Although increasing attention has been paid to the relationships between heavy metal and nitrogen (N) availability, the mechanism underlying adaptation to cadmium (Cd) stress in dioecious plants has been largely overlooked. This study examined Cd accumulation, translocation and allocation among tissues and cellular compartments in Populus cathayana Rehder females and males. Both leaf Cd accumulation and root-to-shoot Cd translocation were significantly greater in females than in males under a normal N supply, but they were reduced in females and enhanced in males under N deficiency. The genes related to Cd uptake and translocation, HMA2, YSL2 and ZIP2, were strongly induced by Cd stress in female roots and in males under a normal N supply. Cadmium largely accumulated in the leaf blades of females and in the leaf veins of males under a normal N supply, while the contrary was true under N deficiency. Furthermore, Cd was mainly distributed in the leaf epidermis and spongy tissues of males, and in the leaf palisade tissues of females. Nitrogen deficiency increased Cd allocation to the spongy tissues of female leaves and to the palisade tissues of males. In roots, Cd was preferentially distributed to the epidermis and cortices in both sexes, and also to the vascular tissues of females under a normal N supply but not under N deficiency. These results suggested that males possess better Cd tolerance compared with females, even under N deficiency, which is associated with their reduced root-to-shoot Cd translocation, specific Cd distribution in organic and/or cellular compartments, and enhanced antioxidation and ion homeostasis. Our study also provides new insights into engineering woody plants for phytoremediation.

中文翻译：

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不同氮素水平下杨树雌雄对镉胁迫的微结构和生理响应。

尽管人们越来越关注重金属与氮（N）的可用性之间的关系，但雌雄异株植物对镉（Cd）胁迫适应的潜在机制已被大大忽略。这项研究检查了Cadulus cathayana Rehder雌性和雄性中镉在组织和细胞区室之间的积累，转运和分配。在正常氮供应下，女性叶片中Cd的积累和根尖Cd的转运均明显高于雄性，但在氮不足的情况下，雌性中的叶片中Cd积累量和雄性中的Cd转运量均明显高于雄性。在正常氮供应下，雌性和雄性中的镉胁迫强烈诱导了与镉吸收和转运相关的基因HMA2，YSL2和ZIP2。在正常的氮供应下，镉大量积累在雌性的叶片和雄性的叶脉中，而氮缺乏时则相反。此外，镉主要分布在雄性的叶表皮和海绵状组织中，以及雌性的叶栅状组织中。氮缺乏增加了镉在雌性叶片海绵状组织和雄性栅栏组织中的分配。在正常的氮供应下，镉在根中优先分布于两性的表皮和皮层以及女性的血管组织，但在氮缺乏的情况下，Cd则优先分布于雌性的血管组织。这些结果表明，即使在氮缺乏的情况下，雄性也比雌性具有更好的Cd耐受性，这与降低的从根到下Cd易位，有机和/或细胞区室中特定的Cd分布有关，以及增强的抗氧化和离子稳态。我们的研究还提供了对工程木本植物进行植物修复的新见解。