The oxygen supply to thermogenic flowers

Area of Science:

• Plant Physiology
• Biochemistry
• Ecology

Background:

• Thermogenic flowers generate significant heat through intense respiration, with oxygen consumption rates (Ṁo2) potentially exceeding those of most plant and animal tissues.
• Understanding the limits of oxygen supply to these tissues is crucial for comprehending their thermogenic capacity.

Purpose of the Study:

• To investigate the oxygen (O2) diffusion limitations in the respiration of thermogenic flowers.
• To quantify the relationship between oxygen consumption rates (Ṁo2) and oxygen pressure (Po2) in different thermogenic plant species.
• To introduce and apply the 'Regulation Index' as a novel tool for assessing O2 dependence in respiration.

Main Methods:

• Measuring oxygen consumption rates (Ṁo2) in intact flowers across a range of oxygen pressures (Po2).
• Quantifying O2 diffusion limitations using the 'Regulation Index' and 'Critical Po2'.
• In-situ measurement of internal O2 distribution within thermogenic tissues using O2-sensitive fiber optics.

Main Results:

• The highest respiration rates in some thermogenic flowers are limited by the capacity of the O2 diffusion pathway, becoming diffusion-limited in atmospheric air.
• Male florets of Arum concinnatum exhibit the highest mass-specific Ṁo2 and are severely diffusion-limited.
• Symplocarpus renifolius spadices show diffusion limitation only at maximal Ṁo2, while Nelumbo nucifera flowers and Arum appendix are not diffusion-limited in air.
• Internal O2 measurements reveal complex diffusion pathways, with O2 supply originating from both tissue surfaces and the peduncle pith.

Conclusions:

• Oxygen diffusion can limit the intense respiration of thermogenic flowers, particularly in species with high mass-specific oxygen consumption rates.
• The 'Regulation Index' provides a quantitative measure of O2 dependence, complementing the 'Critical Po2'.
• Complex internal O2 diffusion pathways contribute to meeting the respiratory demands of thermogenic tissues.