IMAGING OF CHLOROPHYLL-A-FLUORESCENCE IN LEAVES - TOPOGRAPHY OF PHOTOSYNTHETIC OSCILLATIONS IN LEAVES OF GLECHOMA-HEDERACEA

Images of chlorophyll-alpha-fluorescence oscillations were recorded us ing a camera-based fluorescence imaging system. Oscillations with freq uencies around 1 per min were initiated by a transient decrease in lig ht intensity during assimilation at an elevated CO2-concentration. The oscillation was inhomogenously distributed over the leaf. In cells ad jacent to minor veins, frequency and damping rate was high, if there w as any oscillation. In contrast, the amplitude was highest in cells mo st distant from phloem elements (maximal distance about 300 mu m). The appearance of minor veins in oscillation images is explained by a gra dient in the metabolic control in the mesophyll between minor veins an d by transport of sugar from distant cells to phloem elements. The pot ential of fluorescence imaging to visualize 'microscopic' source-sink interactions and metabolic domains in the mesophyll is discussed.