CHARACTERISTICS OF MITOCHONDRIAL PARTICLES IN RELATION TO FLOODING TOLERANCE IN PEAR ROOTSTOCKS

Flooding-tolerant pear rootstocks, Pyrus calleryana, No. 6 and No. 8 s trains and nontolerant rootstocks, P. betulaefolia and P. pyrifolia we re used in the experiment. The rootstocks were flooded, and the change in the density of mitochondrial particles in the fine roots was check ed by sucrose density gradient centrifugation. There was no marked cha nge in the distribution of density of mitochondrial particles in roots of P. betulaefolia and P. pyrfolia before and after the flooding trea tments; the mitochondrial particles (Fraction I) were detected at 1.22 similar to 1.29 M of the sucrose concentrations in the gradient centr ifugation. Conversely, the heavier mitochondrial particles (Fraction I I), which were detected at the 1.42 similar to 1.49 M in the gradient, appeared in the roots of P. calleryana, No. 6 and No. 8 after the flo oding treatment. The level of cyanide-insensitive respiration was meas ured in the mitochondrial fractions, Fraction I and II. Fractions I pr epared from P. calleryana. No. 6 and No. 8 were less sensitive to cyan ide than were those from P. betulaefolia and P. pyrifolia. Fraction II , induced in the roots of P. calleryena by the flooding treatment, was markedly insensitive to cyanide. These results suggest that the chang es in density and respiration chain of mitochondrial particles may be closely related to flooding tolerance in pear rootstocks.