Abstract

Pollen haploids from Nicotiana tabacum L. cv FCV Special were raised by culturing their anthers on MS medium supplemented with .001mg BAP. The haploid plants were grown to adult stage. They flowered profusely but did not produce seeds. A comparison is made between the haploids and their normal parental diploids with reference to the ontogeny and organization of microsporangium, male gametophyte, megasporangium and female gametophyte. The development of microsporangium and male gametophyte in haploids revealed several interesting features. The events pertaining to the development of sporophytic features of microsporangia in haploids were more or less recapitulative of those in normal parental plants. Meiosis in microsporocytes is highly irregular and commences in a few microsporocytes, precociously, at the sporogenous tissue stage itself. Cytomixis, chromosomal disarray and occurrence of laggards are common. Very few 'tetrads' of irregular configurations are organized. Despite anomalous gametogenesis and production of a few microspores, consistently sterile, the anthers dehisced normally as observed in the parental plants. Megasporogenesis and female gametophyte development were highly irregular and unpatternized in haploids. The ovaries were distinctly smaller and possessed fewer ovules than in the diploids. Many ovules degenerated early in their ontogeny. A few that did not, exhibited merely a semblance of embryo sac development and organization, far from the normal patternized events seen in the normal diploids. A bisporic mode of embryo sac ontogeny is prevalent in the haploid ovules. The female gametophytes exhibited precocious organization but never conformed to a uniform pattern. Very few embryo sacs organized into an 8-nucleate Polygonum type of embryo sac. A few apomictic embryoids were noticed in the haploid ovules.

中文摘要

花粉單倍體是來自菸草栽培變種FCV (Nicotina tabacum L. cv FCV) 的花藥，而此花藥培養於添加0.001 mg BAP的MS培養基中。單倍體植株可生長至成熟，其開花數眾多但不能產生種子。依據小孢子囊、雄配子體、大孢子囊和雌配子體的發生與結構，比較單倍體和其正常親代雙倍體的異同。單倍體植株之小孢子囊和雄配子體的發育有許多有趣的現象，而單倍體內小孢子囊之雄配子體特徵之發育大致和正常親代植株相同。小孢子母細胞之減數分裂呈高度不規則，有些提早在造孢組織發育階段就開始進行。胞質融合、染色體脫序和發育遲緩的現象經常發生，其後可產生少許不規則形狀的四分小孢子。雖然有不正常的小孢子發生過程和許多不孕性的小孢子產生，但如同親代植株般，其花藥是可正常開裂的。在單倍體中，大孢子發生和雌配子體發育呈高度不規則且沒有固定模式。比起雙倍體，單倍體的子房較小且內含較少的胚珠，而且很多胚珠在發育早期即已瓦解。一些未瓦解的胚珠僅呈現出類似雙倍體之胚囊發育與構造，而非如雙倍體般有正常的發育模式。在單倍體胚珠中，較普遍的胚囊發生是雙孢子型，而雌配子體呈現出早熟的構造但沒有一固定不變的模式，且少有胚囊能組織成一個八核的蓼型胚囊。在單倍體胚珠中可發現一些無性繁殖的胚狀體。

Keyword: Nicotiana tabacum L. FCV Spl., Haploids, Male and female gametophytes.