無根草與其宿主黃木巴戟在解剖與生理構造上的適應

Characterization of Anatomical and Physiological Adaptations in Cassytha filiformis L.—An Advanced Obligate Hemiparasite on Morinda tinctoria Roxb.

本研究試圖釐清無根草與黃木巴戟在解剖學與生理學上的宿主－寄生物關係。在解剖構造上，無根草的吸器由兩大部分構成：上部吸器及內部吸器；前者為停留在宿主器官外部的吸器，後者則會穿透宿主器官至其組織內部。同時實驗也觀察到宿主會啟動一種讓皮層薄壁細胞去分化的機制，好讓薄壁細胞發展更濃密的細胞質，並使細胞核更明顯及產生比平常更多的澱粉粒，這些細胞反應會在寄生物的上部吸器附著時開始發生。若將無根草與黃木巴戟相比較，會發現它的葉綠素b比葉綠素a及葉黃素都要來得少。為確定光合作用的活化情形，實驗使用了葉綠素a螢光誘導曲線，發現被寄生的植物組織及寄生物的莖，兩者的光合作用效率都同樣低落，這可能是光合系統II發育不佳所導致。

A study was conducted to understand the host-parasite relationship in terms of anatomical and physiological adaptations in Morinda tinctoria Roxb. and Cassytha filiformis L. Anatomically the haustorium of Cassytha is found to have two parts, the upper haustorium and the endophyte. The former is the portion of a haustorium that lies external to the host organ, whereas the endophyte is the portion of a haustorium that penetrates host tissues. It was also observed that the host organ triggers the dedifferentiation of cortical parenchyma to develop dense cytoplasm, conspicuous nuclei and numerous starch grains and these cells are found to serve as the initials of upper haustorium. The level of Chl b was lower than Chl a and xanthophylls in Cassytha when compared to Morinda. The photosynthetic activity was measured in intact leaves/stems of both the host and parasitic plant using Chl a fluorescence induction kinetics, which revealed that the photosynthetic efficiency was very low in the infected sample as well as in the parasite stem. Over all, the reduction in the photosynthetic efficiency was correlated to the poorly developed PS II complex.