Salinity-induced potassium deficiency causes loss of functional photosystem II in leaves of the grey mangrove, Avicennia marina, through depletion of the atrazine-binding polypeptide

Photosynthetic properties were studied in relation to the ionic composition of leaves of Avicennia marina grown in low and high salinity (i.e. 50 and 500 mol m- NaCl) nutrient solution containing either 0.01 or 10 mol m-3 K+. Leaves accumulated high concentrations of NaCl, but changes in photosynthesis were associated with changes in leaf K+ concentrations. The effects occurred at two levels. (1) With decrease in leaf K+ from 379 to 167 mol m-', a 21% decline in light and CO2 saturated rates of oxygen evolution per leaf area was consistent with a 24% decrease in chlorophyll content. (2) Leaves containing only 103 mol m-j K+ showed drastic loss of light and COz saturated photosynthetic capacity (42%) and photochemical dysfunctioning under limiting light conditions as manifest in a 38% decrease in quantum yield. Thylakoids isolated from these low K+ leaves showed no decrease in per chlorophyll concen- trations of photosystem I, cytochrome f/b complex and ATPase, but had 37% fewer atrazine-binding sites (corresp