Changes in propagule formation and plant growth in Potamogeton crispus induced by exogenous application of gibberellic acid (GA3) and 6-benzyladenine (6-BA)

Submerged aquatic macrophytes such as Potamogeton crispus can absorb large quantities of nutrients from sediment and water, and therefore mitigate pollution and improve water quality of polluted lakes. Turions are the main propagules of P. crispus; their formation is an important process in the life cycle of the plant and relates closely to the population dynamics of the species in lakes. The clarification of the physiological mechanisms specific to plant hormone regulation in propagule formation versus plant growth will help to better understand the population decline in eutrophic waters and to develop management strategies for the species. In the present study, different treatment concentrations and application frequencies of gibberellic acid (GA(3)) and 6-benzyladenine (6-BA), a cytokinin substances, were used to investigate their effects on propagule formation and plant growth in this plant. The results showed that, when a cultured plant was treated with GA(3) or 6-BA before propagule morphogenesis, propagule production was inhibited or delayed. Under repeat applications of GA(3) or 6-BA, propagule formation was arrested completely except in the treatment with 2.5 mg l(-1) GA(3), which led to some phylloclade turions. Plants treated with GA(3) had more phylloclade turions and longer turions compared to the control, whereas less difference was observed under 6-BA treatments. This suggests that cytokinin is a more effective substance in regulating propagule differentiation in P. crispus. Morphological and physiological analysis showed that the propagule formation was more sensitive than plant growth to the plant growth regulators. Both plant growth regulators promoted photosynthetic pigments in plants but inhibited starch accumulation in propagules, which may be related closely to the changes in propagule growth and development.