Effect of Salinity on Ribonuclease Activity of Vigna unguiculata Cotyledons during Germination

Abstract

Summary The presence of iso-osmotic solutions (- 4.6 bar) of NaCl (0.1 M) and mannitol (0.19 m) during the germination of Vigna unguiculata (L.) Walp inhibited the growth of seedlings to a similar degree, suggesting that the salt effect is mainly osmotic. In the presence of Salt, RNase activity of the cotyledons rose more slowly than the control during the initial stages of germination, but thereafter rose sharply to values about twice those of the control. The slower initial rise in RNase was apparently an osmotic effect, since an identical curve was obtained with mannitol. The later sharp rise in activity was not seen in mannitol-treated seedlings, suggesting that some specific salt effect was responsible. Cycloheximide, used under conditions that did not inhibit growth, inhibited the increase in RNase. Although polyacrylamide-gel electrophoresis revealed the presence of six RNase isoenzymes in the extracts, essentially all the activity was due to a single isoenzyme. The main RNase isoenzyme hydrolysed RNA producing all four cyclic (2', 3') nucleotides, but no 3'-nucleotides, and had no activity towards DNA.