Plant Growth in Polyethylene Glycol Solutions in Relation to the Osmotic Potential of the Root Medium and the Leaf Water Balance

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Abstract
The changes in leaf extension, plant dryweight, leaf area, net assimilation rate (E), relative growth-rate (RW), and relative leaf growth-rate (RL), have been studied for four species grown for 2 weeks in solutions of polyethylene glycol 4000 of controlled osmotic potentials. All aspects of growth were decreased by decreasing the osmotic potential (πsol) of the root medium and the leaf water potential (π), and ceased when π/ was greater than — 10 bars in bean, cotton, maize. These plants were more susceptible than ryegrass to water stress. Growth of bean stopped at π equal to about —6 bars, but even at —10 bars ryegrass was capable of some growth. Slight decrease in π from the values in the control plants decreased growth during the first week but partial recovery was apparent during the second week's growth in solution culture, when leaf extension, E, RL and RW increased in plants subjected to stress. Examination of the water balance, water potential, osmotic potential and turgor of the leaf in relation to relative water content suggests that recovery was related to increased turgor and that the ability of the plants to grow at reduced values of the osmotic potential of the root medium and of the leaf water potential depend on the maintenance of turgor.

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