Respiration, thermogenesis, and thermoregulation of Victoria cruziana flowers
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The flowers of Victoria cruziana bloom over two consecutive nights, during which time they dramatically increase their metabolic rate (MR) to raise their internal temperature by 7–10◦C above air temperature.To investigate the metabolic cost of thermogenesis in V. cruziana and determine the role of ambient temperature and developmental phase on floral temperature, flowers growing in an outdoor pond were measured in situ by placing them within a temperature-controlled, flow-through respirometry chamber.The flower’s metabolic rate and temperature were recorded simultaneously over the 40 h of their two-night flowering cycle. During this time, flowers were exposed to either a normal (cool nights, warmdays) or an inverted (cool days, warm nights) thermal regime. V. cruziana flowers exposed to normal daily temperature variation showed a large increase in MR on the first evening that declined steadily over the subsequent days. Exposure to experimentally-manipulated cooler daytime temperatures did not stimulate flowers to increase their MR, indicating a lack of thermoregulatory capacity. However,rewarming a cooled flower on the second evening caused a large increase in MR, but not in temperature.This increase appeared to arise due to the delayed consumption of energy reserves that would otherwise have been used over the course of the preceding day, coupled with a more open, and less insulated, floral chamber. The pattern of thermogenesis shown by V. cruziana is unlike that of its closest relative, V.amazonica, which shows large increases in MR and temperature over both nights of flowering.