蓖麻种子结构的解剖和显微观察

Anatomy and microscopic observation of Ricinus communis seed structure

本文通过萌发法、分离法、石蜡切片法和显微观察技术,分别以番红固绿和希夫试剂染色,系统观察了蓖麻种皮、胚乳和胚的结构及其维管束分布。(1)蓖麻种子背侧基部的种孔并未被种阜所覆盖。(2)种皮包括外种皮、内种皮和种阜3部分,其中,外种皮由外至内分别为长柱状表皮层、海绵组织层和栅栏组织层,而内种皮则依次为马氏层、海绵组织层和内珠被内层,在种阜端由内种皮内层和外层共同围成气室,类似于鸡蛋的气室。(3)在外种皮和内种皮中均有维管束分布,其中外种皮的大型维管束仅分布在种子腹侧种脊的海绵组织层内,它从种脐延伸至种阜相对一端;而内种皮维管束也分布在海绵组织层中,通过维管束索,逐级分枝,止于种阜端气室边缘;内、外种皮的维管束通过合点端的连接点相连续,共同构成种皮维管系统。(4)种阜由表皮和薄壁组织构成,其中薄壁组织由外侧小型薄壁细胞和内侧大型薄壁细胞构成。种阜维管束仅2束,分布在种阜中部腹侧,独立构成种阜维管系统;在种阜中,还有种阜管道,其内端开口于内种皮的气室,外端为盲端。(5)胚乳由含大量糊粉粒的薄壁细胞构成,其中未见维管束分布。在胚中,维管束为外韧维管束,它们分化于胚轴,从胚轴顶端两侧分别进入2片子叶主脉,在主脉中由4个逐步减少为1个,在子叶中分枝变细,构成胚维管系统;子叶表皮和叶肉细胞中均含糊粉粒,但在胚芽、胚轴和胚根中未见糊粉粒;2片子叶近轴面分离,远轴面则通过粘液层与胚乳相连接;胚轴和胚根在空间上与胚乳分离。这些结果为全面掌握植物蓖麻种子的结构和研究种子发育和萌发过程及其物质运输提供了解剖学依据。

We systematically observed the structure and distribution of vascular bundles of castor(Ricinus communis)testa,endosperm and embryo with germination,separation,paraffin sectioning technique,and microscopic observation techniques,stained with safranine and fast green,along with schiff’s reagent,respectively.(1)Micropyle at the dorsal base of the seed was not covered by the caruncle.(2)The testa consisted of three parts:episperm,endopleura and the caruncle,in which the episperm was composed of the long columnar epidermal layer,sponge parenchma and palisade parenchma from outside to inside,while the endopleura was composed of Malpighian layer,sponge parenchma and the inner integument layer,with an air chamber surrounded by the inner layer and outer layer of endopleura at the end of the caruncle,similar to that of eggs.(3)Both the episperm and endopleura were distributed with vascular bundles,and the large ones of the episperm only distributed in the spongy parenchma of the ventral raphe of the seed,which extended from the hilum to the opposite end of the caruncle;while those of endopleura were also distributed in the spongy parenchtma,and they branched step by step through the bundle band,ending at the edge of the air chamber at the end of the caruncle;those of both the episperm and endopleura were continuous through the junction point of the chalazal end to form the vascular system of the testa.(4)The caruncle was composed of epidermis and parenchyma,in which parenchyma consisted of small parenchyma cells on the outside and large parenchyma cells on the inside.In the middle and ventral part of the caruncle,there were only two vascular bundles,which constituted the vascular system of the caruncle independently.In the caruncle,caruncle channel was also found,with the inner end opening in the air chamber of the endopleura and the outer end being blind.(5)No vascular bundles were found in the endosperm,which consisted of parenchymal cells containing a large number of aleurone grains.In the embryo,the vascular bundles were collateral,which differentiated in the hypocotyle and entered the main vein of two cotyledons from both sides of the top of the hypocotyle respectively,gradually reduced from 4 to 1 in the main veins,and the branches became thinner in the cotyledon,forming the vascular system of embryo.The cotyledon epidermis and mesophyll cells contained aleurone grains,but no aleurone grains were found in the plumule,hypocotyle and radicle.Two cotyledons separated from each other on the adaxial surface,while their abaxial surfaces were connected with the endosperm through the mucilaginous layers.The hypocotyle and radicle were spatially separated from the endosperm.These results provide an anatomical basis for comprehensively understanding the structure of the seeds and studying the seed development and germination and their material transportation.