POLLEN PISTIL INTERACTIONS AND DEVELOPMENTAL REGULATION OF POLLEN-TUBE GROWTH IN ARABIDOPSIS

A developmental analysis of pollination responses in Arabidopsis impli cates pollen as well as stigma maturation factors in the acquisition o f reproductive function, In the anther, competence of pollen to germin ate and to produce pollen tubes in situ occurred late in development. In the pistil, competence to support pollen germination and tube growt h extended over a broad developmental window, and abundant as well as efficient pollen tube development was observed on pistils at anthesis and for a period of 1-2 days prior to flower opening, In contrast, pol len tube growth on immature pistils was found to proceed at low effici ency, at reduced growth rates, and with lack of directionality. Based on the pattern of pollen tube growth at different stages of pistil mat uration, temporally regulated signals emanating from specialized cells of the pistil are inferred to be operative in each of the four identi fied phases of pollen tube growth, In the stigma and the stylar transm itting tissue, these signals directed the path of intra-specific polle n tubes as well as pollen tubes from another cruciferous genera, Brass ica, By contrast, in the ovary, signaling by the ovule was effective o nly on intra-specific pollen tubes and was thus identified as the basi s of inter-specific incompatibility, Furthermore, the acquisition of r eproductive function was found to involve, in addition to the inductio n of a variety of stimulatory signals, a heretofore unrecognized devel opmental restriction in the capacity of epidermal surfaces of the flow er to support pollen tube growth.