Gametophyte-Sporophyte Interactions in Pollen-Pistil System after Compatible and Incompatible Pollination.

Abstract

The gametophyte-sporophyte interactions govern the reproductive strategy of higher plants by forming different barriers to self-pollination in pollen-pistil system. Self-incompatibility, barrier was studied in the experimental system including 2 clones of petunia : (a) self-compatible (self-pollination results in adhesion, hydration and germination of pollen grains, growth of pollen tubes and fertilization), (b) self-incompatible (with the S-gene of incompatibility, the expression of which inhibits pollen tube growth in sporophyte style tissues). Thus, our experimental model permitted us to study signal systems capable of transmitting not only positive information favoring the growth of compatible pollen tubes to the ovary, but also a negative information preventing the penetration of incompatible pollen tubes. A concept of multilevel system controlling gametophyte-sporophyte interactions was put forward. Here, we provide evidence for the participation of sporophytic proteins and ethylene in the regulation of male gametophyte growth and development. The protein specificity in pollen-pistil system during floral organogenesis is characterized by common antigens to male and female systems, as well as by pollen-and pistil-specific antigens, which are synthesized at the late stages of flower development (including a unique S-antigen in sporophyte tissue of pistil). The pattern of lectin activity observed in pistil transmitting tissue is related to the lectin molecule functioning in the interactions between the cells of male gametophyte and those of pistil sporophytic tissues. We have shown that two enzymes are related to the operation of the gametophyte-sporophyte interactions : style RNase takes part in the gametophytic selfincompatibility mechanism, whereas cholinesterase is the most likely candidate for the specific recognition and signal transduction in pollen-pistil system. It is demonstrated that the sporophyte stigma tissues are the source of ethylene production during pollen tube growth in the pistil in the case of both compatible and incompatible pollination.