Sexual feedback, internode elongation and perfect-flowered dwarfs

--Walton C. Galinat

At the time the floral primordia are laid down that will eventually reach either tassel or ear, they are perfect flowered (bisexual) and below them the vegetative phase is still in the juvenile stage with telescoped internodes and only partly developed leaves. Each type of sexual development has a different feedback effect on the degree of completion of the vegetative phase below.

In the inflorescence terminating a main stalk with strong apical dominance, the female primordia are inhibited, the male primordia develop slowly and a hormonal signal is sent down to the vegetative phase that stimulates internode elongation and completes leaf development by the growth of blades. Meanwhile, the reverse occurs in the lateral branches and their terminal inflorescences. The internodes of the branches remain short, and the leaf blades fail to develop as if suppressed by apical dominance of the main stalk. The male primordia are inhibited and the female primordia develop precociously. As a result, the ears become trapped within their own bud, the leaf sheaths become a jail of protective husks and the styles must elongate until they are at the summit where pollination is possible. Because of the artificially imposed time required for style emergences, maize has been falsely accused of being protandrous.

In the perfect-flowered dwarfs, the internodes of the main stalk can not elongate normally with the result that its apical dominance is weakened and lateral branches freed for male expression. Thus a better balance is achieved between male and female hormones. Development of the female primordia is no longer precocious and the primordial situation of perfect flowers advances onward to floral maturation.

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