ENDORIBONUCLEASE OF VICIA-FABA SSP MINOR RADICLES, AND ENHANCEMENT OFITS ACTIVITY BY CHILLING STRESS OR ABSCISIC-ACID

Endoribonuclease in roots of 3-day-old seedlings of Vicia faba L. ssp. minor is a citrate activated glycoprotein of 35 kDa, with pH and temp erature optima of 6.0 and 50 degrees C. The same holds for endoribonuc lease from seedlings treated with abscisic acid or exposed to a chilli ng stress of -3 degrees C for 24 h, except that the temperature optimu m was decreased to 40 degrees C. The enzyme(s) preferentially hydrolys ed poly(A) and poly(U). RNase activity in the radicles was enhanced by chilling stress or abscisic acid. ABA did not potentiate the effect b l ought about by chilling but slowed down the decrease in RNase activi ty in chill-stressed seedlings upon transfer to 25 degrees C. Both fac tors modified the pattern of the isoelectric-points of the molecular f orms of RNase.