Investigation of drought tolerance at physiological, biochemical and molecular levels in sunflower (Helianthus annuus L.) genotypes

In this study, it was aimed to investigate the responses of registered sunflower cultivars grown in our country with their wild hybrids and wild Helianthus agrophyllus, identified to be drought tolerant, at morphological, physiological, biochemical and molecular (proteomic) levels during drought and recovery. In the first stage, sunflower cultivars were exposed to two different drought treatments (moderate -7 days / severe-9 days) and then recovery (irrigation-5 days). In this stage, photosynthetic activities (chlorophyll a fluorescence measurements), membrane damage (ion leakage), photosynthetic pigment and water contents of the cultivars were measured. Drought-recovery factor indexes and damage-recovery potential indexes were calculated from photosynthetic performance indexes, and physiological and biochemical measurements, respectively. These calculations allowed classification of the genotypes to three tolerance levels: drought-tolerant (Şems, Sirena, Tarsan-1018), moderately tolerant (Duna, Hornet, Tunca) and sensitive (Bosfora, Coral, Kaan). In the second stage of the study, the drought responses of selected cultivars with the wild hybrids of the sunflower (Helianthus annuus x Helianthus agrophyllus and Helianthus annuus x Helianthus deserticola) subjected to drought stress for 9 days and then 5-days recovery were proved by using the morphological, photosynthetic, physiological and biochemical parameters. Genotypes were characterized according to their drought tolerances by calculating damage indexes and recovery potentials from the obtained data. The changes in phenotypic characters (plant height, number of leaves and fresh / dry weight) were determined in all genotypes due to the reduced water content under drought conditions. However, tolerant genotypes compared to sensitive genotypes, were able to conserve photosynthetic activities (absorption/trapping of excitation energy and utilize efficiently), pigment contents (chlorophyll/carotenoid) and enhance defense capacity [flavonoids, anthocyanins, glycine betaine, superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), peroxidase (POD) and aldose reductase (ALR)], thereby the level of H2O2 and stress-induced membrane damage (MDA) were kept low and were able to provide tolerance to stress. In the third stage, the alterations in the protein profiles of tolerant (Tarsan-1018) and sensitive (Tunca) cultivars and wild Helianthus agrophyllus were proved by proteomic analysis. 63 proteins were identified in genotypes with MALDI-TOF / TOF MS / MS mass spectrometry and MASCOT database, and the protein-protein interaction patterns were performed with STRING database. It has been determined that the identified proteins are involved in photosynthesis and carbohydrate, energy and respiration, defense, arginine, nucleotide, fatty acid and glycolipid, protein and signal metabolism and cell wall biogenesis. Different expression of proteins in metabolisms and the reductions in nucleotide and protein metabolisms, as well as protein involved in signal transduction of sensitive cultivar, made Tunca less successful in stress resistance compared to other genotypes. Tolerant genotypes were found to exhibit better performance in terms of photosynthesis and carbon metabolism, as well as protein expression in energy and respiration and fatty acid and glycolipid metabolisms in the same way, and increased the expression of 14-3- 3 like protein in signal transduction pathway increased resistance to drought conditions.