Pollen germination, early pollen tube growth and ovary development of Dendrobium orchid: Dependence on auxin and ethylene

Abstract

Importance of the work: Placing pollinia of some Dendrobium cultivars on the stigma of different cultivars may result in no growth of pollen or the ovary.
Objectives: To clarify the requirements of auxin and ethylene for growth of pollen and ovary of Dendrobium after pollination.
Materials & Methods: Pollinia of Dendrobium ‘Pompadour’ were placed on the stigma surface of ‘Sonia Bom #28’ flowers with and without inhibitors of auxin and ethylene. Pollen germination and growth of pollen tube and ovary were monitored. The auxin (indole acetic acid; IAA) and 1-aminocyclopropane-1-carboxylic acid (ACC) contents in the pollinia of ‘Pompadour’ and ‘Sonia Bom #28’ were determined.
Results: Pollen germination started within 1 d of placement and the pollen tubes and ovary then grew rapidly. Free auxin (IAA) content in the pollinia of ‘Pompadour’ was significantly higher than that in the pollinia of ‘Sonia Bom #28’, while the concentrations of ACC in the pollinia of both cultivars were not significantly different. Pollen germination, pollen tube growth and ovary growth were all inhibited after applications of aminooxyacetic acid (AOA) and 1-methylcyclopropene (1-MCP). Similarly, pollen germination, pollen tube growth and ovary growth were inhibited by alpha-(p-chlorophenoxy) isobutyric acid (CPIBA). AOA and CPIBA also inhibited
naphthaleneacetic acid (NAA)-induced ovary growth and delayed post-pollination development induced by NAA.
Main finding: Auxin in the pollinia was required for normal pollen germination, the growth of the pollen tube and the growth of the ovary of Dendrobium orchid after pollination.