Ecological Anatomy of the Root in Bretschneidera sinensis,a Threatened Endemic Plant in China

Bretschneidera sinensis,a tertiary relict species,is a threatened endemic plant in China.To clarify its adaptation and special habitat needs,the ecological anatomy of its root,i.e.its external morphology,micro-morphological characteristics and anatomic structure,was studied by paraffin section,whole mount section,scanning electron microscopy(SEM)and laser scanning confocal microscope(LSCM).Results showed that root hair was not differentiated in the root tip as a special mycorrhizal plant.The epidermis,cortex and vascular cylinder were encompassed in the primary structure.However,the radicle differentiation was primitive and there were two circles with natural gap in the cortex.The cortex contained secreting cells with myrosinase and the vascular cylinder contained pith.After colonization with mycorrhizal fungi by single hyphae or hyphae net,the epidermis cell walls were deposited with a thick layer of amorphous material.Hyphae could grow and branch in the gap in the cortex,and vesicle from the mycorrhizal fungi also presented in the intercellular space.To form the symbiotic relationship,hyphae in the host cells always surrounded the starch grains to absorb nutrition;simultaneously some of them were decomposed into little vesicles and clastics providing nutrition to the host cell.According to the characteristics of the root above,the detailed study on the appropriate soil condition for B.sinensis should be carried out for in situ and ex situ conservation,to facilitate the occurrence and development of endotrophic mycorrhiza.