摘要:

Diplotaxis erucoidesendosperm receives the degenerated contents of nucellar cells. In the degenerating nucellar cells at first ER dilations can be seen; later the ER cisterns become anastomised and split the cytoplasm into small islands. Nucellus cell-walls also degenerate and all the cell contents are incorporated in the endosperm. The endosperm can be divided into two portions: one surrounding the central vacuole, embryo and suspensor, the other lying in contact with the nucellus. The ultrastructure of these zones is shown during different periods of embryo development before and after endosperm cellularization; this phenomenon interests at first the micropylar portion and only later on the chalazal pole, that is when the ovule is about to become a seed.

ISSN:0008-7114    

DOI:10.1080/00087114.1975.10796640

出版商:Taylor & Francis    

年代:1975

数据来源: Taylor

摘要:

The occurrence of stromacentre in chloroplasts ofAsplenium trichomanesL. is reported. Such structure, so far described by GUNNING and coworkers in some species ofAvenaand by FAVALI and MEYER inOcymum basilicumL, has been found to occur in all stages, from the young to senescent ones, ofAsplenium trichomanes.The stromacentre inA. trichomanesis similar in shape to those ofAvena sativaandOcymum basilicum, but differs from these mainly for the size of its component fibrillar units. The value of both diameter and longitudinal periodicity is in fact 85–90 Å inAvenaandOcymum, whereas inAsplenium trichomanesvalues of 170–180 Å for the diameter and ca. 110 Å for the longitudinal periodicity have been observed. Preliminary investigations on other species of the genusAspleniumhave shown that the stromacentre also occurs on chloroplasts ofA. virideHuds.

ISSN:0008-7114    

DOI:10.1080/00087114.1975.10796641

出版商:Taylor & Francis    

年代:1975

数据来源: Taylor

摘要:

Observation of replicas of freeze-etched spore mother cells ofPsilotum nudum(L.) Beauv. has shown that the nuclear envelope undergoes remarkable changes on passing from premeiotic to meiotic stages. Before meiosis, the nuclear envelope shows an even surface covered by randomly distributed pores, whereas in leptotene-zygotene it becomes uneven and wave-like while the pores progressively gather in separate clusters. As a result, wide portions of nuclear envelope devoid of pores are observed at this stage. It is suggested that such events could be originated by traction forces acting on the inner membrane, at early stages of meiosis, and due to motions of the attached chromosome fibers in the course of spiralization and pairing processes. The decrease in average pore frequency in leptotene- zygotene, as compared to the premeiotic stages, is also related, as a first assumption, to the aforementioned traction forces. Quite similar phenomena to those reported forPsilotum nudum(L.) Beauv. were also observed inArisarum proboscideum(L.) Savi during microsporegenesis.

ISSN:0008-7114    

DOI:10.1080/00087114.1975.10796642

出版商:Taylor & Francis    

年代:1975

数据来源: Taylor