Reduced nitric oxide levels during drought stress promotes drought tolerance in barley associated with elevated polyamine biosynthesis

Trabajo presentado en la 6th Plant Nitric Oxide International Meeting, celebrada en Granada del 14 al 16 de septiembre de 2016.Understanding plant responses to drought is of fundamental importance for breeding drought tolerant crops. Nitric oxide (NO) is a key messenger in plant stress responses but its exact role during drought remains unclear. To investigate the role of NO in drought we employed transgenic barley plants (UHb) overexpressing the barley non-symbiotic hemoglobin gene HvHbl that oxidizes NOto N03-. Reduced NO production under drought conditions in UHb plants was associated with increased drought tolerance compared to wild type controls as measured by different physiological parameters. Since NO biosynthesis is closely related to polyamine metabolism, we investigated whether the NO observed effect in drought tolerance could also involve a role for polyamines. UHb plants showed higher content of spermidine under well-watered conditions that further increased under drought compared to wild type (WT) plants, whereas WT showed increased putrescine content. We further investigated whether NO might 1) exert any effect on the content of the aminoacids precursors of polyamines, and 2) regulate expression of polyamine related genes. UHb plants showed increases in particular amino acids precursor of polyamines, particularly in arginine. Expression of key genes of the polyamine biosynthesis pathway, such as arginine decarboxylase, was significantly correlated with the damage degree according to the disease symptom scale. Interestingly compared to WT plants, UHb plants exhibited a reduced expression of aminocyclopropane-1-carboxylic acid synthase gene, the first committed step in ethylene biosynthesis. Overall, these data suggest a NO-ethylene influenced regulatory node in polyamine biosynthesis linked to drought tolerance/susceptibility in barley.N