WATER-STRESS AND PHOTOINHIBITION IN ACCLIMATIZATION OF ROSA-HYBRIDA PLANTLETS

Micropropagated Rosa hybrida plantlets were simultaneously rooted and acclimatized under 100 and 200 mu mol m(-2) s(-1) light for 2 wk. At t he end of the first week of acclimatization, the plantlets were transf erred onto a low water potential medium (from -0.06 MPa to -0.3 MPa). Dry weight was decreased by increased light and low water potential. P hotoinhibition of photosynthesis, expressed as a decrease in Fv/Fm rat io and Phi PSII and an increase in 1 - qp, occurred in plants grown un der 200 mu mol m(-2) s(-1). When high light (200 mu mol m(-2) s(-1)) a nd water stress were applied simultaneously, their effects on chloroph yll fluorescence parameters depended on stress duration; after 1 d of water stress, photoinhibition was more pronounced; after 7 d of stress , Fv/Fm ratio and Phi PSII were higher than after 1 d of stress; photo inhibition was reduced. This suggests that after a 1-d stress, the eff ect of mater stress alone included a superimposed effect of photoinhib ition to which the water-stressed plants were sensitized; after ? d, p lantlets had adapted to water stress. The photoprotective effects unde r high light might result in energy dissipative mechanisms linked to p hotochemical and nonphotochemical quenching other than CO2 fixation.