Ineffective alfalfa nodules formed by Rhizobium meliloti nif::Tn5 mutants were examined by light and electron microscopy. R. meliloti nifH::Tn5 mutants formed nodules that were similar in structure to wild-type nodules except that nifH- bacteroids accumulated a compact, electron-dense body. In contrast to nodules induced by wild type and nifH mutants, nifDK- R. meliloti mutants induced nodules which contained numerous starch grains and prematurely senescent bacteroids. In addition, meristematic activity in nifDK- nodules ceased significantly earlier than in nifH- nodules. All mutant nodules exhibited elevated levels of rough endoplasmic reticulum and Golgi membranes compared to wild-type nodule cells. These elevated levels may reflect either a response to nitrogen starvation in the ineffective nodules or an abnormal synthesis and export of nodule-specific proteins during later developmental stages.
展开▼
机译：通过光学和电子显微镜检查了由苜蓿根瘤菌nif :: Tn5突变体形成的无效苜蓿结节。 R. meliloti nifH :: Tn5突变体形成的结节与野生型结节的结构相似，只是nifH类细菌积累了紧密的电子致密体。与野生型和nifH突变体诱导的结节相反，nifDK- R. meliloti突变体诱导的结节含有大量淀粉粒和过早衰老的类杆菌。另外，nifDK结节的分生活动比nifH结节明显提前。与野生型结节细胞相比，所有突变结节均显示出高水平的内质网和高尔基膜。这些升高的水平可能反映了无效结节中对氮饥饿的响应，或者反映了后期发育阶段中结节特异性蛋白质的异常合成和输出。
展开▼
