Study On Microstructure And Location Of Semi-permeable Layer In Several Grass Species Seed

Seed semi-permeable layer may be defined as the layer of seed coverings to allow water and gas exchange while solution is restricted or prevented.The research of semi-permeable layer in grass seed is a field which has been paid rare attention previously. Microstructure,semi-permeable layer and it's location of seeds in 3 grass species,namely Sorghum sudanense,Elymus sibiricus and Festuca arundinacea were studied using the techniques of lanthanum tracer,transmission electron microscope and energy dispersive X-ray analysis(EDX).The microstructure of and permeability changes of S.sudanense during seed development were also studied.The main results obtained were as follows:1 The correlations between seed viability and seed leakage of electrical conductivity (EC)were not relevant(P＞0.05)and the EC values were very low for both S.sudanense and E.sibiricus.However significant positive correlation(P＜0.01)presented between viability and EC value in seeds of F.arundinacea.2 The basic structures,under light microscope observation were different between species at seed envelop and endosperm nearby.The epidermis was compact in S. sudanense and E.sibiricus with specialized structure palisade tissues.And 2-3 layers of undifferentiated cells existed between aleurone layer and starch cells in S.sudanense seed. But for F.arundinacea seed,the structure of epidermis and aleurone layer was loose,and palisade tissues and undifferentiated cells did not presented.3 The variations between 3 grass species in seed coat permeability were observed through the detection using lanthanum tracer,electron microscope and EDX.An endosperm semi-permeable layer was found in S.sudanense which located at the innermost of the aleurone layer,close to undifferentiated cells.A seed coat Semi-permeable layer presented in E.sibiricus which lied at the inside of the seed coat, just next to palisade tissues.But no semi-permeable layer was observed in seed coat and endosperm in F.arundinacea.4 Diffusion of La to seed was deeper in aged than unaged seeds in S.sudanense.But La did not diffuse through the undifferentiated cells in both aged and unaged seeds.This indicated that ageing slightly damaged aleurone layer membrane,but did not damage the semi-permeable layer.5 As S.sudanense seed developed,the grain weight and seed germination rate increased,but the EC value and imbibition rate decreased gradually.Seed reached physiological maturity at 25d after full-bloom(AFB).Undifferentiated cells emergenced at 16d AFB.The EC value and imbibition rate had decreased to a lower level,with no significant difference with that of 25d of AFB.The results further proved that seed semi-permeable layer gradually formed during seed maturation.The EC test is not able to detect seed lot deterioration,but it can reflect the degree of seed maturation.