Chlorophyll Fluorescence as a Tool to Assess the Regeneration Potential of African Violet Leaf Explants

Abstract

Micropropagation of many ornamentals has enabled their efficient commercialisation and many problems have been solved by the elaboration of adequate culture protocols. Nevertheless, a non-destructive technique for monitoring the developmental progress of explants would be desirable. The present study focussed on the applicability of chlorophyll fluorescence in leaf explants of African violet (a Saintpaulia ionantha × confusa – hybrid) explanted onto Murashige and Skoog basic medium. The explants that survived on the medium without additional phytohormones had the capacity to develop further into two different kinds of explants: light green explants, characterized by a non-regular size growth and stiffer appearance, and dark green explants capable of organogenesis. Compared to the source leaves of African violet plants, explants were characterized by reduced chlorophyll (Chl) and carotenoid (Car) contents as well as a tendency towards a higher Car/Chl ratio. The Chl a/b ratio decreased significantly in the light green explants. A reduction of maximum quantum efficiency of photosystem II (F_v/F_m) accompanied by a high percentage (> 50%) of thermal energy dissipation as a consequence of an elevated light intensity (800 µmol m^-2 s^-1 quanta) indicated photoinhibition in the light green explants, whereas in the dark green explants the largest percentage (> 50%) of the light energy was dissipated into the fraction of photon energy trapped by ‘closed’ photosystem II reaction centres. These results suggest that the capacity of organogenesis of leaf explants of African violet can be monitored using chlorophyll fluorescence, because it is related to modifications of the photosynthetic system.