Magadlela Anathi, Vardien Waafeka, Kleinert Aleysia, Steenkamp Emma T, Valentine Alexander J
Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa.
Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria 0002, South Africa.
Funct Plant Biol. 2016 Mar;43(3):287-297. doi: 10.1071/FP15262.
Virgilia divaricata Adamson is a forest margin legume that is known to invade the N- and P-poor soils of the mature fynbos, implying that it tolerates variable soil N and P levels. It is not known how the legume uses inorganic N from soil and atmospheric sources under variable P supply. Little is known about how P deficiency affects the root nodule metabolic functioning of V. divaricata and the associated energy costs of N assimilation. This study aimed to determine whether P deficiency affects the metabolic status of roots and nodules, and the impact on the routes of N assimilation in V. divaricata.V. divaricata had reduced biomass, plant P concentration and biological nitrogen fixation during P deficiency. Based on adenylate data, P-stressed nodules maintained their P status better than P-stressed roots. V. divaricata was able to alter C and N metabolism differently in roots and nodules under P stress. This was achieved via internal P cycling by possible replacement of membrane phospholipids with sulfolipids and galactolipids, and increased reliance on the pyrophosphate (PPi)-dependent metabolism of sucrose via UDP-glucose (UDPG) and to fructose-6-phosphate (Fru-6-P). P-stressed roots mostly exported ureides as organic N and recycled amino acids via deaminating glutamate dehydrogenase. In contrast, P-stressed nodules largely exported amino acids. Compared with roots, nodules showed more P conservation during low P supply. The roots and nodules of V. divaricata metabolised N differently during P stress, meaning that these organs may contribute differently to the success of this plant in soils from forest to fynbos.
银荆是一种生长在林缘的豆科植物，已知它能侵入成熟的开普植物群落中氮和磷含量较低的土壤，这意味着它能够耐受不同的土壤氮磷水平。目前尚不清楚这种豆科植物在不同磷供应条件下如何利用来自土壤和大气的无机氮。关于磷缺乏如何影响银荆根瘤的代谢功能以及氮同化相关的能量成本，人们了解甚少。本研究旨在确定磷缺乏是否会影响银荆根和根瘤的代谢状态，以及对其氮同化途径的影响。在缺磷期间，银荆的生物量、植物磷浓度和生物固氮作用均降低。基于腺苷酸数据，磷胁迫下的根瘤比磷胁迫下的根能更好地维持其磷状态。在磷胁迫下，银荆能够在根和根瘤中以不同方式改变碳和氮的代谢。这是通过内部磷循环实现的，可能是用硫脂和半乳糖脂替代膜磷脂，并通过UDP - 葡萄糖（UDPG）和果糖 - 6 - 磷酸（Fru - 6 - P）增加对依赖焦磷酸（PPi）的蔗糖代谢的依赖。磷胁迫下的根主要将酰脲作为有机氮输出，并通过脱氨基谷氨酸脱氢酶循环利用氨基酸。相比之下，磷胁迫下的根瘤主要输出氨基酸。与根相比，在低磷供应期间根瘤表现出更多的磷保留。在磷胁迫期间，银荆的根和根瘤对氮的代谢方式不同，这意味着这些器官对这种植物在从森林到开普植物群落的土壤中成功生长可能有不同的贡献。
