Cytological Study On The Development Of Epidermal Hair Of Solanum Nigrum L. Ang Its Involvement In Cadmium Remediation

Cadmium is the most common element in soil heavy metal pollution,which brings great harm to social economy and human health life.At present,the remediation of polluted soil by superaccumulation plants is an important means to control environmental heavy metal pollution.Solanum nigrum L.is a cadmium superaccumulator and has great potential in soil remediation.More and more evidence shows that plant trichome is one of the heavy metal isolation and detoxification sites.It is worth discussing whether the surface fur of Solanum nigrum L.has detoxification effect.In this study,the development process,the composition,the density and the cadmium content of the trichome of Solanum nigrum L.were studied.It is of great significance for the further development and utilization of the cadmium superenrichment plant Solanum nigrum L.in soil remediation.The main research conclusions are as follows:(1)Types and development of trichome: Solanum nigrum L.has glandular trichome and non-glandular trichome.There are two main types of glandular trichomes,namely single-celled trichome and multicellular trichome(one-layer,two-layer and three-layer multicellular trichome).The growth mode of glandular trichome belongs to apical growth,and new stalk cells always divide peripherally from apical hair cells.Notably,three specific types of multicellular trichome were found: a single layer of multicellular trichome with 2 stalk cells,a single layer of multicellular trichome with 2neck cells,and a double layer of multicellular trichome with 1 neck cell.Non-glandular hairs have one type,both apical growth,and new stalk cells are derived from peripherally divided apical stalk cells.(2)Glandular trichome secretion process: The glandular trichome secretions are stored in the subcutaneous space of the head cells,with a zona pellucida structure,and released.Scanning electron microscopy(SEM)frozen transmission images further showed the changes on the surface of head cells during the secretion process of glandular trichome: the accumulation of secretions led to the formation of lenticular protrusions of different sizes on the surface of head cells,and the changes of the protrusions were blocky and then broken,and the secretions were released to form a thick coating of glandular hair on the surface of glandular trichome.Under transmission electron microscopy,it was found that the endoplasmic reticulum and Golgi bodies in glandular hairs were extremely rich,and active anabolic and secretory activities produced a large number of vesicles coated with osmophilic substances.The osmophilic substances could be temporarily stored in vacuoles,then transported to the cell wall through vesicles and fused with cell membranes,and then transferred to the cell wall and stored in the subcutaneous space under the cuticle through osmosis.Until the cuticle breaks and is released.(3)Composition and distribution in the trichome: Lipids(total lipids and acidic lipids),alkaloids,terpenoids,polysaccharides(neutral and acidic polysaccharides),proteins and phenols were found in unicellular and multicellular glandular trichomes.There were total lipids in both head cells and stalk cells,and the content of acid lipids in head cells was higher than that in stalk cells.There were a lot of terpenoids and alkaloids in both head and stalk cells.There were a lot of proteins,phenols and neutral polysaccharides in the head cells,but less in the stalk cells.The secretion of glandular hair contained total lipids,neutral lipids,alkaloids,terpenoids,neutral polysaccharides and proteins.The non-glandular trichomes consist of total lipids,acid lipids and alkaloids,which are mainly concentrated in the warty protrusions on the surface.(4)Response of trichome density to cadmium stress: at 7,14 and 21 days of stress,the trichome density of stem increased with the increase of stress concentration,and the trichome density of leaves at different positions showed different trends with the increase of stress concentration.(5)Response of secretion activities of glandular trichome to cadmium stress:Cadmium content in secretions of epidermal cells and glandular trichome of mature leaves was higher than that of young leaves,and cadmium content in secretions of multicellular glandular trichome was higher than that of single-celled glandular hair,and cadmium content in secretions of epidermal cells,single-celled glandular hair and multicellular glandular trichome increased with stress time.The cadmium content in the secretion of glandular trichome did not increase with the increase of time when the concentration of cadmium stress remained unchanged.It is speculated that the cadmium content in individual glandular trichome remained unchanged due to the increase of surface fur density.(6)Ultrastructure changes of glandular trichomes after cadmium stress: With the increase of cadmium stress concentration,the vesicles containing osmophilic substances in glandular trichomes of A.mongolica increased substantially and could fuse with the cell wall,resulting in the accumulation of osmophilic substances on the cell wall.At the same time,the subcutaneous space gradually increased,the osmophilic substances gradually increased,and the cuticle gradually became thinner and secreted.It is speculated that the osmophilic substance is cadmium accumulation.