The effect of in vitro culture conditions on the pattern of photoinhibition during acclimation of gardenia plantlets to ex vitro conditions

We tested the effect of growing conditions during micropropagation on the f ast kinetics of chlorophyll (Chl) fluorescence of Gardenia jasminoides Elli s plantlets during a 4-week acclimation to ex vitro. We studied whether pho toautotrophic growing in vitro produced plantlets with less photoinhibition impairment during acclimation. Of the growing conditions stimulating photo autotrophy in vitro, only loose tube caps had a positive effect, whereas lo w sucrose or sucrose-free content in the medium and high PPFD showed a nega tive effect. Thus, plantlets cultured with 3 % (m/v) of sucrose were subseq uently less photoinhibited throughout acclimation than those cultured with low sucrose (0.5 %) or sucrose-free media. Moreover, at the end of acclimat ion the former plantlets showed F-v/F-m and F-v/F-0 ratios typical of unstr essed ex vitro plants as well as a higher Chi content and ratio of Chls to carotenoids. Plantlets cultured at a photosynthetic photon fluence density (PPFD) of 50 mu mol m(-2) s(-1) also showed a better performance at the end of acclimation than those cultured at a higher (110 mu mol m(-2) s(-1)) PP FD. Thus except in the case of loose-tube closure, gardenia plantlets cultu red in vitro under conventional sucrose concentration and PPFD are the leas t photoinhibited during acclimation. Nevertheless, significant interactions between the in vitro growing factors were observed at the end of acclimati on.