Department of Plant Systems Biology, Flanders Institute for Biotechnology, and Department of Plant Biotechnology and Genetics, Ghent University, B-9052 Ghent, Belgium.
Plant Physiol. 2010 Mar;152(3):1574-84. doi: 10.1104/pp.109.151399. Epub 2010 Jan 15.
Mature indeterminate Medicago truncatula nodules are zonated with an apical meristem, an infection zone, a fixation zone with nitrogen-fixing bacteroids, and a "developmental" senescence zone that follows nodule growth with a conical front originating in the center of the fixation zone. In nitrogen-fixing cells, senescence is initiated coincidently with the expression of a family of conserved cysteine proteases that might be involved in the degradation of symbiotic structures. Environmental stress, such as prolonged dark treatment, interferes with nodule functioning and triggers a fast and global nodule senescence. Developmental and dark stress-induced senescence have several different structural and expression features, suggesting at least partly divergent underlying molecular mechanisms.
成熟的不定型苜蓿根瘤呈区域化分布，具有顶端分生组织、感染区、固氮菌的固氮区和“发育”衰老区，随着固氮区中心起源的锥形前缘的生长，衰老区紧随其后。在固氮细胞中，衰老与一类保守的半胱氨酸蛋白酶的表达同时发生，这些蛋白酶可能参与共生结构的降解。环境胁迫，如长时间的黑暗处理，会干扰根瘤的功能并引发快速而全面的根瘤衰老。发育和黑暗胁迫诱导的衰老具有几种不同的结构和表达特征，这表明至少部分不同的潜在分子机制。
