Abstract

The study of photosynthetic responses in plants provides useful information for understanding the physiological processes involved in the salinity tolerance and susceptibility mechanisms of sunflower cultivars. The aim of the present study was to evaluate the gas exchange responses, water relations (stress hydric), and growth characteristics of two sunflower cultivars, Agrobel 963 and Aguará 4, subjected to different salt concentrations. The study was conducted in a randomized block experimental design through a 2 x 5 factorial arrangement, with the factors being two sunflower cultivars (Agrobel 963 and Aguará 4) and five salt concentrations (0, 25, 50, 100 and 150 mM NaCl) applied in Hoagland nutrient solution, with five replicates. Gas exchange, water relations and growth characteristics were evaluated. The gas exchange measurements showed that the two sunflower cultivars maintained the photosynthetic activity per unit of leaf area even at the highest NaCl concentration tested (150 mM). With the increasing salinity in the nutrient solution, the leaf water potential decreased, while the concentration of optically active substances increased in both the leaves and roots, which helped maintain the plant’s water status. Reduction on dry mass of sunflowers was response to decreasing on the leaf total area and not as effect of salinity on the photosynthetic rate by leaf area unity.

Key words: Helianthus annuus L., gas exchange, NaCl, osmotic adjustment.