Respiration of thermogenic inflorescences of Philodendron melinonii: natural pattern and responses to experimental temperatures

Abstract

The patterns of temperature and respiratory changes in the protogynous inflorescences of Philodendron melinonii (Araceae) were studied in the field in French Guiana. These are the first respiratory measurements from a member of the large subgenus Philodendron, a group previously thought to lack thermoregulatory inflorescences, in contrast to thermoregulatory Philodendron species of the subgenus Meconostigma. Heating by the male and sterile male florets was strong on the first evening of anthesis when beetles are attracted and the female florets are receptive. Heat production of the inflorescence peaked at approximately 0.9 W and spadix temperature reached approximately 39.5 degrees C, a level somewhat independent of ambient temperature. Thermogenesis continued throughout the night and the next day, but at a lower level, and floral temperatures fell. On the second evening, when pollen was shed, there was a small elevation in respiration and spadix temperature. Responses of cut spadix sections to experimental step changes in ambient temperature resulted in a prompt response in floral temperature and respiration rate in the direction of the change and then a much slower regulatory adjustment in the opposite direction. These responses are consistent with an immediate van 't Hoff effect, followed by up- or down-regulation of thermogenesis. However, the responses required several hours. It is concluded that the male floret tissues possess the same thermoregulatory mechanism of more precise thermoregulatory species, but a combination of small spadix size (that favours heat loss), moderate thermogenic capacity (that limits heating rate), and slow reaction time (that causes long lags between temperature change and the regulatory response) result in poor thermoregulatory performance during the second day.

Thermogenesis, Flowering and the Association with Variation in Floral Odour Attractants in Magnolia sprengeri (Magnoliaceae)

“…In some thermogenic plants, floral temperature is maintained at a constant range, independent of ambient temperature, for a long period throughout anthesis [8],[35],[36]. Floral temperature stability of these plants is achieved by means of physiological thermoregulation [35],[36]. In this study, floral temperature of M. sprengeri changed constantly throughout anthesis and major thermogenic episodes were short, which indicated that M. sprengeri was not thermoregulated.…”

“…Distinct heating patterns have been reported in different thermogenic species [35],[36]. In some thermogenic plants, floral temperature is maintained at a constant range, independent of ambient temperature, for a long period throughout anthesis [8],[35],[36]. Floral temperature stability of these plants is achieved by means of physiological thermoregulation [35],[36].…”

Developmental changes and organelle biogenesis in the reproductive organs of thermogenic skunk cabbage (Symplocarpus renifolius)

“…It was shown that heat is generated from the appendix and male florets in some species, such as Arum maculatum (Bermadinger-Stabentheiner and Stabentheiner, 1995), Arum italicum (Skubatz et al , 1990; Albre et al , 2003), dead horse ( Helicodiceros muscivorus ) (Seymour et al , 2003 a ), and voodoo lily ( Sauromatum guttatum ) (Skubatz et al , 1991), and the male florets in dragon lily ( Dracunculus vulgaris ) (Ito and Seymour, 2005), the male and sterile male florets in Philodendron melinonii (Barabe et al , 2002; Seymour and Gibernau, 2008), and the spadix in skunk cabbage (Ito et al , 2003). It should be noted that in such well-known arum species, heat is generated by the male florets consisting of dense stamens, and not by the female florets consisting of dense pistils.…”

“…Ecological and physiological studies of many arum species have revealed that thermogenesis is positively correlated to their oxygen consumption rate (Seymour and Blaylock, 1999; Seymour and Schultze-Motel, 1999; Seymour et al , 2003 a , b ; Seymour and Gibernau, 2008). The possible involvement in thermogenesis of mitochondrial factors, such as the alternative oxidase (AOX), the uncoupling protein (UCP), and the reduction levels of ubiquinone (UQ), has also been studied (Wagner et al , 1998, 2008; Crichton et al , 2005; Sluse et al , 2006; Onda et al , 2007; Ito-Inaba et al , 2008 a , b ).…”

Thermal clamping of temperature-regulating flowers reveals the precision and limits of the biochemical regulatory mechanism

“…The slope of the line that relates floral temperature to ambient temperature theoretically ranges from 1 (no regulation) to 0 (perfect regulation). By this measure, data from intact, thermoregulating flowers in the field reveal a range of apparent thermoregulatory precisions: Nelumbo nucifera (0.17, , Philodendron selloum (0.18 in the peak heating phase and 0.52 in the longer plateau phase, Nagy et al 1972;Seymour 1999), Philodendron melinonii (0.33, Seymour and Gibernau 2008), Dracunculus vulgaris (0.59, Seymour and SchultzeMotel 1999), and Symplocarpus foetidus (0.29, Knutson 1974); 0.51 (Seymour and Blaylock 1999). Inflorescences of S. foetidus exposed to constant temperatures (CTs) until equilibrium is reached reveal a slope of 0.09 and the most precise so far recorded (Seymour 2004).…”