In situ measurements of oxygen production and consumption using paramagnetic fusinite particles injected into a bean leaf

Abstract

Photosynthetic oxygen production and respiratory oxygen consumption in the interior of a bean leaf ( Vicia faba) were monitored by following the amplitude of the electron paramagnetic resonance spectra of coal derivative particles (fusinite) injected into a leaf. We observed the explicit decrease in oxygen concentration due to respiration in the dark, and the light-induced oxygen production (about 2-fold increase in the oxygen partial pressure) only in the case of a closed water-filled chamber which prevented oxygen exchange with the surrounding atmosphere. However, under normal physiological conditions, when the sample was exposed to air (a leaf in the open holder) we did not observe any significant changes in the level of the oxygen partial pressure inside the leaf, neither in the dark nor during illumination. This observation, together with our earlier measurements of oxygen concentration in the aqueous phase of the leaf interior with the microscopic spin-label probes (Ligeza, A., Wisniewska, A. Subczynski, W.K., and Tikhonov, A.N. (1994) Biochim. Biophys. Acta 1186, 201–208), has led us to the conclusion that the ventilation of the leaf interior appears to be sufficient for maintaining the oxygen partial pressure practically on the same level, both in the dark and in the course of intensive light-induced production of oxygen by chloroplasts. Such ventilation should protect leaf tissues against the dangerous increase in the level of oxygen evolved by chloroplasts.