Volume 20, Issue 1
January 1995, pages 1-139
pp 1-6 January 1995
Taking advantage of the fact that static electricity in plastic Petri dishes will produce very long, thin migrating slugs ofDictyostelium discoideum, it was shown that these slugs moved particularly rapidly. This is consistent with the demonstration of Inouye and Takeuchi that speed varies with length for slugs migrating on agar. Based on these observations it is suggested that slug speed is controlled by both the resistance at the tip and some factor that correlates With slug size, such as the concentration of endogenously produced ammonia
pp 7-16 January 1995
Autocorrelation and spectrum analyses of amino acid residues along protein chains in a large data base has been performed. Results reveal the presence of general long range correlations. Similar analyses of simulated (random) peptides do not exhibit any such long range correlations. Based on the results of nur analysis, an attempt has been made to model the distribution of residues in protein sequences on a fractional Brownian motion and individual sequences as multi-fractals. For this purpose, the characteristics of an fractional Brownian motion namely, the scaling parameterH. the spectral exponent β and the fractal dimensionD, have been described
pp 17-28 January 1995
Rhizobial purine auxotrophs have earlier been shown to be defective in symbiosis, though the exact reason for this failure is not clear. Using various dyes that specifically bind different cell surface molecules, we show that there are multiple changes in the cell surface molecules associated with different purine auxotrophs. Affected molecules in different purine auxotrophs that were tested include (i) acidic exopolysaccharides, (ii) cellulose fibrils, and (iii) beta (1–3) glucans. Our results show that the symbiotic deficiency of purine auxotrophs is likely to be a result of these associated changes on the cell surface
pp 29-33 January 1995
Urine and tissues (brain, liver, kidney, fat and triceps muscles) from rodents (rats, guinea pigs and albino mice) treated with sulphur mustard percutaneously were examined for the presence of sulphur mustard and/or metobolites using electron impact direct inlet and GC-mass spectrometry. Sulphur mustard and thiodiglycol sulphoxide were not detected in these samples even after application of massive doses. However, thiodiglycol was identified in urine only
pp 35-47 January 1995
Light, controls the “blueprint” for chloroplast development, but at high intensities is toxic to the chloroplast. Excessive light intensities inhibit primarily photosystem II electron transport. This results in generation of toxic singlet oxygen due to impairment of electron transport on the acceptor side between pheophytin and QB -the secondary electron acceptor. High light stress also impairs electron transport on the donor side of photosystem II generating highly oxidizing species Z+ and P680+. A conformationsl change in the photosystem II reaction centre protein Dl affecting its QB-binding site is involved in turning the damaged protein into a substrate for proteolysis.
The evidence indicates that the degradation of D1 is an enzymatic process and the protease that degrades D1 protein has been shown to be a serine protease Although there is evidence to indicate that the chlorophyll a-protein complex CP43 acts as a serine-type protease degrading Dl, the observed degradation of Dl protein in photosystem II reaction centre particlesin vitro argues against the involvement of CP43 in Dl degradation. Besides the degradation during high light stress of Dl, and to a lesser extent D2-the other reaction centre protein, CP43 and CP29 have also been shown to undergo degradation.
In an oxygenic environment, Dl is cleaved from its N-and C-termini and the disassembly of the photosystem II complex involves simultaneous release of manganese and three extrinsic proteins involved in oxygen evolution. It is known that protein with PEST sequences are subject to degradation; D1 protein contains a PEST sequence adjacent to the site of cleavage on the outer side of thylakoid membrane between helices IV and V.
The molecular processes of “triggering” of Dl for proteolytic degradation are not clearly understood. The changes in structural organization of photosystem II due to generation of oxy-radicals and other highly oxidizing species have also not been resolved. Whether CP43 or a component of the photosystem II reaction centre itself (Dl. D2 or cy1 b559 subunits), which may be responsible for degradation of Dl, is also subject to light modification to become an active protease, is also not known. The identity of proteases degrading Dl, LHCII and CP43 and C29 remains to be established
pp 49-58 January 1995
Rate of photosynthesis and activities of photosynthetic carbon reduction cycle enzymes were determined in pods (siliqua), whereas rate of dark CO2 fixation, oil content and activities of enzymes involved in dark CO2 metabolism were measured in seeds ofBrassica campestris L. cv. Toria at different stages of pod/seed development. The period between 14 and 35 days after anthesis corresponded to active phase of seed development during which period, seed dry weight and oil content increased sharply. Rate of pod photosynthesis and activities of photosynthetic carbon reduction cycle enzymes were maximum in younger pods but sufficiently high levels were retained up to 40 days after anthesis. The rate of dark14CO2 fixation in seeds increased up to 21 days after anthesis and declined thereafter but maintaining sufficiently high rates till 35 days after anthesis. Similarly various enzymes viz., phosphoenolpyruvate carboxylase, NAD+-malate dehydrogenase and NADP+-malic enzyme, involved in dark CO2 metabolism retained sufficient activities during the above period. These enzyme activities were more than adequate to maintain the desired supply of malate which mainly arises from dark CO2 fixation in seeds and further translocated to leucoplasts for onward synthesis of fatty acids. Enzyme localization experiments revealed phosphoenolpyruvate carboxylase and enzymes of sucrose metabolism to be present only in cytosol, whereas enzymes of glycolysis were present both in cytosolic and leucoplastic fractions. These results indicated that oil synthesis in developingBrassica seeds is supported by pod photosynthesis and dark CO2 fixation in seeds as the former serves as the source of sucrose and the latter as a source of malate
pp 59-68 January 1995
Intact chloroplasts isolated from sulphur dioxide fumigatedHardwickia binata leaves showed inhibition of PS II electron transport activity without any significant effect on photosystem I. Sulphur dioxide exposed leaves accumulated more hydrogen peroxide than those from non-fumigated plants and this was caused by increase in superoxide radical production. Hydrogen peroxide formation was inhibited by addition of cytochrome C and superoxide disrnutase. In sulphur dioxide fumigated leaves, increase in superoxide dismutase activity showed resistance to sulphite toxicity. The localization of ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase activities in chloroplasts provide evidence for the photogeneration of ascorbate. The scavenging of hydrogen peroxide in chloroplast due to ascorbate regenerated from DHA by the system: PS I → Fd → NADP → glutathione. The system can be considered as a means for preliminary detoxification of sulphur dioxide by chloroplasts
pp 69-81 January 1995
Filarial parasite, responsible for filariasis is known to remain in the host for long periods of time. A 29 kDa protein isolated fromSetaria digitata by gel electrophoresis and electroelution of detergent soluble surface antigens showed a 70% inhibition of the cell mediated immune response. On evaluation of its diagnostic application, the same protein was found to be very sensitive in detecting antibody at an antigenic protein concentration as low as 1 ng per μl. The cross reactivity of surface antigen with bancroftian filarial patient’s sera was tested by Dot-ELISA and ELISA. Both the antigen as well as antibody detection tests showed 100% positivity with all types of filariasis cases. It did not produce any positive reaction with non-endemic control sera. However, a proportion of endemic normal subjects showed positivity and this is attributed to the fact that people in endemic areas are exposed to infective mosquito bites. The biological property of inhibition and 100% positivity of filariasis cases in both antibody and antigen detection tests point towards the bifunctional nature of the surface proteins before and after release. The same may be happening under normal conditions also, perhaps at a much lower rate
pp 83-88 January 1995
Bacillus pasteurii DR2, a broad-spectrum Hg-resistant bacterial strain, exhibited delayed sporulation and less mercury volatilization in the presence of mercury compounds. However, Hg-sensitiveBacillus subtilis sporulated quickly in the presence of HgCl2 and volatilized no mercury. Levels of Hg2+-reductase and organomercurial lyase in the endospores ofBacillus pasteurii DR2 were lower than those in vegetative cells
pp 89-103 January 1995
It is suggested that maternal parent and offspring have conflicting interests over the extent of resource allocation to developing seeds. While maternal parent would be selected to allocate her resources optimally among her offspring, the latter would be selected to demand more. In animals, offspring are known to demand additional resources either visibly (through intense vocal calls) or subtly through the production of hormones. In plants though parent offspring conflict over resource allocation has been invoked, the mechanism through which the parent and offspring interact in regulating resource allocation into developing seeds is not yet clear.
In this paper, we propose that the strategies and counter-strategies of the offspring and mother during the development of seeds might be manifested through the production of appropriate growth hormones. Accordingly, we predict (i) hormones that mobilize resources into seeds (e.g. auxins and gibberellic acid) shall be synthesized exclusively by the offspring tissue and (ii) hormones that inhibit resource flow in to seeds (e.g. abscisic acid) be produced exclusively by the maternal tissue. We show that these predictions are supported by existing literature on the temporal dynamics and source of production of growth hormones during seed development. Finally, we suggest that such analysis viewing the production of different hormones during early seed development, as strategies and counter-strategies of mother and offspring tissue, helps ofer a meaningful interpretation of the otherwise complex dynamics of hormone fluxes
pp 105-139 January 1995
The multinucleated plasmodia ofPhysarum polycephalum, a myxomycete, have been extensively used in cell cycle studies. The natural synchrony of mitosis and DNA synthesis, easy culture methods, the ready fusions obtainable between plasmodia, and the amenability to phase specific studies, employing physical and chemical perturbers, are some of the attractive features of this organism. Because of the absence of a Gl phase in the plasmodia, there is a crowding of cell cycle specific marker events at the G2/M boundary, which reflect features of both the G2/M and the Gl/S boundaries of a typical eukaryotic cell. Prominent among these are the synthesis and overall activity of thymidine kinase, the co-triggering of tubulin and histone genes, translation of their mRNA, the organization and duplication of the microtubular organizing centres of the mitotic spindle and the triggering of cdc 2 kinase activity. These above events have not only served as good markers to monitor the progress of the plasmodial cell cycle, but have also been fairly thoroughly analysed by means of specific perturbers such as DNA synthesis inhibitors, antimicrotubular drugs, UV-irradiation, heat-shock etc. Along with fusion studies, these perturbation studies have been helpful in the formulation of various models on regulation of mitosis. These above aspects as well as prospects for future studies employing this organism are discussed
Volume 44 | Issue 5
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