Characteristics of Mitochondrial Particles in Relation to Flooding Tolerance in Pear Rootstocks.

Abstract

Flooding-tolerant pear rootstocks, Pyrus calleryana, No. 6 and No. 8 strains and nontolerant rootstocks, P. betulaefolia and P. pyrifolia were used in the experiment.The rootstocks were flooded, and the change in the density of mitochondrial particles in the fine roots was checked by sucrose density gradient centrifugation. There was no marked change in the distribution of density of mitochondrial particles in roots of P. betulaefolia and P. pyrifolia before and after the flooding treatments; the mitochondrial particles (Fraction I) were detected at 1.221.29 M of the sucrose concentrations in the gradient centrifugation. Conversely, the heavier mitochondrial particles (Fraction II), which were detected at the 1.421.49 M in the gradient, appeared in the roots of P. calleryana, No. 6 and No. 8 after the flooding treatment.The level of cyanide-insensitive respiration was measured in the mitochondrial fractions, Fraction I and II. Fractions I prepared from P. calleryana, No. 6 and No. 8 were less sensitive to cyanide than were those from P. betulaefolia and P. pyrifolia. Fraction II, induced in the roots of P. calleryana by the flooding treatment, was markedly insensitive to cyanide.These results suggest that the changes in density and respiration chain of mitochon-drial particles may be closely related to flooding tolerance in pear rootstocks.