Abstract
Cold and freezing stress is one of the most harmful environmental stresses, especially in temperate and subtropical areas, that adversely affects plant growth, development, and yield production. Betula platyphylla Sukaczev, also known as white birch, is one of the most valuable, important, and widely distributed tree species in East Asia. This study explored the effects of cold acclimation (CA) in reducing the destructive effect of freezing stress in B. platyphylla seedlings. We measured the physiological and biochemical characteristics of B. platyphylla seedlings, such as chlorophyll content, electrolyte leakage (EL), malondialdehyde (MDA), antioxidant enzymes (such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), and proline content before and after freezing stress to observe the contribution of CA in reducing the detrimental effects of freezing stress. The results showed that CA increased physiological and biochemical characteristics of B. platyphylla seedlings before and after freezing stress, except for chlorophyll content. Antioxidant enzymes were significantly positively correlated with proline, MDA, and EL content, and negatively correlated with chlorophyll content. Moreover, histochemical detection (H2O2 and O2−) and cell death were revealed to be induced by cold stress in B. platyphylla seedlings. Furthermore, it was revealed that increased time and decreased temperature of the CA process significantly influenced the physiological and biochemical parameters. Overall, the CA process significantly reduced the detrimental effects of freezing stress compared to the control treatment in B. platyphylla seedlings. Taken together, these findings provide beneficial information toward understanding the mechanism of CA and freezing stress in B. platyphylla. Furthermore, the substantial activity of physiological and biochemical results could be used as selection criteria for screening time and temperature points of cold/freezing stress in further omics analyses. In addition, the combination of current study results, further omics analyses, and genetic engineering techniques directly contribute to sustainable forest management systems, tree plantations, and conservation of tree species, especially non-cold/non-freezing tolerant tree species.
Highlights
White birch (Betula platyphylla S.) is a revolutionary forest plant in northeastern China [1], which is one of the most valuable, important, and widely distributed tree species in east Asia, mostly in China, Korea, and Japan [2]
The results showed that the difference in temperature and time point significantly inhibited B. platyphylla seedling growth
2w8d seedlings had a red stem and yellow leaves (Figure 1b). This suggests that low temperatures and long exposures interfere with seedling growth, causing stunted, red stems, and yellow leaves/chlorosis
Summary
White birch (Betula platyphylla S.) is a revolutionary forest plant in northeastern China [1], which is one of the most valuable, important, and widely distributed tree species in east Asia, mostly in China, Korea, and Japan [2]. Cold stress has been studied in B. platyphylla, there have been few studies, which results in a knowledge gap and limited understanding of this cold-tolerant tree species. It was specified that cold or freezing stress affects the molecular, physiological, and biochemical traits [18,19]. Physiological and biochemical markers such as chlorophyll contents, electrolyte leakage (EL), malondialdehyde (MDA), antioxidant enzymes, and proline may be considered as excellent criteria for plant tolerance evaluation [20,21]. High levels of ROS, caused by cold stress, result in chloroplast changes and decrease the photosynthesis rate. Proline acts as a water-soluble material with low molecular weight and is considered an effective osmotic regulatory chemical in plant abiotic stress response [20]
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