Comparative Research On The Life History Of Sphaeropteris Lepifera Under Single And Combined Stress Of Pb And Cd

Cyatheaceae is an important material to study the origin and evolution of plants,geographical flora,ecological adaptation and paleoclimate.It has been continuously endangered due to habitat fragmentation and loss.Since Cyatheaceae is an extremely rare woody fern,the researches mainly focus on morphological taxonomy,molecular phylogeny,spore culture,and adaptive evolution in the sporophyte period,and few on the gametophytic period.Pb and Cd are common pollutants and non-essential elements for plant development,which will affect the development and growth of above-ground plants,species diversity and environmental steady-state,the research on the growth and development of ferns mainly focuses on physiological response,tolerance and application of ecological restoration of the fern's sporophyte.Research on important gametophytic generations in life history is weak.Therefore,this paper chooses Sphaeropteris lepifera,the representative plant of Cyatheaceae as the experimental material,using 1/2 ms semi-solid medium and soil culture.Observation by optical microscope and continuous paraffin sectioning of sexual organs and embryos,the effects of single and compound stress of lead and cadmium at different concentrations on the whole life cycle of Sphaeropteris lepifera,including spore germination,gametophyte development,organ development,embryo development and sporophyte development,were studied,and the characteristics of the characters were compared.To explore the causes of restricted reproduction of Sphaeropteris lepifera and its relationship with heavy metal pollution,to provide reference for the protection of Cyatheaceae in China.The results show that:(1)The average germination time of the spores of Sphaeropteris lepifera was 5 days,and the way of germination was Vittaria-type.The spore germination time was prolonged with the increase of heavy metal concentration after exogenous Pb2+ and Cd2+treatment.The morphological response of Sphaeropteris lepifera to heavy metal stress is mainly reflected from the prothallus,the specific manifestations are uniseriate germ filament,prothallial plate and prothallus growth retardation and morphological abnormality.If the concentrations of two heavy metals exceed a certain value,the number of chloroplasts will be significantly reduced,and the shape and color will change in different degrees.Under the stress of two heavy metals,most of the rhizoids showed abnormal morphology,including helix,swelling and length inhibition.After Cd2+stress in gametophyte cells,the plasma membrane was damaged and the contents disappeared;the color of cells changed after Pb2+ stress;the large area necrosis of gametophyte of Sphaeropteris lepifera after combined stress.When low concentration Cd2+was added,a large number of green globular bodies were produced with the extension of culture time.(2)Most of the gametophytes of Sphaeropteris lepifera are hermaphroditic,but the ratio of male gametophytes will be increased after Pb2+ treatment.The ratio of female gametophyte differentiation caused by low concentration of Cd2+was higher than that of control group and Pb2+ stress,while the ratio of asexual gametophytes increased under high concentration of Pb2+ and Cd2+stress.After the treatment of Pb2+ stress,the differentiation process of antheridium was blocked,the cytoplasm of antheridium was inhomogeneous,and the whole body was browning.After Cd2+stress,the changes of substance in antheridium were more obvious.The effect of Pb2+ stress on sperm flagellum is more common,and Cd2+stress usually makes sperm nucleus development abnormal.The morphology,color and development process of the archegonium all changed to a certain extent,and the damage of the archegonium after high concentration stress was more serious than that under low concentration conditions.(3)Sphaeropteris lepifera has the characteristic embryo division characteristic of the core leptosporangiates.The difference after heavy metal stress is mainly the time at which each embryo division stage begins.In each stage of embryo development,there are differences between the embryo and the control group due to the stress of certain concentrations of heavy metals,such as fission rate,embryo integrity and so on.Browning is the main response of the embryo after heavy metal stress.(4)After chronic stress,the occurrence time of vegetative organs was delayed more,and part of the structure and color of sporophyte changed and its volume was smaller.Acute stress of Pb2+ and Cd2+at a certain concentration had a negative effect on many characters and characteristics of sporophyte in Sphaeropteris lepifera.Pb2+ and Cd2+have synergistic effect on inhibiting the growth and development of Sphaeropteris lepifera.Artificial seedling cultivation can improve survival rate of Sphaeropteris lepifera to some extent.Based on the above research results,this paper believes that the single and combined Pb2+ and Cd2+stress have caused different degrees of influence on the whole reproductive process of Sphaeropteris lepifera,and this influence will be intensified with the increase of concentration and the extension of treatment time.The gametophyte stage of Sphaeropteris lepifera is more sensitive to heavy metal stress than the sporophyte stage.Pb2+ and Cd2+can affect the sex differentiation of gametophyte of Sphaeropteris lepifera.The sperm of Sphaeropteris lepifera is the most vulnerable link in the whole alternation process under the stress of heavy metals,which may be one of the reasons for the continuous endangerment of Cyatheaceae.Pb2+ and Cd2+have synergistic effect on inhibiting the growth and development of Sphaeropteris lepifera.The toxic phenomena of the structure and morphology of Sphaeropteris lepifera under the stress of two kinds of heavy metals suggest that Sphaeropteris lepifera can be used as environmental indicator plants to some extent.