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Thursday 19 September 2013

Hd Flower Wallpapers

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At low ambient temperatures during the night, heat production by the flower rises to about 1 Watt. On hot days, flower temperature drops as much as 10°C below effective ambient temperature by evaporative cooling. Respiration clearly responds to ambient temperature, not time of day (Seymour et al., 1998). However, it is apparent that the flowers do not detect ambient temperature directly, but only respond to changes in the temperature of their own cells. Close examination of the data reveals that there is a small decrease in flower temperature that occurs with falling ambient temperature. Therefore is it clear that respiration in these species is negatively related to tissue temperature, opposite to the expected positive relationship between temperature and rates of biochemical reactions.

The physiological thermoregulatory control mechanism is not yet known. It is certain, however, that it is unlike the mechanism in birds and mammals that relies on a complex nervous interaction between temperature receptors, central nervous system processing and finally control of organs that affect rates of heat production and loss. In the plants, the regulation must occur at a strictly biochemical or molecular level. One clue is that the rate of AOX-mediated respiration of mitochondria isolated from Arum maculatum increases with temperature to a peak at about 32oC, above which it falls steeply (Wagner et al., 2008). Control of AOX activity has been shown to respond to changes in the disulfide bridge that binds the two halves of the AOX dimer (Umbach and Siedow, 1993) or activation by α-keto acids (Millar et al., 1993). However neither of these mechanisms seems to occur in A. maculatum, and thermoregulation has been proposed to result from an interaction between the thermal profiles of the AOX and dehydrogenases earlier in the metabolic pathway (Wagner et al., 2008).

Temperature regulation is an adaptation shared by homeothermic (warm-blooded) birds and mammals and many groups of flying insects. High and stable body temperatures permit them to be active in cold environments. Compared to thermally compliant poikilotherms (cold-blooded animals), animal homeotherms are able to find more food, better compete for territory and mates, and reproduce faster—all evolutionarily advantageous in many circumstances. So homeothermy in immobile flowers is at first difficult to explain. Temperature regulation is not a requirement to enhance the vaporization of scents; unregulated high temperatures would suffice, as they do in the appendix of Dracunculus vulgaris inflorescences (Seymour and Schultze-Motel, 1999). However, we now have evidence that thermoregulation in the flowers is a service offered as a reward to insect visitors (Seymour et al., 2003b). Thermoregulatory flowers are often pollinated by large flying insects, chiefly beetles, which remain within the flower for about 24 h. For example, large scarab beetles congregate in the evening inside the floral chamber of Philodendron solimoesense in lowlands French Guiana, and they are active throughout the night, consuming floral parts and mating avidly. Temperature regulation is an adaptation shared by homeothermic (warm-blooded) birds and mammals and many groups of flying insects. High and stable body temperatures permit them to be active in cold environments.

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