Volume 87, Issue 8
August 1978, pages 161-253
pp 161-190 August 1978
Evidences showing that chromosomes in eukaryota, with their complex organization, exhibit dynamism in structure and behaviour for controlling differentiation, variability and reproduction have been reviewed. An outline has been given of the stepwise evolution of the functionally differentiated chromosome segments and their chemical make up including protein components and sequence complexity of DNA. The outline includes the origin of chromosomal control of metabolism in extranuclear organelles.
During organogenesis, the chromosomes, maintaining the basic genetic skeleton, undergo variation in structure and chemical components, thus exhibiting dynamism. Addition, loss and inactivation of heterochromatic segments have been correlated with adaptation and alteration in chromosome size. Data on the possible role of repeated sequences in control and integration have been presented.
Endomitotic replication of the chromosome, in place of normal mitosis, during differentiation is an example of dynamic behaviour, adapted to meet the need of uninterrupted transcription during differentiation without increasing the number of cells. The predetermined symmetrical growth of the organism is thus maintained.
In several asexually reproducing species, dynamism is manifested in genetically controlled unusual behaviour of chromosomes, where the somatic tissue often represents a chromosome mosaic. It has been adapted to meet the need of generating variability and genotypes through bud mutation in the absence of effective sexual reproduction.
Data in favour of the concept of dynamism indicate that evolution of eukaryotic chromosome has involved progressive complexity of chromosome structure on the one hand, and flexibility in its behaviour and structure, maintaining the basic genetic make up, on the other. It has enabled the chromosomes to exert supreme control on all aspects of metabolism which are sequential and phasic in higher organisms.
pp 191-195 August 1978
One of the most interesting internal features of the several species ofRhizophora has been the presence of varied types of foliar sclereids. This feature has been examined with a view to find out their utility in the satisfactory revision of this genus.
pp 197-203 August 1978
One of the most interesting endomorphic features of several species ofBoronia has been the discovery of varied types of terminal sclereids and tracheoids throughout the leaf expanses. Their typology has been examined with a view to find out their diagnostic or taxonomic value and also in solving problems of nomenclatural synonymy in the systematic treatment ofBoronia.
pp 205-214 August 1978
Life history ofBursaria spinosa Cav., has been studied. The male archesporium is a plate of 3-cells. The anther wall comprises the epidermis, endothecium with banded thickenings, a middle layer and secretory tapetum. The tapetal cells are two to many nucleate and some of them become vesicular with 2–5 nuclei. Cytokinesis takes place by furrowing. The pollen grains are shed at the 3-celled stage. The ovule is ana-campylotrapous, unitegmic and tenuinucellate. Embryo sac develops according to the polygonum type. Fertilization is porogamous. The endosperm is nuclear to start with but becomes cellular in later stages. The embryogeny has been described for the first time and it conforms to the asterad type and keys out to the geum variation. A single instance of suspensor polyembryony has been noticed. The seed is endospermic. The seed coat is 2–3 layered. The pericarp consists of 3–4 layers of thin walled cells followed by 3–4 layers of sclerotic cells.
pp 215-221 August 1978
The five sepal primordia arise successively in clockwise sequence. Interprimordial growth initiates a short calyx tube. The petal primordia are formed almost simultaneously alternate to the sepal primordia. They are followed by the antesepalous stamen primordia which also appear simultaneously opposite the sepal primordia. The primordia of the antepetalous stamens are formed after the inception of the gynoecium. They are inserted inside the antesepalous stamen primordia. The floral apex grows up into a crescent-shaped gynoecial primordia. In floral developmentCassia differs from members of the Papilionaceae and Mimosaceae. The position of insertion of the leguminous carpel on the floral apex has been discussed and it was concluded that the carpel ofCassia is a terminal structure.
pp 223-230 August 1978
Polyacrylamide gel electrophoretic (PAGE) analysis ofFusarium infected cotton plants showed the disappearance of some erstwhile protein bands and the appearance of new bands to a greater degree in the compatible host-parasite combinations (Gossypium hirsutum/A1 strain;G. arboreum/I2 strain ofF. vasinfectum). Also, an increase in the number of antigenic proteins of the host following infection has been noticed only in the compatible host-parasite combinations as shown by agar double diffusion and immunoelectrophoretic studies. The newly formed antigens did not appear to originate either from the extracellular or intracellular protein pool of the pathogen; probably these are products of altered metabolism of the host species.
pp 231-242 August 1978
Observations on the leaf galls ofCasearia tomentosa Roxb., induced byGynaikothrips flaviantennatus Moulton have shown that the form of the gall is controlled by the developmental stage of the leaf and the impact of the gall maker(s) in terms of population. Population trends of gall maker, predator and inquiline have been analysed in the context of gall development.
pp 243-253 August 1978
The interference between wheat andChenopodium album was studied in pure and mixed stands at two nutrient levels. Wheat responded to density by plasticity whileC. album responded both by mortality and plasticity. In mixtures, crop had an adverse effect on survival and yield of the weed, though to a lesser degree the effect weed on the crop was also noticed. The ecological aspects of the mortal and plastic responses of the competing species are discussed.