Anatomical Structure And Histochemistry Of Adventitious Roots Of Rare Plant Metasequoia Glyptostroboides Adapted To Wetland And Terrestrial Environment

Metasequoia glyptostroboides is a rare and endangered gymnosperms endemic to China.In this experiment,the roots of M.glyptostroboides from land and Wetland environment were used as experimental materials,and the anatomical structure and barrier structure characteristics of fine adventitious M.glyptostroboides roots in two environments were studied by using the methods of plant anatomy and histochemistry.The results can provide theoretical guidance for the cultivation,management and rational development of M.glyptostroboides in the future.It is of great significance to study the theory of biology.The main results of this study are as follows:(1)Similar to other gymnosperms and most dicotyledons,M.glyptostroboides has secondary growth.The roots of M.glyptostroboides in the two environments have similar anatomical and histochemical characteristics.The primary structure of adventitious roots included the stele,the cortex with the endodermis,the exodermis,the lignified Φthickenings and aerenchyma,and the rhizodermis;The secondary structure of the adventitious roots contained secondary xylem,secondary phloem,aerenchyma and cork.The apoplastic barriers in the M.glyptostroboides fine adventitious roots consisted of the endodermis and exodermis with Casparian bands,suberin lamellae,lignin,and suberized cork.(2)The differentiation of endoderm and exoderm of fine roots of M.glyptostroboides was obvious.The cortical parenchyma continued to expand in the wetland environment,from the outside of the endodermis to the inside of the exodermis,the cell wall became lignified Φ thickenings.The root of land M.glyptostroboides had only lignified Φthickenings in medial cortex.We speculate that lignified Φ thickenings in the M.glyptostroboides roots might relate to the absorption of ions in aquatic habitats.(3)The fine roots of M.glyptostroboides have schizolysigenous and lysigenous aerenchyma.The roots of M.glyptostroboides from wetland habitats had large,irregular air spaces in the cortex and phloem,in contrast to the roots of terrestrial M.glyptostroboides,which had narrower,smaller air spaces in the cortex and secondary phloem.(4)Mycorrhizal spores and mycorrhizae were present in the cortex,stele,and parenchyma of the phloem of the roots of M.glyptostroboides from wetland habitats.Mycorrhizal spores and mycorrhizae were present in the cortex of the roots of terrestrial M.glyptostroboides.Mycorrhizae might also participate in ion absorption.Studies on the anatomical structure of adventitious roots of M.glyptostroboides have clarified the structural reasons for the adaptation of M.glyptostroboides to both terrestrial and wetland environments,and explained the phenotypic plasticity of M.glyptostroboides to both aquatic and terrestrial environments.In the fine adventitious roots of M.glyptostroboides from terrestrial habitats,the cortex was observed to be closer to the root tip than in the roots from wetland habitats,the cortex falls off earlier and the air spaces is narrow.In the wetland environment with abundant water,the cortex fell off late and many cells lignified Φ thickenings.A large amount of suberin and lignin were deposited in the exodermis,resulting in cork cambium and more developed aerenchyma.In the process of growth and evolution,M.glyptostroboides has formed morphological and structural characteristics adapted to its living environment.