苏铁(Cycas revoluta Thunb.)种子的胚与胚乳解剖结构研究

对苏铁(Cycas revoluta Thunb.)种子的胚和胚乳组织进行了解剖研究。结果表明:苏铁种子为有胚乳种子,兼有胚乳和外胚乳,成熟时具直立型胚。胚乳的表层细胞含有角蜡质,胞核大,不含淀粉粒;中层细胞胞核明显;内层细胞胞核不明显,富含淀粉颗粒,淀粉粒单脐点明显。胚孔端的胚乳内陷成一凹槽,似贮藏窖。成熟的子叶胚为倒生胚胎,位于胚乳细胞解体后形成的囊腔中,子叶胚长度在胚乳中占到种子的1/3至2/3,已达到生理成熟阶段。双子叶直立,半合生。胚状体基部呈喙状突起,喙状突起下端连着一根肠叠着的丝状吸器,吸器基部连着一个小气囊。胚芽由顶端分生组织和数枚真叶组成,此时真叶已具羽状叶原基和绒毛原始体。在胚状体中发现有长管细胞及螺纹加厚的导管,在子叶中脉有数条并列的螺环纹导管。

Embryo and Endosperm Structures of Cycas revoluta Thunb. Seeds

The embryo and endosperm anatomy of Cycas revoluta Thunb.seeds showed that seeds were albuminous,both endosperm and perisperm and involved an erect embryo when mature.The outer skin of the endosperm was deposited by epicuticular wax.The epidermal cells had angle cell nuclei but no starch.The middle cell nucleus was obvious.The inner cells had rich starch granules with a single umbilical point but no visible cell nucleus.The endosperm at the end with blastopores invaginated into a groove as a storage cellar.The mature anatropous embryo was located in the sac formed after the endosperm cells degenerated.The mature embryo accounted for 1/3 to 2/3 of the endosperm and reached physiological maturity,with twin cotyledons vertical and semi-connate.At the base of embryoid was a beak-like protuberance attached to a gut-folded filamentous haustorium with a small sac.The plumule was composed of apical meristem and several pieces of primary leaf with pinnate leaf primordium and fluff precursor.The embryoid had long tubular cells and thickening spiral vessels.Several spiral vessels or annular vessels were clearly visible side-by-side in the cotyledon midrib.