Regulation of chlorophyll biosynthesis and degradation by salt stress in sunflower leaves

Helianthus annuus L. plants when exposed to increasing concentrations of NaCl showed a reduction of chlorophyll content and fluorescence (mainly due to a reduction of Fm). Chlorophyllase activity was higher in 15-day-old unstressed leaves. It increased during the first days in 25 mM NaCl stressed leaves decreasing with higher concentrations. NaCl effect on chlorophyll synthesis was then studied: only 50 and 100 mM NaCl inhibited synthesis of 5-aminolaevulinic acid, a precursor of chlorophyll. Our results show that: (1) chlorophyllase is stimulated during the first days in leaves under moderate stress but it is affected by high salt concentrations; (2) salt stress affects more drastically chlorophyll synthesis (decreasing ALA synthesis) than chlorophyllase-mediated degradation. (C) 2004 Elsevier B.V. All rights reserved.