[Influence of NaCl- and abscisic acid treatment on protein metabolism and some further enzymes of amino acid metabolism in seedlings of Pennisetum typhoides]

Effect of sodium chloride on the response of the halophyte species Sesuvium portulacastrum grown in mannitol-induced water stress

Sesuvium portulacastrum is a halophytic species well adapted to salinity and drought. In order to evaluate the physiological impact of salt on water deficit-induced stress response, we cultivated seedlings for 12 days, in the presence or absence of 100 mmol l(-1) NaCl, on a nutrient solution containing either 0 mmol l(-1) or 25 mmol l(-1) mannitol. Mannitol-induced water stress reduced growth, increased the root/shoot ratio, and led to a significant decrease in water potential and leaf relative water content, whereas leaf Na(+) and K(+) concentrations remained unchanged. The addition of 100 mmol l(-1) NaCl to 25 mmol l(-1) mannitol-containing medium mitigated the deleterious impact of water stress on growth of S. portulacastrum, improved the relative water content, induced a significant decrease in leaf water potential and, concomitantly, resulted in enhancement of overall plant photosynthetic activity (i.e. CO(2) net assimilation rate, stomatal conductance). Presence of NaCl in the culture medium, together with mannitol, significantly increased the level of Na(+) and proline in the leaves, but it had no effect on leaf soluble sugar content. These findings suggest that the ability of NaCl to improve plant performance under mannitol-induced water stress may be due to its effect on osmotic adjustment through Na(+) and proline accumulation, which is coupled with an improvement in photosynthetic activity. A striking recovery in relative water content and growth of the seedlings was also recorded in the presence of NaCl on release of the water stress induced by mannitol.

Does abscisic acid influence proline accumulation in stressed leaves?

Root treatments of barley (Hordeum distichum L.) plants with 10(-7) to 10(-4) M abscisic acid (ABA) caused an increase in proline content, especially at higher concentrations, within 2-3 h. Even 3 h after the removal of ABA from the medium the plants continued to accumulate proline. The higher the concentration of the ABA, the higher was the proline level at 6 h. When the highest ABA concentration, 10(-4) M, was tested with polyethylene glycol (PEG) (-5.0 bars) in the medium, the ABA treatment resulted in a higher proline content than in control plants. The treatments "PEG alone" and "PEG + ABA" resulted in heavy accumulation of proline, especially, 3 h after releasing the plants from the stress. The proline content in PEG+ABA-treated plants was always higher than plants treated with PGE or ABA alone. In peas (Pisum sativum L. cv Alaska) the same trend occurred although to a lesser degree. These findings indicate an influence of ABA on proline accumulation in water-stressed plants.