Auxin and flavonoids in the progame phase of fertilization in petunia

The contents of IAA and flavonoids (Fls) were monitored in developing anthers, in vitro growing pollen tubes, and in the in vivo pollen-pistil system of two petunia (Petunia hybrida L.) clones, self-compatible and self-incompatible. In both clones, the development of male gametophytes was accompanied by the increase in the IAA (from 10 to 60–70 ng/g fr wt) and Fls (from 2 to 20 mg/g fr wt) contents. In both clones, pollen grain germination was accompanied by a substantial (by 10–30%) increase in the IAA content during the first two hours and Fl content during the first hour. Treatments with IAA and Fls stimulated both in vitro pollen grain germination and pollen tube growth by 25–30%. Male gametophyte germination in vivo, on the pistil surface, was accompanied by the increase in the IAA content from 90 to 200 ng/g fr wt during 8 h, whereas the content of Fl increased from 2 to 3 mg/g fr wt during the first hour and was maintained later at this level. In the pollen-pistil system, IAA and Fls were distributed evenly in the tissues of stigma, style, and ovary. On the basis of data obtained, we concluded that Fls might be endogenous mediators of IAA transport, which is one of the principal regulators of male gametophyte growth and development in the progame phase of fertilization, but are not involved in the mechanism of gametophyte incompatibility.