Wycoff KL, Hunt S, Gonzales MB, VandenBosch KA, Layzell DB, Hirsch AM
Plant Physiol. 1998 Jun;117(2):385-95. doi: 10.1104/pp.117.2.385.
Early nodulin 2 (ENOD2) transcripts and protein are specifically found in the inner cortex of legume nodules, a location that coincides with the site of a barrier to O2 diffusion. The extracellular glycoprotein that binds the monoclonal antibody MAC236 has also been localized to this site. Thus, it has been proposed that these proteins function in the regulation of nodule permeability to O2 diffusion. It would then be expected that the levels of ENOD2 mRNA/protein and MAC236 antigen would differ in nodules with different permeabilities to O2. We examined the expression of ENOD2 and other nodule-expressed genes in Rhizobium meliloti-induced alfalfa nodules grown under 8, 20, or 50% O2. Although there was a change in the amount of MAC236 glycoprotein, the levels of ENOD2 mRNA and protein did not differ significantly among nodules grown at the different [O2], suggesting that neither ENOD2 transcription nor synthesis is involved in the long-term regulation of nodule permeability. Moreover, although nodules from all treatments reduced their permeability to O2 as the partial pressure of O2 (pO2) was increased to 100%, the levels of extractable ENOD2 and MAC236 proteins did not differ from those measured at the growth pO2, further suggesting that if these proteins are involved in a short-term regulation of the diffusion barrier, they must be involved in a way that does not require increased transcription or protein synthesis.
早期结瘤素2（ENOD2）转录本和蛋白质特异性地存在于豆科植物根瘤的内皮层中，该位置与氧气扩散屏障的位置一致。与单克隆抗体MAC236结合的细胞外糖蛋白也定位于此位点。因此，有人提出这些蛋白质在调节根瘤对氧气扩散的通透性中起作用。那么可以预期，ENOD2 mRNA/蛋白质和MAC236抗原的水平在对氧气具有不同通透性的根瘤中会有所不同。我们检测了在8%、20%或50%氧气条件下生长的苜蓿根瘤中，由苜蓿中华根瘤菌诱导产生的ENOD2和其他根瘤表达基因的表达情况。尽管MAC236糖蛋白的量有所变化，但在不同氧气浓度下生长的根瘤中，ENOD2 mRNA和蛋白质的水平并无显著差异，这表明ENOD2的转录和合成均不参与根瘤通透性的长期调节。此外，尽管随着氧气分压（pO2）增加到100%，所有处理的根瘤对氧气的通透性均降低，但可提取的ENOD2和MAC236蛋白质水平与在生长pO2下测得的水平并无差异，这进一步表明，如果这些蛋白质参与扩散屏障的短期调节，它们的参与方式必定不涉及转录增加或蛋白质合成增加。
