Abstract: | Yamashita, T. 1987. Modulated degradation of ribulose ftisphosphatecarboxylase in leaves on top-pruned shoots of the mulberry tree(Morus alba L.).J. exp. Bot. 38: 19571964. The effects of pruning shoot tops on the synthesis and degradationof ribulose 1,5Wsphosphate carboxylase (RuBPCase) inleaves on remaining shoots were investigated in mulberry trees.Leucine labelled with 14C was fed to leaf discs from field-grownmulberry trees and 14C incorporation into RuBPCase was examined.Proportion of 14C in RuBPCase to leucine14C absorbedby leaf discs was remarkably lowered by top-pruning, thoughoccasionally a slight increase was observed soon after pruning.Yet RuBPCase content in leaves on top-pruned shoots became progressivelyhigher than that in leaves on intact shoots. Changes in 14Cin Ru1BPCase in leaves of mulberry saplings previously fed 14CO2were followed. Following 14CO2 feeding, the attainment of themaximal level of 14C in RuBPCase was retarded by top-pruning.The highest level of 14C in RuBPCase was maintained in leaveson top-pruned shoots but decreased in leaves on intact shoots.Specific radioactivity in RuBPCase continued to increase inleaves on top-pruned shoots even after attaining a maximum levelin the control leaves. These facts suggest that the increasein RuBPCase by top-pruning results from a cessation of its degradationfor the remobilization of nitrogen for newly developing leaveson shoot tops. Key words: RuBP carboxylase, shoot pruning, mulberry (Morus alba) |