Tetcyclacis and Abscisic Acid Differentially Affect Growth of Wheat (Triticum aestivum L.) Seedlings Isogenic for Reduced-Height Genes
2000
Klein, Joshua D. | Hebbe, Yonit
Wheat (Triticum aestivum L.) varieties with the dwarfing Rht (reduced height) alleles have reduced sensitivity to endogenous or exogenous gibberellin (GA). The Rht isolines are also less sensitive to the effects of chlormequat and other compounds which cause dwarfing by depressing GA synthesis. Abscisic acid (ABA) inhibits cereal seed germination and is in dynamic tension with GA, which enhances germination. Tetcyclacis is a cytochrome P450 mono-oxygenase inhibitor of GA synthesis. It also inhibits ABA hydroxylase, thus extending ABA activity. In preliminary experiments, wheat varieties differing in Rht complement responded differently to ABA and/or tetcyclacis. We therefore investigated the effect of seed applications of ABA (100 μM), with or without tetcyclacis (25 μM), on germination and initial growth of Rht wheat isolines Rht-B1b, Rht-B1a (dwarf); Rht-B1b,Rht-D1b (dwarf); Rht-B1b + Rht-D1b (double-dwarf); and Rht-B1a, Rht-D1a (tall) to determine a possible genetic basis for the observed varietal differences. Treating seeds with ABA, tetcyclacis, or both, delayed emergence by 1, 1.8, or 3.7 d, respectively, compared with controls. ABA had little or no effect on final emergence, shoot height, or fresh weight, but led to a slight reduction in dry weight of Rht-D1b and Rht-B1b+D1b Tetcyclacis reduced growth rate (mm/d), shoot height, fresh weight, and percentage dry weight in proportion to Rht dosage, as is typical of GA synthesis inhibitors. Synergistic effects of ABA and tetcyclacis were not detected for any parameter measured, except for rate of emergence. ABA did not exert a profound effect on seedling germination or initial growth of the Rht wheat isolines examined in this study.
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