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Inflorescence leaves of citrus (Citrus sinensis L. Osbeck) accumulatecarbohydrate reserves at the beginning of the fruit set period.This effect is mimicked by exogenous GA3 applications in deflorateinflorescences. The effect of the hormone on two processes thatcould result in carbohydrate accumulation, i.e. increased ribulosebisphosphate carboxylase (RuBPCase) activity and changes inthe import/export balance of assimilates in the sprouts, wasstudied. Neither RuBPCase activity nor respiration rates were affectedby the hormonal treatment. On the other hand, blocking of thephloem connections with the rest of the plant induced an increasein carbohydrate contents in the leaves that was proportionallylower in GA3-treated sprouts than in control deflorate inflorescences.This increase was minimal in leaves from inflorescences at laterstages of fruit development. This was in spite of a lower fruitgrowth rate that, in turn, brought about a decrease in totaldry weight of the sprout. In contrast, total dry weight washigher in girdled deflorate inflorescences, whether or not theywere treated with the hormone. The presence of the fruit induceda thickening of the stems of intact inflorescences that wasalso seen in ungirdled GA2-treated sprouts. This increase indry weight per unit length, however, had a different chemicalbasis depending upon whether it was caused by the fruit or thehormone. From these data, the possible causes for the enhancement ofcarbohydrate accumulation in inflorescence leaves, and the involvementof gibberellin in the effect of fruit on the sprouts is discussed. Carbohydrates, Citrus sinensis L. Osbeck, gibberellic acid, girdling, orange, ribulose bisphosphate carboxylase, source-sink 相似文献
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Survival of caddis larvae in relation to their case material in a group of temporary and permanent pools 总被引:3,自引:0,他引:3
1. The occurrence of larvae of Limnephilus coenosus and L. vittatus (Trichoptera) was recorded in 103 rock pools both before and after the dry periods in spring–summer (April–May and July–early August), when a great number of the pools dried out. In early spring, 84% of the pools sampled contained larvae of at least one of the species. Limnephilus coenosus larvae were present in a higher proportion of pools that later dried out than in the permanent ones, while L. vittatus larvae were predominantly found in permanent pools. Larvae of both species were found together in 31% of the inhabited pools.
2. Laboratory experiments, designed to elucidate differential survival under drought conditions, demonstrated that the organic cases of L. coenosus larvae held water more efficiently than did the mineral L. vittatus cases. Full-grown (fifth instar) L. coenosus larvae also survived dry conditions better than did L. vittatus larvae. The higher survival of L. coenosus was due to a combination of drought-resistant case material and a higher survival ability of the larvae themselves.
3. Limnephilus vittatus larvae were restricted by their low capability to withstand desiccation, although case material and food were available for L. vittatus larvae in all pools. Absence of case material and high-quality food in many pools, however, restricted the presence of L. coenosus larvae, but this species did not suffer from heavy mortality because of desiccation and all pool populations of L. coenosus survived until pupation.
4. The differences in species composition in these temporary and permanent pools can be explained by the differential site selection by ovipositing females, as well as by larval survival. The intrinsically greater survival of L. coenosus larvae during drought, together with the water-retaining properties of the cases, allowed this species to exploit stressful and risky habitats, such as temporary pools. 相似文献
2. Laboratory experiments, designed to elucidate differential survival under drought conditions, demonstrated that the organic cases of L. coenosus larvae held water more efficiently than did the mineral L. vittatus cases. Full-grown (fifth instar) L. coenosus larvae also survived dry conditions better than did L. vittatus larvae. The higher survival of L. coenosus was due to a combination of drought-resistant case material and a higher survival ability of the larvae themselves.
3. Limnephilus vittatus larvae were restricted by their low capability to withstand desiccation, although case material and food were available for L. vittatus larvae in all pools. Absence of case material and high-quality food in many pools, however, restricted the presence of L. coenosus larvae, but this species did not suffer from heavy mortality because of desiccation and all pool populations of L. coenosus survived until pupation.
4. The differences in species composition in these temporary and permanent pools can be explained by the differential site selection by ovipositing females, as well as by larval survival. The intrinsically greater survival of L. coenosus larvae during drought, together with the water-retaining properties of the cases, allowed this species to exploit stressful and risky habitats, such as temporary pools. 相似文献
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FERNANDO L. RENAUD IRIS COLON JOSE LEBRON NERIAN ORTIZ FERNANDO RODRIGUEZ CARMEN CADILLA 《The Journal of eukaryotic microbiology》1995,42(3):205-207
ABSTRACT. We have previously reported that a β-endorphin-like substance inhibits phagocytosis in Tetrahymena perhaps by a mu-like opioid receptor. We now report a further characterization of the elements involved in the signal transduction mechanism of this opioid. Affinity chromatography followed by immunoblots of both intracellular extracts and extracellular medium reveal the presence of two main proteins of 64 and 75 kDa. These molecular weights are much higher than that of any known opioid peptide or precursor protein and suggest that we may be dealing with either a novel opioid or with proteins that by chance cross-react with anti-β-endorphin antibody. Nevertheless, when the biological activity of these proteins was tested it was found that they had an effect similar to that of mammalian β-endorphin, namely inhibition of phagocytosis by a naloxone-reversible mechanism. We have probed a size-selected Tetrahymena library with a pro-opiomelanocortin probe and have obtained several positive clones; the sequencing of their inserts should establish whether we are dealing with a bona fide member of the opioid family. Another aspect we have been studying is the G-proteins which appear to be involved in the modulation of phagocytosis. We have found, by means of Western blotting (using an antibody against the conserved GTP-binding region of the α-subunit), two bands of 51 and 59 kDa; no α-subunit of 59 kDa had been reported previously and may represent a novel G-protein. In spite of these differences, the opioid signal transduction mechanism appears to remarkably resemble that present in more complex organisms. 相似文献
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Specimens of Miscellania dentata gen. et sp.n. were collected in Catalunya, the Balearic Islands, and Strait of Gibraltar. They are characterized by an anterior tooth and an incomplete crown of denticles on the tip of the pharynx, short and smooth antennae and cirri, bases of palps separated, and the presence of compound and simple setae. Specimens were found living inside calcareous algal concretions. 相似文献
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JORDI MOYA-LARAÑO PHILLIP W. TAYLOR CARMEN FERNÁNDEZ-MONTRAVETA 《Biological journal of the Linnean Society. Linnean Society of London》2003,78(3):355-364
Signal costs, and associated trade-offs, are widely thought of as fundamental to the evolution and maintenance of reliable signals. Contrasting this view, the amplifier mechanism postulates that signals may be deemed reliable by design rather than by costs. Although the idea is not new, investigation of amplifier signals in nature remains scant. Here we show that displays and body markings on the Mediterranean tarantula, Lycosa tarantula (L.) (Lycosidae), are consistent with interpretation as amplifiers of size and body condition. The size of tibia and abdomen ventral markings (which alternate between dark and pale patterns) presented to rivals during contests are highly correlated with body size and condition, respectively. Abdomen markings have the additional feature of placement on a region especially influenced by abdomen distension and therefore has greater proportional variation than the underlying amplified trait. In spite of the differences in size and in body patterns between spiders of two isolated and ecologically different populations, correlation between body marking and dimensions, and relatively high proportional variation of the abdomen markings, was maintained, probably reflecting the adaptive value of these traits. We conducted a feeding experiment which showed that the abdominal markings enlarged (stretched with abdomen distension) at a higher rate if spiders were provided with more food, further supporting the idea that this marking amplifies body condition. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 355–364. 相似文献