• Volume 100, Issue 3

      June 1990,   pages  153-210

    • Nutrient acquisition by fungi—the relation between physiological understanding and ecological reality

      D H Jennings

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      The measure of the ability of a fungus to acquire a soluble nutrient is given by the flux of that nutrient across the plasma membrane. The determination of fluxes into fungi, the factors which govern the magnitude of a flux, particularly external substrate concentration, and pH are discussed. The difficulties of determining fluxes in the natural environment are considered. Reference is made to studies on unicells, bacteria and fungi, in enhancing understanding of the relationship between growth and the flux of a nutrient into a fungus. The artificial system is considered to be a valuable step between laboratory experiment and ecological reality. Likewise, the generation of mathematical models relating flux of nutrient to growth can provide an insight as to the significance of various physiological processes influencing growth of a fungus in its natural environment.

    • Degradation of α-, β- and γ-isomers of hexachlorocyclohexane by rhizosphere soil suspension from sugarcane

      S K Sahu K K Patnaik N Sethunathan

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      A suspension of soil from the rhizosphere of sugarcane plants grown from sugarcane setts treated with a commercial formulation of hexachlorocyclohexane effected exceptionally rapid degradation of α- and γ-isomers of hexachlorocyclohexane in a mineral salts medium under aerobic conditions. β-Hexachlorocyclohexane was also degraded, but slowly. No degradation of γ-hexachlorocyclohexane occurred in the medium inoculated with sterilized sugarcane rhizosphere soil suspension. During degradation, about 40% of the14C from the ring-14C-γ-hexachlorocyclohexane was released as CO2 indicating ring cleavage. A bacterium,Pseudomonas sp., isolated from hexachlorocyclohexane-treated sugarcane rhizosphere soil readily degraded γ-hexachlorocyclohexane added to a mineral salts medium as a sole source of carbon under aerobic conditions. An increase in temperature from 20–25 and 30°C progressively increased the degradation of α- and γ-hexachlorocyclohexane by rhizosphere soil.

    • Interactive effect of NaCl salinity and gibberellic acid on shoot growth, content of abscisic acid and gibberellin-like substances and yield of rice (Oryza sativa L. var GR-3)

      L Prakash G Prathapasenan

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      When rice (Oryza sativa L. var GR-3) plants were subjected to salt stress (12 dS/m) the extension growth and dry weight of the shoot system as well as the content of chlorophyll and gibberellin-like substances were found to be markedly reduced. Contrarily, the level of abscisic acid in the shoot system registered a rapid and massive increase in response to salinity. Compared to control, salt stressed plants showed higher concentration of Na+ and Cl and lower concentration of K+ in the leaf tissue. Salinization also resulted in a considerable reduction in grain yield. Exogenous application of gibberellic acid (10 ppm) significantly increased the growth and yield of salt stressed plants. Gibberellic acid treatment reduced the net accumulation of Na+ and Cl and maintained high level of K+ in the leaves of salinized plants. A significant fall in the content of abscisic acid and a marked increase in the amount of chlorophyll were also noticed in salinized plants in response to gibberellic acid administration. These results suggest that gibberellic acid improved the growth and yield of stressed rice plants presumably by hormonising the ionic status of the plants as well as by modulating the endogenous level of abscisic acid.

    • Pollen analysis ofApis cerana andApis florea honeys from Adikmet area, Hyderabad

      T P Kalpana Khatija Fatima C G K Ramanujam

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      Pollen analysis of 3 squeezed honey samples (one ofApis cerana varindica and two ofApis florea) and 160 pollen loads (100 ofApis cerana, 45 ofApis florea I and 15 ofApis florea II) has been carried out with a view to identify the bee forage plants and to evaluate the sources of pollen to honey bees at Adikmet area, Hyderabad.

      All the 3 honey samples were found to be unifloral. WhileMangifera indica (68·7%) formed the predominant pollen type inApis cerana sample,Tridax procumbens (62%) andPhoenix sylvestris (61%) constituted the predominant pollen types inApis florea I and II samples respectively. Altogether 24 pollen types referable to 20 families have been recorded. Based on the absolute pollen counts, the 3 samples are referable to group V of International Commission for Bee Botany. Out of 160 pollen loads studied, 137 were found to be unifloral, while 23 were of the mixed type.

    • Pollination ecology ofAlangium lamarkii (Alangiaceae)

      T Byragi Reddy Ch Aruna

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      Alangium lamarkii flowers during February–April. Buds are opening around the clock and offer pollen and nectar as the reward to their insect visitors. The breeding system incorporates both geitonogamy and xenogamy. Flowers are large, hermaphrodite, essential organs are centrally situated, stigma longer than anthers. Nectar contains glucose, sucrose and fructose. The glucose being dominant. Sugar concentration ranges from 25–29%. Protein and amino acids were present. Pollen-ovule ratio is 27300∶1.

      Altogether 18 insect species were found foraging at the flowers. Of the 18 species of insect foragers bees (Apis florea, Trigona, Amegilla, Ceratina, Xylocopa latipes, Xylocopa pubescens) and wasps (Delta sp.,Rhynchium) promote both geitonogamy and xenogamy. The bees collected pollen as well as nectar. The wasps while foraging for nectar their dorsal side touches the anthers and causes nototribic pollination. The butterflies visit the flowers for nectar only, but the contact between proboscis and the essential organs is unlikely.

    • Numerical and structural inconstancy in the chromosome complements ofBelamchanda chinensis Dc. (Iridaceae)

      A K Srivastava Purnima

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      Chromosome polymorphism inBelamchanda chinensis Dc. of the family Iridaceae, has been explored in detail. The root tip cells exhibited aneusomaty and differences in the morphology of chromosomes. About 70% cells were with 2n=30, 20% cells has 2n=28 and 10% cells were with 2n=32. Critical analysis of 3 typical cells with different chromosome numbers, selected out of several cells studied, exhibited varying proportions of long, medium and short chromosomes and different numbers of metacentric and submetacentric chromosomes. In these cells, while on one hand, all chromosomes could not be grouped in two's on the basis of chromosome morphology, certain chromosome paris were present more than once, on the other hand. The cytological basis of inconstancy in the chromosome complements within the cells of the same tissue and it's significance in the evolution of the vegetatively propagated plants have been discussed.

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