C-C bond formation at the 3'-position of nucleosides by the use of their enol esters

Nucleosides having an enol ester structure in the sugar portion were synthesized and their reaction with several types of electrophiles were carried out. This furnished a new method for constructing C-C bond at the 3'-position.     

Protective Effect of External Ca2+ on Elongation and the Intracellular Concentration of K+ in Intact Mung Bean Roots under High NaCl Stress

The effects of Ca²⁺ in the external medium on intact mung beanroots under high NaCl stress were investigated. With increasingexternal concentrations of NaCl, mung bean roots showed suppressionof elongation and a decrease in the intracellular concentrationof K⁺. Addition of Ca²⁺ to the external medium alleviated theinhibition of root elongation under the high NaCl stress andmaintained a high intracellular concentration of K⁺ in the elongatingregion of the roots. This counter effect of Ca²⁺ against theNaCl stress on roots was correlated with the ratio of [Ca²⁺]/[Na⁺]²in the external medium. A value above 5.0 ? 10^–4 mM^–1resulted in almost complete recovery of root elongation undervarious high concentrations of NaCl. Root elongation for 24h under NaCl stress was correlated with the extent to whichthe intracellular concentration of K⁺ was in excess of 10 mM.Maintenance of an adequate concentration of K⁺ in root cellsis essential for root elongation under salt stress. These findingsindicate that Ca²⁺ prevents the leakage of intracellular K⁺and thereby supports the elongation of roots under salt stress. (Received November 13, 1989; Accepted June 5, 1990)