Relationship of nuclease activity and synthesis to senescence of corn (Zea mays L.) stalk pith, cob parenchyma and first developed leaf tissues.

An increase in total RNase activity was associated with three patterns of cell senescence in corn (Zea mays L.) (cv. WF9 X 38-11) cob parenchyma during the first two weeks following silking, stalk pith tissue after internode elongation and the first developed leaf of seedlings. Stalk pith tissue had two RNase activities, one inhibited by EDTA and one not. Both remained in approximately equal amounts in young to old pith tissue. In the first developed leaf of seedlings, the activity not inhibited by EDTA remained at a constant low level during the period studied, while the other activity varied. No inhibition by EDTA was found in cob parenchyma tissue. Incubation of sections of cob parenchyma and stalk pith tissues suggested that the total RNase activity of cob parenchyma is very stable and that of stalk pith tissue is relatively stable. An age-related increase in DNase activity was found in stalk pith tissue and in the first developed leaf of seedlings, but not in cob parenchyma tissue.