Cytokinins (CKs) are one of the main regulators of in vitro growth and development and might affect the
developmental state and function of the photosynthetic apparatus of in vitro shoots. Effects of different
cytokinin regimes including different types of aromatic cytokinins, such as benzyl-adenine, benzyladenine
riboside and 3-hydroxy-benzyladenine alone or in combination were studied on the capacity
of the photosynthetic apparatus and the pigment content of in vitro apple leaves after 3 weeks of culture.
We found that the type of cytokinins affected both chlorophyll a and b contents and its ratio. Chlorophyll
content of in vitro apple leaves was the highest when benzyl-adenine was applied as a single source of
cytokinin in the medium (1846–2176 g/1 g fresh weight (FW) of the leaf). Increasing the concentration
of benzyl-adenine riboside significantly decreased the chlorophyll content of the leaves (from 1923
to 1183 g/1 g FW). The highest chl a/chl b ratio was detected after application of meta-topolin (TOP)
at concentrations of 2.0 and 6.0 M (2.706 and 2.804). Chlorophyll fluorescence was measured both in
dark-adapted (Fv/Fm test) and in light-adapted leaf samples (Yield test; Y(II)). The maximum quantum
yield and efficiency of leaves depended on the cytokinin source of the medium varied between 0.683 and
0.861 (Fv/Fm) indicating a well-developed and functional photosynthetic apparatus. Our results indicate
that the type and concentration of aromatic cytokinins applied in the medium affect the chlorophyll
content of the leaves in in vitro apple shoots. Performance of the photosynthetic apparatus measured
by chlorophyll fluorescence in the leaves was also modified by the cytokinin supply. This is the first
ever study on the relationship between the cytokinin supply and the functionability of photosystem II
in plant tissue culture and our findings might help to increase plantlet survival after transfer to ex vitro
conditions.