Days Of Water Stress Research Articles

A HYDRUS model for irrigation management of green roofs with a water storage layer

Green roofs suffer from water stress during prolonged dry periods. Periodically irrigation is usually needed to maintain the health of green roofs. This paper presents a green roof model for simulating the long term variation of soil moisture of green roofs with a storage layer. The model mainly incorporates a HYDRUS-1D model for the soil layer and an evaporation model for the storage layer. It explicitly accounts for the effects of evaporation from the storage layer on the soil moisture. After calibration and validation with the observed data of a pilot green roof, the model was implemented to evaluate the efficiency of various irrigation schemes for the green roofs built with different structural designs under typical weather conditions in Shenzhen, China. The results indicate that without irrigation the green roofs experience water stress (defined as soil moisture <60% of the field capacity) in more than 35% of days in a year. As the irrigation frequency increases, the days of water stress decrease but the total irrigation amount increases. Irrigation to the field capacity every 3days and irrigation to the saturation moisture content every 7days are two relatively efficient irrigation schemes, which can achieve optimal tradeoffs between the objectives of saving irrigation water and maintaining adequate soil water availability to the green roof plants. Furthermore, as the soil layer depth increases, the days of water stress decrease but the total irrigation amount increases. While as the storage layer depth increases, both the days of water stress and the total irrigation amount decrease. The study demonstrates that the model has the capacity to evaluating the efficiency of the irrigation schemes for the green roof. Therefore, it can help support the irrigation management of green roofs.

Assessing the supplementary irrigation for improving crop productivity in water stress region using spatial hydrological model

Water stress during crop cultivation due to inconsistent rainfall is a common phenomenon in maize growing area of Shanmuganadi watershed, located in the semi-arid region of southern peninsular India. The objective is to estimate the supplementary irrigation required to improve the crop productivity during water stress period. Spatial hydrological model, Soil and Water Assessment Tool, has been applied to simulate the watershed hydrology and crop growth for rabi season (October–February) considering the rainfed and irrigated scenarios. The average water stress days of rainfed maize was 60 days with yield of 1.6 t/ha. Irrigated maize with supplementary irrigation of 93–126 mm was resulted in improved yield of 3.8 t/ha with 28 water stress days. The results also suggest that supplemental irrigation can be obtained from groundwater reserves and by adopting early sowing strategy can provide opportunities for improving water productivity in rainfed farming.

Plant and Leaf Physiological Responses to Water Stress in Potted ‘Vignoles’ Grapevine

Several studies have investigated water relationships in grapevines, but the responses to water limitation on individual leaves developed in different shoot positions are scarce in the literature. To begin to fill-in this gap, we examined the adaptive responses of vines at the leaf level to varying amounts of water stress using young hybrid ‘Vignoles’ in a controlled growth chamber. We found that the reduction in water availability to 40% of daily evapotranspiration limited shoot and leaf growth, affecting leaf number, shoot elongation, and leaf area. After 2 days of water stress we observed young developing leaves (nodes six to eight from the shoot apex) to have drastically reduced stomatal conductance (gS, about 20 mmol H2O/m2/s) and net photosynthesis (Pn, 2 μmol CO2/m2/s). On the 4th day Pn in mature leaves (nodes 9 to 12 from the shoot apex) fell to values below 2 μmol CO2/m2/s. After 6 days, both Pn and gS stabilized at lower values with fluctuations related only to leaf position along the shoot axis. Young leaves revealed substantial enrichment of carbon-13 (13C) and high water-use efficiency suggesting a higher and faster adaptive capacity to water shortage conditions as compared with mature leaves.

Role of phytosterols in drought stress tolerance in rice

Phytosterols are integral components of the membrane lipid bilayer in plants. They regulate membrane fluidity to influence its properties, functions and structure. An increase in accumulation of phytosterols namely campesterol, stigmasterol and β-sitosterol was observed in rice as seedlings matured. The levels of the major phytosterol, β-sitosterol in N22 (drought tolerant) rice seedlings was found to increase proportionately with severity of drought stress. Its levels were 145, 216, 345 and 364 μg/g FW after subjecting to water stress for 3, 6, 9 and 12 days respectively, while for IR64 (drought susceptible), levels were 137, 198, 227 and 287 μg/g FW at the same stages. Phytosterols were also found to increase with maturity as observed at 30, 50 and 75 days after planting. The activity of HMG-CoA reductase (EC 1.1.1.34) which is considered to be a key limiting enzyme in the biosynthesis of phytosterols was 0.55, 0.56, 0.78 and 0.85 μmol/min/L at 3, 6, 9 and 12 days of water stress in N22 and 0.31, 0.50, 0.54 and 0.65 μmol/min/L in case of IR64 respectively. The elevation in the levels of phytosterols as well as the activity of HMG-CoA reductase during drought stress indicates the role of phytosterols in providing tolerance to stress.

Partial rootzone drying (PRD) and regulated deficit irrigation (RDI) effects on stomatal conductance, growth, photosynthetic capacity, and water-use efficiency of papaya

Papaya (Carica papaya, L.) is an important economic crop in tropical and subtropical countries. It is a giant herbaceous species; maintaining adequate tissue turgidity and water availability is necessary to maintain the rigidity of the stem as well as increase productivity. Water-saving irrigation techniques for papaya will be needed in the future due to the possibility of water shortages related to climate change. The morphological and physiological responses of ‘Grand Golden’ papaya to partial root drying (PRD), regulated deficit irrigation (RDI) and no irrigation followed by re-hydration (NI-gh) in a greenhouse study or no irrigation (NI-field) in a field study were compared with full irrigation (FI). In the greenhouse study, plants were grown in pot with roots split equally between two soil columns. In the field study, drip emitters on opposite sides of the plant delivered irrigation water. In FI, the whole root system was irrigated at 100% of water use; in RDI 50% or 70% of FI water use was supplied to the whole root system (greenhouse and field study, respectively); in PRD 100% of FI was supplied to half the root zone while the other was allowed to dry to 50% or 70% of FI (greenhouse, and field study, respectively). In the field study, PRD was achieved by applying different amounts of irrigation water to alternate sides of the root system within the plant row. The application of 50% water use in PRD and RDI in the greenhouse study decreased shoot and root dry weight production, with a more pronounced effect on root dry weight compared to FI. This decrease in biomass was associated with a decrease in the net photosynthetic rate in the day of most intense water stress for the plants in NI-gh. In the field study, a 30% water deficit in both PRD and RDI treatments did not significantly reduce vegetative growth or yield components (number fruitplant−1, average weight (g)fruit−1, kgfruitha−1, kgfruitplant−1), compared to FI. In greenhouse conditions there was evidence of a non-hydraulic signal in the PRD treatments decreasing Gs compared to RDI at comparable soil water tension but it was insufficient to affect shoot growth or yield components in field conditions. There was no difference in the instantaneous leaf water use efficiency (WUE, A/E) of PRD or RDI treatments in the greenhouse or the agronomic water use efficiency (AWUE) (kgfruitL−1 and number fruitL−1) in the PRD and RDI treatments in the field but both treatments improved AWUE compared to FI. It appears that papaya can tolerate some water deficits without a significant reduction in yield components indicating that <100% ET0 irrigation replacement can be scheduled but there is little or no benefit to PRD.

Silicon supplementation improves drought tolerance in canola plants

This paper reports the effects of silicon (Si) supplementation (0.35 g Na2SiO3/kg soil, 2.73 mmol Si/kg soil) on some physiological characteristics of canola (Brassica napus L. cv. Okapi) plants grown in pots and treated with or without Si under water stress for 25 days. In this study, Si-supplied plants showed the higher shoot dry weight (SDW), root dry weight (RDW), relative growth rate (RGR), net assimilation rate (NAR), and relative water content (RWC) as compared to those without application of Si under drought conditions. However, Si did not significantly affect dry weight accumulation under well-watered conditions. CO2 absorbance (A) was increased by silicon under water stress conditions. The intracellular CO2 concentration (Ci), which was significantly elevated under water stress, was decreased by Si. Silicon application significantly increased the root amino acid content after 20 and 25 days of water stress. In Si-supplemented water-deficit plants, the amount of MDA remained unchanged after 25 days of water stress, obviously because of an efficient scavenging following significant enhancement of superoxide dismutase (SOD) and peroxidase (POD) activities. These results indicated that Si ameliorated growth reduction of drought-stressed canola plants, accompanied by an increase in the root water uptake through the formation of more fine roots and more amino acids as osmotica for supporting water uptake. The results of this study revealed that Si application alleviated water stress damages because of the higher water uptake, better photosynthetic rate, and the lowered lipid peroxidation in canola plants.

Instantaneously measured traits may detect non-plastic ecophysiological performances in response to drought, explaining distributions of Styrax species in the Cerrado

We analyzed the differences between irrigated and non-irrigated plants of three congeneric Styrax species that present distinct distribution patterns in the physiognomies of the Cerrado vegetation in Brazil. Styrax ferrugineus showed a stomatal conductance (g s) unresponsive to soil water deficit in potted plants. This may explain the high gas exchange and photochemical efficiency found in this species, which is well adapted to the Cerrado sensu stricto (s. str.), a savanna-type vegetation. S. camporum, which is widely distributed in the Cerrado sensu lato (s. l.) areas, was the only species that exhibited increased intrinsic water use efficiency on the days of maximum water deficit. This result distinguishes S. camporum from S. pohlii, which is a forest species, since the g s of both species decreased during the days of maximum water stress. In contrast to other studies, we propose that instantaneously measured traits, such as leaf gas exchange rates and chlorophyll fluorescence, may be used to detect non-plastic performances in response to environmental stress, helping explain distinct geographical distributions of congeneric species in the Cerrado vegetation.

Differential accumulation of osmolytes in 4 cultivars of peanut (Arachis hypogaea L.) under drought stress

The study investigates the differential accumulation of osmolytes and their contribution to osmotic adjustment in leaf tissue of peanut under drought stress. Plants of four peanut cultivars, obtained from ICRISAT, with varying degrees of drought tolerance were subjected to 10, 15, and 20 days of drought stress by withholding irrigation to 20-day-old seedlings. Leaf samples were collected on 31st, 36th, and 41st days from these stressed plants along with their respective controls. The results indicated that ICGV 91114 was the most drought-tolerant variety followed by ICGS 76 and J 11, while JL 24 was the most drought susceptible. The leaves of ICGV 91114 maintained higher RWC and chlorophyll pigments under water stress compared to JL 24. The contents of all the biochemicals were found to be the maximum in ICGV 91114 and least in JL 24 during stress periods. Drought induced increase in the contents of TSS and TRS were significantly higher in ICGV 91114 under 15 days of water stress compared to the other three varieties and stress periods, while TLP, total free amino acids and total proline were higher in 20-day-old stressed plants of ICGV 91114 and the lowest in 10-day-old stressed plants of JL 24. In the control plants of all four varieties, there was a steady increase in the contents of all these biochemicals with an increase in the age of the plants. The results suggest that osmolytes act as important compatible solutes to maintain osmotic balance, to protect cellular macromolecules, and scavenge free radicals under water stress conditions.

Simulating the hydrologic response of a semiarid watershed to switchgrass cultivation

The conversion of land from existing uses to biofuel cultivation is expected to increase given concerns about the sustainability of fossil fuel supplies. Nonetheless, research into the environmental impacts of biofuel crops, primarily the hydrological impacts of their cultivation, is in its infancy. To investigate such issues, the response of a 1,649 km2 semiarid basin to the incremental substitution of the widely discussed biofuel candidate switchgrass (Panicum virgatum L.) for native land uses was modeled using the Soil and Water Assessment Tool (SWAT). Median discharges decreased by 5.6–20.6% during the spring and by 6.4–31.2% during the summer, depending on the quantity of acreage converted. These were driven by an increased spring and summer evapotranspiration of 3.4–32.0% and 1.5–18.9%, respectively, depending on the quantity of switchgrass biomass produced. The substitution of switchgrass also resulted in larger quantities of water stress days than in baseline scenarios. The authors encourage the exploration of alternative biofuel crops in semiarid areas to mitigate such negative impacts.

Water relations, growth, and leaf gas exchange as affected by water stress in Jatropha curcas

Here we examined the response mechanisms and the strategies adopted to cope with drought stress in Jatropha curcas L. Response mechanisms to water stress were explored in three different accessions (from Brazil, Tanzania and Suriname) of J. curcas in terms of water and osmotic relations, gas exchange, PSII photochemistry, and growth performances. Plants were exposed to 18 days of water stress (irrigation was kept at 20% of water holding capacity) followed by 13 days of relief from stress. J. curcas withstands drought stress with a drought-avoidance mechanism through a water saving strategy. These responses include selective abscission of leaves, and marked decreases in net photosynthetic rates and water use efficiency. This allows plants to maintain an “above-lethal” water potential during stress, and to recover net assimilation rate promptly when water availability to the roots is resumed. The Suriname accession displayed greater reductions in net photosynthesis, maximal efficiency of PSII photochemistry (Fv/Fm), total leaf area and plant dry weight, as compared with both Tanzania and, particularly, the Brazil accession, during drought stress. Impairment of PSII photochemistry was also observed in the Suriname accession at the end of the relief period. Water-stressed J. curcas, irrespective of seed source, was capable to recover net photosynthesis to the level of the well watered counterparts by the end of the relief period. Our data allow to conclude that J. curcas may survive to drought spells of moderate intensities but, at the same time pose serious concerns for its profitable cultivation in arid/semi-arid regions worldwide.

Water stress during grain development affects starch synthesis, composition and physicochemical properties in triticale

Triticale, a man-made cereal crop developed from a cross between wheat and rye, has excellent agronomic traits to produce starch for bioindustrial applications. The effects of different levels of water stress on expression of starch synthesis genes and starch composition and physicochemical properties were investigated in this study. Three triticale varieties from 5 days post-anthesis were treated with three levels of water stress: low water stress (LWS) at 55–60% of soil moisture, moderate water stress (MWS) at 30–35% soil moisture and severe water stress (SWS) at 10–15% soil moisture. Water stress led to a significant reduction in seed weight at SWS (35–45%). A decrease in starch content was noticeable from MWS onwards and the values were decreased by 42–55% at SWS across all varieties. Such decrease was associated with the reduced expression of starch synthesis genes at 19 days of water stress (DWS). MWS favoured an increase of amylose proportion in triticale starch and it was accompanied by a significant up-regulation of GBSSI expression throughout the grain development. Triticale starch synthesized under water stress showed a reduced population of small granules and an increase of A-type to B-type ratio. SWS caused pitting on starch granules but did not alter the biconcave disc shape of mature granules. An inverse relationship between water stress and a range of starch gelatinization temperature was observed and the MWS environment specifically decreased the peak temperature (Tp) and increased the enthalpy. Our results signify that starch morphology, composition and physicochemical properties in triticale grains could be altered if triticale is grown under drought conditions.

Drought tolerance of passion fruit plants assessed by the OJIP chlorophyll a fluorescence transient

Chlorophyll a fluorescence of two passion fruit cultivars grown in a greenhouse were evaluated to determine the effect of induced water stress and recovery on young plants. One month-old passion (Passiflora edulis Sims) cv. Yellow Master (FB200) and Maguary (FB300) plants were evaluated in 11.0L pots after 11 days of water withholding, imposed by suspension of irrigation, and after six days of rewatering. Drought treatment increased all points of the OJIP curves in FB200 plants. With water stress, reductions of ΔVOP occurred in FB300 only in J–I phase, while all phases from OJIP curve were reduced in FB200. J–I phase showed signals of recovery within six days in FB200 but this period of rewatering was not sufficient for recovery of O–J and I–P phases. There was total recovery of ΔVOP values in FB300 followed by an increment of efficiency which an electron is transfer to photosystem I (PSI) acceptor side, evidenced by a positive increase of I–P phase after stress. To FB200, L and K-band increased after five days of water stress with partial recovery after one week rewatering. But, to FB300, significant difference of bands was only observed at 11 days from water withholding and the difference between water treatments was very evident, with total recovery after rewatering. On the day of maximum stress, the maximum efficiency of PSII (Fv/Fm ratio) decreased significantly in both passion cultivars while the effective antenna size of an active reaction center (ABS/RC) values increased 24 and 11% in FB200 and FB300, respectively. With rewatering of plants, declines of Fv/Fm values persisted by at least three days in FB200 passion cultivar. Also, increases of ABS/RC in FB200 (+110%) was irreversible and persisted until the six day after rewatering. These findings showed that two passion cultivars differed in the plasticity of their response to drought and rewatering and further shows that under drought conditions the FB300 plants possess an advantage over FB200 plants in terms of stability and efficiency in utilizing energy. Measurements of OJJIP fluorescence transients, Fv/Fm and ABS/RC ratios, analyzed using the JIP-test, were good tools for the screening of the potential to cope with and to recover from drought.

ROS production, H2O2 detection and biochemical characterization of water stressed wheat (Triticum aestivum L.) varieties

One month old plant of four varieties (MW, KD, GY and GN) of wheat (Triticum aestivum L.) was taken and subjected to water stress for 3, 6 and 9 days. RWC was found to be higher in case of GY and KD when compared to MW and GY. There was an initial enhancement in the activities of all five tested antioxidative enzymes- peroxidase, ascorbate peroxidase, catalase, glutathione reductase and superoxide dismutase in K and GN varieties, while in MW and GY, the activity of catalase and superoxide dismutase showed a decline at all periods of water stress. Peroxidase and glutathione reductase activities increased even on 9th day of stress in K and GN, but all other activities showed a decline after 3 days of stress. The accumulation of H202, showed an increase with increasing days of water stress but in K and GN there was a decline during prolonged water stress. Lipid peroxidation increased significantly which was higher in case of MW and GY. With increase in the duration of water stress proline, phenol and ascorbate content increased. Higher values of MSI and total antioxidant were observed in the cultivar KD and GY with increase in the severity of water stress than in MW and GY. After an initial enhancement the content of carotenoid increased followed by a decline. Total chlorophylls showed a general decline during water stress, but the ratio of chla/b showed an initial increase in the 3rd day of water stress which declined during the latter stages of water stress. Results of the present study indicate that two of the varieties- MW and GY are susceptible to water stress, while the other two-K and GN is tolerant.

Screening and resistance of traditional and improved cultivars of rice to drought stress at Badeggi, Niger State, Nigeria

One hundred and nine rice varieties were screened for drought to select promising varieties for hybridization programs and to be used in drought prone environments. The experiment was conducted in an open screen house in non- rainy days. The test entries were laid out in a randomized complete block design replicated three times. They were planted in a single row of 5 m each spaced at 20x20 cm. The plants were watered for 21 days before the stress was imposed. Leaf rolling score was taken at 18 days of water stress. Drought score was recorded at 28 days of water stress and 7 days after reapplication of water to access recovery. Result indicated that most varieties had scores between 4-6 that is at susceptible level. Two varieties had score of 2 and eight had score of 3. At 28 days of stress Danboto had a score of 4 and was better than other varieties. Thirteen entries could be selected for both drought tolerance and recovery. Danboto a local variety was the best variety with drought score of 4 and recovery score of 2. These entries were expected to provide higher yields after severe drought than those entries with high susceptibility.

Chlorophyll fluorescence technique as a rapid tool for in vitro screening of olive cultivars ( Olea europaea L.) tolerant to drought stress

The olive tree ( Olea europaea), a representative drought-stress-tolerant plant, is one of the most typical and economically important plant species grown in the Mediterranean area. As olive cultivars may exhibit a different level of drought tolerance, the selection of the most drought-tolerant cultivars acquires relevance. For this purpose the use of a chlorophyll fluorescence technique can be considered to be a promising tool, in order to rapidly quantify the response to physiological stress in higher plants. The aim of this study was to determine whether the information obtained with chlorophyll fluorescence measurements, carried out on detached olive leaves subjected to dehydration in vitro, could be translated in vivo to whole olive plants. For the in vitro measurements, a screening was carried out on detached leaves of 24 olive cultivars which were subjected to dehydration in an environmentally controlled growth chamber. The results showed that in vitro measurements were effective in evidencing sizeable differences in the F v/ F m ratio decline among the cultivars during the dehydration time period. Within 24 h, a strong decline in both the F v/ F m ratio and the leaf fresh weight could be appreciated. Indeed, the F v/ F m ratio decreased by 90% in the “susceptible” cultivars, whereas the “tolerant” ones did not show any decrease in F v/ F m. These results were confirmed by further measurements, which were carried out during the subsequent period under stress conditions and evidenced three different levels of “putative” drought tolerance. In accordance with this screening, six cultivars, defined as “putative” drought-tolerant ( Maurino and Ascolana tenera), “intermedium” ( Leccino and Nocellara del Belice), and “susceptible” ( Carolea and Biancolilla), were selected for the in vivo trials. The cultivars chosen were subjected to 28 days of severe water stress in a greenhouse. The in vivo measurements pointed out that the response of the whole plants to drought was correlated to the level of tolerance to leaf dehydration observed in vitro. For example, the Biancolilla and Carolea were found to be the most sensitive to drought stress, while Ascolana tenera and Maurino showed the highest level of tolerance, under both in vitro and in vivo conditions. The in vivo results indicated that chlorophyll fluorescence measurement was a valid tool for rapid in vitro screening of drought-stress tolerance in olive cultivars.

DROUGHT STRESS: Role of Carbohydrate Metabolism in Drought‐Induced Male Sterility in Rice Anthers*

AbstractRice plants exposed to three consecutive days of water stress (−0.5 MPa) show a reduction in male fertility and grain set, which is attributed to increased levels of reactive oxygen species (ROS) and activation of a programmed cell death. This current research was conducted to further investigate the association of sugar metabolism with microspore abortion in rice anthers. Biochemical assays showed that sucrose, glucose and fructose contents were found to be significantly increased in anthers from water stressed plants compared with the control. qRT‐PCR analyses and in situ hybridization of metabolic genes (sugar transporters, invertase and phosphotransferase/kinases) demonstrated that the supply of sugars for developing microspores and the initial steps of sugar utilization e.g. glycolysis, were not repressed. However, it appears that the accumulation of sugars in stressed anthers might involve a reduction of mitochondrial activity during the tricarboxylic acid cycle, which could result in excessive production of ROS and a depletion of the ATP pool. These results also suggest that higher levels of sugars at all stages of anther development seemed to be associated with some measure of protection to the anthers against oxidative stress. Induced expression of sugar transporter genes might have maintained the high levels of sugar in the tapetum and the locules, which alleviated oxidant damage caused by excessive ROS generation. Thus, the increased level of sugars might potentially be a natural response in providing protection against oxidant damage by strengthening the antioxidant system in anthers.

Growth and Yield of Rice (Oryza sativa L.) as affected by Cultivars, Seeding Depth and Water Deficits at Vegetative Stage

This study investigates the effects of different seeding depths and water stress on growth and yield of direct-seeded rice. The experiment was a 3x2x2 factorial in a randomized complete block design with four replications. The main factors (03) were seeding depths (0, 1 and 5 cm), water level (well watered and water stress at 30 days after seeding (DAS) and rice cultivars (Pathum Thani 1 and Suphan Buri 1). Above-ground biomass and root length density were significantly affected by rice cultivars, seeding depths and water stress. The Suphan Buri 1 had a higher above ground biomass and root length density than the Pathum Thani 1. At the first 7 days of water stress, maximum above-ground biomass was obtained at 1 cm seeding depth. But at a later stage, the highest above ground biomass was observed with a seeding depth of 5 cm at both 60 and 90 days after seeding. The greatest root length density was obtained at a seeding depth of 5 cm. Grain yield was significantly affected by seeding depths and water stress. The highest grain yield was obtained in 5 cm seeding depths compared with other low depth under water stress at vegetative stage (30 DAS). It was concluded that yield loss under water stress at vegetative stage may be compensated for by increasing seeding depth above shallow depth levels. (Resume d'auteur)

NOCTURNAL HEAT-PULSE SAP FLOW AS A SENSITIVE SYSTEM TO ASSESS DROUGHT EFFECTS ON GRAPEVINES: AN IRRIGATION SCHEDULING APPLICATION?

The compensated heat-pulse method, New Zealand (cHP) was tested on grapevines (Vitis vinifera L. cv. Shiraz) under a PRD trial in Benalla, Victoria (season 2003-2004). Results showed that vines (all treatments) where in constant stress during the season and PRD treatments were able to maintain an almost constant transpiration rate, independently of atmospheric demand, which could indicate a better stomatal control. Other whole-tree water status monitoring methods were midday stem water potential (Ψs) and infrared thermography (IR). The cHP offered a continuous and sensitive physiological technique to monitor the effect of watering at very low transpiration rates. Therefore, the sensors used were able to register night time sap flow (SN), which was more evident after irrigations and decreased gradually over time until the next irrigation. SN was significantly correlated to Ψs obtained from the day before. Monitoring SN could be a suitable method to assess grapevine water status and the capacity of vines to recover from the daily water stress. We propose SN as a possible irrigation scheduling technique.

Effect and after-effect of water stress on the distribution of newly-fixed 14C-photoassimilate in micropropagated apple plants

The effect and after-effect of water stress on the distribution of photoassimilate, fixed at different times during and after water stress, were investigated in one-year-old micropropagated ‘Gala’ apple plants ( Malus domestica Borkh.) by feeding mature leaves with 14CO 2. Plants grown in Hoagland's nutrition solution were subjected either to water stress at moderate intensity, induced by polyethylene glycol (PEG6000), for 15 days (prolonged water stress, PWS) or for 3 days, and then transferred to the solution without PEG for a recovery of 12 days (rewatering after water stress, RAWS), compared with plants under normal water conditions (CK). Three parameters were used to quantify the 14C-photoassimilate distribution: specific radioactivity (SRA), which gives a measure of the actual amount of photoassimilates obtained by organs; the proportion distribution value, which reflects the relative distribution pattern among different organs within a given plant; the distribution coefficient ( K), which gives an indication of the competitive sink strength, respectively. The carbon fixation rate and export capacity of source leaves were significantly reduced 24 h after initiating water stress, while the strength of sink organs ( K) was increased in roots but decreased in other organs (shoot apex, phloem, xylem) with different response velocities. For the first 5 days of water stress, the enhanced sink strength of fine roots in PWS plants compensated for the reduced carbon availability due to the decreased total carbon fixation. As a result, fine roots obtained the same or even greater amounts of 14C-photoassimilates (SRA) than those of CK plants, but the compensatory effect became insufficient as water stress continued. The rapid decrease in the distribution parameters of shoot apexes under water stress indicates that shoot apexes are highly sensitive to water stress. The shift of 14C-photoassimilates from above-ground to the roots, caused by the sensitivity of shoot apexes and the enhanced sink strength of roots under water stress, should be advantageous to maintaining root growth and tolerance to water stress. Upon rewatering, 5- and 3-day lags occurred for the carbon fixation rate and export capacity, respectively, in order to complete recovery to pre-stress levels after removing water stress. In contrast, the percentage distribution values and SRA of 14C-photoassimilates obtained by fine roots in RAWS plants did not return to the pre-stress levels, but instead remained at higher levels than those of CK plants during the rewatering stage. This greater investment of photoassimilate into the roots during the rewatering period might provide abundant carbon substrates and energy for the restoration of the metabolic activity of the roots. Apparently, there was also an after-effect of water stress on the other organ sink strengths, as revealed by the delayed recovery of SRA, the proportion distribution value and K in RAWS plants, depending on organ sensitivities to water stress. On the other hand, the percentage of 14C-photoassimilate distributed to the phloem declined linearly with the increased retention in the labeled leaf, confirming that the phloem was just a pathway for transporting photoassimilate, and the higher K revealed during water stress did not signify a stronger sink strength of water-stressed phloem.

Differential sensitivity of Desi (small‐seeded) and Kabuli (large‐seeded) chickpea genotypes to water stress during seed filling: effects on accumulation of seed reserves and yield

AbstractWater stress during the reproductive phase, especially during seed development, is considered detrimental for chickpea yield. In the present study, the relative sensitivity of Desi and Kabuli chickpea types to water stress during seed filling was assessed in terms of effects on quantitative and qualitative aspects of seed yield. Leaves of both types experienced stress injury (evaluated as electrolyte leakage) to the same extent and possessed almost similar values of water potential at the end of 14 days of water stress. The stressed plants of Kabuli type lost more chlorophyll and had less photosynthesis than Desi type. At maturity, Desi type showed more diminution of vegetative dry matter due to stress over control than Kabuli type. On the other hand, Kabuli type showed a proportionally greater reduction in seed weight per plant, average seed weight, average seed size, number of pods (single‐ and double‐seeded) and harvest index. The stressed seeds of Kabuli type showed 48 and 46% reduction over control in starch and protein content compared with 25 and 40%, respectively in Desi type. The accumulation of soluble sugars was relatively greater due to stress in Kabuli (47%) than Desi type (23%). Fat and fiber content declined by 39 and 35% over control in Desi seeds because of stress whereas Kabuli type showed 46 and 67% decreases, respectively. Protein fractions, namely albumins, globulins, glutelins and prolamins, decreased in stressed seeds of Kabuli by 32, 40, 16 and 15% over control relative to 40, 48, 30 and 28%, respectively, in Kabuli type. The activities of sucrose synthase, invertase and soluble starch synthase were inhibited to a higher extent in Kabuli seeds than Desi seeds under stress. Kabuli seeds showed significantly more reduction in the accumulation of amino acids such as phenylalanine + tyrosine, tryptophan, valine, alanine and histidine and minerals (Ca, P, Fe) due to stress compared with Desi type. Copyright © 2006 Society of Chemical Industry