A new highly sensitive and rapidly responding gravimetric method was used for the investigation of rapid responses manifesting in water inflow and outflow from roots in the intact seedlings of tomato Lycopersicon esculentumMill. and sunflower Helianthus annuusL. The effects of K+, Na+, and Ca2+chlorides were studied in solutions with concentrations of 0.3–500 mM. Any sudden increase in the osmotic pressure of an external solution brought about a typical gravimetric response in the roots of seedlings that started practically without a lag period and comprised rapid and slow phases of water loss. The total amplitude of the response depended on the osmotic gradient produced by the changes of solutions. Responses were reversible and well reproduced upon the repeated treatment of the same plant if the treatment was noninvasive. The notable characteristics of water inflow and outflow included a very short lag period, a gradual pattern, and a low selectivity to different salts. This was especially true for the initial (rapid) phase of response. However, mono- and bivalent cations showed some specificity of action. Some data suggest the osmotic nature of rapid responses of water uptake and loss by roots. One may assume that a dynamic osmotic equilibrium exists between the root and the outer solution so that any change in the osmotic pressure of the medium would induce an instant and then a more gradual change in the water content. When plotted in logarithmic coordinates, two straight lines with different slopes described the relationship between the gravimetric response and the salt concentration. The point where these lines intersected corresponded to about 50 mM NaCl. Lower and higher salt concentrations seem to induce rapid water inflow and outflow in plant roots by means of different mechanisms.
Russian Journal of Plant Physiology – Springer Journals
Published: Oct 10, 2004
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