Comparative hormonal and metabolic profile analysis based on mass spectrometry provides information on the regulation of water-deficit stress response of sunflower (Helianthus annuus L.) inbred lines with different water-deficit stress sensitivity.

Water-deficit stress is the most important abiotic stress restricting plant growth, development and yield. The effects of this stress, however, depend on genotypes, among other factors. This study assembles morpho-physiological and metabolic approaches to assess hormonal and metabolic profile changes, upon water-deficit stress, in the shoot and roots of two contrasting sunflower inbred lines, B59 (water-deficit stress sensitive) and B71 (water-deficit stress tolerant). The analyses were carried out using mass spectrometry and performing a multivariate statistical analysis to identify relationships between the analyzed variables. Water-deficit stress reduced all morpho-physiological parameters, except for root length in the tolerant inbred line. The hormonal pathways were active in mediating the seedling performance to imposed water-deficit stress in both lines, although with some differences between lines at the organ level. B59 displayed a diverse metabolite battery, including organic acids, organic compounds as well as sugars, mainly in the shoot, whereas B71 showed primary amino acids, organic acids and organic compounds predominantly in its roots. The discrimination between control and water-deficit stress conditions was possible thanks to potential biomarkers of stress treatment, e.g., proline, maleic acid and malonic acid. This study indicated that the studied organs of sunflower seedlings have different mechanisms of regulation under water-deficit stress. These findings could help to better understand the physio-biochemical pathways underlying stress tolerance in sunflower at early-growth stage.

Biochemical and molecular approach of oxidative damage triggered by water stress and rewatering in sunflower seedlings of two inbred lines with different ability to tolerate water stress.

Water stress accelerates the generation of reactive oxygen species, which trigger a cascade of antioxidative defence mechanisms comprising enzymatic and nonenzymatic antioxidants. The aim of this study was to investigate the oxidative damage and the antioxidative defence systems in seedlings of the water stress-tolerant (B71) and the sensitive (B59) inbred lines of sunflower (Helianthus annuus L.) in response to water stress and rewatering. In addition, we characterised the transcriptomic profile associated with enzymatic antioxidative defence. An elevated electrolyte leakage in B59 indicated increased plasmatic membrane permeability, which correlated with greater sensitivity to water stress. In response to water stress, both lines showed an increase in malondialdehyde and H2O2 content but these increases were more noticeable in the sensitive line. In both lines, an increase in enzymatic activity (e.g. peroxidase and ascorbate peroxidase) was not sufficient to overcome the H2O2 accumulation triggered by water stress. Upon water stress, the overall expression level of genes associated with the enzymatic antioxidant system increased in B71 and decreased in B59, which showed downregulated levels of most genes in the shoots. The general profile of phenolic compounds was clearly different between organs and between inbred lines. The B59 line activated nonenzymatic antioxidant responses to counteract the oxidative stress caused by water stress. The tolerance of B71 to water stress could be associated with compensatory antioxidant mechanisms based on the expression of genes encoding enzyme components of the ascorbate-glutathione and redoxin cycles, which contributed to explaining, at least partly, the response of this line.