Further Studies on Growth and Osmoregulation of Sugar Beet Leaves under Low Salinity Conditions

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Abstract
In previous work, Nunes and Dias (1980) demonstrated that low sodium concentrations in the root medium of intact or decapitated young sugar beet plants grown under controlled conditions modified leaf water relations and increased leaf area and dry weight. The present study confirms these findings and presents further results concerning the effect of salt on the concentrations of the main osmotic substrates and on the structural and chemical fractions of the cell dry weight. Increases of water and turgor potentials (0.25 MPa and 0.4 MPa, respectively) and a small decrease in osmotic potential (0.16 MPa) were found in the leaves of salt treated plants. In these plants, osmotic potentials estimated from the concentration of ions and organic solutes in the leaf sap agree with those measured showing that the observed increase in sodium concentration may account for the small decrease in the osmotic potential. No changes were detected in the concentration of orthophosphate or malic acid but total acidity of the leaf sap from salt treated plants was significantly lower. It was found that all the main components of cell dry matter (total protein, soluble sugars, pigments and crude cell wall) contributed to the dry weight increase in the salt treated plants. Among the polysaccharide fractions of the cell wall, pectins increased significantly relative to hemicellulose and cellulose.

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