Abscisic Acid and Transpiration in Leaves in Relation to Osmotic Root Stress

Abstract

The adaptive response of plants to a decrease in osmotic potential of the root medium involves adjustments that facilitate the maintenance of their water balance. Thus Bernstein (2,3) showed that turgor pressure may be maintained under salinization through a decrease in the osmotic potential of the whole plant. However, actual turgor may also be maintained by a decrease in transpirational water loss. Indeed, the turgor of salinized cotton plants was even higher than the controls according to Gale et al. (4) Steveninck (10) reported that ABA3 affected closure of stomata and reduced transpiration in excised first leaves of wheat and barley. Earlier, Tal (18) had described a wilting tomato mutant in which transpiration was excessive owing to the inability of the stomata to close. Imber and Tal ("Phenotypic reversion of flacca, a wilting mutant of tomato, by abscisic acid." Science. In press.) recently discovered that when ABA was sprayed on these mutants, the stomata would close as in normal plants; transpiration was reduced and the wilting mutant resumed a normal appearance. There is thus good evidence for the involvement of both cytokinins and ABA in regulating stomatal aperture and transpiration.This study is part of a broader project to test the hypothesis that ABA plays a controlling role in the adaptation of plants to decreased osmotic potential in the root medium. This particular investigation queries whether ABA could be involved in the reduction of transpiration that generally follows a decrease in the osmotic potential of the root medium.Sixty-day-old tobacco plants (Nicotiana tabacum) grown in a (Fig. 1). Treatment with kinetin and ABA increased and decreased, respectively, the rate of transpiration of leaves from both stressed and nonstressed plants. In leaves of stressed plants, treatment with kinetin increased the rate of transpiration to that of the nonstressed, water-sprayed plants. In leaves of the nonstressed plants, ABA reduced the level of transpiration to that of the stressed, watersprayed plants. The same patterns were obtained whether the root stress was imposed with NaCl or with mannitol. These patterns proved reproducible in several repetitions of the experiment. The transpiration rate exhibited by leaves sprayed with both ABA and kinetin lies between those rates obtained by application of each of the two hormones alone (Table I). These experiments were run three times, with two replications each, and the same patterns of transpiration were observed each time. Thus in our system, one hormone seemed to negate the effect of the other hormone, as observed for other physiological phenomena (7,13,14,17). This is reminiscent of other cases where the ratio of hormones plays a regulatory role in the control of a physiological process (12,15). Possible differences in water content in the various test plants were evaluated by determining the relative water content of the leaf tissue (16), with the use of leaf discs measuring 23 mm in diameter. Although initially, 4 hr after the application of the ...

Uptake and Transport of Ions in Barley Seedlings III. Correlation Between Transport to the Shoot and Relative Growth Rate

“…A possible mechanism of control when photosynthesis is not limiting uptake could be through cytokinins and abscisic acid. Osmotic stress has been shown to lead to increased abscisic acid level in the shoot (Mizrahi, Blumenfeld, and Richmond 1970). In the root, abscisic acid can inhibit secretion of ions into the stele (Cram and Pitman 1972).…”

Hormonal Activity in Detached Lettuce Leaves as Affected by Leaf Water Content

“…ABA is known to induce stomatal closure with resulting decreased transpiration in many types of leaves (9,16,19,23,27,28). Furthermore, a very close relationship between leaf ABA content and the extent of stomatal opening was found in leaves of plants exposed to a cycle of mineral deprivation or salination and subsequent recovery (7).…”

Hormonal Modification of Plant Response to Water Stress

“…Therefore, addition of cytokinins to cytokinin-deficient, stressed plants does not alleviate the symptoms associated with water stress, but rather intensifies them. Similarly, the increase in the content ofleaf ABA upon exposure to water stress (Wright and Hiron 1969;Mizrahi, Blumenfeld, and Richmond 1970) may be interpreted as reflecting a feature of a mechanism which facilitates lower W.S.D. upon exposure to conditions which impair the plant's water balance.…”

“…Cytokinins increase transpiration by effecting stomatal opening (Livne and Vaadia 1965;Meidner 1967;Luke and Freeman 1968), and abscisic acid (ABA) effects closure of stomata and consequent reduction of transpiration (Little and Eidt 1968;Mittelheuser and Van Steveninck 1969;Jones and Mansfield 1970;Mizrahi, Blumenfeld, and Richmond 1970), as well as enhancement of root exudation (Tal and Imber 1971). It was also reported recently that ABA increases the permeability of plant tissues to water (Glinka and Reinhold 1971).…”