Phytoglobin Scavenging of Nitric Oxide Is Associated With Ethylene Reduction and Drought Tolerance in Oat ( <i>Avena sativa</i> )

Drought stress significantly impacts crop productivity and plant physiology. Nitric oxide (NO) signalling is essential for drought tolerance. This study explores the relationship between in vivo NO levels, mediated by NO scavenging phytoglobin (encoded by Pgb, non-symbiosis associated hemoglobin), and drought tolerance in oat (Avena sativa). Real-time in vivo NO measurements suggested increased production under moderate to high water stress in the susceptible cultivar Flega compared to the resistant Patones. This elevated NO correlated with increased senescence in Flega. Conversely, the resistant cultivar Patones showed a marked increase in Pgb gene expression, which correlated with reduced NO levels in vivo. This suggested that Pgb acts as a protective mechanism against NO-induced stress. Water stress-induced NO increases fed into the polyamine pathway, leading to a significant rise in arginine decarboxylase (ADC) expression, leading to putrescine accumulation in the susceptible cultivar, whereas the resistant Patones maintained lower ADC expression and polyamine levels. Elevated in vivo ethylene production was also observed in the susceptible cultivar Flega, correlating with severe drought-induced senescence symptoms and linked to the naturally high NO levels in this cultivar. Assessment of other oat genotypes confirmed a negative correlation between Pgb expression and drought symptoms. These results underscore an important role of phytoglobins in modulating NO levels to counter drought in oat and suggest a potential target for genetic improvement of oat for drought tolerance.