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

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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.degree. 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 growth at 10 and 25.degree. 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.degree. C than at 10.degree. C. At 10.degree. C the endogenous GA1 was at a similar level in all the genotypes (except Rht2+3). At 25.degree. 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.degree. C, but were only slight and often unsignificant at 11.degree. C. The response of leaf length of applied GA3 in the Rht1, Rht2, and Rht1+2 genotypes increased significantly with lowering to temperature. These results suggest the possibility that the temperature effect on leaf elongation is mediated through its effect on thelevel 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.