Development Of Drought Stress Research Articles

Eco-Physiological Behavior of Five Tunisian Olive Tree Cultivars under Drought Stress

Tunisia is known to be a country with poor water resources, and water scarcity is evident in certain regions. In the long term, this situation could worsen, given the increased risk of drought. The olive tree (Olea europaea L.) is one of the plants best adapted to this climate, and numerous studies have been carried out to assess the effects of water stress. The aim of this work was to study and compare the ecophysiological behavior of a main Tunisian olive cultivar (Chetoui) and four rare Tunisian olive cultivars (Chemchali, Besbessi, Sayali and Jarboui) under drought stress and to identify the main parameters while comparing the tolerance of the cultivars studied to this abiotic stress. One-year-old olive trees grown in pots in a greenhouse were subjected to four drought treatments (i.e., 15, 30, 45 and 60 days of drought stress) in comparison with control trees. The evaluation of the response of the olives to this induced stress was based on five parameters: relative water content (RWC), stomatal resistance (SR), photosystem PSII, maximal photochemical efficiency (FV/FM), performance index on absorption basis (PI), measured by the handy PEA, and chlorophyll index, measured by SPAD. The relative water content (RWC) of the five cultivars decreased with increasing drought stress. Jarboui showed lower RWC values than Chemchali, especially under severe drought stress. This result was confirmed by changes in fluorescence characteristics. FV/FM, PI and SPAD index decreased during the development of drought stress. These observations are discussed in relation to the strategies developed by the cultivars to grow under drought stress. The Principal Component Analysis allowed the parameter with the strongest loading factor, which is FV/FM, to be highlighted and the cultivars most tolerant to drought stress to be distinguished. These cultivars, Besbessi and Sayali in the north of Tunisia and Chemchali in the south, can present a possible alternative to replace the local or foreign cultivars most cultivated in the country, which are characterized by high water needs.

The functional role of xylem parenchyma cells and aquaporins during recovery from severe water stress.

Xylem parenchyma cells [vessel associated cells (VACs)] constitute a significant fraction of the xylem in woody plants. These cells are often closely connected with xylem vessels or tracheids via simple pores (remnants of plasmodesmata fields). The close contact and biological activity of VACs during times of severe water stress and recovery from stress suggest that they are involved in the maintenance of xylem transport capacity and responsible for the restoration of vessel/tracheid functionality following embolism events. As recovery from embolism requires the transport of water across xylem parenchyma cell membranes, an understanding of stem-specific aquaporin expression patterns, localization and activity is a crucial part of any biological model dealing with embolism recovery processes in woody plants. In this review, we provide a short overview of xylem parenchyma cell biology with a special focus on aquaporins. In particular we address their distributions and activity during the development of drought stress, during the formation of embolism and the subsequent recovery from stress that may result in refilling. Complemented by the current biological model of parenchyma cell function during recovery from stress, this overview highlights recent breakthroughs on the unique ability of long-lived perennial plants to undergo cycles of embolism-recovery related to drought/rewetting or freeze/thaw events.

速生树种尾巨桉和竹柳幼苗耗水特性和水分利用效率研究

速生树种尾巨桉和竹柳因其水分消耗和利用问题引起了一些争议，因而受到了广泛的关注，由于尚缺乏科学的观测数据，而其中许多指责或支持也尚无定论，因此必须深入研究此2种树种耗水性能和水分利用效率，以期科学评价其水分消耗和利用性能。采用盆栽苗木称重法和Li-6400光合系统测定方法分别测定尾巨桉（<em>Eucalyptus urophylla</em>× <em>Eucalyptus</em> <em>grandis</em>）和竹柳（<em>Salix </em>sp.）苗木在不同土壤水分条件下耗水量、耗水速率和苗木不同生长期叶片净光合速率（<em>Pn</em>）、蒸腾速率（<em>Tr</em>）和水分利用效率（WUE），研究表明：（1）正常水分条件下，尾巨桉和竹柳日总耗水量和最大耗水速率分别为（182.05±12.74）g/d、（100.48±10.95）g/d和（66.31±9.91）g·m^-2·h^-1、（89.50±13.54）g·m^-2·h^-1，土壤水分条件下降时，2种苗木耗水量和耗水速率均呈显著下降趋势，严重干旱胁迫时尾巨桉降幅更大。（2）正常水分条件和轻度水分胁迫下2种苗木耗水速率日变化趋势均为明显单峰曲线，且峰值均出现在12：00-14：00，中度干旱胁迫时则其变化趋势呈“双峰”曲线，峰值分别在10：00-12：00和14：00-16：00出现，严重干旱胁迫时日变化规律不明显。（3）正常水分条件和轻度水分胁迫下2种苗木耗水速率与环境温度显著正相关，与相对湿度显著负相关，随着干旱胁迫的发展，环境因子对耗水速率的影响有所减弱。（4）叶片水平来看，与尾巨桉相比，竹柳具有高光合、低蒸腾、高水分利用效率的特点，2种苗木由生长初期进入生长旺期时，净光合速率和蒸腾速率均发生相同幅度增加，而水分利用效率基本保持不变。（5）从单株耗水量和耗水速率以及叶片水分利用效率综合来看，竹柳属节水性能较好速生树种，而尾巨桉虽然存在叶片水平高蒸腾和低水分利用效率的情况，但从单株苗木水平上来讲，其耗水速率甚至低于竹柳，特别在土壤水分严重亏缺情况下其白天平均耗水速率仅为（4.02±0.60）g·m^-2·h^-1，也表现出了一定的抗旱节水能力。;<em>Eucalyptus urophylla</em> × <em>Eucalyptus grandis</em> and bamboo-willow have attracted wide concerns due to the debates on their water consumption (WC) and utilization efficiency problems. Insufficiency of scientific observation data and consequent uncertainty of the rationality of blame or support on the two trees' development make it a necessity to further study their WC characteristics and water use efficiency (WUE). In this study, WC and water consumption rate (WCR) of<em> E. urophylla</em> × <em>E. grandis</em> and bamboo-willow seedlings under different soil moisture conditions were measured by pot seedling weight method, and net photosynthetic rate (<em>Pn</em>), transpiration rate (<em>Tr</em>) and WUE of them in different growth periods were investigated by Li-6400 photosynthetic system measuring method. Under normal water condition, day-and-night WC and maximum WCR of <em>E. urophylla</em> × <em>E. grandis</em> and bamboo-willow seedlings were(182.05±12.74)g/d,(100.48±10.95)g/d, (66.31±9.91)g·m^-2·h^-1 and(89.50±13.54)g·m^-2·h^-1, respectively. Water consumption and WCR of the seedlings significantly declined with soil moisture decreases, with those of <em>E. urophylla</em> × <em>E. grandis</em> declining more sharply than bamboo-willow under serious drought stress. The daily variation of WCR exhibited a one-peak curve (the peak appearing at 12:00-14:00) under normal water condition and light drought stress, but changed to a double-peak curve (the peaks appearing at 10:00-12:00 and 14:00-16:00, respectively)under moderate drought stress, and showed no regular pattern under serious drought stress. Under normal water condition and light drought stress, a significant positive correlation and a significant negative correlation were observed between WCR and environmental temperature and between WCR and relative humidity, respectively. The influence of environmental factors on WCR weakened along with the development of drought stress. At leaf level, bamboo-willow had higher photosynthetic rate and WUE, and lower transpiration rate than <em>E. urophylla</em> × <em>E. grandis.</em> In initial through vigorous growth period, net photosynthetic rate and transpiration rate of both seedlings increased at similar amplitude, while their WUE remained unchanged. In terms of WC and WCR of individual seedling and leaf WUE, bamboo-willow was a good water-saving fast-growing tree species. <em>E. urophylla</em> × <em>E. grandis</em> had higher leaf transpiration rate and lower WUE at leaf level, but had lower WCR at individual seedling level than bamboo-willow, which was particularly true when under serious drought stress, with its average daytime WCR being only (4.02±0.60) g·m^-2·h^-1. Therefore, <em>E. urophylla</em> × <em>E. grandis</em> seedlings also showed a certain ability of drought resistance and water-saving.

Antioxidant enzyme activities and gene expression patterns in peanut nodules during a drought and rehydration cycle.

Drought stress is one of the most important environmental factors that affect plant growth and limit biomass production. Most studies focus on drought stress development but the reversibility of the effects receives less attention. Therefore, the present work aims to explore the biological nitrogen fixation (BNF) of the symbiotic association between peanut (Arachis hypogaea L.) and Bradyrhizobium sp. during a drought-recovery cycle with a focus on the response of enzyme activity and gene expression of the antioxidant system. Peanuts exposed to drought stress had impaired BNF, as indicated by lower nitrogenase activity, and decreased leghaemoglobin content; the latter was reversed to control values upon rehydration. Previous results demonstrated that reactive oxygen species (O2·- and H2O2) were accumulated as a consequence of drought stress, suggesting that nodules experience oxidative stress. In addition, marker transcripts responsive to drought, abscisic acid and H2O2 were upregulated. Increased transcript levels of glutathione reductase were associated with an increased enzyme activity but superoxide dismutase and glutathione S-transferase activities were unchanged, despite upregulated gene transcription. In contrast, increased activity of ascorbate peroxidase (APX) was unrelated with changes in cytosolic APX transcript levels suggesting isogene specificity. In conclusion, the work exemplarily demonstrates the efficient and dynamic regulation of antioxidant enzymes and marker compounds during drought cycling, which is likely to be a prerequisite for functional optimisation of nodule metabolism.

Study of the effect of abiotic stress on the antioxidant enzyme activity of cereals under regulated environmental conditions

The impacts of climate modification were examined in terms of changes in the stress tolerance of winter wheat varieties. The enzyme reactions of two winter wheat varieties to drought stress, simulated by water withholding in three different phenophases, were analysed in a phytotron experiment in the Centre for Agricultural Research, Hungarian Academy of Sciences. Plants were raised either at ambient CO2 level or at twice this concentration. The quantities of glutathione reductase (GR), glutathione-S-transferase (GST), catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX) were determined from leaf samples collected at the end of the drought treatment.The results showed that antioxidant enzymes may help to counterbalance the reactive oxygen species induced by stress during various stages of the vegetation period. Although there were substantial differences in the changes induced in the activity of individual enzymes by modifications in environmental factors, this activity and its response to stress depended not only on these factors, but also on the developmental stage of the plant. Modifications in enzyme activity could indicate that enhanced CO2 concentration delayed the development of drought stress up to first node appearance, and stimulated antioxidant enzyme activity when drought occurred during ripening.

Clear link between drought stress, photosynthesis and biogenic volatile organic compounds in Fagus sylvatica L.

Direct plant stress sensing is the key for a quantitative understanding of drought stress effects on biogenic volatile organic compound (BVOC) emissions. A given level of drought stress might have a fundamentally different effect on the BVOC emissions of different plants. For the first time, we continuously quantified the level of drought stress in a young potted beech (Fagus sylvatica L.) with a linear variable displacement transducer (LVDT) installed at stem level in combination with simultaneous measurements of BVOC emissions and photosynthesis rates at leaf level. This continuous set of measurements allowed us to examine how beech alters its pattern of photosynthesis and carbon allocation to BVOC emissions (mainly monoterpenes, MTs) and radial stem growth during the development of drought stress. We observed an increasing-decreasing trend in the MT emissions as well as in the fraction of assimilated carbon re-emitted back into the atmosphere (ranging between 0.14 and 0.01%). We were able to link these dynamics to pronounced changes in radial stem growth, which served as a direct plant stress indicator. Interestingly, we detected a sudden burst in emission of a non-identified, non-MT BVOC species when drought stress was acute (i.e. pronounced negative stem growth). This burst might have been caused by a certain stress-related green leaf volatile, which disappeared immediately upon re-watering and thus the alleviation of drought stress. These results highlight that direct plant stress sensing creates opportunities to understand the overall complexity of stress-related BVOC emissions.

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.

Drought can be more critical in the shade than in the sun: a field study of carbon gain and photo‐inhibition in a Californian shrub during a dry El Niño year

AbstractDiurnal courses of leaf water potential (Ψl), gas exchange and chlorophyll fluorescence were measured in natural sun and shade populations of Heteromeles arbutifolia throughout the seasons of an unusually dry El Niño year in Central California. The onset of drought resulted in decreased stomatal conductance and net photosynthesis in both sun and shade plants. However, the decline in Ψl was much greater and carbon gain was much more strongly limited by the development of drought stress in the shade than in the sun. Photorespiratory energy dissipation was significantly higher in the sun than in the shade in spring and autumn, but not during the summer. Pre‐dawn photochemical efficiency (Fv/Fm) was significantly higher in the shade than in the sun during the spring but the differences disappeared during the summer and autumn. The strong irradiance in the open field site studied led to a chronic but only mild reduction in Fv/Fm, with values around 0·79. Summer sunflecks led to a sustained photo‐inhibition in shade plants, which exhibited a significant reduction in pre‐dawn Fv/Fm of 10% with the onset of drought. Photo‐inhibition became relatively more important for carbon gain in the shade than in the sun due to the low photochemical efficiency under the low light that follows sunflecks. Sun plants of H. arbutifolia exhibited a rather efficient photoprotection against strong irradiance conferred by both the architecture of the crown and the physiology of the leaves. There is evidence that El Niño events and the associated droughts have become more frequent and severe. Counter‐intuitively, the effects on plant performance of such extreme droughts could be more critical in the shade than in the sun.

Water Transfer in a Papaya/Corn Split-root Culture System

`Honey Jean #3' sweet corn was planted in one-half of a split-root culture system containing `Tainung 1' or `Known You 1' papaya seedlings to determine if papaya roots could transfer water to the corn seedlings. After the corn seedlings were established, water was withheld from both compartments (2/2) or only the compartment containing the corn seedlings (1/2). Control plants were grown with both halves well-watered. Pre-dawn relative water content (RWC) of corn leaves was measured as an indicator of drought stress. Following 11 days, root competition was relieved in half of the 1/2 plants by cutting the papaya root connection between the half with corn from the rest of the papaya culture system. RWC of 1/2 corn plants was maintained above that of 2/2 plants, but below that of control plants. After relieving root competition, the 1/2 plants in competition with papaya roots maintained higher RWC than the 1/2 plants relieved of competition. Leaf tissue of all corn plants except the control plants was necrotic by 30 days. The results indicate that development of drought stress in corn using this culture system was retarded by watering a portion of the papaya roots not associated with the corn roots. Drought stress was accelerated by relief of competition with papaya, which is evidence that water was being supplied by the papaya roots within the papaya/corn system.