Gibberellin Metabolism in Maize: Tissue Specificity
The single-gene dwarf mutants d1, d2, d3, and d5 have been used to analyze the early-13-hydroxylation pathway of gibberellin (GA) biosynthesis in the shoots of maize (Zea mays L.). These dwarf mutants are GA mutants in that they exhibit normal growth in response to exogenous GA; they do not respond to any other plant hormones or growth regulators. The location of the specific steps blocked by the mutants has been based on the following information: (1) the identification of the GAs native to maize shoots1; (2) the relative bioactivities of the maize GAs on each of the four mutants2; (3) the quantification of the GAs present in normal, d1, d2, d3, and d5 maize shoots1; and (4) the metabolic fate of the label after feeds of double-labeled GAs and their precursors to normal and mutant maize shoots3 and to cell-free systems.4 The results clearly establish the early-13-hydroxylation pathway as the major pathway of GA biosynthesis in maize shoots; the results clearly define the specific steps controlled by two of the mutants (d1 and d5). The above studies have led to the conclusion that GA1 is the only GA bioactive per se in the pathway controlling stem elongation in maize shoots5,6; the other GAs in the pathway are active through their metabolism to GA1.
KeywordsLeaf Sheath Dwarf Mutant Normal Maize Hydroxylation Pathway Epidermal Region
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