Abstract
SummaryApplications of ABA to Cymbidium flowers induce some, but not all, post‐pollination symptoms. Anthocyanin levels in sepals, petals, columns and labella are raised; flowers wilt; dorsal sepals become hooded; calli develop colouration while losing turgidity; columns do not swell, lose very little curvature; and stigmas do not close. Combinations of ABA and NAA induce all post‐pollination phenomena, but lower anthocyanin content than treatments with ABA only. ABA plus GA3 have effects which are similar to those of ABA alone, except that anthocyanin levels are reduced. The same is essentially true of ABA‐kinetin mixtures but intensities of the effects are different and with some concentration ratios, stigmatic closure also occurs. The effects of ABA and its interactions with GA3, kinetin or NAA are explained in terms of the roles these hormones may play in synthesis of nucleic acids and enzymes.
Highlights
Orchid flowers, including those of Cymbidium, undergo remarkable changes following pollination
Wilting of the perianth is an aspect of senescence; closing of the stigma and swelling of the column represent growth due to cell enlargement; greening and persistence of the column are modifications in function; changes in segments of the perianth involve organogenesis; ovule development is morphogenesis; synthesis of anthocyanins results from newly expressed biochemical capabilities; and the reduced turgidity of the calli implies changes in water relations
On the assumption that the known plant hormones may play different roles in anthocyanin production and the induction of other post-pollination phenomena in orchid flowers, and that our investigation of their interactions will contribute to the understanding of fruit-set in general, we have studied the effects of abscisic acid (ABA), an auxin (NAA), one cytokinin and gibberellin (GA3) singly and in combinations with one of the other three
Summary
Orchid flowers, including those of Cymbidium, undergo remarkable changes following pollination. Applications of auxins to the stigma initiate most of these changes, ovule development is aborted (for a short review see Arditti and Knauft, 1969). This is of particular interest since either pollination or auxin initiate events of such diversity that they would seem to be normally unrelated. Wilting of the perianth is an aspect of senescence; closing of the stigma and swelling of the column represent growth due to cell enlargement; greening and persistence of the column are modifications in function; changes in segments of the perianth involve organogenesis; ovule development is morphogenesis; synthesis of anthocyanins results from newly expressed biochemical capabilities; and the reduced turgidity of the calli implies changes in water relations
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