Pollen-pistil interactions and developmental regulation of pollen tube growth in Arabidopsis

ABSTRACT A developmental analysis of pollination responses in Arabidopsis implicates pollen as well as stigma maturation factors in the acquisition of reproductive function. In the anther, competence of pollen to germinate and to produce pollen tubes in situ occurred late in development. In the pistil, competence to support pollen germination and tube growth 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, pollen tube growth on immature pistils was found to proceed at low efficiency, at reduced growth rates, and with lack of directionality. Based on the pattern of pollen tube growth at different stages of pistil maturation, temporally regulated signals emanating from specialized cells of the pistil are inferred to be operative in each of the four identified phases of pollen tube growth. In the stigma and the stylar transmitting tissue, these signals directed the path of intra-specific pollen tubes as well as pollen tubes from another cruciferous genera, Brassica. By contrast, in the ovary, signaling by the ovule was effective only on intra-specific pollen tubes and was thus identified as the basis of inter-specific incompatibility. Furthermore, the acquisition of reproductive function was found to involve, in addition to the induction of a variety of stimulatory signals, a heretofore unrecognized developmental restriction in the capacity of epidermal surfaces of the flower to support pollen tube growth.