We examined the effects of temperature and photoperiod on metabolic thermogenesis and the thermogenic characteristics of brown adipose tissue in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus), the dominant species of small mammals in the alpine meadow ecosystems on the Qinghai-Tibetan Plateau. Pikas and voles were acclimated in the following groups: (1) Long day-warm temperature (16L:8D, 23 degrees C) (2) Long day-cold temperature (16L:8D, 5 degrees C), (3) short day-warm temperature (8L:16D, 23 degrees C), and (4) short day-cold temperature (8L:16D, 5 degrees C). Both temperature and photoperiod were important environmental cues for changes in thermogenesis for both species. Low temperature and short photoperiod induced increases in metabolic rate, nonshivering thermogenesis (NST), mitochondrial protein contents of brown adipose tissue, and cytochrome C oxidase activity of brown adipose tissue mitochondria in both species. Plateau pikas were more sensitive to cold (79% of the total NST response) than to short photoperiod (21%), while root voles were more sensitive to short photoperiod (60% of the total NST response) than to cold (40%), although cold clearly enhanced thermogenesis. Their thermogenic characteristics correlated with their preferred habitats: plateau pikas are found mainly in more exposed microhabitats in open sunny meadow, while root voles live in more sheltered microhabitats in relatively closed shrub. Our results also showed that temperature and photoperiod combined induce thermogenic adjustments in both species in seasonal acclimatization in their alpine meadow macrohabitat.
The current experiments were designed to determine the diurnal carbon partitioning among sorbitol, sucrose, and starch in mature apple (Malus domestica Borhk. cv. Gala) leaves and to determine whether photoperiod altered photosynthate partitioning among carbohydrates. Sorbitol accounted for > 80% of newly fixed 14C-labelled carbohydrate during the light period. Forty-seven percent of sorbitol that had accumulated at the end of the light period disappeared during the dark period. As photoperiod increased from 1 to 10 h, sorbitol, glucose, fructose, and starch concentrations in mature apple leaves increased, but were stable from 10 to 14 h. Sucrose concentration, on the other hand, decreased slightly as photoperiod increased. As a result, sorbitol to sucrose ratios increased from 2 in the 1-h photoperiod to 5 in the 10-h photoperiod. The relative partitioning of 14C into sorbitol increased, whereas the partitioning into sucrose, glucose, and fructose decreased as photoperiod increased from 1 to 10 h. Our results suggest that longer photoperiods favoured sorbitol over sucrose accumulation while shorter photoperiods favoured sucrose over sorbitol synthesis. The observed changes in sorbitol and sucrose concentrations with changes in photoperiod may result from different rates of synthesis and export.
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