Glycine Betaine Enhances Poplar Cultivar (Populus deltoides × Populus euramericana) Tolerance to Confront NaCl Stress

Glycine betaine (GB) serves as a compatible solute crucial for stress tolerance across numerous plant species. Populus trichocarpa grows along coastal regions and often suffers from salt stress. In this study, we explored the effects of foliar spraying of GB on the growth, physicochemical indexes, gene expression, and stress tolerance of poplar under salt stress. To achieve this, poplar plants (Populus deltoides × Populus euramericana “Nanlin 895”) were grown under four NaCl concentrations: 0, 50, 100, and 150 mM. Additionally, they were treated with 0, 5, 15, and 25 mM GB. The degree of effect on potted poplars was observed after 8 weeks. A GB treatment of about 15 mM significantly reduced the impact of salt stress and photosynthetic pigments and caused an improvement in the activity of the antioxidant enzymes peroxidase (POD) and superoxide dismutase (SOD). Moreover, GB-treated poplars had significantly more malonaldehyde (MDA) than the control lines. This study indicated that GB treatment reduces salt stress symptoms in poplars. This research helps to develop safe levels of endogenous GB, which will make poplars more resistant to environmental stresses.