摘要:

Behaviour of the diploid nucleus in the ascus ofEpichloe cinerea, a typically tropical fungus was studied. The haploid chromosome complement was determined asn=2.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796686

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

In all gall midges (Cecidomyiidae, Diptera) spermatogenesis is unorthodox. The case ofMycophila speyeriwas investigatedin vitroand by electron microscopy. In the first meiotic division in males three chromosomes (sperm chromosomes) segregate from the residual chromosomes by monocentric chromosome movement. The spermatogonial divisions prior to this are completely normal. In the interphase before meiosis I the three sperm chromosomes can be recognized: they are already condensed, in obvious contact with the nuclear envelope and separated from the residual chromosomes by lamellae of nucleolus-like material. In prophase these lamellae disappear and the residual chromosomes condense too. Near a pair of centrioles a spindle precursor forms. After the disappearance of the nuclear envelope a morphologically bipolar spindle appears, containing only the sperm chromosomes. These look like normal metaphase chromosomes each having two kinetochores which point to the poles. The chromosomal fibres are long individual bundles. In addition to microtubules they contain a lot of ER-like membranes which are connected to the microtubules by bridges. During anaphase the sperm chromosomes do not divide.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796687

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

In the course on an investigation on lizard spermiogenesis, we have observed events connected with the differentiation of the acrosome and middle-piece of the spermatozoa. Some differences from other reptilians were found as well as: the presence of a subacrosomal space, the absence of the fibrous sheath in the middle-pice and a very short neck in the mature spermatozoa.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796688

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

Leaves of three ivy (Hedera helixL.) varieties, one with green leaves and two with variegated leaves, respectively with green centre and white-yellow margin (« Aureo-marginata ») and with white-yellow centre and green margin (« Goldheart »), have been studied by light and electron microscopy. At the same time chlorophyll and carotenoid content was studied. Light microscope observations suggest the hypothesis that the two variegated varieties are chimaeras of periclinal « green over white » type, altough the leaf phenotype is considerably different. The plastid ultrastructure of white-yellow areas of « Aureomarginata » and « Goldheart » are similar. The similarity of pigments between green and white-yellow areas and the normal ultrastructure of all the chloroplasts in young leaves, related to hystological observations, suggest that chloroplast degeneration in « Aureomarginata » is caused by the deficiency of some factor having general importance in cell differentiation and therefore, necessary also for plastid development. On the contrary, in « Goldheart » the data about pigments, hystology and ultrastructure of young leaves suggest that in this case the alterations concern particularly the photosynthetic apparatus. In all the cells of the two variegated varieties a paracrystalline body has been observed, both in normal and in altered plastids; in the green leaves variety the paracrystalline structure has been detected only in plastids of epidermal cells. The significance of this structure has been discussed.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796689

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

Viene seguito il comportamento di una Gimnosperma variegata (Libocedrus decurrens « aurea »Terr.) nella quale il manifestarsi del fenotipo mutato è evidentemente connesso con l'intensità di illuminazione a cui il mutante è sottoposto.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796690

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

In belladonna leaves, as well as in tobacco (AVERY 1933), there are cell differentiation gradients. One is along the major leaf-axis, and another from the midrib towards the leaf margin. Moreover, in both leaf laminae there are seven cell layers. In the least differentiated regions of the youngest leaves all cell layers show plastids with a membrane-bound body. As mesophyll differentiates, the frequency of such plastids decreases and, at the same time, their distribution in the different cell layers varies. According to our surveys, carried out into successively older leaves, we can assume that the plastid differentiation speed is not determined by light as much as by the cell's internal environment.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796691

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

The fourth chromosome ofDrosophila melanogaster, analysed with different techniques, results predominantly heterochromatic. The short euchromatic portion corresponds to the banded region visible in the salivary chromosomes.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796692

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

The cap cells ofAllium cepa, labeled with 3HTdR, are displaced from the meristem and sloughed from the cap; after 72h the whole cap appears renewed. During the cap cell differentiation processes, some nuclear cytopbotometric and ultrastructural aspects were analyzed. Though all the nuclei of the root cap differentiate with the same Dna content per nucleus, histones/Dna ratio shows differences both between and within columella and peripheral cell nuclei. Besides, histones/Dna ratio shows a wider heterogeneity in mature than in undifferentiated cells. The ultrastructural observations are in agreement with histones/Dna data, showing changes in chromatin structure.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796693

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

Trisomic lines ofTriticum durumvar Cappelli were crossed with aneuploid _lines of T.aestivumvar. Chinese Spring which are, in turn, ditelocentric for the chromosomes of the genomes A and B. The pairing pattern in such type of F1hybrids allows the correct identification of the chromosomes involved in the trisomic condition.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796694

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor

摘要:

The duration of the mitotic cycle and its phases was measured in the root tips of two crops (1966 and 1974) ofTriticum durumcv. Cappelli, by autoradiographyc technique, after labelling with3H-thymidine. The average total duration of the mitotic cycle was found to be 18h 45′ in crop 1966 and 16h 25′ in crop 1974. This time included, in crop 1966, a synthetic period (S) of 9h 35′, a post-synthetic period (G2) of 2h 36′, a mitotic duration of about lh and a pre-synthetic period (G1) of 5h 36′. In crop 1974, S was found to be 9h 20′, G24h 30′, mitosis 56′ and G1lh 38′. The single phases duration was also considered as percentage of the total time of the cycle.

ISSN:0008-7114    

DOI:10.1080/00087114.1977.10796695

出版商:Taylor & Francis    

年代:1977

数据来源: Taylor