Effect of Temperature on Gibberellin (GA) Responsiveness and on Endogenous GA₁ Content of Tall and Dwarf Wheat Genotypes

Abstract

Near-isogenic wheat (Triticum aestivum L.) lines differing in height-reducing (Rht) alleles were used to investigate the effects of temperature on endogenous gibberellin (GA) levels and seedling growth response to applied GA₃. Sheath and lamina lengths of the first leaf were measured in GA treated and control seedlings, grown at 11, 18, and 25°C, of six Rht genotypes in each of two varietal backgrounds, cv Maris Huntsman and cv April Bearded. Endogenous GA₁ levels in the leaf extension zone of untreated seedlings were determined by gas chromatography-mass spectrometry with a deuterated internal standard in the six Maris Huntsman Rht lines grown at 10 and 25°C. Higher temperature increased leaf length considerably in the tall genotype, less so in the Rht1 and Rht2 genotypes, and had no consistent effect on the Rht1+2, Rht3 and Rht2+3 genotypes. In all genotypes, endogenous GA₁ was higher at 25°C than at 10°C. At 10°C the endogenous GA₁ was at a similar level in all the genotypes (except Rht2+3). At 25°C it increased 1.6-fold in the tall genotype, 3-fold in Rht1 and Rht2, 6-fold in Rht3, and 9-fold in Rht1+2. Likewise, the genotypic differences in leaf length were very conspicuous at 25°C, but were only slight and often unsignificant at 11°C. The response of leaf length to applied GA₃ in the Rht1, Rht2, and Rht1+2 genotypes increased significantly with lowering of temperature. These results suggest the possibility that the temperature effect on leaf elongation is mediated through its effect on the level of endogenous GA₁ and that leaf elongation response to endogenous or applied GAs is restricted by the upper limits set by the different Rht alleles.