The effect of salt stress on nitrogen fixation, in relation to sucrose transport towards nodules and other sink organs and the potential of sucrose breakdown by nodules, was investigated in two lines of Medicago ciliaris. Under salt stress conditions, the two lines showed a decrease of total biomass production, but TNC 1.8 was less affected by salt than TNC 11.9. The chlorophyll content was not changed in TNC 1.8, in contrast to TNC 11.9. Shoot, root, and nodule biomass were also affected in the two lines, but TNC 1.8 exhibited the higher potentialities of biomass production of these organs. Nitrogen fixation also decreased in the two lines, and was more sensitive to salt than growth parameters. TNC 1.8 consistently exhibited the higher values of nitrogen fixation. Unlike nodules, leaves of both lines were well supplied in nutrients with some exceptions. Specifically, the calcium content decreased in the sensitive line leaves, and the nodule magnesium content was not changed in either line. The tolerant line accumulated more sodium in its leaves. The two lines did not show any differences in the nodule sodium content. Sucrose allocation towards nodules was affected by salt in the two lines, but this constraint did not seem to affect the repartition of sucrose between sink organs. Salt stress induced perturbations in nodule sucrolytic activities in the two lines. It inhibited sucrose synthase, but the inhibition was more marked in TNC 11.9; alkaline/neutral activity was not altered in TNC 1.8, whereas it decreased more than half in TNC 11.9. Thus, the relative tolerance of TNC 1.8 to salt stress could be attributed to a better use of these photoassimilates by nodules and a better supply of bacteroids in malate. The hypothesis of a competition for sucrose between nodules and other sink organs under salt stress could not be verified.

译文

在两条纤毛紫花苜蓿中研究了盐胁迫对固氮的影响,与蔗糖向结节和其他汇器官的转运以及结节对蔗糖分解的潜力有关。在盐胁迫条件下,两品系的总生物量产量均有所下降,但TNC 1.8受盐的影响小于TNC 11.9。与TNC 1.8相比,TNC 11.9的叶绿素含量没有变化。在这两个品系中,芽,根和根瘤生物量也受到影响,但是TNC 1.8显示出这些器官产生生物量的更高潜力。两品系的固氮作用也有所降低,并且对盐的敏感性高于生长参数。TNC 1.8始终表现出较高的固氮值。与结节不同,这两个品系的叶子都有很好的营养供应,但有一些例外。具体来说,敏感品系叶片中的钙含量降低,而根瘤镁含量在任一品系中均没有变化。耐性品系在其叶片中积累了更多的钠。两条线没有显示结节钠含量的任何差异。蔗糖向结节的分配受到两行盐的影响,但是这种限制似乎并未影响蔗糖在汇器官之间的重新分配。盐胁迫在两行中引起根瘤蔗糖活性的扰动。它抑制了蔗糖合酶,但在TNC 11.9中抑制作用更为明显; 在TNC 1.8中,碱性/中性活性没有改变,而在TNC 11.9中,碱性/中性活性下降了一半以上。因此,TNC 1.8对盐胁迫的相对耐受性可归因于结节更好地利用这些光同化物和苹果酸中更好地供应类细菌。无法验证在盐胁迫下结核和其他汇器官之间竞争蔗糖的假设。

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