Responses of woody plant Dalbergia odorifera treated with glycine betaine to drought and cold stresses: involvement of the alternative oxidase

Woody plants faced multiple abiotic stresses in forest plantation that can influence their growth and development. Dalbergia odorifera T. Chen is a vulnerably endangered tree species, and references about its responses to abiotic stresses are very rare in literature. Furthermore, the mechanisms underlying the abiotic stress tolerance in plants induced by exogenous glycine betaine (GB) remains unclear. Indeed, the alternative oxidase (AOX) is one of the major components of antioxidant enzymatic machinery, and there are no studies that focused on the effects of GB on the amount of AOX protein in plants under drought or cold stresses. Thus, the aim of this study was to investigate the effect of exogenous GB on the phenotype, osmoprotectants, photosynthetic pigments, and antioxidant systems in D. odorifera under cold and drought stresses. The layout of the trial was a factorial experiment in a completely randomized design using two factors including abiotic stress (drought and cold) and GB. Moreover, the principal component analysis based on the measured parameters manifested how the selected ROS scavengers were dispersed throughout the treatments. The results showed huge beneficial impacts of GB on the phenotypic traits of D. odorifera; GB also influences positively the antioxidant machinery, photosynthetic pigments, redox-homeostasis, and water status in D. odorifera seedlings under both stresses. Moreover, exogenous GB affects more the AOX pathway in D. odorifera under cold stress than under drought stress.