Hartmann Klaus, Peiter Edgar, Koch Kerstin, Schubert Sven, Schreiber Lukas
Botanisches Institut und Botanischer Garten, Kirschallee 1, 53115 Bonn, Germany.
Planta. 2002 May;215(1):14-25. doi: 10.1007/s00425-001-0715-z. Epub 2002 Feb 6.
Ultrastructure and development of apoplastic barriers within indeterminate root nodules formed by Vicia faba L. were examined by light and electron microscopy. The nodule outer cortex is separated from the inner cortex by a heavily suberized nodule endodermis, which matures in submeristematic regions and possesses suberin lamellae. Unsuberized passage cells are present near vascular strands, which are surrounded by a vascular endodermis attached on the inner side of the nodule endodermal cell walls. The vascular endodermis appears immediately below the meristematic apex in developmental state I (Casparian bands), gradually develops suberin lamellae, and attains developmental state II at the base of the nodule. For chemical analysis apoplastic barrier tissues were dissected after enzymatic digestion of non-impregnated tissues. Root epidermal and endodermal cell walls as well as nodule outer cortex could be isolated as pure fractions; nodule endodermal cell walls could not be separated from vascular endodermal cell walls and enclosed xylem vessels. Gas chromatography-flame ionization detection and gas chromatography-mass spectrometry were applied for quantitative and qualitative analysis of suberin and lignin in isolated cell walls of these tissues. The suberin content of isolated endodermal cell walls of nodules was approximately twice that of the root endodermal cell walls. The suberin content of the nodule outer cortex and root epidermal cell walls was less than one-tenth of that of the nodule endodermal cell wall. Substantial amounts of lignin could only be found in the nodule endodermal cell wall fraction. Organic solvent extracts of the isolated tissues revealed long-chain aliphatic acids, steroids, and triterpenoid structures of the lupeol type. Surprisingly, extract from the outer cortex consisted of 89% triterpenoids whereas extracts from all other cell wall isolates contained not more than 16% total triterpenoids. The results of ultrastructural and chemical composition are in good correspondence and underline the important role of the examined tissues as apoplastic barriers.
通过光学显微镜和电子显微镜对蚕豆形成的不定根瘤中质外体屏障的超微结构和发育进行了研究。根瘤外皮层通过高度栓质化的根瘤内皮层与内皮层隔开，内皮层在亚分生组织区域成熟并具有栓质化层片。未栓质化的通道细胞存在于维管束附近，维管束被附着在根瘤内皮层细胞壁内侧的维管束内皮层包围。在发育状态I（凯氏带）中，维管束内皮层出现在分生组织顶端下方，逐渐形成栓质化层片，并在根瘤基部达到发育状态II。为了进行化学分析，在对未浸渍组织进行酶消化后，解剖质外体屏障组织。根表皮和内皮层细胞壁以及根瘤外皮层可以作为纯组分分离出来；根瘤内皮层细胞壁无法与维管束内皮层细胞壁和包围的木质部导管分离。气相色谱 - 火焰离子化检测和气相色谱 - 质谱法用于对这些组织分离细胞壁中的栓质和木质素进行定量和定性分析。根瘤分离内皮层细胞壁的栓质含量约为根内皮层细胞壁的两倍。根瘤外皮层和根表皮细胞壁的栓质含量不到根瘤内皮层细胞壁的十分之一。仅在根瘤内皮层细胞壁组分中发现了大量木质素。分离组织的有机溶剂提取物显示出长链脂肪酸、类固醇和羽扇豆醇型三萜结构。令人惊讶的是，外皮层提取物由89%的三萜类化合物组成，而所有其他细胞壁分离物的提取物中总三萜类化合物含量不超过16%。超微结构和化学成分的结果具有良好的一致性，并强调了所研究组织作为质外体屏障的重要作用。
