GIBBERELLIN STATUS AND RESPONSIVENESS IN SHOOTS OF TALL AND DWARF GENOTYPES OF DIPLOID RYE (SECALE-CEREALE)

The recessive dwarfing alleles of rye (Secale cereale L.), ct1 and ct2, caused a 35-55% reduction in the length of leaf 2 compared with corresponding tall lines grown at both 10-degrees-C and 20-degrees-C. The dwarf lines were 45-50% as responsive to applied GA3 as the tall lines at 20-degrees-C but the absolute GA-responsiveness of the dwarfs, was greater at 10-degrees-C than at 20-degrees-C. There was no significant difference in the contents of GA19, GA20, GA29, GA1, GA3, and GA8 in the leaf extension zone of tall and dwarf seedlings grown at 20-degrees-C. It was concluded that the mechanism whereby GA homeostasis is maintained is functional in both tall and dwarf lines despite marked differences in leaf extension rate. The recessive rye mutations may cause loss of function late in the GA-cell elongation pathway or, alternatively. indirectly affect GA-responsiveness in vegetative tissues. The genetic and physiological evidence indicates that ct1 and ct2 are unrelated to the GA-insensitive Rht genes in hexaploid bread wheat.