Cytological studies have been carried out on ten different species and varieties belonging to two genera of Araliaceae, viz. Aralia and Polyscias. A detailed analysis of karyotypes has been performed in all of them. Striking uniformity in the chromosome number (2n=24) has been emphasized and the report 2n=36 chromosomes has been made for the first time and the twelve chromosomes appear to constitute the basic set in the family. Although gross homogeneity in the karyotype among the members of the two genera is noticed, yet a critical analysis shows that each species and variety is characterized by the distinctive karyotype of its own, particularly in the nature of the secondary constrictions. Taking into account all these facts, it has been considered that structural alterations of chromosomes have been the prime factor in evolution within the family. The cytological data indicating homogeneity in chromosome number and gross similarity in karyotypes taken in conjunction with the marked similarity in external morphological characters suggest that the different genera of the family are very much interrelated. Nomenclatural changes and the transference of a species from one genus to another as done in the family has been emphasized in this connection.
The morphology, meiotic behavior and karyotypes of Hordeum halophilum, H. muticum and of the natural interspecific sterile hybrid have been studied. Evidence from meiotic behavior in the hybrid as well as the study of the karyotype in both diploid species indicates that their genomes are largely homologous. They differ, however, in at least one reciprocal translocation and one paracentric inversion. The isolating mechanisms between both species and the formation of dineocentric bridges at second anaphase are discussed.
The morphological characters of nine species and six F1 hybrids were compared. It was found that with respect to characters such as tillering, panicle branching, floret shape, colour of the midrib, stigma and grains, the hybrids were intermediate but for characters such as plant height, leaf length and number of nodes, the hybrids were usually heterotic. The awned condition was found to be recessive to awnlessness and the non-staminate condition of pedicellate florets to staminate condition. Critical analysis of chromosomes at pachytene and later stages of microsporogenesis in the seven Eu-sorghum species and six F1 hybrids were made. Pachytene chromosomes are depicted on the basis of total length, relative length, arm-ratio, amount and distribution of heterochromatin and number and position of chromomeres. The characteristics of each of the ten chromosomes in the haploid complement are described in ten different classes bringing out the similarities and differences among these seven species. Studies on the pairing properties of the differentially stained regions show that synapsis starts from the proximal to the distal and separation of the split chromosomes starts from the distal to the proximal. Pachytene analysis in the four F1 hybrids revealed the presence of some minute, though cytologically detectable, structural differences such as terminal as well as interstitial non-paired regions, small duplication and small terminl deletions and differential segments between the parental species. Pachytene pairing was found to be complete and apparently normal in the remaining two hybrids. Inspite of the existence of these meiotic irregularities in some hybrids, high percentage of stainable pollen and good seed setting were recorded in all the hybrids under consideration. The distribution of chiasmata at various stages was studied in both species and species hybrids and the average chiasma frequency did not show any significant deviation from those in the parental species. It is suggested that the existing chromosomal differences are quite small and do not lead to abnormal behaviour of the hybrids either in respect of morphological characters or in the meiotic process in the F1 generation. Cytogenetical mechanisms underlying species differentiation in the genus are discussed.
The present investigation deals with a morphological and cytological comparison between the colchiploids of Capsicum frutescens cultiver Oshkhosh and its diploid progenitor. The most effective treatment for the induction of tetraploids was found to be 0.2% aqueous colchicine applied to the growing point of young seedlings for 12 hours. On the whole 64% of the plants became polyploids and survived. The induced tetraploid was characterised by deep green, thick and rough leaves with larger epidermal cells, stomata, palisade and spongy parenchyma. The number of stomata per unit area in the tetraploid was less than that of the diploid. In general the morphological characters were larger in the polyploids than their counterparts in the diploids. The 4n plants were completely sterile and no fruit setting was observed in them. The cause of complete failure of fruit formation lies in the premature disintegration of the stigma which blocks the passage of the pollen tube to reach the egg. Pollen germination in situ has been observed in anthers of a polyploid bud. The induced polyploids exhibit cytological abnormalities such as univalents, laggards, restitution nuclei, non-congression and non-orientation of certain bivalents and other irregularities such as subdivision of the chromosome complement into 2 or more groups that function independently within the cell, nondisjunction of chromosomes and unequal distribution of the chromosomes to the polar regions at anaphase were noted at either or both meiotic divisions in the PMC's. The number of microspores per PMC varied from 1-12. The gametes produced by a polyploid with such a cytological mechanism will have extremely variable chromosome number. Those gametes which have balanced genomes will be functional. The evolutionary significance of the various anomalies observed and their importance to plant breeder have been discussed.
In Pteris vittata L., callus formation was induced in young gametophytes by dark-culturing on the complex medium. Calli could readily be subcultured and maintained on the same medium. One of thus obtained calli is characterized by extreme friableness. Friable callus tissues placed in liquid medium in the test tube with agitation produce small tissue pieces and a suspension consisting of cell aggregates and isolated cells. When a suspension was distributed on the surface of the complex medium, large calli were re-formed. When a suspension was placed on the defined medium devoid of organic substances, gametophytes differentiated. The development of mature gametophytes from cell aggregates or directly even from isolated single cells was described in detail. The development of gametophytes from isolated cells resembled to the pattern of spore germination in Pteris vittata. The gametophytes cultured were grown up to the formation of sex organs and sporophyte formation.
By means of the in vivo observation, the effect of various herbicides on cells in the metabolic as well as in the mitotic state was studied in the staminal hair cells of Tradescantia, the stipular cells of Vicia faba, the petal cells of Allium fistulosum and Allium cepa, the isolated cells of Triticum vulgare root tips and the cells of pollen grains in Tradescantia. The effect of the five hormonic herbicides, 2, 4-D, 2, 4, 5-T, 2, 5-D, MCP and SES, was summarized in Table 1. The abnormal mitoses induced by these chemicals, showed chromosome bridges due to stickiness, a retardation of chromosome movement in anaphase, a binucleate cell, a multinucleate cell with multi-septa, a formation of the incomplete cell wall and an impediment in the differentiation of meristematic tissues. These effects of the herbicides on the mitotic cells revealed intimate connections with the herbicidal activity to weeds and with malformations to cultivated plants. The different resistance of cells to the herbicides between monocotyledonous plants and dicotyledonous ones was discussed at the cellular level from the results of their different behaviour with regard to the occurrence of abnormal mitoses and the survival of cells.
The cytology of a number of morphologically similar Bothriochloa species was studied. The Australian B. decipiens (2n=40) and B. ambigua (2n=60) are morphologically allied, sexually reproducing allopolyploids based on n=10. The Indian endemic B. longifolia is a sexually reproducing diploid. The remaining species studied are gametophytic apomicts, and behave cytologically like segmental allopolyploids. Tetraploid and hexaploid races characterize B. pertusa. Cytological and morphological data indicated that the hexaploids originated from the fertilization of a cytologically unreduced gamete. Bothriochloa radicans and B. glabra are tetraploids, while B. insculpta is characterized by pentaploid and hexaploid races. Morphological data indicated that hexaploid B. insculpta could have originated from a cross between plants resembling B. radicans and B. glabra. These hexaploids are of two morphological types, and it was proposed that the one combines the complete chromosome complement of B. glabra and the haploid complement of B. radicans, while the other originated from fertilization of the cytologically unreduced gamete of B. radicans. Pentaploids apparently represent backcross populations to either parent.
1. The nuclear origin of karyokinetic spindle and the presence of spindle membrane have been demonstrated in pollen mother cells of Tradescantia reflexa and in endosperm cells of Zephyranthes candida by using the fixative which contains CdCl2 solution. 2. Polar caps in root tip cells, multipolar spindles in pollen mother cells and a clear zone in endosperm cells have been discussed on their common characters. 3. It can be given as a conclusion that the nuclear origin of karyokinetic spindle and the presence of spindle membrane are common to all the mitoses in higher and lower plants.
The membrane of karyokinetic spindle in Ehrlich ascites tumor cells and that in ovary tissue cells of mouse are demonstrated by applying Pb(NO3)2 solution as pretreatment and Bouin's fluid as post-fixation. CdCl2 solution as pretreatment is also effective for the conservation of spindle membrane in tumor cells. So far as karyokinetic spindles are concerned, there is no essential difference in the origin and developmental process between the mitosis in both plant and animal cells.