Assimilation images of leaves of Glechoma hederacea: Analysis of non-synchronous stomata related oscillations

Abstract

An experimental system is described to analyze the spacial distribution of leaf assimilation from chlorophyll-a fluorescence images. Fluorescence parameters were determined with a digitized camera system pixel-by-pixel and calibrated against the assimilation rate from integrated gas exchange. The approach is an extension of the work by P.F. Daley, et al. (1989, Plant Physiol. 90, 1233–1238) and allows the visualisation of assimilation images of leaves with high resolution. With a leaf of Glechoma hederacea L., assimilation images were taken at short time intervals during stomata-related oscillations of the assimilation rate (period about 13 min) over a time period of more than 3 h. Mathematical pixel-by-pixel analysis of images shows nearly Gaussian distribution of assimilation values around a minimum (5 μmol CO2 · m−2 · s−1) and maximum (13 μmol CO2 · m−2 · s−1) peak value during oscillations. Synchronous oscillations, initiated by rapid changes in gas composition, changed into non-synchronous oscillations, due to slight local variations in the period. As a consequence, the oscillation of gas exchange (H2O and CO2) died out whilst leaf assimilation continued to oscillate non-synchronously and patchily. Patchy distribution of frequencies largely followed gas-exchange compartmentation (‘alveoli’), whilst non-homogeneous distribution of the amplitude was on a larger scale, with a decrease in amplitudes from the leaf base towards distal areas. The data are discussed considering the framework of physiological processes involved in stomatal control.