Role of auxin and cytokinin in the regulation of the actin cytoskeleton in the in vitro germinating male gametophyte of petunia

Abstract

Pollen tubes germinating in vitro, which has become in recent years the object of detail and intensive research, is a model for studying the mechanisms of sexual reproduction of higher plants. The potential role of the actin cytoskeleton (F-actin) in the transduction of hormonal signals in the progamic phase of fertilization was studied on in vitro germinating male gametophyte of petunia (Petunia hybrida L.). It was established for the first time that treatments with phytohormones, such as auxin (IAA) and cytokinin (kinetin), affected germination and polar growth of the pollen tubes, e.g., stimulated or inhibited these processes, and also induced the actin cytoskeleton rearrangement. The addition of IAA to nutrient medium increased the content of F-actin in the apical and subapical zones of pollen tubes and, as it is supposed, is responsible for the stimulation of their polar growth due to the intensification of the cytoplasm flow and apically directed vesicle transport. The inhibitor of actin polymerization, latrunculin B, disturbed actin cytoskeleton spatial organization, decreased the content of endogenous IAA, and, as a consequence, retarded germination and/or blocked male gametophyte polar growth. In contrast, kinetin suppressed pollen tube growth, reducing the content of polymer actin along the entire tube length. In pollen tubes germinating in the presence of latrunculin B for 4 h, the content of cytokinins was not significantly changed as compared with control. These results allow a conclusion that auxin and cytokinin are involved in the regulation of pollen tube polar growth via their effects on actin polymerization and spatial organization.