The Characterization And Formation Of Semi-permeable Layer In Eight Kinds Of Grass Speeies Sceds

Semi-permeability may be defined as the ability of seed coverings to allow water uptake and gas exchange while solute diffusion is restricted or prevented. It is a lifeless physical obstacle. The location and chemical composition of semi-permeable layer have been reported a few in the before researches, however, the information on the anatomical of the layer formation is limited. A series of experiments were carried out under biological microtechnic, chemical element tracer and monitoring technique; using seeds of eight kinds of grass species which are valuable for ecology and economy, namely, Roegneria nutans, Festuca sinensis, Achnatherum inebrians, Hordeum vulgare var. nudum, Bromus inermis, Triticale, Elymus nutans and Elymus sibiricus. The thesis firstly demonstrated that all the tested forage seeds have the semi-permeable layer which were located at the seed coat, but the chemical composition have the diversity in different seeds. It was found that the semi-permeable layer was formed by the outer periclinal wall of the inner integument thicken and identified the formation time of this layer for all the seeds. All the researches further revealed the structure of the seed coat and provided the scientific basis for the importance of the semi-permeable layer in seeds development. The main findings obtained are as follow:1The forage seeds contained a semi-permeable layer, which resembled a gray line and a transparent film surrounding the seed coat (testa) under the light and the transmission electron microscope respectively. It was easy distinguished pericarp and seed coat.2The chemical composition of the grass seeds has the diversity, among which the Roegneria nutans. Achnatherum inebrians, Hordeum vulgare var. nudum. Triticale, Elymus nutans and Elymus sibiricus have lipid in the semipermeable layer. Festuca sinensis has pectin while Bromus inermis has cellulose in this layer.3The formation of the semi-permeable layer in Roegneria nutans, Festuca sinensis, Achnatherum inebrians, Hordeum vulgare var. nudum, Elymus nutans and Elymus sibiricus had been researched. This layer had been formed before the seeds researched the physiological maturity and this layer will not disappear with the seeds continued to develop. This layer was formed by the outer periclinal walls of the inner integument and the different species had the different formation time, Hordeum vulgare var. nudum was the longest about21days post anthesis (dpa), the others were about8-12dpa.4The difference presented in the anatomy structure of caryopsis coat and near the endosperm tissue in the tested grass seeds. The pericarp of Hordeum vulgare var. nudum was thick and tight, but the others was loose and no special form; Achnatherum inebrians and Triticale had the tube cells, but the others had no; Hordeum vulgare var. nudum had2-3layer of aleurone cells which were arranged orderliness and Festuca sinensis and Bromus inermis owned sporadic2aleurone cells, but the others had no this kind of cell. The anticlinal and periclinal wall of aleurone cells in Festuca sinensis and Bromus inermis were thick respectively, but the others had no different.