Abstract

Casuarina equisetifolia Linn. is an introduced actinorhizal plant grown as roadside ornamental tree and as forest plantation in Pakistan. Actinorhizal nodules are formed on the roots of C. equisetifolia as a response to infection by Frankia. Structure of C. equisetifolia nodules is described using histochemical methods to elucidate the nature of micro-symbiont within the nodules. C. equisetifolia nodules were similar to a root in general anatomical structure and resembled with Myrica-type nodules. The nodule consisted of a distinct periderm enclosing the cortex. The cortex showed patches of infected cells interspersed among uninfected ones. Inside the cortex there was a stele bounded by an endodermis, which contained tannins. The phloem-xylem relationship was amphicribral. A poorly defined meristem was also observed. Apart from simple nodules, dichotomously branched and coralloid nodules were also observed. The stele in simple and branched nodules reached up to the tip of the nodules. The micro-symbiont was observed in the nodule tissues in hyphal form only. The histochemical tests revealed absence of vacuoles and starch grains, and presence of tannins and lignin.

中文摘要

木麻黃是一種引進的放射菌根瘤的植物，在巴基斯坦它是路旁的景觀植物，也是種植於森林中的植物。它的根部被放射菌Frankia 感染後即形成根瘤，使用組織化學的方法觀察根瘤內部構造，發現此放射菌根瘤與楊梅型根瘤相似。根瘤皮層外圍有一層明顯的外皮，皮層內部可看到感染的細胞散佈於未感染細胞之間。內皮層含有單寧，內部有中柱。韌皮部－木質部呈環生維管束，其中有一難以辨識的分生組織。根瘤除了簡單型外，尚有分叉(分枝)型及珊瑚型。簡單型及分枝型的根瘤，其中柱可延伸到根瘤的頂尖部位。根瘤組織內的共生菌成菌絲狀，用組織化學分析，發現根瘤中沒有液泡及澱粉粒，但含有單寧及木質素。

Keyword: Casuarina, Frankia, Actinorhizae, Hyphae.