Comparison of flash-induced light-scattering transients and proton efflux from auxinic-herbicide resistant and susceptible wild mustard protoplasts: a possible role for calcium in mediating auxinic herbicide resistance.
Comparison of flash-induced light-scattering signals from protoplasts of auxinic herbicide-resistant ('R') and -susceptible ('S') wild mustard biotypes suggest that ATP-dependent activity manifested as a conformational change differs between the biotypes. The signal obtained from R protoplasts is unaffected by 50 microM picloram, an auxin analogue. In comparison, the signal amplitude from the S protoplasts decreases 40% in 20 microM picloram and is abolished in 50 microM picloram. Signal amplitude from the R protoplasts can be decreased by simultaneous incubation with 50 microM picloram and 50 microM verapamil, a calcium channel blocker. Incubation of the S protoplasts with the calcium ionophore A23187 in the presence of 0.5 mM calcium reduced the inhibitory effect of picloram. Absorbance spectrophotometry using acridine orange as a pH indicator suggests that picloram affects the proton flux in the S biotype only. Based on these results, we hypothesize that picloram affects the calcium and hydrogen dynamics in the S biotype. Because the scattering characteristics of S protoplasts incubated with picloram can be nearly reproduced in the R protoplasts by simultaneous incubation with picloram and verapamil, calcium may have a significant role in modulating auxinic herbicide resistance. To our knowledge, this is the first report to implicate such a role for calcium.
Deshpande
S
S
Department of Environmental Biology, University of Guelph, Ontario, Canada.
Hall
J C
JC
D000165:Acridine Orange; D000255:Adenosine Triphosphate / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004351:Drug Resistance; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007210:Indoleacetic Acids / Q000494:pharmacology*; D008027:Light; D009149:Mustard Plant / Q000187:drug effects*; D010846:Picloram / Q000494:pharmacology*; D010946:Plants, Medicinal; D012542:Scattering, Radiation; D014700:Verapamil / Q000494:pharmacology
D007210:Indoleacetic Acids; D000001:Calcimycin; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate; D014700:Verapamil; D000165:Acridine Orange; D010846:Picloram