Effect of NaCl Stress on the Anatomical Structure and Ultrastructure of Leaves of Berberis thunbergii var. atropurpurea and Berberis thunbergii ‘bingchuanhongye’

Abstract

In this study, we first investigated the effects of different concentrations of NaCl stress treatments (0%, 0.1%, 0.2%, 0.3%, and 0.4%) on the anatomical structure and ultrastructure of plant leaves using annual seedlings of Berberis thunbergii var. atropurpurea and Berberis thunbergii ‘bingchuanhongye.’ To provide a detailed analysis, scanning and transmission electron microscopy was utilized. Scanning electron microscopy indicated that the increased NaCl stress concentration decreased the number of stomatal openings, open stomatal percentage, and stomatal length, width, and size of the lower epidermis of both Berberis species. The epidermal cells and stomata of Berberis thunbergii ‘bingchuanhongye’ were significantly wrinkled and damaged, while the arrangement of the palisade tissue and spongy tissue of Berberis thunbergii var. atropurpurea was more orderly than that of Berberis thunbergii ‘bingchuanhongye.’ Transmission electron microscopy showed that the cytoplasm of Berberis thunbergii var. atropurpurea gradually shrank and exhibited serious plasmolysis with the increase of NaCl stress concentration. At the same time, the chloroplasts became larger and deformed, and the number of mitochondria, osmiophilic granules, and starch granules gradually increased. In contrast, the inward contraction of the protoplasm of Berberis thunbergii ‘bingchuanhongye’ was not obvious, the chloroplasts were smaller and fewer in number, and the number of mitochondria, osmiophilic granules, and starch granules gradually decreased until degradation. This study not only preliminarily determined that Berberis thunbergii var. atropurpurea showed slightly higher salt tolerance than Berberis thunbergii ‘bingchuanhongye,’ but also provided insights into their response mechanisms to saline environments.