In vitro germination, growth, morphogenesis and flowering of an aquatic angiosperm, Polypleurum stylosum (Podostemacee)

Abstract

Podostemads grow attached to rocks in fast-flowing streams. Their plant body is highly reduced with no clear distinction between shoot and root. The present paper deals with the in vitro developmental biology of Polypleurum stylosum (Wight) Hall, a plant occurring in south India. Murashige and Skoog's liquid medium of 1/20 strength with 2% sucrose promoted optimum percentage seed germination and sustained growth of the plants. The regenerative propensity of the plant has been described. Incorporation of kinetin and abscisic acid at different concentrations in the basal medium did not promote growth. Four-month-old, continuously growing cultures were induced to flower by transferring them from liquid medium to semi-solid medium gelled with 0.8% agar. This is the first report of in vitro flowering in Podostemaceae. Water is suggested to play a key role in the control of flowering in vitro. The high degree of structural reduction and the adaptive strategy for survival of this haptophyte have been discussed. Polypleurum stylosum is highly specialised and deviates widely from the classical root-shoot model typical of most angiosperms.