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- Le stress hydrique, ou stress osmotique, est le stress abiotique subi par une plante placée dans un environnement qui amène à ce que la quantité d'eau transpirée par la plante soit supérieure à la quantité qu'elle absorbe. Ce stress se rencontre en période de sécheresse du sol ou de l'atmosphère, mais aussi lors de l'augmentation de la salinité du milieu (conduisant à l'abaissement du potentiel osmotique du milieu) ou en période de froid. Tout d'abord, le stress hydrique baisse la croissance et la productivité encore plus que tous les autres stress (Kramer, 1983). Parfois, des changements dans les gènes ou dans la biochimie de la plante peuvent induire plus de productivité, par exemple la plante va faire de nouvelles racines, en particulier en surface, pour pouvoir absorber plus d'eau. Au niveau cellulaire, la conformation des membranes, l'organisation des chloroplastes et l'activité des enzymes sont affectées. La plante devient plus sensible aux autres stress. Les végétaux qui poussent sur des sols ayant peu de réserve en eau utilisent deux stratégies : la tolérance et l'évitement. Dans le cas de la tolérance, le métabolisme fonctionne malgré une faible quantité d'eau, des ions et des solutés (composés osmotiquement actifs) s'accumulent dans la vacuole. En effet, plus la solution est concentrée et plus l’attraction est forte, plus le potentiel hydrique est faible et moins l’eau est libre de quitter la solution. Une plante comme Craterostigma plantagineum a été identifiée comme particulièrement résistante au stress hydrique. Dans le cas de l'évitement, la réduction de la transpiration est un élément essentiel de la résistance à la sécheresse car elle permet le maintien d'un potentiel hydrique élevé. Cette diminution s'obtient par la réduction et la protection de la surface transpirante, ou encore l'enfoncement des stomates, et même la production d'hormones comme la cytokinine. Exemple d'espèces adaptées au stress hydrique : sclérophytes, malacophytes, éphémérophyte, psammophores... D'autres espèces sont adaptées à l'inondation, comme le riz, grâce à diverses enzymes. (fr)
- Moisture stress is a form of abiotic stress that occurs when the moisture of plant tissues is reduced to suboptimal levels. Water stress occurs in response to atmospheric and soil water availability when the transpiration rate exceeds the rate of water uptake by the roots and cells lose turgor pressure. Moisture stress is described by two main metrics, water potential and water content. Moisture stress has an effect on stomatal opening, mainly causing a closure in stomata as to reduce the amount of carbon dioxide assimilation. Closing of the stomata also slows the rate of transpiration, which limits water loss and helps to prevent the wilting effects of moisture stress. This closing can be trigged by the roots sensing dry soil and in response producing the hormone ABA which when transported up the xylem into the leaves will reduce stomatal conductance and wall extensibility of growing cells. This lowers the rates of transpiration, photosynthesis and leaf expansion. ABA also increases the loosening of growing root cell walls and in turn increases root growth in an effort to find water in the soil. Phenotypic response of plants to long-term water stress was measured in corn and showed that plants respond to water stress with both an increase in root growth both laterally and vertically. In all Droughted conditions the corn showed decrease in plant height and yield due to the decrease in water availability. Genes induced during water-stress conditions are thought to function not only in protecting cells from water deficit by the production of important metabolic proteins but also in the regulation of genes for signal transduction in the water-stress response. There are four pathways that have been described that show the plants genetic response to moisture stress; two are ABA dependent while two are ABA independent. They all affect gene expression that increases the plants water stress tolerance. The effects of moisture stress on photosynthesis can depend as much on the velocity and degree of photosynthetic recovery, as it depends on the degree and velocity of photosynthesis decline during water depletion. Plants that are subjected to mild stress can recover in 1–2 days however, plants subjected to severe water stress will only recover 40-60% of its maximum photosynthetic rates the day after re watering and may never reach maximum photosynthetic rates. The recovery from moisture stress starts with an increase in water content in leaves reopening the stomata then the synthesis of photosynthetic proteins. (en)
- Estresse hídrico ou stress hídrico é uma situação em que a procura de água por habitante (mg0/h) é maior que a capacidade de oferta de um corpo hídrico. É também quando uma pessoa tem menos de 1000 m³ de água. Ou seja, quando não há água suficiente para abastecer a população, isto é, quando não existe água suficiente para satisfazer as necessidades de cada um. A distribuição da água doce no mundo é desigual muitos países enfrentam sérios problemas com a carência de água potável. No caso específico das plantas, ocorre quando não existe água suficiente para a planta absorver de modo a substituir a perda de água por evapotranspiração. Para períodos longos de estresse hídrico, a planta pode parar de crescer e eventualmente morrer. (pt)
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- Moisture stress is a form of abiotic stress that occurs when the moisture of plant tissues is reduced to suboptimal levels. Water stress occurs in response to atmospheric and soil water availability when the transpiration rate exceeds the rate of water uptake by the roots and cells lose turgor pressure. Moisture stress is described by two main metrics, water potential and water content. (en)
- Le stress hydrique, ou stress osmotique, est le stress abiotique subi par une plante placée dans un environnement qui amène à ce que la quantité d'eau transpirée par la plante soit supérieure à la quantité qu'elle absorbe. Ce stress se rencontre en période de sécheresse du sol ou de l'atmosphère, mais aussi lors de l'augmentation de la salinité du milieu (conduisant à l'abaissement du potentiel osmotique du milieu) ou en période de froid. Les végétaux qui poussent sur des sols ayant peu de réserve en eau utilisent deux stratégies : la tolérance et l'évitement. (fr)
- Estresse hídrico ou stress hídrico é uma situação em que a procura de água por habitante (mg0/h) é maior que a capacidade de oferta de um corpo hídrico. É também quando uma pessoa tem menos de 1000 m³ de água. Ou seja, quando não há água suficiente para abastecer a população, isto é, quando não existe água suficiente para satisfazer as necessidades de cada um. A distribuição da água doce no mundo é desigual muitos países enfrentam sérios problemas com a carência de água potável. (pt)
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