Showing papers by "Government College published in 1975"
TL;DR: Heterocysts are found in many species of filamentous blue‐green algae and are cells of slightly larger size and with a more thickened wall than the vegetative cells.
Abstract: Summary
1. Heterocysts are found in many species of filamentous blue-green algae. They are cells of slightly larger size and with a more thickened wall than the vegetative cells.
2. Structural details of the heterocyst are: the presence of three additional wall layers, the absence of granules, sparse thylakoid network throughout, except at the poles where a dense coiling of membranes occurs. Other characters include the two pores at opposite poles ‘plugged’ with refractive material called the polar granule.
3. Peculiarities in the pigment composition of the heterocyst include an abundance of carotenoids and absence of phycobilins, and a short-wave form of chlorophyll a.
4. Unique glycolipids and an acyl lipid, not found in the vegetative cells of the algae or in other plant cells, are associated with the heterocyst. The glycolipids constitute the laminated layer of the wall and probably regulate diffusion of substances through it, whereas the acyl lipids are supposed to function as carriers and intermediates in the biosynthesis of the wall.
5. The heterocysts develop from vegetative cells, and the visible changes during differentiation include cell enlargement, synthesis of additional wall layers, disappearance of granules and reorientation and synthesis of the thylakoids.
6. Heterocysts are formed sequentially with characteristic cellular spacing during the growth of cultures in medium free from combined nitrogen.
7. Various sources of combined nitrogen inhibit heterocyst formation when supplied in the culture medium. Ammonium salts are among the most powerful inhibitors. Heterocysts are formed simultaneously and within a short period after transference of ammonia-grown non-heterocystous filaments to ammonia-free medium.
8. Incompletely differentiated heterocysts or proheterocysts are found in cultures grown in the presence of combined nitrogen. If two or more proheterocysts are close together generally a single one develops to maturity after a competitive interaction in medium free from combined nitrogen. This indicates that heterocyst formation is completed in two phases: phase I, synthesis and conservation of macromolecules, which takes place during growth in ammonia-containing medium: and phase 11, morphological differentiation of the heterocyst which is unaccompanied by growth in cell number. In the ammonia-free medium phase 11 quickly succeeds phase 1 and the whole process appears as a continuum.
9. Heterocyst formation shows a definite requirement for light. Red light favours heterocyst formation, whereas green and blue light do not. The effects of light seem to be mainly due to photosynthesis, although some effects may be morphogenetic.
10. Studies with metabolic inhibitors have revealed the involvement of photosynthesis, respiration and protein synthesis in heterocyst formation. Photosynthesis provides carbon skeletons, whereas ATP is most probably supplied by oxidative metabolism.
11. Various functions have been assigned to the heterocyst from time to time. Their role in akinete formation is suggested by (i) the formation of akinetes adjacent to the heterocysts and (ii) prevention of sporulation by detachment of the heterocysts from the vegetative cells (potential akinetes). Despite substantial evidence for such a role, it is not applicable to all akinete-forming genera.
12. Heterocysts are now widely believed to be the site of nitrogen fixation in blue-green algae. The main facts in favour of such a role are: (i) fixation of nitrogen by all heterocystous algae, (ii) inhibition of heterocyst formation by combined nitrogen and (iii) direct observations on acetylene reduction by isolated heterocysts.
13. Some non-heterocystous and unicellular algae, and vegetative cells of heterocystous algae fix nitrogen under microaerophilic conditions suggesting that absence of oxygen favours nitrogenase activity. Heterocysts lack the oxygen-evolving photo-system 11, possess oxidative enzymes, and reduce externally supplied tetrazolium salts - all indicating that they are the most suitable sites for harbouring nitrogenase in aerobic conditions.
14. Heterocysts probably originated in the Precambrian in response to the earth's changing environment and seem to be the first example of morphological differentiation in the plant kingdom.
39 citations
TL;DR: In this article, the mechanism of energy transfer between Tb and Nd in sodium borate glass has been examined at 80, 300 and 500 K. By the measurements of the concentration dependence of intensity and lifetime, it has been found that the transfer from the 5D4 level of Tb is predominantly by dipole-dipole interaction at high Nd concentrations.
19 citations
TL;DR: A basilar membrane has been found at the opening of the testis follicle into the sperm duct of Aulacophora foveicollis, which consists of a dome-like arrangement of a whorl of specially elongated cells.
Abstract: Summary In the testis of Aulacophora foveicollis a basilar membrane has been found at the opening of the testis follicle into the sperm duct. The membrane consists of a dome-like arrangement of a whorl of specially elongated cells. Sperms have to move across it to enter the sperm duct.
6 citations
TL;DR: In this paper, a study of Virginia Woolf's "Mrs. Dalloway" is presented, with a focus on the aesthetic vision of the author and her aesthetic vision.
Abstract: (1975). Feminism as aesthetic vision: A study of Virginia Woolf's “Mrs. Dalloway' Women's Studies: Vol. 3, No. 1, pp. 61-73.
5 citations
2 citations
01 Jan 1975
TL;DR: Oviposition of some species of black flies occurring in the Darjeeling area of India was exhibited by freely dropping eggs from the air; tapping the abdomen through the water while hovering or while alighting; and by crawling under the water.
Abstract: This paper incorporates observations on the ecology of sixteen species of black flies occurring in the Darjeeling area of India. Of the species ofSimulium, himalayense was most abundant;rufibasis andgrisescens moderately abundant; anddentatum, ramosum, nigrifacies andbiforaminiferum confined to certain pockets of the area. Of the species ofEusimulium, praelargum was very abundant;gracilis moderately abundant; andpurii, aureohirtum, nemorivagum anddasguptai almost rare. Of the species ofGomphostilbia, tenuistylum was moderately abundant, whiledarjeelingense andmetatarsale were localized. The species ofSimulium exceptnigrifacies andbiforaminiferum selected rapid water; the species ofEusimulium, andbiforaminiferum andnigrifacies, preferred very slow or sometimes quiet water, while the species ofGomphostilbia were often adapted to medium current for oviposition. Oviposition was exhibited by (i) freely dropping eggs from the air; (ii) tapping the abdomen through the water while hovering or (iii) while alighting; and by (iv) crawling under the water. The peak period of oviposition was normally in the evening before sunset. Hibernation was observed in the egg-stage inhimalayense, rufibasis, grisescens (in a lowland river) andtenuistylum; and in the larval stage inpraelargum, gracilis and probablygrisescens (in upland streams). One generation per year was observed intenuistylum; two generations inpraelargum, gracilis andgrisescens (in upland streams); three generations inrufibasis andgrisescens (in a lowland river) and at least three generations inhimalayense. Larvae of some species were found to remain in association with those of others, depending upon environmental conditions. Larvae ofEusimulium especially, almost always hid themselves under the substrata to get constant supply of sufficient oxygen from trickles of water they were found to inhabit.
2 citations
1 citations
TL;DR: In this article, the phase velocity and attenuation distance of a wave propagating arbitrarily in a homogeneous, driftless, warm electron magnetoplasma were investigated. And the phase velocities and the attenuation distances of wave propagations were analyzed analytically to study the dispersion relation for plasma wave.
Abstract: This paper presents the study of behaviour of the phase velocity and the attenuation distance of waves propagating arbitrarily in a homogeneous, driftless, warm electron magnetoplasma Some illustrative graphs showing the variation of the phase velocity and the attenuation distance with respect to normalized source frequency for various values of normalized collision frequency are developed analytically to study the dispersion relation for plasma wave For getting simplified expression, the phase velocity and the attenuation distance are expanded in a power series in terms of normalized collision frequency and inverse of normalized collision frequency by Taylor's series theorem for the respective low-loss and high-loss cases of warm plasma The approximate values of the phase velocity and the attenuation distance are also obtained in some regions of the frequency spectrum
Journal Article•
TL;DR: The taste receptors or buds are ovoid clusters of modified epithelial cells which are embedded in the epithelium of various organs and are distinct from the neuromast organs of the lateral-line system.
Abstract: The taste receptors or buds are ovoid clusters of modified epithelial cells which are embedded in the:s^fttifled epithelium of various organs. They are distinct frcmi the neuromast organs of the lateral-line system and, accordingly, Walter (1928) has named the ta$te receptors as gustoreceptors and the neuromast organs as rheoreceptors
TL;DR: In this paper, the Mossbauer spectrum of ferrous zirconium double sulphate FeZrO(SO 4 ) 2 ·8H 2 O shows a quadrupole split doublet at room temperature.
01 Sep 1975
TL;DR: A sublethal dose of Dieldrin induced changes in the neurosecretory system of Gryllus asimilis and entailed degeneration of oocytes and a fall in the haemolymphal acid phosphatase was also noted.
Abstract: Effects of Dieldrin on the neurosecretory system and the ovarian development ofGryllus assimilis F. (Orth., Gryllidae)