Abstract:The puff-like structure (PLS) is a loose, fibrillar, spherical structure which has been found in the nucleus of some higher plants and often referred to intranuclear bodies, centromeres, micropuffs and puff-like fibrillar structures. Opinions on the nature of the PLS are still diverged. In order to gain further information upon the nature of the structure, ultrastructural and cytochemical features of the PLS in the nucleus of root tip meristematic cells of Allium cepa L. and the effect of α-amanitin(α-A, a specific inhibitor of RNA polymerase Ⅱ which is responsible for the transcription of genes coding for mRNA) on it were studied. Two types of PLSs were found in the conventionally-stained samples: one was composed of compact fibres while the other consisted of loose, decondensed fibres. In the PLS of the latter type, a brush-like structure comprising both an axial fibre and lateral fibres was observed, suggesting that transcription was taking place in the PLS. When stained by Bernhard‘s method, the PLS was shown to contain both RNP and DNP. After the treatment with α-A, the PLS composed of compact fibres was still seen but the one consisting of loose fibres was destroyed ultrastructurally and the brush-like structures disappeared. Based on these observations, it is suggested that the PLS would be a morphological manifestation of transcription of the non-nucleolar gene coding for mRNA.