Salt secretion is an important strategy for mangrove plant Aegiceras corniculatum to adapt the coastal intertidal environment. However, the structural, developmental and functional analyses on the leaf salt glands, particularly the salt secretion mechanism are not well documented. In this study, we investigated the structural, developmental and degenerative characteristics, and the salt secretion mechanisms of salt glands to further elucidate the mechanisms of salt tolerance of A. corniculatum. The results showed that the salt gland cells have a large number of mitochondria and vesicles, and plenty of plasmodesmata as well, while chloroplasts were found in the collecting cells. The salt glands developed early and began to differentiate at the leaf primordium stage. We observed and defined three stages of salt gland degradation for the first time in A. corniculatum, where the secretory cells gradually twisted and wrinkled inwards and collapsed downwards as the salt gland degeneration increased and the intensity of salt gland autofluorescence gradually diminished. Besides, we found that the salt secretion rate from salt glands increased with the treated concentration of NaCl increased, reaching the maximum at 400 mM NaCl. The salt-secreting capacity from salt glands of the adaxial epidermis is significantly greater than that of the abaxial epidermis. The qRT-PCR results indicate that SAD2, TTG1, GL2 and RBR1 may be involved in regulating the development of the salt glands of A. corniculatum. Moreover, Na+/H+ antiporter, H+-ATPase, K+ channel, and Cl- channel may be play important roles in salt secretion from salt glands. In sum, this study strengthens the understanding of the structural, developmental, and degenerative patterns of salt glands and salt secretion mechanisms in mangrove recretohalophyte A. corniculatum, providing an important reference for further studies at the molecular level.

中文翻译：

---

红树林续盐植物桐花树叶盐腺的结构、发育和功能分析。

盐分分泌是红树林植物桐花树适应沿海潮间带环境的重要策略。然而，对叶盐腺的结构、发育和功能分析，特别是盐分泌机制的分析还没有很好的记录。本研究通过研究盐腺的结构、发育和退化特征以及盐分泌机制，以进一步阐明羊角藻的耐盐机制。结果表明，盐腺细胞内有大量的线粒体和囊泡，还有大量的胞间连丝，收集细胞内有叶绿体。盐腺发育较早，在叶原基阶段开始分化。我们首次观察并定义了羊角藻盐腺退化的三个阶段，随着盐腺退化的加剧和盐腺自发荧光强度的逐渐减弱，分泌细胞逐渐向内扭曲、起皱并向下塌陷。此外，我们发现盐腺的盐分泌率随着 NaCl 处理浓度的增加而增加，在 400 mM NaCl 时达到最大值。近轴表皮盐腺的泌盐能力明显大于远轴表皮。qRT-PCR结果表明，SAD2、TTG1、GL2和RBR1可能参与调节千里香盐腺的发育。此外，Na+/H+逆向转运蛋白、H+-ATP酶、K+通道和Cl-通道可能在盐腺盐分泌中发挥重要作用。总之，本研究加强了对红树林续盐植物A. corniculatum盐腺结构、发育和退化模式以及盐分泌机制的认识，为分子水平的进一步研究提供了重要参考。