Induced Water Stress Research Articles

Screening Wheat (Triticum spp.) Genotypes for Root Length under Contrasting Water Regimes: Potential Sources of Variability for Drought Resistance Breeding

AbstractScreening for root traits has been one of the most difficult areas to practise over large number of genotypes. Hydroponic systems enable easy access to roots while high‐molecular weight polyethylene glycol (PEG) is used to induce water stress. A total of 838 genotypes were evaluated for root length in a hydroponic trial under PEG‐induced stress and non‐stress growing conditions. Augmented complete block design with seven blocks and six standard control varieties was used. Root length differences were highly significant (P < 0.01) under both stress and non‐stress growing conditions among genotypes. Osmotic stress has caused an average reduction of 54 % in root length. Among the genotypes, root length ranged from 1.4 to 13.3 cm under stress, and 4.4 to 23.3 cm under non‐stress conditions, respectively. The best control variety for drought resistance was significantly (P < 0.05) outperformed by four new entries namely Colotana 296‐52, Compare, Santa Elena and Tammarin Rock, while the shortest roots were measured on genotypes Aus 16356, Elia, Camm, Portugal 3, and Sentinel. Differences among ploidy levels, domesticated and wild forms were also significant (P < 0.05). Hexaploid wheat showed significantly longer roots in both growing conditions while wild tetraploids showed the shortest roots under stress. There was a change in the ranking of genotypes under the two water regimes, which indicates the difficulty of selecting drought resistant varieties under optimum environments.

Impacts of environmental stress on growth, secondary metabolite biosynthetic gene clusters and metabolite production of xerotolerant/xerophilic fungi.

This paper examines the impact that single and interacting environmental stress factors have on tolerance mechanisms, molecular ecology and the relationship with secondary metabolite production by a group of mycotoxigenic species of economic importance. Growth of these fungi (Aspergillus flavus, A.ochraceus, A.carbonarius, Penicillium nordicum and P. verrucosum) is influenced by water and temperature interactions and type of solute used to induce water stress. Such abiotic stresses are overcome by the synthesis of increased amounts of low molecular weight sugar alcohols, especially glycerol and erythritol, to enable them to remain active under abiotic stress. This is accompanied by increased expression of sugar transporter genes, e.g., in A. flavus, which provides the nutritional means of tolerating such stress. The optimum conditions of water activity (a w) × temperature stress for growth are often different from those for secondary metabolite production. The genes for toxin production are clustered together and their relative expression is influenced by abiotic interacting stress factors. For example., A. flavus synthesises aflatoxins under water stress in non-ionic solutes. In contrast, P. nordicum specifically occupies a high salt (0.87 a w = 22% NaCl) niche such as cured meats, and produces ochratoxin A (OTA). There is differential and temporal expression of the genes in the secondary metabolite clusters in response to a w × temperature stress. We have used a microarray and integrated data on growth, relative expression of key genes in the biosynthetic pathways for secondary metabolite production and toxin production using a mixed growth model. This was used to correlate these factors and predict the toxin levels produced under different abiotic stress conditions. This system approach to integrate these different data sets and model the relationships could be a powerful tool for predicting the relative toxin production under extreme stress conditions, including climate change scenarios. This approach will facilitate a better functional understanding of the influence that environmental stress has on these mycotoxigenic fungi and enable better prevention strategies to be developed based on this system-based approach.

Antioxidant enzyme activity, proline accumulation, leaf area and cell membrane stability in water stressed Amaranthus leaves

Traditional crops are extremely important for food production in low income, food-deficit countries (LIFDCs) where they continue to be maintained by socio-cultural preferences and traditional uses. Significant potential exists to improve these crops, one of which is to select for improved productivity during moisture stress conditions. Germplasm of Amaranthus tricolor, Amaranthus hypochondriacus and Amaranthus hybridus were subjected to various screening methods to measure metabolic and physiological changes during water stress. The activities of enzymes involved in the oxygen-scavenging system during abiotic stress conditions (superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR)), free proline production, leaf area (LA), cell membrane stability (CMS), leaf water potential (LWP) and relative water content (RWC) were measured in these three amaranth species during induced water stress. This study showed significant differences in metabolic responses during water deficit of the three species tested. Moisture stress and a decrease in RWC and LWP were first experienced in A. hybridus and A. hypochondriacus, followed by A. tricolor. There was an indirect correlation between leaf water status (RWC and LWP), enzyme activity, proline production and leaf area. The combined effect of GR, APX and SOD could ensure higher levels of regulation of the toxic effect of H2O2 which could be associated with drought tolerance in Amaranthus. Distinct differences in onset of proline accumulation and the amount of accumulated in leaves upon induced water stress was noticed for the three amaranth species tested. Proline accumulation during water stress conditions in amaranth seems to be indirect and could possibly have a protective role apart from osmoregulation during stress conditions. This contention is supported by the decrease in leaf area and high cell membrane stability for two of the species tested. This study forms part of a project aimed at the development of improved traditional crops to contribute to food production and quality for subsistence farmers in areas with low precipitation or variable rainfall patterns.

Leaf respiration responsiveness to induced water stress in Mediterranean species

Water stress considerably affects physiological processes such as photosynthesis which is considered one of the most negatively affected processes. By contrast, it is still unclear the effect of water stress on respiration metabolism. Understanding the respiratory dynamics when photosynthesis is impaired may help to hypothesize more accurately species behavior under the forecasted new climatic conditions driven by climate change. The main objective of this study was to analyze how simulated water stress/recovery cycles affected leaf respiration (RD) and carbon balance (LCB) of six Mediterranean species. In addition, given that membrane integrity is a target of water stress and that part of the maintenance respiration is associated with maintenance of the ion gradient across membranes, we hypothesized that a higher membrane destabilization, evaluated in terms of electrolyte leakage (EL), could lead to an increased respiration. Our results showed that during the first water stress cycle RD decreased at low or moderate stress level by 15% (mean value) compared with the control. The response pattern changed among the species when severe water stress was reached. Cistus incanus, Erica multiflora and Rosmarinus officinalis showed a slight but significant RD increase (by 9%, 7% and 4%, respectively) compared with the control, whereas RD decreased in Erica arborea, Pistacia lentiscus and Quercus ilex (by 46, 35 and 33%, respectively). As water stress progressed, EL increased in all the species to a different extent. C. incanus, E. multiflora and R. officinalis showed the highest EL (25.5±3.6%, mean value) at severe water stress levels while Q. ilex, P. lentiscus and E. arborea showed a lower EL (12.3±2.7%, mean value). Moreover, there was a significant relationship between RD and EL in C. incanus, E. multiflora and R. officinalis. The capacity of Q. ilex, P. lentiscus and E. arborea to maintain low RD rates during severe water stress associated to a high LCB as well as to a high membrane resistance to dehydration make them more able to cope with subsequent water stress events. By contrast, C. incanus, E. multiflora and R. officinalis had a lower water stress resistance as well as a low resistance to cell membrane destabilization which leads to increased respiratory flux in order to sustain a higher plant maintenance cost.

Water stress is a component of cold acclimation process essential for inducing full freezing tolerance in strawberry

The factors involved in cold acclimation process and their role in inducing freezing tolerance were studied in strawberry (Fragaria×ananassa) plants. The results show that low temperature and water stress are two key components of cold acclimation, in that low temperature typically induced water stress in the plants. After a 2-week exposure of plants to 3/1°C (day/night temperature), the leaf water potential decreased markedly to below −1.6MPa. While both of these components contribute significantly to the induction of freezing tolerance, water stress is a dominant factor in inducing freezing tolerance, contributing roughly to 56% of freezing tolerance acquired by natural cold acclimation. Typical cold acclimation treatment of plants for 2 weeks increased their freezing tolerance by about 14°C to −20.7°C while the same treatment, in the absence of the accompanying water stress, increased their freezing tolerance only by 5°C, which indicates the importance of water stress during cold acclimation. Furthermore, both low temperature and water stress independently induced the orthologs of cold-responsive genes, COR47 and COR78, however, stronger expression of these genes was observed in response to cold acclimating conditions. Thus, these results show that both of these factors are essential elements of cold acclimation process and play an important role in inducing freezing tolerance in strawberry plants.

Effect of short-term water deficit stress on antioxidative systems in cucumber seedling roots.

BackgroundCucumber is one of the most popular vegetables, and have little tolerance for water stress. The antioxidant defense system is one of major drought defense and adaptive mechanisms in plants, however, relatively few data are available regarding antioxidant systems in responses of cucumber to water deficit. The effect of short-term drought stress on the antioxidant system, lipid peroxidation and water content in cucumber seedlings roots was investigated.ResultsThe results showed that polyethylene glycol (PEG) induced water stress markedly decreased water content of cucumber seedling roots after treatment of 36 h, and caused excessive generation of reactive oxygen species (ROS) including superoxide (O2.−), hydrogen peroxide (H2O2). Meanwhile, malondialdehyde (MDA) content increased. Antioxidant enzymes including superoxide dismutases (SOD), peroxidases (POD), catalase (CAT) and ascorbate peroxidase (APX) activities increased in different time and different extent under water stress, while ascorbate (AsA) and glutathione (GSH) content, glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities all decreased when compared to control.ConclusionsTherefore, it can be concluded that water stress strongly disrupted the normal metabolism of roots and restrained water absorption, and seemingly enzymatic system played more important roles in protecting cucumber seedling roots against oxidative damage than non-enzymatic system in short-term water deficit stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-014-0046-6) contains supplementary material, which is available to authorized users.

Combined effects of defoliation and water stress on pine growth and non-structural carbohydrates.

Climate change is expected to increase both pest insect damage and the occurrence of severe drought. There is therefore a need to better understand the combined effects of biotic and abiotic damage on tree growth in order to predict the multi-factorial effect of climate change on forest ecosystem productivity. Indeed, the effect of stress interactions on tree growth is an increasingly important topic that greatly lacks experiments and data, and it is unlikely that the impact of combined stresses can be extrapolated from the outcomes of studies that focused on a single stress. We developed an original manipulative study under real field conditions where we applied artificial defoliation and induced water stress on 10-year-old (∼10 m high) maritime pine trees (Pinus pinaster Ait.). Tree response to combined stresses was quantitatively assessed following tree secondary growth and carbohydrate pools. Such a design allowed us to address the crucial question of combined stresses on trees under stand conditions, sharing soil supplies with neighboring trees. Our initial hypotheses were that (i) moderate defoliation can limit the impact of water stress on tree growth through reduced transpiration demand by a tree canopy partly defoliated and that (ii) defoliation results in reduced non-structural carbohydrate (NSC) pools, affecting tree tolerance to drought. Our results showed additive effects of defoliation and water stress on tree growth and contradict our initial hypothesis. Indeed, under stand conditions, we found that partial defoliation does not limit the impact of water stress through reduced transpiration. Our study also highlighted that, even if NSC in all organs were affected by defoliation, tree response to water stress was not triggered. We found that stem NSC were maintained or increased during the entire growing season, supporting literature-based hypotheses such as an active maintenance of the hydraulic system or another limiting resource for tree growth under defoliation. We also observed a significant decrease in root carbohydrates, which suggests a shift in the root carbon balance under defoliation. The decrease in carbohydrate supply under defoliation may not counterbalance the carbon use for mineral and water uptakes or a translocation to other tissues.

Antioxidative enzyme responses under single and combined effect of water and heavy metal stress in two Pigeon pea cultivars

Heavy metal toxicity and water stress are the two frequently co-occurring abiotic stresses restraining the growth of crop plants as the metal contaminated sites are over alarmingly increasing due to industrial pollution. The present study is to evaluate the effect of heavy metals (Cadmium, Chromium), PEG induced water stress and their combination on antioxidative enzyme activities in two Pigeon pea cultivars LRG-41 and Yashoda-45. The activities of antioxidative enzymes Superoxide dismutase, Catalase, Ascorbate peroxidase, Polyphenol Oxidase and Glutathione Reductase registered higher values in both roots and shoots with all the single stress treatments when compared to their controls. The levels of antioxidative enzyme activities and lipid peroxidation were high in cv. Yashoda-45 than cv. LRG-41. Overall, cv Yashoda-45 has shown better tolerance to both heavy metal and water stress. These results may show the novel insight in to the responses associated with combined stress in the cultivars of economically important crop, Pigeon pea.

Cork oak physiological responses to manipulated water availability in a Mediterranean woodland

This study details the physiological responses of cork oak (Quercus suber L.) to manipulated water inputs. Treatments named as dry, ambient and wet, which received 80, 100 and 120% of the annual precipitation, respectively, were applied to a Mediterranean woodland in southern Portugal. Tree ecophysiology and growth were monitored from 2003 to 2005.The impacts of the water manipulation were primarily observed in tree transpiration, especially during summer drought. Rainfall exclusion reduced the annual stand canopy transpiration by 10% over the 2-year study period, while irrigation increased it by 11%. The accumulated tree transpiration matched precipitation in spring 2004 and 2005 at the stand level, suggesting that cork oak trees rely on precipitation water sources during the peak of the growing season. However, during the summer droughts, groundwater was the main water source for trees.Despite the significant differences in soil water content and tree transpiration, no treatment effects could be detected in leaf water potential and leaf gas exchange, except for a single event after spring irrigations in the very dry year 2005. These irrigations were intentionally delayed to reduce dry spell duration during the peak of tree growing season. They resulted in an acute positive physiological response of trees from the wet treatment one week after the last irrigation event leading to a 32% raise of stem diameter increment the following months. Our results suggest that in a semi-arid environment precipitation changes in spring (amount and timing) have a stronger impact on cork oak physiology and growth than an overall change in the total annual precipitation.The extreme drought of 2005 had a negative impact on tree growth. The annual increment of tree trunk diameter in the ambient and dry treatments was reduced, while it increased for trees from the wet treatment. Water shortage also significantly reduced leaf area. The latter dropped by 10.4% in response to the extreme drought of 2005 in trees from the ambient treatment. The reduction was less pronounced in trees of the wet treatment (−7.6%), and more pronounced in trees of the dry treatment (−14.7%).Cork oak showed high resiliency to inter-annual precipitation variability. The annual accumulated tree transpiration, the minimum midday leaf water potential and the absolute amount of groundwater used by trees appeared unaffected by the extreme drought of 2005. Our study shows that cork oak rapidly and completely recovered from the extreme dry year of 2005 or from rainfall exclusion. Our results support the eco-hydrological equilibrium theory by which plant acquire complementary protective mechanisms to buffer the large variability in water availability experienced in semi-arid ecosystems. In optimizing their structural biomass increase in response to increasing drought stress, cork oak trees succeeded in restricting water losses to maintain the minimum leaf water potential above the critical threshold of xylem embolism, though with narrower hydraulic safety margins in 2005.Our findings highlight cork oak's sensitivity to the amount and timing of late spring precipitation. This could be critical as future climate scenarios predict a reduction of spring precipitation as well as enhanced severity of droughts in the Iberian Peninsula by the end of the 21st century. In inducing water stress before the onset of summer droughts, the predicted spring precipitation decline could drive the species closer to the threshold of catastrophic xylem embolism at the peak of the drought period.

Combination of typical meteorological year with regulated deficit irrigation to improve the profitability of garlic growing in central spain

This paper shows an adaptation of the typical meteorological year (TMY) method for irrigation schedule forecasting in combination with the optimized regulated deficit irrigation (ORDI) strategy to increase the water productivity of crops and their profitability. This methodology has been simulated using the MOPECO model on garlic (Mulvico cultivar) under deficit irrigation conditions in Castilla-La Mancha (Spain), although it may be useful for other crops and areas in the world. Experimental data from a three-year field test were collected for the calibration (2001) and validation (2000 and 2002) processes. Key objectives of this research were: (1) to adapt the TMY methodology for irrigation schedule forecasting; (2) to calibrate and validate the parameters required for simulating garlic using the MOPECO model; and (3) to determine the most suitable irrigation strategy for the Protected Geographical Indication “Ajo morado de Las Pedroñeras” considering four deficit targets (100, 90, 80, and 70% of maximum evapotranspiration) using ORDI and TMY methodologies. The growing-degree-days for the whole growth cycle are approximately 2044°C, while the calibrated crop yield response (Ky) values for the growth stages proposed by FAO-56 are 0.45 (vegetative period), 0.75 (yield formation), and 0.3 (ripening). The combination of TMY with ORDI may increase yield by 3–9% and gross margin by up to 59% compared to a constant deficit irrigation strategy. When water deficit conditions are present, it is of interest to guarantee nascence but also favour the bulb formation stages as much as possible, inducing water stress during the vegetative development stage. Under the current harvest sale price scenario (1.15€kg−1), this crop reaches a gross margin of around 3400€ha−1 for maximum yield (11,200kgha). Thus, irrigation advisory services can supply important information to farmers that may be translated to higher profitability and crop yield at the farm and/or basin scale.

High-resolution airborne hyperspectral and thermal imagery for early detection of Verticillium wilt of olive using fluorescence, temperature and narrow-band spectral indices

Verticillium wilt (VW) caused by the soil-borne fungus Verticillium dahliae Kleb, is the most limiting disease in all traditional olive-growing regions worldwide. This pathogen colonizes the vascular system of plants, blocking water flow and eventually inducing water stress. The present study explored the use of high-resolution thermal imagery, chlorophyll fluorescence, structural and physiological indices (xanthophyll, chlorophyll a+b, carotenoids and blue/green/red B/G/R indices) calculated from multispectral and hyperspectral imagery as early indicators of water stress caused by VW infection and severity. The study was conducted in two olive orchards naturally infected with V. dahliae. Time series of airborne thermal, multispectral and hyperspectral imagery was acquired in three consecutive years and related to VW severity at the time of the flights. Concurrently to the airborne campaigns, field measurements conducted at leaf and tree-crown levels showed a significant increase in crown temperature (Tc) minus air temperature (Ta) and a decrease in leaf stomatal conductance (G) across VW severity levels, identifying VW-infected trees at early stages of the disease. Higher Tc−Ta and G values measured in the field were associated with higher VW severity levels. At leaf level, the reduction in G caused by VW infection was associated with a significant increase in the Photochemical Reflectance Index (PRI570) and a decrease in chlorophyll fluorescence (F). The airborne flights enabled the early detection of VW by using canopy-level image-derived airborne Tc−Ta, Crop Water Stress Index (CWSI) calculated from the thermal imagery, blue/blue–green/blue–red ratios (B/BG/BR indices) and chlorophyll fluorescence, confirming the results obtained in the field. Airborne Tc−Ta showed rising values with a significant increase of ~2K at low VW severity levels, and was significantly correlated with G (R2=0.76, P=0.002) and PRI570 (R2=0.51, P=0.032). Early stages of disease development could be differentiated based on a CWSI increase as VW developed, obtaining a strong correlation with G (R2=0.83, P<0.001). Likewise, the canopy-level chlorophyll fluorescence dropped at high VW severity levels, showing a significant increase as disease progressed. These results indicate the potentials of an early detection of V. dahliae infection and discrimination of VW severity levels using remote sensing. Indicators based on crown temperature such as CWSI, and visible ratios B/BG/BR as well as fluorescence were effective in detecting VW at early stages of disease development. In affected trees, the structural indices PRI, chlorophyll and carotenoid indices, and the R/G ratio were good indicators to assess the damage caused by the disease.

Elevated [CO2] Does Not Ameliorate the Negative Consequences of Infection with the Xylem-Limited BacteriaXylella fastidiosainQuercus rubraSeedlings

Elevated atmospheric carbon dioxide concentration ([CO2]) alters the physiology, growth, and development of plants. These changes in plant functioning are likely to impact the relationship between some plant pathogens and their hosts. This study examined the interactive effects of elevated [CO2] and the economically important, xylem-limited bacterial pathogen Xylella fastidiosa Wells et al. on the physiology and growth of Quercus rubra L. (red oak) seedlings. We hypothesized that growth at elevated [CO2] would ameliorate the negative consequences of infection on Q. rubra growth and physiology. Oak seedlings were inoculated with a natural strain of X. fastidiosa and grown under “ambient” (400 ppm) and “elevated” (1,000 ppm) [CO2] for 24 wk. Gas exchange, plant growth, and biomass allocation were measured to determine if elevated [CO2] alleviated the severity of X. fastidiosa–induced water stress. Xylella fastidiosa infection decreased photosynthesis, stomatal conductance, and transpiration, as well as leaf area and total biomass. Although photosynthesis increased in both noninfected and X. fastidiosa–infected plants grown at elevated [CO2], the lack of a significant [CO2] × infection interaction indicated that elevated [CO2] did not ameliorate the effects of X. fastidiosa infection on leaf-level physiology. Additionally, photosynthetic increases at elevated [CO2] did not translate to relief of infection symptoms at the whole-plant scale. The findings of this experiment did not support the hypothesis that growth at elevated [CO2] ameliorates the negative consequences of X. fastidiosa infection on seedling physiology and growth. Future studies should continue to explore the interactive effects of [CO2] and infection by X. fastidiosa on plant performance.

Evaluating climate change induced water stress: A case study of the Lower Cape Fear basin, NC

With the possibility of future fresh water shortages increasing, a methodology that incorporates climatic and anthropogenic factors is needed. This research estimates future water availability in the Lower Cape Fear basin using changes in climate, land use, and population growth. The USGS Thornthwaite monthly water balance model is used with estimates of climate change and land use change parameters to assess future water resources based on predicted monthly fluxes of the water balance.The southern United States is a rapidly growing region. Trends present in the population data are used to produce future estimates of population for the basin. Precipitation and temperature estimates based on Intergovernmental Panel on Climate Change (IPCC) predictions and current climatology are inputs to the model. Projected increases in impervious surface cover due to population growth and urbanization are incorporated through the model runoff factor. Water stress indicators are used to categorize the sub-watersheds as water rich, water stressed, or water scarce. Scenarios incorporating regional predictions of climate change indicate a decrease in summer soil moisture minima and increases in summer water deficits. Ensemble runs indicate a shift toward water stress in the Lower Cape Fear River basin, due to a warming climate as well as increased demand. While climate change has a significant impact on water resources, population growth was found to have the most substantial impact. The methods and findings have application to water managers at local and regional levels.

Impact of silicon on various agro-morphological and physiological&lt;br&gt;parameters in maize and revealing its role in enhancing water stress&lt;br&gt;tolerance

Silicon (Si) is the second most abundant element in earth's crust and is considered as beneficial element for providing tolerance against various biotic and abiotic stresses. The aim of the present study was to investigate the role of silicon in water stress tolerance in maize as depicted through agro- morphological/ physiological parameters. We evaluated 15 diverse maize genotypes/ inbred lines under rain-fed conditions with, as well as without, Si application. Significant differences were observed in various agro-morphological and physiological parameters under Si+ and Si- conditions. The number of kernel per ear was significantly higher in Si+ conditions. The various physiological parameters observed include; anthesis- silking interval, relative water content, stomatal density and canopy temperature. All these parameters indicated the positive impact of Si on water stress tolerance in case of maize genotypes under study. These results specified that Si plays an important role in giving tolerance against drought/ water stress. The study can be further extended to investigate the molecular mechanism involved in Si induced water stress tolerance in maize.

Response of the physiological parameters of mango fruit (transpiration, water relations and antioxidant system) to its light and temperature environment

Depending on the position of the fruit in the tree, mango fruit may be exposed to high temperature and intense light conditions that may lead to metabolic and physiological disorders and affect yield and quality. The present study aimed to determine how mango fruit adapted its functioning in terms of fruit water relations, epicarp characteristics and the antioxidant defence system in peel, to environmental conditions. The effect of contrasted temperature and light conditions was evaluated under natural solar radiation and temperature by comparing well-exposed and shaded fruit at three stages of fruit development. The sun-exposed and shaded peels of the two sides of the well-exposed fruit were also compared.Depending on fruit position within the canopy and on the side of a well-exposed fruit, the temperature gradient over a day affected fruit characteristics such as transpiration, as revealed by the water potential gradient as a function of the treatments, and led to a significant decrease in water conductance for well-exposed fruits compared to fruits within the canopy. Changes in cuticle thickness according to fruit position were consistent with those of fruit water conductance. Osmotic potential was also affected by climatic environment and harvest stage. Environmental conditions that induced water stress and greater light exposure, like on the sunny side of well-exposed fruit, increased the hydrogen peroxide, malondialdehyde and total and reduced ascorbate contents, as well as SOD, APX and MDHAR activities, regardless of the maturity stage. The lowest values were measured in the peel of the shaded fruit, that of the shaded side of well-exposed fruit being intermediate.Mango fruits exposed to water-stress-induced conditions during growth adapt their functioning by reducing their transpiration. Moreover, oxidative stress was limited as a consequence of the increase in antioxidant content and enzyme activities. This adaptive response of mango fruit to its climatic environment during growth could affect postharvest behaviour and quality.

Improving Water Use Efficiency and Yield of Maize (Zea mays L.) by Foliar Application of Glycinebetaine under Induced Water Stress Conditions

Improving Water Use Efficiency and Yield of Maize (Zea mays L.) by Foliar Application of Glycinebetaine under Induced Water Stress Conditions

Hazard and Effects of Pollution by Lead on Vegetable Crops

Lead (Pb) contamination of the environment is an important human health problem. Children are vulnerable to Pb toxicity; it causes damage to the central nervous system and, in some extreme cases, can cause death. Lead is widespread, especially in the urban environment, and is present in the atmosphere, soil, water and food. Pb tends to accumulate in surface soil because of its low solubility, mobility, and relative freedom from microbial degradation of this element in the soil. Lead is present in soil as a result to weathering and other pedogenic processes acting on the soil parent material; or from pollution arising caused by the anthropogenic activities; such as mining, smelting and waste disposal; or through the adoption of the unsafe and unethical agricultural practices such as using of sewage sludge, and waste water in production of vegetable crops or cultivation of vegetables near highways and industry regions. Lead concentrations are generally higher in the leafy vegetables than the other vegetables. Factors affecting lead uptake included its concentration in the soil, soil pH, soil type, organic matter content, plant species, and unsafe agriculture practices. Generally, as Pb concentration increased; dry matter yields of roots, stems and leaves as well as total yield decreased. The mechanism of growth inhibition by lead involve: a decrease in number of dividing cells, a reduction on chlorophyll synthesis, induced water stress to plants, and decreased NO3- uptake, reduced nitrate and nitrite reductase activity, a direct effect of lead on protein synthesis, a decrease on the uptake and concentration of nutrients in plants. The strategies to minimize Pb hazard can be represented in: (a) Phytoremediation, through natural plants are able to bio-accumulate Pb in their above–ground parts, which are then harvested for removal such as, using Indian Mustard (Brassica juncea), Ragweed (Ambrosiaartemisiifolia), Hemp Dogbane (Apocynum cannabium), or Poplar trees, which sequester lead in its biomass. (b) Good and ethical agricultural practices such as cultivation of vegetables crops as far from busy streets or highways and industry regions as well as nonuse of sewage sludge and waste water in cultivated soils. (c) Increasing the absorptive capacity of the soil by adding organic matter and humic acid. (d) Growing vegetable crops and cultivars with a low potential to accumulate lead, especially in soils exposed to atmospheric pollution. (e) Washing of leafy vegetables by water containing 1 % vinegar or peeling roots, tubers, and some fruits of vegetables before consumption may be an important factor in reducing the lead concentration.

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.

Morphological and anatomical response of Acacia ehrenbergiana Hayne and Acacia tortilis (Forssk) Haynes subspp. raddiana seedlings to induced water stress

The response of Acacia ehrenbergiana Hayne and Acacia tortilis (Forssk) Haynes subspp. raddiana seedlings to 100, 50 and 25% field capacity (FC) watering regimes was studied to determine their morphological and anatomical behaviour. Both species responded morphologically as well as anatomically to water stress. Water stress caused significant (P=0.05) decrease in relative water content, leaf number and area and leaf water potential, chlorophyll content, and stem height and diameter. Seedlings of both species responded to water stress by the development of longer roots. Vessel segment length, radial diameter, tangential diameter, wall thickness and density were significantly (P=0.05) affected by water stress at 25 and 50% FC. It can be concluded that both species can adapt well under dry conditions. Keywords: Anatomical deviations, drought, morphological response, root elongation

Effect of methyl jasmonate treatments on alleviation of polyethylene glycol -mediated water stress in banana (Musa acuminata cv. ‘Berangan’, AAA) shoot tip cultures

The role of exogenous methyl jasmonate (MeJA) application in moderating in vitro water stress on banana growth was investigated. Shoot tips were treated using various levels (0, 5, 10, 20, 40, 80, 100, 120, 140 and 160 μM) of MeJA before and during the imposition of 30 g L−1 PEG induced water stress in the media. Proliferation rate significantly improved with increasing doses of MeJA up to 80 μM whether the shoot tips were stressed by PEG or unstressed. The same trend was observed in terms of enhanced fresh weight increase and shoot vigour rate under water stress. PEG significantly reduced the relative water content (%) of shoot tips by about 35 % as compared with those of unstressed conditions, while MeJA application up to 40 μM reduced the inhibitory effect of PEG on leaf water loss (%). Shoot tips under water stressed conditions, responded positively to MeJA by exhibiting a significant increase in proline, although increasing levels to 100 μM and higher had no effect. MeJA alleviated the effect of PEG—induced loss of chlorophyll, although it had no additional benefit by altering the dosages. Under water stress, MeJA application up to 40 μM was also effective in reducing oxidative injury as indicated by significant reduction in H2O2 and MDA contents of shoot tips; higher dosages exhibited no further advantageous effect. These results suggested the participation of MeJA in improving drought tolerance of banana and moderating oxidative stress leading to enhanced plant performance.