Rooting affects the photosystem II activity: in vitro and ex vitro studies on energy hybrid sorrel

Rumex tianschanicus × Rumex patientia is a high-biomass-yielding plant suitable for fuel and biogas production. The protocol of the hybrid sorrel micropropagation was used to study the changes in the photosystem II (PSII) activity as well as to analyse the ultrastructure of the chloroplasts. The lowest effective PSII quantum yield [Y(II)] and an apparent electron transport rate of PSII [ETR(II)] were observed for adventitious shoots that had been regenerated in vitro, before rooting. These fluorescence parameters were higher and similar for both the leaves of the same adventitious shoots that had been rooted under in vitro conditions and for the shoots that had been acclimated and grown in ex vitro conditions. The analysis indicated that the PSII activity strongly depends on the formation of properly functioning roots and that in vitro or ex vitro culture conditions are, at least to some degree, less important. TEM analysis revealed that chloroplasts from plants rooted in vitro were sufficiently mature and acclimatization processes have less impact on their development. This is the first report concerning the analysis of PSII activity and the ultrastructure of the chloroplasts at all of the stages of micropropagation, i.e. adventitious shoot formation in vitro, rooting in vitro and acclimation to ex vitro conditions. It strongly indicated that rooting under in vitro conditions, rather than the acclimation to ex vitro conditions, plays a key role in the development of a completely functional photosynthetic apparatus in hybrid sorrel.