薏苡胚乳细胞化的超微结构观察

THE ULTRASTRUCTURAL STUDY ON CELLULARIZATION OF ENDOSPERM IN COIX LACRYMA JOBI L.

采用透射电镜对薏苡（Ｃｏｉｘｌａｃｒｙｍａ－ｊｏｂｉＬ．）早期的胚乳细胞化进行了研究。在胚乳游离核时期，胚乳游离核及细胞质环绕中央细胞分布，游离核间没有发现胚囊壁内突、成膜体等结构。胚乳细胞化过程中初始垂周壁形成过程如下：（１）胚乳细胞质中出现液泡，使细胞质和核向中央液泡推进；（２）一对相邻细胞核间液泡成对存在，且呈垂周分布，而且两液泡间的细胞质很狭窄；（３）在这狭窄的细胞质中出现成行排列的小泡；（４）小泡融合形成细胞板，细胞板悬于两液泡间；（５）细胞板向两端延伸，一端与胚囊壁相连，另一端继续随细胞质向中央液泡推进而向前生长。与中央液泡相邻的胚乳细胞为开放细胞。参与初始周壁形成的物质可能来源于高尔基体产生的小泡和液泡。

Cellularization of endosperm at early development stage in Coix lacryma jobi L.was investigated using transmission electron microscopy.At the free nuclear endosperm stage,the nuclei are located in a thin layer of cytoplasm at the periphery of the large central vacuole.There are no wall ingrowths around the embryo sac,no phragmoplast between any two adjacent free nuclei.The processes of cellularization of free nuclear endosperm are as follows:(1) Vacuoles appear in endosperm cytoplasm,and nuclei and cytoplasm extend inward towards the large central vacuole.(2) A pair of vacuoles,between which the cytoplasm appears to be very narrow,often exist between the adjacent nuclei.(3) Aligned vesicles appear in the narrow cytoplasm.(4) A cell plate is formed by the fusion of the vesicles,and suspends between the two vacuoles.(5) The cell plate alongates towards the two ends:one end fuses with embryo sac wall while the other end extends progressively and anticlinally in the cytoplasm growing towards the central vacuole.Therefore,the position and formation of the incipient anticlinal wall maybe have nothing to do with a phragmoplast,but something to do with vacuoles between the adjacent free nuclei.The substance forming the initial anticlinal wall maybe originate from dictyosome derived vesicles,and also maybe from the vacuoles.There may exist three patterns for the vacuoles to participate in the formation of anticlinal wall.Firstly the vacuoles intrude directly into the cytoplasm between two vacuoles and form vesicles,which are in alignment,secondly,many vesicles appear in the vacuoles and are transferred to fuse with the anticlinal wall.Thirdly,multivesicular bodies appear in the vacuole,and the vesicles enter the cytoplasm and fuse with newly formed cell walls.