CHEMICAL-CHANGES AND O2(.-) PRODUCTION IN THYLAKOID MEMBRANES UNDER WATER-STRESS

Sunflower seedlings (Helianthus annuus cv. Isabel) subjected to a moderate level of water stress showed a reduced growth and a 0.1 MPa osmotic adjustment came into play. Thylakoid membranes isolated from stressed leaves showed decreased chlorophyll (Chl) and protein contents but the Chl a/Chl b and protein/Chl ratios were unchanged. Water stress caused a preferential hydrolysis in thylakoid proteins: the hydrophilic to hydrophobic protein ratio increased from 0.8 in the control to 4.5 in the stressed plants. However, the degree of unsaturation was unchanged and the electron spin resonance (ESR) measurements did not show an increased level of O2.-radical production by photosynthetic membranes.