INVITRO GERMINATION, GROWTH, MORPHOGENESIS AND FLOWERING OF AN AQUATIC ANGIOSPERM, POLYPLEURUM-STYLOSUM (PODOSTEMACEAE)

Podostemads grow attached to rocks in fast-flowing streams. Their plan t body is highly reduced with no clear distinction between shoot and r oot. The present paper deals with the in vitro developmental biology o f 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 t he plants. The regenerative propensity of the plant has been described . Incorporation of kinetin and abscisic acid at different concentratio ns in the basal medium did not promote growth. Four-month-old, continu ously growing cultures were induced to flower by transferring them fro m liquid medium to semi-solid medium gelled with 0.8% agar. This is th e first report of in vitro flowering in Podostemaceae. Water stress is suggested to play a key role in the control of flowering in vitro. Th e high degree of structural reduction and the adaptive strategy for su rvival of this haptophyte have been discussed. Polypleurum stylosum is highly specialised and deviates widely from the classical root-shoot model typical of most angiosperms.