De Simone Oliviero, Haase Karen, Müller Ewald, Junk Wolfgang J, Gonsior Guido, Schmidt Wolfgang
Tropical Ecology Workgroup, Max-Planck-Institute for Limnology, PO Box 165, D-24302 Plön, Germany.
Department of Biology, University of Oldenburg, PO Box 2503, D-26111 Oldenburg, Germany.
Funct Plant Biol. 2002 Aug;29(9):1025-1035. doi: 10.1071/PP01239.
Adaptation to prolonged flooding was investigated using cuttings of two tree species from the Central Amazon white-water floodplain (Várzea). Morphological features and oxygen distribution patterns were correlated with metabolic changes under hypoxia, such as alterations in alcohol dehydrogenase (ADH) activity and adenylate energy charge (AEC) of root cells. Salix martiana (Leyb.) was able to react to hypoxic growth conditions with formation of adventitious roots rich in lysigenous aerenchyma, which facilitates root aeration by longitudinal oxygen transport and rhizosphere oxidation by radial oxygen loss (ROL). The oxygen concentration on the surface of adventitious roots of S. martiana reached 2-3 mg O2 L. The low resistance to gas exchange in Salix roots was reflected by low ADH activities, which ranged between 0.03-0.1 μmol NADH mg min, and AEC values of 0.8-1 under hypoxic conditions. Adventitious roots were also formed by Tabernaemontana juruana ([Markgr.] Schumann ex. J.F. Macbride) during growth under low-oxygen conditions, although at a later stage. The gas-space continuum in roots of T. juruana was less pronounced, resulting in a 10-fold lower oxygen concentration in the root cortex under oxygen stress compared with adventitious roots of Salix. The lower oxygen content was reflected in 6-fold higher ADH activities and decreased AEC values. ROL occurred only at the non-suberized root tip, suggesting that the suberized hypodermis functions as a barrier against gas exchange between the root and the rhizosphere. These findings indicate that different strategies of adaptation to low oxygen levels are realized in the two species under investigation that occur naturally in the same ecosystem but inhabit different elevation sites.
利用来自亚马逊中部白水河漫滩（várzea）的两种树种的插条，研究了对长期洪水的适应性。形态特征和氧气分布模式与缺氧条件下的代谢变化相关，如根细胞中乙醇脱氢酶（ADH）活性和腺苷酸能荷（AEC）的改变。柳叶菜柳（Salix martiana (Leyb.)）能够对缺氧生长条件做出反应，形成富含溶生性通气组织的不定根，通过纵向氧气运输促进根部通气，并通过径向氧气损失（ROL）进行根际氧化。柳叶菜柳不定根表面的氧气浓度达到2 - 3 mg O₂/L。柳树根对气体交换的低抗性表现为低ADH活性（在缺氧条件下为0.03 - 0.1 μmol NADH mg⁻¹ min⁻¹）和AEC值为0.8 - 1。在低氧条件下生长时，朱鲁纳狗牙花（Tabernaemontana juruana ([Markgr.] Schumann ex. J.F. Macbride)）也会形成不定根，不过时间较晚。朱鲁纳狗牙花根中的气腔连续体不太明显，与柳树不定根相比，在氧气胁迫下根皮层中的氧气浓度低10倍。较低的氧气含量表现为ADH活性高6倍和AEC值降低。ROL仅发生在未栓化的根尖，这表明栓化的皮下组织起到了根与根际之间气体交换屏障的作用。这些发现表明，在所研究的两个物种中实现了不同的适应低氧水平的策略，这两个物种自然生长在同一生态系统中，但栖息在不同海拔高度的地点。
