A study of senescence and the post-pollination response in flowers of Dianthus caryophyllus L. cv. 'White Sim'

Paul Brian Larsen, Purdue University

Abstract

Both senescence and the post-pollination response in carnation flowers result from an induction of ethylene production and concomitantly ethylene responsive genes, especially in petals and styles. This is true of the two genes unique to ethylene biosynthesis, ACC synthase and ACC oxidase, which, in combination, lead to the rise in ethylene production that is observed during senescence. Isolation and analysis of SAM synthetase, the first step in ethylene biosynthesis, shows that SAM synthetase is opposite to this and is in fact downregulated with the production of elevated levels of ethylene and the initiation of senescence. Ethylene also appears to play an integral role in the initiation of the post-pollination response in carnation flowers. This response consists of an increase in stylar ethylene, triggering of petal senescence, and initiation of ovary maturation. It is not clear as to what primary interaction between the pollen and pistil mediates this response. In other systems, most notably petunias, it has been speculated that the induction of this response is triggered either by high levels of pollen-borne ACC or by release of active cell wall fragments as the pollen tube digests a path through the transmitting tract. By comparing two carnation pollen types, one that induces senescence and one that does not, I was able to show that neither pollen-borne ACC nor pollen tube penetration alone are sufficient to trigger the post-pollination response in carnations. Further examination of the interaction of the senescence-inducing pollen type with 'White Sim' flowers shows a dependence of pollination-inducible senescence on interorgan communication, which appears to be mediated by increased levels of ethylene. This interorgan communication seems to be coordinated by the ovary, which is shown to accumulate high levels of ethylene. This ethylene, or its precursor ACC, may diffuse to other tissues, thus stimulating ethylene production and senescence in these tissues. Based on these and other observations, a model for how pollination triggers senescence and ovary maturation in carnation flowers has been developed and is presented here.

Degree

Ph.D.

Advisors

Woodson, Purdue University.

Subject Area

Botany

COinS