Effects Of Pb²⁺ And Cd²⁺ Stress On Morphological Structure And Physiological Characteristics Of Gametophytes Of Parahemionitis Cordata

Mainly distributed in Taiwan,Hainan and Yunnan in China,(parahemionitis cordata(Roxburgh ex Hooker?Greville)Fraser-Jenkins)is known for its natural medicinal chemical and biopesticide values.As a rare and endangered fern,an evolutionary progressive species and ideal material for global ecological evaluation,it has been recommended for national protection as a Grade II plant.Heavy metal pollution is among the major environmental pollutions facing the country.As primary heavy metal pollutants,plumbum(Pb²⁺)and cadmium(Cd²⁺)undermine the morphology,physiology,and reproduction of plants.Gametophyte is a sexual generation of ferns,with its growth and development subjected to adverse environmental influences.To date,there has been little academic discussion of the effects of heavy metals on fern gametophyte,and even less on parahemionitis cordata gametophyte.Hence,this paper focuses on parahemionitis cordata gametophyte to explore the effects of Pb²⁺and Cd²⁺stress on its morphological structure and physiological properties.On the one hand,it reveals the mechanism of injury and specific forms of action of Pb²⁺and Cd²⁺stress on parahemionitis cordata gametophyte,as well as the tolerance of parahemionitis cordata gametophyte to Pb²⁺and Cd²⁺,thus providing a rationale for parahemionitis cordata protection.On the other hand,it may serve as a basis for the population recovery and expansion of parahemionitis cordata.According to the results:(1)At low concentrations of Pb²⁺and Cd²⁺stress,parahemionitis cordata gametophyte had larger numbers of chloroplasts,with yellowing and agglutination.At high concentrations of Pb²⁺and Cd²⁺stress,parahemionitis cordata gametophyte had smaller numbers of chloroplasts,with greater yellowing and agglutination,as well as fusion and necrosis.At low concentrations of Pb and Cd stress,parahemionitis cordata gametophyte had yellowed spermatophore and archegonium.At high concentrations of Pb²⁺and Cd²⁺stress,the spermatophore was yellowed and necrotic,and the sperm could not be discharged;the archegonium was yellowed,necrotic and could not be opened,with brown foreign bodies in the sulcus.At low concentrations of Pb²⁺and Cd²⁺stress,parahemionitis cordata gametophyte had irregularly curved,short,and yellowed rhizoid.At high concentrations of Pb and Cd stress,there were"wavy"distortions and the rhizoid ends were enlarged.(2)As the concentration of Pb²⁺and Cd²⁺stress increased,the chlorophyll content of parahemionitis cordata gametophyte was on the decline,and the net photosynthetic rate and transpiration rate were suppressed as well.The relative conductivity and MDA levels rose with increasing stress concentrations,leading to severe damage to the membrane system.At low concentrations of Pb²⁺and Cd²⁺stress,the protective enzyme activity was overall on the rise,but fell as the concentration of Pb²⁺and Cd²⁺stress increased.The photosynthetic and membrane systems of parahemionitis cordata gametophyte were severely impaired by the accumulated reactive oxygen species that could not be removed in a timely manner.(3)Through comprehensive analysis of the physiological indicators of parahemionitis cordata gametophyte under Pb²⁺and Cd²⁺stress,Pb²⁺was less resistant to Pb²⁺and Cd²⁺stress than Cd²⁺.In summary,Pb²⁺and Cd²⁺stress exerted influence on the morphological structure and physiological properties of parahemionitis cordata gametophyte,which rose with increasing stress concentrations.