Study on chloroplast ultrastructure, photosynthetic pigments, and chlorophyll fluorescence characteristics of leaf color mutants in Dendrobium officinale Kimura et Migo

The naturally mutated white-green chimera mutant (‘TP-MA’) and space-mutated green-yellow chimera mutant ('TP-MG’) of Dendrobium officinale (‘TP35’) were used as research materials. We investigated changes in chloroplast ultrastructure, photosynthetic pigment content, and chlorophyll fluorescence kinetic parameters of leaves after treatment with different light intensities (0, 50, 100 μmol·m^-2·s^-1), and clarified the differences in photo-synthetic characteristics between leaf color mutants and normal plants. Results showed that the chloroplast morphology of ‘TP-MA’ and ‘TP-MG’ both had a certain degree of deletion. The chloroplasts were unevenly distributed and irregular, and the basal layer structure was incomplete and loosely arranged, which was basically consistent with phenotypic traits. The photosynthetic pigment content and chlorophyll fluorescence parameters F_v/F_m， Φ_PSⅡ and F_v'/F_m' of ‘TP-MA’ were significantly lower than those of ‘TP35’, but the chlorophyll quenching coefficients (NPQ and q_P) were relatively higher. The photosynthetic pigment content and chlorophyll fluorescence parameters of ‘TP-MG’ were lower than those of ‘TP35’, but the differences were not significant, and it exhibited a certain adaptability to strong illumination (100 μmol·m^-2·s^-1). Thus, results showed that under different light intensities, the chloroplast structure and photosynthetic physiological indices of the D. officinale mutants changed to varying degrees and had certain effects on the chlorophyll content and fluorescence parameters of the plants. Too low or too high light intensity was not conducive to the normal growth of the plants.