Ion flux kinetics in blue light-grown field dodder (Cuscuta campestris) seedlings

Previous studies have revealed that blue light stimulates coiling and prehaustoria development in young de-etiolated dodder seedlings prior to host attachment. In this study, the Ca²⁺ and H⁺ flux kinetics that are associated with blue light-mediated coiling and prehaustoria development in de-etiolated dodder seedlings were measured uninvasively using the ion-selective, vibrating microelectrode ion flux system. The findings showed that blue light induces rapid transient changes in the net Ca²⁺ and H⁺ fluxes. A clearly pronounced lag of about several minutes was observed between the blue light-induced changes in the Ca²⁺ and H⁺ fluxes, with H⁺ being a leading ion. The addition of 1 mol L⁻¹ vanadate, a known blocker of the plasma-membrane H⁺-ATPase, to the bathing solution completely prevented both the H⁺ and the Ca²⁺ flux responses and inhibited coiling and prehaustoria development, suggesting a causal relationship between the blue light-induced changes in the net Ca²⁺ and H⁺ fluxes and seedling movements. It is concluded that the plasma-membrane H⁺-ATPase plays a key role in a dodder's parasitic mode of growth and its adaptive response to the environment.