Ultrastructure, CO2 Assimilation and Chlorophyll Fluorescence Kinetics in Photosynthesizing Glycine max Callus and Leaf Mesophyll Tissues

Abstract

The ultrastructural and functional features of photosynthesizing callus cells are poorly known. Electron microscopy studies on green, compact Glycine max calluses have shown that they are composed of photosynthesizing cells characterized by clear ultrastructural signs of senescence. Studies on chlorophyll fluorescence and CO2 assimilation kinetics have shown that such cells were still able to maintain photosynthesis but could not compensate for the respiratory CO2 uptake. Having a one-step CO2 assimilation kinetics, photosynthesis in calluses differed from photosynthesis in leaves, which had a two-step CO2 assimilation kinetics. In contrast to leaves, the fluorescence induction curves in G. max calluses strongly differed in shape depending on the color of actinic light (red or blue). Red (in contrast to blue) light excitation did not lead to CO2 assimilation in the calluses, thus suggesting anoxygenic photosynthesis in this case. In particular, the data obtained indicate that the actinic light spectrum should be considered when cultivating calluses for micropropagation of plants and for callus tissue research.