Identification and characterization of gibberellin-insensitive mutants selected from among dwarf mutants of rice

Abstract

In rice, many dwarf mutants have been isolated and characterized. We have investigated the relationship between dwarfism and the gibberellin (GA)-mediated control of physiological processes. Twenty-three rice cultivars and mutants (9 normal, 3 semi-dwarf, 11 dwarf) were analyzed in terms of two GA-mediated processes, namely, elongation of shoots and production of α-amylase activity in the endosperm. As a result, we identified four different groups (groups N, T, D and E). Two-dimensional plotting of the extent of induction of α-amylase in the endosperm versus the extent of enhancement of shoot elongation upon treatment with exogenous gibberellic acid (GA3) provided a useful method for the rapid allocation of large numbers of dwarf mutants of rice to the various groups. Members of group N (normal type), which included all normal cultivars and semi-dwarf mutants, showed a slight increase in elongation of shoots and a remarkable increase in production of α-amylase with the application of GA3 during germination. All of the dwarf mutants were classified as being members of the other three groups. Members of group T (Tan-ginbozu type), including three dwarf mutants, were highly responsive to exogenous GA3 in terms of elongation of shoots and production of α-amylase, with associated lower levels of endogenous GA. In contrast, members of the other three groups, including group N, had normal levels of endogenous GAs. Members of group D (Daikoku type) were only slightly responsive to exogenous GA3, an indication that they are GA-insensitive mutants. Members of group E (Ebisu type) had responses to GA3 similar to those of group N, not only in terms of elongation of shoots but also in terms of α-amylase production, an indication that they are dwarf mutants that can be considered as neither GA-deficient nor GA-insensitive mutants. We also examined a GA-insensitive mutant selected from among 19 near-isogenic dwarf lines of ‘Shiokari’, and we concluded that the d-1 gene is associated with the phenotype of GA-insensitive dwarf mutants. © 1994, Springer-Verlag. All rights reserved.