Studies On Endosperm Weakening Mechanism Of Polygonatum Sibiricum Red.Seeds

Polygonatum sibiricum Red. seeds belong to combined dormancy. The research in dormancy-broken aspect about Polygonatum sibiricum Red. seeds has been a lot of production at present. However, the mechanism of germination is not clear still. The embryo of Polygonatum sibiricum Red. seeds are enclosed by the thick and solid endosperm. During the seed germination process, simply depending on the mechanism sthength generated by hypocotyl enlongation growth are not enough to break through the endosperm tissue which has higher mechnical strength, endosperm itself also has a weakening process, which is named endosperm weakening. This article studied the endosperm weakening mechanism of Polygonatum sibiricum Red. seeds by measuring and observing the change of cell walldegrading enzymes activity, metabolic substance, hydrogen peroxide and developmental anatomy during germination process. And combined with the germination test. The mainly research results are as follows:(1) The seeds of Polygonatum sibiricum have two kinds of endosperm cells: one kind of cells are common cells with obvious cytoderm and cytoplasm, the other kind are similar to sclereid with thicken secondary wall as well as disappeared protoplast. During seed germination process of Polygonatum sibiricum, cytoderm gradually become thinner, cytoplasm space become bigger, finally the cytoderm will be thoroughly degraded.(2) During the seed germination process of Polygonatum sibiricum, the mainly action time of enzymes which participate in the process of endosperm weakening should prior to forty days. By comparing enzymes activity horizontal differentiation in two different treatments, this rearch obtain the enzymes in relation to endosperm weakening as well as its function. The research shows that beta-mannanase, polygalacturonase, pectin methylesterase, cellulase, beta-galactosidase, and beta-mannosidase have close relationship with endosperm weakening of Polygonatum sibiricum Red.seed and play an active role, arabinosidase and xylosidase have low effect on endosperm weakening. During the endosperm weakening process of Polygonatum sibiricum Red. seeds: the variation of beta-mannanase with betamannosidase keeps accordance and mainly appears rising tendency, which coincide with the fact that the thoroughly degrading of galactomannan need these two enzymes synergistic effect. Polygalacturonase and pectin methylesterase all shows a trend of fast-rising first then slow-rising, which agrees with that both of them participate in the degrading of pectin substance synergistically. The mainly action time of cellulase is in the later stage of endosperm weakening and its action level shows a trend of steady first then rising. Betagalactosidase is mainly on a rise tendency.(3) During the seed germination process of Polygonatum sibiricum, the stored substances will be hydrolyzed and removed, which resulting to constantly consumption of endosperm organization, and the product will be used to various physiological and biochemical reaction during the seed germination process of Polygonatum sibiricum. During the cultivation process of Polygonatum sibiricum Red. seeds, the starch content mainly present a trend of declining, the result coincide with the variation tendency of amylase activity, which illustrating that starch grain is degraded and consumed all the way by amylase. In the process, the maximum value of starch content is 8.5%, indicating that starch is not the mainly metabolic substance of Polygonatum sibiricum Red. seeds. Cellulose content present a continuous declination tendency, and the rate of descent become quickly at the later stage, the result of which coincide with change of cellulase activity. The highest content of cellulose reach up to 32.1%, almost be four times as content as starch. For cell wall-degrading enzymes which containing hemicellulase, pectinase and cellulose have a crucial effect on seed endosperm weakening, therefore we consider that the main endosperm metabolic substance of Polygonatum sibiricum Red. seeds is composed by hemicellulose, pectin and cellulose. Content level of soluble sugar exist fluctuation but present a rise tendency overall, which may have a relationship with continuous degration of cell wall polysaccharide and cytoplasm carbohydrate in the process of endosperm weakening. Content level of soluble pectin also appears a rise tendency as a whole, it may be attibute to that the original pectic substances continuously translating to soluble pectin in the process of endosperm weakening, finally soluble pectin degraded by pectinase. The content of soluble protein appears a tendency of fast rising first then declining and mounting again. The fast rising means a lot of soluble protein is produced,while the declining illustrate that meanwhile the hydrolyzing is also conducting. The hydrolyzed production can be used to synthesis of new protein as well as respiration. The content of amino acid shows rapidly increase at early stage, then drop with rise appears alternately at the middle and latter periods by a large margin, which illustrate that the metabolism of amino acid is relatively active during the seed endosperm weakening process of Polygonatum sibiricum. The content of crude fat entirely shows a tendency of slowly declining, declaring that lipid is not the major germination energy substance for Polygonatum sibiricum.(4) In the cultivation process of Polygonatum sibiricum Red. seeds, The content of hydrogen peroxide increasing continuously, and reaching up to maximum value just prior to quick incremental stage of seed germination rate.Therefore we obtain the conclusion that hydrogen peroxide may play a role in the endosperm weakening process of Polygonatum sibiricum Red. seeds, which may accelerate cell wall degrading rate by attacking cytoderm polysaccharide.