Effects of air pollutants on proton and sucrose transport at the plasma membrane of Ricinus communis

Abstract

The effects of the air pollutants O 3 , SO 2 and NO 2 on aspects of sucrose/proton cotransport across the plasma membrane of Ricinus communis plants have been investigated. The H + -ATPase hydrolytic activity in cotyledon plasma membrane vesicles purified by phase partitioning showed small stimulations by Na 2 SO 3 or NaNO 3 added separately or together to the assay medium. ATPase activity from plants pretreated by fumigation with SO 2 or O 3 also showed an increase, the effect of O 3 being quite marked. Plasma membrane H + -pumping in KI-treated microsomal fractions and medium acidification by intact cotyledons both showed small decreases in the presence of Na 2 SO 3 or NaNO 2 . Both Na 2 SO 3 and NaNO 2 at high concentrations (2 mol m -3 ) had significant effects on sucrose uptake by intact cotyledons, although sucrose efflux was unaffected. No significant effects on sucrose uptake or efflux by intact cotyledons were observed in plants pretreated by fumigation with SO 2 or O 3 . Proton-coupled sucrose transport in isolated plasma membrane vesicles was inhibited in the presence of Na 2 SO 3 or NaNO 2 . However, both pollutants also significantly inhibited the uptake of acetate by the vesicles, indicating a dissipation of the pH gradient across the membrane. It was concluded that no specific aspect of the sucrose/proton cotransport mechanism was damaged by these air pollutants, and that the effects of these pollutants on carbohydrate partitioning are more likely to be due to general effects on membrane integrity or on other aspects such as leaf carbohydrate metabolism.

Ecological ramifications of the direct foliar uptake of nitrogen

“…However, detrimental physiological responses including decreased photosynthesis (Saxe 1986), effects on plasma membranes (Russell et al 1999) and plant water-use efficiency (Siegwolf et al 2001) have been reported coincident with leaf fumigation with reactive N.…”