Hormonal interactions in Ceratophyllum demersum

Abstract

Ceratophyllum demersum L. is a submerged aquatic macrophyte without roots. It occurs in winter in the dormant form and in summer in the active form. The effect of application of mixtures of indole acetic acid (IAA), abscisic acid (ABA) and gibberellic acid (GA 3) on subsequent growth after treatment in the quiescent stage was studied. The endogenous levels of several phytohormones were assessed during the annual cycle of the plant. In winter, when no growth occurs under natural conditions, the concentration of ABA was high and that of IAA low. In summer, however, when the transitions from the resting period to active growth and, subsequently, to dormancy, occur, the IAA levels were at their maximum, while the ABA levels were variable. The total activity of GA 3 was considerably lower in rapidly growing plants as compared to that of dormant or quiescent plants GA 3 antagonized the effect of ABA on the subsequent growth of plants released from quiescence, but IAA was ineffective in this regard. The significance of the natural phytohormones in the growth of Ceratophyllum at various periods of its annual cycle is discussed. Although ABA induced to a limited extent the changes in the levels of protein and total carbohydrates, it failed to induce a dormant morphology, and therefore its role in the induction of dormancy is still unclear.