An induced water deficit in lO-day barley seedlings resulted in a decrease in leaf dry weight within a 28-hr period, although the shoots and roots continued to increase in weight. Primordium formation and apex elongation on the main shoot were also inhibited but floral development at the apex continued.

Barley plants (cv. Prior) were grown in soil in a controlled environment and subjected to one, two, or three cycles of water stress by witholding water for short periods interspersed with periods of adequate water supply. The water potentials of the leaf tissues during and following these periods of stress were unaffected by the previous stress history of the plants.

Shoot apices and excised root systems and sections of the lamina and leaf sheath of the first leaf of to-day barley (cv. Prior) plants were incubated on aerated polyethylene glycol solution (osmotic potential -20 bars) or distilled water. The imino acid proline accumulated rapidly in the leaf lamina sections subjected to osmotic stress and less rapidly, after a delay of 16 hr, in those floated on water.

Spraying a solution of abscisic acid (ABA) of O· 5 or 5· 0 ,..g/ml onto intact barley plants led to an accumulation of free proline in the leaves in certain experiments, as did suspension of the root system in an ABA solution. Proline did not accumulate in the roots of intact barley so treated even when the hormone was taken into the plant through the roots.Sections excised from the leaves of barley or L. temulentum seedlings also accumulated free proline when incubated on ABA solutions. The accumulation resembled the increase in proline concentration produced by incubating the leaf sections on solutions of decreased osmotic potential (polyethylene glycol). With barley leaf sections, incubation on water led to an accumulation of proline with a peak concentration at 48 hr, followed by a rapid loss of proline. Treatment with ABA resulted in an earlier attainment of the peak concentration of proline and a higher maximum concentration. Very little proline leaked out of the tissue into the ambient solution within 4 days of incubation. Excised root segments of either species did not accumulate proline when incubated with ABA.The data are discussed in relation to the reported increase in ABA concentration in plant tissues subjected to water stress.

Wheat plants (cv. Gabo) were grown in nutrient solution and supplied with (2- chloroethyl)trimethylammonium chloride (CCC) in the rooting medium 1 week after germination. Ten days later the plants were subjected to water stress by substituting polyethylene glycol solution (mol. wt. 4(00) for the nutrient solution.