ATP-dependent auxin- and auxinic herbicide-induced volume changes in isolated protoplast suspensions from Sinapis arvensis L

Auxin- and auxinic herbicide-induced volume changes in enzymatically isolated protoplast suspensions from both auxinic herbicide-susceptible (S) and picloram-resistant (R) wild mustard (Sinapis arvensis L.) biotypes were monitored by right-angle light scattering. The scattering profile of the volume change induced by IAA consisted of an initial shrinkage phase followed by swelling in both biotypes. Kinetic analysis of the swelling phase indicated two first-order processes for the S protoplasts, whereas a single first-order process was observed for the R. In the presence of picloram, only a swelling phase was observed for the S protoplasts, whereas both shrinkage and swelling phases were observed in R protoplasts. When protoplasts from the R biotype were incubated with dicamba or MCPA, which are effective to varying degrees against this biotype, the scattering profiles were similar to those observed for the S biotype with picloram. Simultaneous incubation of R protoplasts with picloram and the calcium channel blocker verapamil reduced the initial shrinkage phase. The differences in response between R and S protoplasts to IAA and the auxinic herbicides at the cellular level suggest certain similarities with respect to the dynamics of protoplast volume changes and provide insight into auxin and auxinic herbicide action. (C) 1996 Academic Press.