Effects of NaCl Stress on Chlorophyll Content and Chlorophyll Fluorescence in Sunflower (Helianthus annuus L.) Lines

Abstract

Salinity is one of the important abiotic stresses that have adverse effects on photosynthesis, chlorophyll, fluorescence and their components. In this study, the influence of salinity (0, 100 and 200 mM NaCl) on chlorophyll and fluorescence was investigated in sunflower (H. annuus) lines (12 sunflower lines) for a period of one month in hydroponic culture system. The results showed that salt stress enhanced chlorophyll content in the first three weeks, but at last week, both levels of salinity declined it slightly. However, in non-stressed plants chlorophyll content increased during four weeks. The results indicated that salt stress affected chlorophyll content negatively only in long-term, but in shortterm salinity increased chlorophyll content by secondary effects. Among the 12 sunflower lines, the highest increase in chlorophyll content was observed in both sensitive and tolerant lines. Moreover, the results showed that severe stress increased Fv/Fm ratio from week 1 to week 3, but in week 4 this ratio decreased. After week 2 and unlike control plants, results represented an increase in both F and Fm values in stressed plants. It seems that Fm more increased than F, causing enhancement of Fv/Fm. It appeared that top (young) leaves in sunflower are adapted to remain active under salt stress to survive plant under long-term stress.