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 amer icanum Mill. (American black nightshade), when measured as the photore duction of ferricyanide by thylakoid membranes, was significantly lowe r 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 ex ceeded by the S biotype. Superoxide production by nontreated, illumina ted thylakoid membranes was also lower in the R biotype, and the incre ase in oxidative stress that resulted from paraquat treatment was grea ter in the S biotype. Paraquat-treated thylakoids of the R biotype and nontreated thylakoids of the S biotype had similar rates of O-2(-) pr oduction. The low rates of electron transport and correspondingly low levels of oxidative stress in nontreated thylakoids of the R biotype i mply that paraquat resistance in S. americanum is due to reduced photo synthetic electron flow. (C)1998 Academic Press.