Morphological, physiological and oxidative stress markers during acclimatization and field transfer of micropropagated Tuberaria major plants

Tuberaria major (Willk.) P. Silva and Rozeira is a critically-endangered rock rose species endemic to Portugal. Because the species needs to be preserved, this study evaluated the morphological and physiological traits of micropropagated T. major plants during acclimatization and field transfer. There were no significant differences between wild and micropropagated plants in the field, although the latter underwent significant changes during acclimatization. Leaf pubescence and leaf mass per area increased during acclimatization whereas the chlorophyll content and chlorophyll/carotenoid ratio declined to eventually match those of wild plants. Stomatal conductance (g(s)) and transpiration rates (E) also declined substantially during acclimatization, thus preventing uncontrolled wilting. Photosynthetic rate (P-N) was initially negative but increased during the later stages of acclimatization. Maximum quantum yield of PSII (F-v/F-m) remained constant at 0.78-0.85, showing that the plants were healthy and unstressed. PSII quantum efficiency (I center dot(PSII)) was initially low but increased during acclimatization along with photosynthetic performance as the energy partitioning in PSII was adjusted. This was balanced by the decline in non-regulated energy dissipation (I center dot(NO)) from an initially high value. Electrolyte leakage and malondialdehyde content remained constant at similar levels in both groups of plants, but H2O2 levels were higher in the field, perhaps indicating the early induction of antioxidant defense systems. The present study shows that T. major has enough phenotypic plasticity to adapt to changing environments and that the procedure described herein can be used for the restoration and preservation of this species