• Volume 98, Issue 3

      June 1988,   pages  157-226

    • Rhythmic oscillations in wheat chloroplast photochemical activity. I. Oscillations in whole chain, photosystem II and photosystem I electron transport activities

      Shabbir A Sayeed Prasanna Mohanty

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      Chloroplasts isolated from the primary leaves of wheat seedlings grown under different light in the laboratory as well as from the leaves of field grown seedlings exhibited distinct rhythmic oscillations in photosynthetic electron transport activities. Chlorophyll content in the primary leaves of continuous light grown wheat seedlings did not oscillate. Whole chain electron transport and partial reactions measured as photosystem II and photosystem I activities estimated at regular intervals oscillated with a periodicity of about 12–16 h. The periodicity of less than 22 h suggested that the rhythms are of a non-circadian type. The oscillations in photochemical activity persisted whether the seedlings were raised under continuous light or under light-dark cycles, indicating their endogenous nature. The photochemical activities attained maximal levels during both the light and dark phases of the cycles. The rhythm pattern persisted in the presence of photophosphorylation uncouplers. A time dependent sensitivity of uncouplers to stimulate electron transport activity was observed. The timings of the activity maxima for photosystem II and photosystem I mediated reactions alternated each other during the day. The ratios of photosystem II to photosystem I activities were out of phase of photosystem I and closely resembled the rhythm pattern in photosystem II activity indicating a possible oscillation in the population of active photosystem units. The results suggest that the temporal modulation of the photochemical activity in wheat chloroplasts is brought about by some sort of reversible conformational change in the thylakoid membranes.

    • Rhythmic oscillations in wheat chloroplast photochemical activity. II. Further characterization of the rhythm in photosystem II photoelectron transport activity

      Shabbir A Sayeed Prasanna Mohanty

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      Chloroplasts isolated at defined times from the primary leaves of wheat seedlings grown under continuous light as well as 12 h light-dark cycles exhibited endogenous oscillations in photosystem II activity monitored as photoreduction of 2,6-dichlorophenol indophenol with water as electron donor. The 12 h rhythmicity in photoreduction of 2,6-dichlorophenol indophenol resembled the oscillation pattern in photosystem II supported O2 evolution. Room temperature chlorophylla fluorescence intensity ratios (F+DCMU/F−DCMU) yielded a rhythmicity closely comparable to that of 2,6-dichlorophenol indophenol photoreduction rhythm. Photosystem II mediated photoreduction of 2,6-dichlorophenol indophenol monitored with the exogenous electron donor hydroxylamine which bypasses the electron donation by water also exhibited similar 12 h oscillations. These results suggest that the O2 evolving complex does not entirely contribute to the origin of the rhythmicity in photosystem II. Instead, periodic changes in the reaction centre-antenna complexes may represent the rate limiting step for the generation of the time triggered rhythms in chloroplast photochemical activity. It is postulated that a temporal reversible control over the functional coupling and uncoupling between the reaction centres and antenna complexes or temporal changes in active and inactive reaction centres may induce the periodic oscillations in PS II activity.

    • Seed protein electrophoresis in six species and two F1s ofCicer

      G Kabir R M Singh

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      The water soluble fraction of the seed protein of 6Cicer species and of the two F1 hybrids ofCicer arietinum andCicer reticulatum was analyzed by disc electrophoresis. Each species and F1 ofCicer had its own pattern and also a different number of bands. In general banding pattern revealed variation in number and intensity of bands in all the species and F1s. A little difference was in the protein profile of the two strains, NEWC-21 and Jm-2106 ofCicer reticulatum. Common and kabuli types ofCicer arietinum were found to possess 7 bands but one band in each type was at differentRf. The bands inCicer arietinum had homologues in other wild species and none of the wild species possessed all 7Cicer arietinum bands. All the species, exceptCicer arietinum andCicer judaicum, possessed some typical bands in their protein profiles in the sense that no one was found at that particularRf in other species. As regards the similarity indices between hybrids and their respective parents it was found that each cross showed more than 50% homology with their parents. On the basis of seed protein profile,Cicer reticulatum seemed to be the most suitable for wild progenitor ofCicer arietinum. The difference between the profiles ofCicer judaicum andCicer pinnatifidum supported the idea that they are indeed two separate species.

    • Airborne fungal spores at Nagarjunanagar

      P Siva Sankara Rao K V Mallaiah

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      Airborne fungal flora of Nagarjunanagar was studied by using vertical cylinders for a period of two years, from 1st January 1982 to 31st December 1983 at 12 m height and for one year (during 1982) at 1 m height. Out of 75 fungal spore types identified, only 10–30 types were observed on more than 200 days in a year.Cladosporium was the dominant type and contributed more than 25% to the total counts. Aspergilli,Alternaria, Periconia andNigrospora were the other major spore types. The total airborne fungal spora showed a distinct seasonal peak in winter at 1 m and at 12 m a summer peak was observed during 1982 in addition to the winter peak. Circadian rhythms were recorded for 18 spore types by using rotorod samplers.

    • Ammonium accumulation and glutamine synthetase activity in C3 and C4 plants

      M Maheswari T V R Nair Y P Abrol

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      Glutamine synthetase activity was found to be several fold higher in the leaves of a few C3 as compared to C4 plants. Differences in NH4+ levels were marginal. Methionine sulphoximine inhibition of glutamine synthetase resulted in increased in NH4+ levels more in wheat than in sorghum. The decrease in methionine sulphoximine induced accumulation of free NH4+ by photorespiratory inhibitors, isonicotinic acid hydrazide and α-hydroxy methane pyridine sulphate was also several fold higher in wheat than in sorghum. Feeding of glycine and glycolate, intermediates of photorespiration, showed the presence of active glycine decarboxylation system in sorghum but the metabolism of glycolate was more efficient in wheat. Higher glutamine synthetase activity in C3 plants may be a necessary adaptation to a higher photorespiratory NH4+ production and explain the similar or higher N losses in C4 as compared to C3 plants. These results also support the hypothesis that glutamine synthetase is important in the assimilation of photorespiratory ammonia.

    • Chemotaxonomic studies on some members of Anacardiaceae

      I Umadevi M Daniel S D Sabnis

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      Nineteen taxa belonging to 13 genera of the Anacardiaceae have been screened for leaf flavonoids, phenolic acids, saponins, tannins, alkaloids and iridoids. The family characteristically contains highly hydroxylated compounds like myricetin and gallic acid. It is also rich in proanthocyanidins and flavonols such as quercetin, kaempferol and their methoxylated derivatives. Tannins are common, saponins rare and alkaloids and iridoids are absent. The chemical differences among the various tribes are not very pronounced. However, the tribe Mangiferae does not contain any flavone whereas the tribe Spondieae is comparatively rich in these compounds. The tribes Rhoideae and Semecarpeae are similar in nany chemical features. The separate identity ofChaerospondias away fromSpondias is also established in the light of chemical evidences.

    • Influence of rice crop canopy on growth and nitrogen fixation of water fernAzolla pinnata

      D P Singh P K Singh

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      Effect of the rice crop canopy was studied as regards the availability of solar radiation toAzolla (Azolla pinnata R Brown) and its growth and nitrogen fixation while using late inoculation of 0·5 or 1 t fresh fronds/ha during both wet and dry seasons. The higher leaf area index of rice due to increasing rates of fertilizer-N application caused more shading to theAzolla plants and reduced their biomass and fixed nitrogen, irrespective of the season. The biomass and nitrogen content ofAzolla were higher using an inoculum of 1 t/ha than using 0·5 t/ha.Azolla growth and fixed nitrogen in treatments of 40 and 80 kg N/ha urea were comparatively higher when rice seedlings were transplanted with double narrow-row spacing than that of normal spacing.

    • Pattern of immobilization and release of nitrogen in decomposing leaf litter in Himalayan forests

      V P Upadhyay

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      The nitrogen dynamics in decomposing leaf litter, incubated on different forest sites were observed for a two year period. There existed an inverse relationship between the per cent dry matter remaining and its nitrogen concentration (r=−0·713 to −0·966). Litter, placed at sal, pine-mixed broadleaf and mixed oak forest sites showed larger slopes (showing greater weight loss per unit of nitrogen immobilization) compared to pine and mixed oak-pine forest sites. The magnitude of immobilization of nitrogen was different among species at different forest sites. The decomposition constant (k) for organic matter ranged from −1·29 to −4·61 and for N release −1·05 to 3·91. Analysis of variance indicated significant differences in N concentration due to days, species and species × days interaction (P<0·01).

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