为探讨紫荆种子成熟过程中种皮结构和胚乳细胞内含物的变化,对不同成熟期紫荆种子的种皮和胚乳分别进行了扫描电镜(SEM)和透射电镜(TEM)观察。扫描电镜观察发现:在紫荆种子发育初期,种皮表面出现孔状结构; 随着种子的逐渐成熟,种皮表面气孔消失,蜡质开始形成并逐渐加厚,种孔和种脐也逐渐开裂。从种皮的纵切面可以看出,种脐部位栅栏层形成较早,为单层细胞结构。花后105 d可观察到由种脐沿种子表面延伸的输水管道,花后135 d时,输水管道内出现由种脐沿种皮延伸至种子另一端的管胞群。种子发育成熟时,种子中间部位的种皮由外到内依次为角质层、栅栏层和薄壁细胞层,角质层主要由蜡质及其他覆盖物组成,栅栏层则由单层紧密排列的长柱状厚壁的大石细胞构成。角质层和栅栏层的这种结构可能是影响紫荆种子种皮透性进而引起休眠的原因之一。透射电镜观察发现:紫荆种子发育初期,胚乳细胞内存在大液泡,但脂滴与高电子致密物质数量较少。随着种子的不断成熟,线粒体、内质网、高尔基体等细胞器逐渐形成,胚乳中营养物质的代谢速度较快,之后这些细胞器又逐渐降解消融,脂滴和高电子致密物质则不断增加,说明随着种子的发育,胚乳内大分子贮藏物质不断积累,物质代谢活动降低,种子逐渐进入休眠期。
Abstract
In this study, the ultrastructure of seed coat and endosperm ingredients of Cercis chinensis seed was systematically investigated by using scanning electron microscope(SEM)and transmission electron microscope(TEM)during the process of maturity. SEM images showed that during the early stage of maturity some pores appeared at the surface of seed coat, and then disappeared with the subsequent development of seeds. At a later stage, waxy of seed coat appeared and became thicker as the seed matures, and micropyle and hilar groove cracked gradually. By the longitudinal section of seed coat, we found that the palisade layer near hilum formed earlier than the middle part of seed coat and the palisade cells in this area was monolayer. One hundred and five days after blossoming, a water entry from the hilum extending along the seed coat could be observed. A reticular tracheidal bar from hilar groove to the opposite end was found in the water entry pathway while 135 days after blossoming. After seed maturation, from the exterior to the interior, the seed coat of C. chinensis consisted of three layers: the waxy cuticle, the palisade layer and the parenchymatous layer. The cuticle was composed of wax and the other covering. The palisade layer consisted of a monolayer macrosclereids with thick walls elongated longitudinally. The macrosclereids were tightly arranged. The waxy cuticle and the palisade layer may be the main barrier controlling the entrance of water through seed coat. By the TEM, we found that at the early seed-filling stage, the endosperm cells were characterized by a large central vacuole with a small quantity of lipid droplets and density electron substances. As the maturity of seed, mitochondria, endoplasmic reticulum and Golgi apparatus formed and then degraded gradually. Meanwhile, the quantity of lipid droplets and density electron substances were increased continuously. It indicated that with the development and maturity of seed,the storage macromolecules accumulated and the metabolism decreased continuously, after which the seed turned to dormancy.
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基金
基金项目:国家自然科学基金项目(31270711); 江苏省青蓝工程创新团队项目
第一作者:周健(1035867560@qq.com)。
*通信作者:李淑娴(shuxianli@njfu.com.cn),教授。
引文格式:周健,苏友谊,代松,等. 紫荆种子成熟过程中种皮和胚乳超微结构观察[J]. 南京林业大学学报(自然科学版),2016,40(6):27-32.
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