The effects of sodium chloride stress on some biochemical characteristics and antioxidative enzymes activities in two sunflower (Helianthus annuus L.) genotypes

Salinity is one of the most important non-biological stresses that affect plant growth and development. Effect of different levels of NaCl (0, 2, 4, 6 and 8 dS/m) were investigated on enzymatic and non-enzymatic activities in C64 and C68 oilseed sunflower genotypes at two times; 3 and 12 days after salinity stress application. Net photosynthesis rate, chlorophyll content and soluble proteins amount decreased by increasing salinity level but proline and malondialdehyde (MDA) contents increased. However, the changes in net photosynthesis in the two studied genotypes was different across time and do not follow statistically the same trend line. In genotype C86, the reduction of photosynthesis rate at all studied salinity levels was very high compared to normal condition (0 dS/m) after 3 days; especially at salinity levels of 2, 4 and 6 dS/m, while 12 days later, the decrease of photosynthesis rate was moderate at salinity levels of 2 and 4 dS/m but severe at 6 and 8 dS/m salinity levels. The highest amount of proline (31.36%) related to tolerant genotype and the lowest amount (7.72%) related to susceptible one was measured 12 days after 2 dS/m salt stress treatment. Considerable MDA was observed in both tolerant and sensitive genotypes 12 days post salt stress application; the highest amount (83%) was observed at 8 dS/m treatment. Catalase and ascorbate peroxidase activity increased with increasing salt intensity. The rate of increase in guaiacol peroxidase activity was higher in C86 genotype than C64. Chlorophyll a and total chlorophyll contents decreased in both sunflower genotypes under salinity stress. The lowest amount of total chlorophyll (8.6%) was observed in the salinity level of 8 dS/m in the sensitive line (C64). Results revealed the C64 and C68 selected genotypes from two our identified sunflower heterotic groups have different physiological response to salinity stress and C68 is more tolerant to salt stress than C64. So, they can be potentially used as parents in sunflower breeding programs to produce salt stress tolerant hybrids.