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 al/Chlb 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.