兩種菸草葉肉原生質體再生植株染色體的變異

Abstract

培養二種單倍體野生菸草Nicotiana sylvetris及N. plumbaginifolia的葉肉原生質體，所獲得的再生植株之染色體套數均已增加，而且自同一個原生質體衍生來的再生植株，其染色體套數亦不相同。藉著細胞學的方法，觀察原生質體早期培養時的細胞核行?，發現引起此類變異的原因，有核融合(nuclear fusion)及核內再複製(endoreduplication)兩種現象。多核原生質體在間期(interphase)、中期(metaphase)及末期(anaphase)分別發現有核融合現象，導致在一個原生質體內有不同染色體套數的核，造成其後來形成的癒傷組織內的細胞，及其再生植株間染色體套數的差異。另外，在第一次有絲分裂的單核原生質體中，有些雖具單倍體的核，但其染色體是由四條染色分體組成的雙染色體(diplochromosomes)，顯示這類原生質體在間期發生了二次DNA複製。進入中期後，染色分體漸漸地成對分開，形成二倍體的原生質體。在所檢查的745棵再生植株中，祗發現一棵?非整倍數體，其具有58條染色體。文中除探討染色體數目變異的原因之外，也討論減少此類變異發生的對策。

Chromosome counts of plants regenerated from mesophyll protoplasts of haploid Nicotiana sylrestris (2n = 2x = 24) and N. plumbaginifolia (2n = 2x = 20) showed that they were all diploid or polyploid; no plants with the original haploid number of chromosomes were observed. Variation in ploidy level was also observed among plants derived from the callus of single protoplast origin. Cytological examination of protoplasts and protoplast-derived cells suggests that two nuclear abnormalities are mainly responsible for the ploidy level variation. (1) Nuclear division was often unaccompanied by cytokinesis and wall formation during the first few days of culture. Subsequently, nuclear fusion occurred at interphase and mitotic stages. (2) During the very early phase of culture, presumably at the first division of the protoplasts, the chromosomes of some protoplasts were found to be each consisting of four chromatids instead of the normal number of two. This indicated that the nuclei had undergone two rounds of DNA synthesis before they actually entered mitosis. Realizing these being the main causes for ploidy variation, some possible ways to reduce the variation were suggested.