Osmotic & specific effects of excess salts on beans

Abstract

These effects have been separated by applying "Carbowax" (Union carbide Chemical Company) polyethylene glycol, molecular weight about 20,000 (C20M), to dwarf red kidney beans. The plants were grown in isosmotic solutions of which the osmotic pressure (OP) was due to a base nutrient plus either an excess of NaCl, CaCl2, and MgCl2, or dialytically purified C20M. Different ionic compositions were established at each of a number of levels of OP. Results indicated that the yield of "Carbowax"-treated plants was greater than that of plants grown in isosmotic solutions containing ions only. On the basis of a previous study, the difference was attributed to specific effects of the salts mentioned. Extrapolation to the salt level of incipient significance of these effects was possible. The contents of Na, Ca, and Cl of the leaves, and the OP of the leaf sap reflected the lower concentrations prevailing in C20M-containing solutions relative to leaves of plants grown in isosmotic solutions containing ions only. The content of K was much higher in the leaves of C20M-treated plants, probably due to diminished competition by Ca. A separate experiment involved excess-salt containing solutions similar to the ones above except that they were graded with respect to K. Small increments of K caused significant increases in the OP of leaf sap. Yet, this did not always result in a yield reduction. It appeared that the growth of kidney beans, while strongly influenced by the OP of the nutrient solution, is not contingent upon the internal OP of the plant system.