Differential photosynthetic electron transport and oxidative stress in paraquat-resistant and sensitive biotypes of Solanum americanum

Electron transport in a paraquat-resistant (R) biotype of Solanum americanum Mill. (American black nightshade), when measured as the photoreduction of ferricyanide by thylakoid membranes, was significantly lower than that of a sensitive (S) biotype. The discrepancy in the rate of photosynthesis was confirmed by measuring carbon dioxide fixation at the whole plant level. Dry matter accumulation ty the R biotype was exceeded by the S biotype. Superoxide production by nontreated, illuminated thylakoid membranes was also lower in the R biotype, and the increase in oxidative stress that resulted from paraquat treatment was greater in the S biotype. Paraquat-treated thylakoids of the R biotype and nontreated thylakoids of the S biotype had similar rates of O-2(-) production. The low rates of electron transport and correspondingly low levels of oxidative stress in nontreated thylakoids of the R biotype imply that paraquat resistance in S. americanum is due to reduced photosynthetic electron flow. (C)1998 Academic Press.