 5) of each group of ABA-treated plants were subjected to 4°C for 12 h, followed by a recovery period of 3 d under greenhouse conditions (25°/18°C day/night). The remaining plants in each treatment group were kept at 24°C. Cold stress increased H₂O₂ and malondialdehyde (MDA) concentrations in vine leaves, whereas all foliar ABA treatments significantly reduced their levels. Chilled plants showed marked increases in their total soluble protein contents in response to each ABA treatment. ABA significantly increased the activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase in cold-stressed grapevine leaves. In contrast, cold stress markedly decreased the rates of leaf photosynthesis (A) and evaporation (E), stomatal conductance (g_s), and chlorophyll concentrations in leaves, but increased intercellular CO₂ concentrations (C_i) in leaves. Treatment with all concentrations of ABA resulted in lower leaf A, E, and g_s values, but higher C_i values at 24°C. However, following cold stress, ABA-treated vines showed higher leaf A, E, and g_s values, but lower C_i values compared to control vines without ABA treatment. The application of 50–200 µM ABA allowed chilled vines to recover more quickly when re-exposed to normal temperatures, enabling the vines to resume their photosynthetic capacity more efficiently following cold stress. These results showed that, by stimulating anti-oxidant enzyme systems and alleviating cold-induced stomatal limitations, ABA reduced the inhibitory effect of cold stress on the rate of CO₂ fixation in ‘Sultana’ grapevine plants.     

六个牡丹品种对干旱胁迫的生理响应机制及抗性评价

以"胡红""姚黄""洛阳红""银红巧对""雨后风光""金岛"6个牡丹品种为试材,研究了干旱条件对牡丹叶内渗透调节物质、丙二醛(MDA)、超氧阴离子O₂^-·含量和抗氧化酶活性变化等生理机制的影响,并利用隶属函数法进行了综合抗性评价,以期探求干旱胁迫下,牡丹叶内渗透调节物质和抗氧化系统对干旱胁迫的调节机制,并利用这些抗性指标评价品种间的抗性关系。结果表明:随干旱程度的增加6种牡丹叶内脯氨酸、可溶性蛋白质、MDA、O₂^-·含量及超氧化物歧化酶(SOD)活性逐渐升高;可溶性糖含量先降后升;过氧化物酶(POD)、过氧化氢酶(CAT)活性前期升高后期降低。重度干旱时,"姚黄""胡红"脯氨酸、可溶性蛋白质含量增加幅度最大,"洛阳红""银红巧对""雨后风光""金岛"增幅较小;"胡红""姚黄"叶内MDA、O₂^-·含量较低,受到的伤害轻于其余4个品种。抗坏血酸过氧化物酶(APX)活性变化品种间差异显著,随着胁迫程度增加,"胡红""金岛""姚黄"APX活性逐渐升高,"雨后风光""洛阳红""银红巧对"APX活性先升高后降低。复水后牡丹生理机能恢复,MDA和O₂^-·含量显著降低,干旱胁迫危害有效缓解。经隶属函数法综合评价,耐旱能力由强到弱顺序为"胡红">"姚黄">"金岛">"雨后风光">"银红巧对">"洛阳红"。     

Effects of Ascorbic Acid and Reduced Glutathione on the Alleviation of Salinity Stress in Olive Plants

The aim of this study was to evaluate the effects of low molecular mass antioxidants and NaCl salinity on growth, ionic balance, proline, and water contents of ‘Zard’ olive trees under controlled greenhouse conditions. The experiment was carried out by spraying 2 mM of ascorbic acid (Asc) and 3 mM of reduced glutathione (GSH) on the plants that were treated with two salinity levels (0 and 100 mM NaCl) on their root medium. Plant growth parameters (leaf fresh weight, leaf dry weight, leaf number, total fresh weight, and total dry weight) were significantly improved by Asc compared with growth parameters in GSH and control plants. Higher concentrations of Na⁺ and Cl^– were observed in salt-stressed plants, while Na⁺ and Cl^– concentrations were decreased in the olive leaves that were sprayed with Asc. Salinity in the root zone caused a considerable decline in both K⁺ concentration and K/Na ratio. K⁺ concentration and K/Na ratio were significantly increased by application of Asc on plant leaves. Salinity caused an increase in electrolyte leakage (EL) compared with the control plants. Lowest EL and tissue water content (TWC) was obtained in Asc-sprayed plants, whereas TWC was increased in salt-stressed plants. Plants were subjected to salt stress and showed a higher relative water content (RWC) than the control plants. Salt stress induced proline accumulation in olive leaves. In conclusion, exogenous application of Asc is recommended to improve tolerance of olive plants under saline conditions.     

土壤干旱和复水对结缕草生理特性的影响

通过对结缕草在土壤干旱及复水过程中叶片相对含水量(RWC)、游离脯氨酸含量(Pro)、叶绿素含量、超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量、可溶性糖(TSC)含量等生理指标的测定,研究土壤干旱对结缕草生理特性的影响.结果表明:干旱胁迫引起结缕草的叶片相对含水量明显下降,游离脯氨酸含量、丙二醛含量及可溶性糖含量均随干旱天数的增加呈持续增加的趋势,而叶绿素含量和SOD酶活性先增后减.复水后各项生理指标除相对含水量、游离脯氨酸含量外均随着复水时间的增加逐渐恢复至对照水平.干旱胁迫下,结缕草水分平衡的保持、SOD酶活性及丙二醛含量的增加以及脯氨酸和可溶性糖等渗透调节物质的积累,是结缕草抗旱的重要生理机制.     

Effect of brassinosteroids on drought resistance and abscisic acid concentration in tomato under water stress

The effect of brassinosteroid (BR) on relative water content (RWC), stomatal conductance (g_s), net photosynthetic rate (PN), intercellular CO₂ concentration (Ci), lipid peroxidation level, activities of antioxidant enzymes and abscisic acid concentration (ABA) in tomato (Lycopersicon esculentum) seedlings under water stress was investigated. Two tomato genotypes, Mill. cv. Ailsa Craig (AC) and its ABA-deficient mutant notabilis (not), were used. Water stress was achieved by withholding water and both the AC and not plants were treated with 1 μM 24-epibrassinolide (EBR) or distilled water as a control. The RWC, g_s, Ci and PN were significantly decreased under water stress. However, EBR treatment significantly alleviated water stress and increased the RWC and PN. EBR application also markedly increased the activities of antioxidant enzymes (catalase, ascorbate peroxidase and superoxide dismutase) while it decreased g_s, Ci and the contents of H₂O₂ and malondialdehyde (MDA). Interestingly, ABA concentration in AC and not plants was markedly elevated after EBR treatment although the increasing rate and amplitude of ABA in not plants treated by EBR was significantly lower than those in AC plants. Our study suggested that amelioration of the drought stress of tomato seedlings may be caused by EBR-induced elevation of endogenous ABA concentration and/or the activities of antioxidant enzymes.     

三种暖季型草坪草在干旱条件下脯氨酸含量和抗氧化酶活性的变化

 测定了土壤干旱条件下矮生狗牙根、沟叶结缕草和地毯草相对含水量和相对电导率的变化。结果表明，矮生狗牙根的耐旱性较强，沟叶结缕草次之，而地毯草对干旱敏感。干旱胁迫下，地毯草积累脯氨酸最多，沟叶结缕草次之，矮生狗牙根最少，草坪草的脯氨酸的积累与耐旱性呈负相关。地毯草超氧化物歧化酶(SOD)活性持续升高，过氧化氢酶(CAT)活性在短暂升高后降低，过氧化物酶(POD)活性降低；矮生狗牙根和沟叶结缕草的SOD活性先升后降，CAT和POD活性则维持较高水平，表明草坪草的耐旱性与抗氧化酶活性有关。     

Effect of native habitat on the cooling ability of six nursery-grown tree species and cultivars for future roadside plantings

Vegetation in urban areas provides benefits to people, which are increasingly assessed and valued as ecosystem services (ESS). The regulation of the urban microclimate is one of these services, since trees have the potential to reduce urban heat loads by evapotranspiration and shading. Simultaneously, it has been suggested that trees from dry habitats should be used to cope with the increasing risks of drought under climate change in Central Europe. The underlying properties that enable those trees to reduce dependence on the environment, however, are assumed to come at the expense of biomass production and water loss. In the potentially conflicted area between drought tolerance and ESS we compared water consumption, water-use efficiency (WUE), crown structure and growth of six roadside species/cultivars, which are assumed to vary in drought tolerance, due to differing resource supplies in their native habitats. Acer platanoides, Carpinus betulus ‘Fastigiata’, and Tilia cordata ‘Greenspire’ were compared with Acer campestre, Ostrya carpinifolia, and Tilia tomentosa ‘Brabant’, the latter presumably being less water-demanding. Measurements took place in the municipal nursery of Munich during summer 2016.Surprisingly, the less water-demanding species/cultivars exhibited on average 1.24 times higher values of maximum daily sap flux density and up to seven times higher growth rates, both contributing to higher WUE. Scaled to leaf level, however, their mean daily transpiration rates were on average lower (0.21 and 0.31 kg H₂O m⁻² d⁻¹, respectively). They also showed higher flexibility in response to changing weather with increased growth and transpiration under favorable conditions in early summer, but a more conservative water use in dry late summer. The results suggest that these species/cultivars tend to regulate their water use stronger under increasing dryness, whereas canopy size and leaf amount are still the main important determinants of species and cultivar differences in water use.     

Gas-exchange responses of rose plants to CO2 enrichment and light

Summary

This paper describes the response of gas exchange rates and water use efficiency of rose plants, by means of the characterization in situ and the analysis of the response of photosynthesis, transpiration and water use efficiency of whole plants to CO₂ enrichment under the irradiance conditions prevailing in greenhouses of southern France. Net CO₂ assimilation (A_n) and transpiration (E) of whole rose plants (Rosa hybrida, cv. Sonia) were measured during winter and spring periods. The response of A_n to light and CO₂ were fitted to a double hyperbola function (r² = 0.84). Maximum net assimilation rate (A_nmax), light and CO₂ utilization efficiencies (α₁, α_c) as well as light and CO₂ compensation points (Γ₁ , Γ_c) were calculated for the whole plant and compared with leaf and canopy data in the literature. The whole-plant characteristics generally had values intermediate between those related to leaf and canopy. Light saturation at sub-ambient air CO₂ concentration (C_a) was reached for relatively low PFFD values (300 µmol m^?2 s^?1), whereas at ambient and enriched C_a light saturation occurs for PPFD ≈ 1000 µmol m^?2 s^?1. Doubling C_a from 350 to 700 µmol mol^?1 increased A_nmax and α₁ by respectively 40% and 30%, while reducing Γ₁ by 27%. A threefold increase of C_a from 350 to 1050 µmol mol^?1 induced a reduction of 20% of E. Instantaneous transpirational water use efficiency, WUE (=A_n/E), is relatively insensitive to PPFD, although a slight decrease with PPFD is observed at high CO₂ concentration, but shows marked variations with C_a and leaf to air vapour pressure defiçit (D₁). Increase of C_a from 350 to 1000 µmol mol^?1 gave about 50% increase in WUE. Increase of D₁ from 0 to 2 kPa induced 30% decrease in WUE at ambient C_a and 50% decrease at 1000 µmol mol^?1.     

Changes in nutrient concentrations and leaf gas exchange parameters in banana plantlets under gradual soil moisture depletion

Changes in mineral nutrient concentration, growth, water status and gas exchange parameters were investigated in young banana plants (Musa acuminata cv. ‘Grand Nain’) subjected to gradual soil moisture diminution. Experiments were performed in glasshouse under controlled temperature, and water stress was imposed by ceasing irrigation for 62 days. The data showed a parallel decrease of leaf gas exchange parameters and soil moisture initiated few days after the imposition of water stress. However, the leaf relative water content (RWC) showed a minor decrease in response to drought. The onset of growth reduction evaluated as plant height, pseudostem circumference, number of newly emerged leaves, leaf area, and leaf and root biomass took place approximately between 34 and 40 days after the beginning of the stress period. In addition, drought did not modify nitrogen and phosphorus concentrations in foliar and root tissues; however, it increased potassium, calcium, magnesium, sodium and chloride in leaves, and only calcium, sodium and chloride in roots. Collectively, the data reveal that banana plants show a drought avoidance mechanism in response to water stress. After a prolonged drought period, leaf RWC was hardly reduced, while gas exchange and growth parameters were reduced drastically. Increasing leaf mineral concentration could have help to maintain leaf RWC due to osmotic adjustment mechanism.     

Response to water stress of some oleander cultivars suitable for pot plant production

Oleander (Nerium oleander L.) is an evergreen shrub of great ornamental interest which, in recent times, has been increasingly used as a flowering pot plant. Plants grown in pots undergo more frequent water stress conditions than those grown in the soil, due to the limited volume of substrate available for the roots. Oleander is a species adaptable to dry conditions and able to survive long periods of drought. It is well known that under water stress conditions all plants reduce photosynthetic activity, resulting in reduced plant growth. In case of severe water stress, leaves undergo strong wilting and senescence resulting in the loss of ornamental value. In the present work, a study was conducted to evaluate the ecophysiological response to water stress in four oleander cultivars previously recognised (on the basis of traits such as size, habit, earliness, abundance and duration of flowering, aptitude for cutting propagation and rapidity of growth) as suitable for pot plant production. Our data confirm the high drought tolerance of oleander. In the studied cultivars, plants submitted to water stress showed only minor variations in leaf gas exchange parameters [transpiration (E), stomatal conductance (g_s) and CO₂ net assimilation (A)] for at least 10 days without a change in leaf water content [assessed as relative water content (RWC)] for 22 days from the beginning of the stress treatment. During this period, non-irrigated plants maintained the same water status as control plants and were visually undistinguishable from them. Moreover, plants survived without water supply for one month. Following the supply of water again, they were able to restore RWC, gas exchange parameters and instantaneous water use efficiency [A/E ratio (WUE_inst)] to the values of control plants. Furthermore, if at the end of the stress period plants appeared withered and were pale green in colour, they regained their normal appearance after they were irrigated again. Although the four studied cultivars showed some minor differences in leaf gas exchange parameters and in the manner in which the latter parameters changed after irrigation was stopped, the response to water stress was essentially the same. Therefore, as far as drought tolerance is concerned, all these cultivars have a good aptitude for use as flowering pot plants.     

Stock-Scion Incompatibility in Citrus and its Cause

Summary

The effects of 75 mM and 150 mM NaCl (EC 8.50 and 15.35 dS m^–1) were studied on a salt-tolerant and a salt-sensitive pepper (Capsicum annuum L.) genotype. The salt-tolerant genotype showed lower declines in relative water content (RWC), no change in chlorophyll (Chl) content, lower increases in lipid peroxidation, and greater increases in superoxide dismutase (SOD) activity, total protein content, and glutathione content. The salt-sensitive genotype showed greater decreases in RWC, Chl content, SOD activity, and in guaiacol peroxidase (GPOX) activity, and higher increases in lipid perxidation and the amount of proline, with a negligible increase in glutathione content.These results revealed that increases occurred in some anti-oxidative stress enzymes in the salt-tolerant pepper genotype, as well as increases in glutathione content under salinity stress. These may provide better protection against reactive oxygen species (ROS).     

Morphological,anatomical and physiological responses of Campylotropis polyantha (Franch.) Schindl. seedlings to progressive water stress

In this study we implemented a potted water supply experiment for 100 days by a completely random sole-factored design with five treatments: 100% (W₁₀₀), 80% (W₈₀), 60% (W₆₀), 40% (W₄₀) and 20% (W₂₀) of water holding capacity (WHC), corresponding to the soil volumetric water content (SVWC) maintained at 38.8 ± 0.3%, 31.6 ± 1.7%, 25.6 ± 1.3%, 16.5 ± 0.7%, and 8.1 ± 1.1%, respectively. The objective was to evaluate the ability of the 2-month-old Campylotropis polyantha (Franch.) Schindl. seedlings to tolerate drought and to explore the mechanism resisting drought. We monitored the growth process of seedling height and leaf number monthly and further investigated those changes in plant growth, dry mass accumulation and allocation, water-use efficiency (WUE), leaf functional traits, chlorophyll a fluorescence and pigment contents across the water deficit gradient. We found that the seedlings presented optimal growth, dry mass production, and physiological activity only at the W₁₀₀ and W₈₀ treatments and afterwards significantly decreased with progressive water deficit; the WUE was improved under moderate water stress (W₆₀ and W₄₀) but reduced under severe stress (W₂₀). The serious leaf shedding, growth stopping and seedling death under the W₂₀ condition revealed that the current-year shrub seedlings could not withstand severe drought. Water stress-induced decrease in total plant leaf area due to a combination of limited expansion of younger leaves and shedding of old leaves caused the leaf area ratio reduction under drought. The reduced mesophyll cell was a major anatomical response of leaves along the water stress gradient. The progressive water stress significantly damaged light harvesting complex and reduced photochemical processes and PSII activity. Our results clearly showed that the current-year shrub seedlings took the avoidance and tolerance mechanisms to withstand progressive drought stress and around 25.6% SVWC and around 12.3% SVWC separately are thresholds to limit the optimal growth and dry mass production and to last growing and surviving for the current-year shrub seedlings.     

Response to drought of two olive tree cultivars (cv Koroneki and Meski)

The effect of water deprivation on plant water status, photosynthetic gas exchange and fluorescence parameters in two different olive tree varieties (Olea europaea L. var. ‘koroneiki’, ‘Meski’) was studied. Two-year-old olive trees, grown in pots in greenhouse, were subjected to one of three drought treatments (i.e., mild, moderate and severe drought stress) and compared to control trees. Both the leaf water potential (Ψ_w) and the relative water content (RWC) of the two varieties decreased with increasing levels of drought stress. Koroneiki showed higher (less negative) values of Ψ_w and lower values of RWC than the Meski, particularly during severe drought stress.

Net photosynthetic assimilation and stomatal conductance declined with drought. This inactivation of photosynthetic activity was accompanied by changes in the fluorescence characteristics. The PSII maximal photochemical efficiency (F_v/F_m), the intrinsic efficiency of open PSII reaction centres (F_v′/F_m′), the photochemical efficiency of PSII (Φ_PSII) and the total electron flow (J_t) decreased during the development of drought stress.

The non-quenching photochimique (q_N) showed an increase in the response to water deficit. These observations are discussed in relation to the strategies developed to grow drought-resistant olive trees in arid areas.     

Hydro-priming increases seed germination and early seedling growth in two cultivars of Napa cabbage (Brassica rapa subsp. pekinensis) grown under salt stress

To assess the effects of hydro-priming on enhancing germination and seedling growth in Napa cabbage (Brassica rapa subsp. pekinensis) under salt stress, seeds of two Napa cabbage cultivars that differed in salt tolerance, ‘Lainong 50’ (salt-tolerant) and ‘Xiaoza-56’ (salt-sensitive), were soaked in distilled water at 20°C in the dark for 10 h. Hydro-primed and non-primed seeds were then germinated under six levels of salinity (0, 50, 100, 150, 200, or 250 mM NaCl) under laboratory conditions. Various germination traits (e.g., germination percentages, germination potential, and seedling vigour index), anti-oxidant enzyme [catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD)] activities, and proline and malondialdehyde (MDA) concentrations were then measured in 7-d-old seedlings. The results showed that salt-stress decreased seed germination traits and reduced early seedling growth in both Napa cabbage cultivars. Hydro-priming increased the seed germination percentages and early seedling growth in both cultivars grown under salt stress. These effects were significantly positively correlated with the activities of POD and CAT, and the accumulation of proline, which can alleviate oxidative membrane damage and result in decreased MDA concentrations. These findings suggest that hydro-priming is an effective method to increase seed germination percentages, germination potential, and early seedling growth in Napa cabbage grown under salt stress.     

Photosynthetic characteristics of highbush blueberry (Vaccinium corymbosum cv. Bluecrop) leaves in response to water stress and subsequent re-irrigation

SUMMARY

Gas exchange and photosystem II (PSII) activities in the leaves of 2-year-old ‘Bluecrop’ highbush blueberry (Vaccinium corymbosum) were monitored during water stress and subsequent re-irrigation to investigate the effects of the intensity of water stress on changes in photosynthetic characteristics. The blueberry shrubs were not irrigated for 3 to 5 weeks, then re-irrigated daily up to 8 weeks. The decrease in soil water potential during water stress caused a progressive decrease in leaf water potential. Soil water potentials decreased to -0.26 MPa and -0.34 MPa at 3 and 5 weeks, respectively, following water stress, but recovered following subsequent re-irrigation, while the soil water potential in daily-irrigated shrubs was maintained at over -0.13 MPa throughout the experiment. Chlorophyll concentrations decreased with an increasing duration of water stress. Chlorophyll concentrations in leaves on shrubs subjected to water stress for 5 weeks did not recover following re-irrigation, unlike those subjected to water stress for 3 weeks. The leaves on shrubs subjected to water stress for 5 weeks maintained lower levels of chlorophyll during reirrigation. The net rate of CO₂ assimilation (A_n) decreased significantly with an increasing duration of water stress. Reirrigation reversed the decrease in A_n in leaves on shrubs subjected to water stress for 3 weeks. Stomatal conductance (g_s) exhibited a similar pattern to A_n. The actual quantum yield of photosystem II (Φ_PSII) and the electron transport rate (ETR) also decreased significantly with an increasing duration of water stress, although the F_v/F_m ratio was not affected. Φ_PPSII and ETR values in the leaves on shrubs subjected to water stress for 5 weeks did not recover after reirrigation, unlike those subjected to water stress for 3 weeks. Non-photochemical quenching increased with an increasing duration of water stress, but subsequent re-irrigation did not reverse the increase. These results indicate that the timing of re-irrigation of water-stressed ‘Bluecrop’ highbush blueberry is critical in order to maintain their photosynthetic capacity. Among the photosynthetic characteristics measured, Φ_PSII and ETR could be used as sensitive indicators to assess the physiological status of leaves of ‘Bluecrop’ highbush blueberry growing under water stress conditions.     

Effect of water deficit and rewatering on leaf gas exchange and transpiration decline of excised leaves of four grapevine (Vitis vinifera L.) cultivars

Grapevine cultivars are known to differ in their drought adaptation mechanisms, but there is little knowledge on how they behave when recovering after a drought event. The effects of increasing water deficit and recovery after rewatering were evaluated on four widely grown red grapevine cultivars native from different climates (Cabernet Sauvignon, Cs; Garnacha, syn. Grenache, Ga; Merlot, Me; and Tempranillo, Te) through the study of gas exchange (GE) measurements and transpiration decline curves (TDC). As a whole, Ga has proved to be the cultivar best adapted to water deficit, since it showed the highest water use efficiency (WUE) and the greatest water saving ability after leaf excision. Te, on the contrary showed the lowest values for those parameters under increasing stress, although when rewatered showed greater acclimation ability than Cs and Me, remarkably improving its behaviour. The two methodological approaches (GE and TDC) used at different water deficit levels and after rewatering, have complemented each other, allowing a better cultivar characterization than each method would had allowed itself.     

Photosynthetic and physiological responses to high temperature in grapevine (Vitis vinifera L.) leaves during the seedling stage

To study the effects of high temperature (HT) on grape growth, a controlled experiment with grapevine (Vitis vinifera L., cv. Hongti) was conducted from July to October, 2015. The HT treatments were 34, 36, 38, and 40°C, with 28°C as control. The changes to photosynthetic pigment characteristics, antioxidant enzyme activities, and relative water content (RWC) under different HTs were investigated. Severe chlorosis was observed during the late stages of HT treatment. Chlorophyll a (Chl a), chlorophyll b (Chl b), photosynthetic rate at irradiation saturation (P_max), light saturation point (LSP), apparent quantum efficiency (AQE), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity in grape leaves increased at first, and then decreased under high-temperature stress (HTS), but the light compensation point acted contrary to the LSP. The carotenoid, malondialdehyde and relative electrical conductivity (REC) increased under HTS; and the Chl/carotenoid ratio and RWC were contrary to the REC. The results suggested that grapes subjected to 38°C for 4 d decreased their RWC, but Chl a, Chl b, P_max, AQE, LSP, SOD, POD, and CAT reached their maximums. Therefore, the high-temperature limit of Hongti was 38°C and the duration time was 4 d.     

Osmotic adjustment,proline accumulation and cell membrane stability in leaves of Cocos nucifera submitted to drought stress

The role of drought-induced proline accumulation in coconut leaves is still unclear. With the objective of evaluating the impact of water shortage on leaf osmotic potential, proline accumulation and cell membrane stability in young plants of two Brazilian Green Dwarf coconut ecotypes from contrasting areas (Brazilian Green Dwarf from Una, Bahia, UGD, and from Jiqui, Rio Grande do Norte, JGD), a pot experiment was conducted under greenhouse conditions. Three drought cycles consisting of suspension of irrigation until the net photosynthetic rate (A) approached zero and rewatering until recovery of A to 85% of the irrigated control plants. Pre-dawn leaf water potential (Ψ_PD) reached −1.2 MPa at the point of maximum stress (PMS). Dry matter production and leaf area were severely reduced by drought treatment in the two ecotypes. Corrected values of osmotic potential were significantly reduced in stressed plants of the two ecotypes. Green dwarf coconut palm showed low osmotic adjustment (from 0.05 to 0.24 MPa) and significant accumulation of proline (from 1.5 to 2.1 times in relation to control) in leaflets in response to water deficit. Considering the growth reduction observed in both ecotypes, proline was not associated to osmoregulation. On the other hand, the absence of membrane damage, as indicated by electrolyte leakage method, suggests that the protective role of proline in this specie can be more important. The two ecotypes of Green dwarf coconut palm behaved similarly in the present experiment for most traits evaluated. Slight differences among the ecotypes were observed with respect to the response to treatments, such as higher proline accumulation in JGD.     

Effect of cold and drought stress on blueberry dehydrin accumulation

Summary

Dehydrins are a group of plant proteins which respond to any type of stress that causes dehydration at the cellular level, such as cold and drought stress. Previously, three dehydrins of 65, 60, and 14.kDa were identified as the predominant proteins present in cold acclimated blueberry (Vaccinium corymbosumLinn.) floral buds. Levels were shown to increase with cold acclimation and decrease with deacclimation and resumption of growth. In the present study, to determine if dehydrins are induced in other organs in response to low temperature treatment (48C) and in response to drought, accumulation of dehydrins was examined in leaves, stems, and roots of two cultivars and one wild selection (a V. corymbosum cultivar, a V. ashei Reade cultivar, and a V. darrowi Camp selection) of blueberry by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) followed by immunoblotting. Cold treatment involved placing plants in a cold room maintained at 48C for five weeks; drought stress was imposed by withholding water from potted, greenhouse-grown plants for 34.d. Relative water content (RWC) of shoots was determined periodically throughout the drought treatment. Dehydrins accumulated with both cold and drought stress but their molecular masses varied depending upon blueberry species. Dehydrins accumulated to higher levels in stems and roots than in leaves with cold stress and to higher levels in stems than in either roots or leaves with drought stress. Furthermore, cold treatment combined with dark treatment induced higher levels of dehydrins than cold treatment combined with a 10.h light/14.h dark photoperiod, suggesting that dehydrins may be responsive to changes in photoperiod as well. In the cold-stress experiment, the level of dehydrin accumulation was correlated with expected level of plant cold hardiness in the three genotypes. In the drought stress experiment, dehydrins accumulated prior to significant changes in RWC, and dehydrin levels did not appear to be closely correlated with RWC either among or within genotypes.