RELATIONSHIP BETWEEN WATER TOLERANCE AND CYANIDE-RESISTANT RESPIRATION IN PEAR ROOTSTOCKS

1. To estimate flooding tolerance of several pear rootstocks, wilting of leaves, shoot growth and triphenyl tetrazolium chloride (TTC) reduc ing activity of fine roots were measured under an experimental floodin g condition. Two strains of Pyrus calleryana, No. 6 and No. 8, were mo st tolerant to flooding, followed by strains No. 7 and No. 10. Seed li ngs of P. betulaefolia and P. pyrifolia were not tolerant to flooding. 2. Evolution of HCN from the pear roots was determined by treating th em with N-2 gas and NaN3 solution. Root systems of the plants evolved the same level of HCN whether they were kept anaerobic or treated with NaN3. Untreated control pear roots did not evolve any HCN. 3. The fin e roots were collected before and after seven days of flooding and oxy gen uptake measured in a 1mM KCN solution. KCN inhibited oxygen uptake about 10% in the fine roots of P. calleryana strains No. 6 and No. 8 collected before flooding; the inhibition decreased after seven days o f flooding. But in the cases of P. betulaefolia and P. pyrifolia, KCN inhibited oxygen uptake of,fine roots by more than 30% after flooding.