Effects of micropropagation conditions of rose shootlets on chlorophyll fluorescence

Rosa hybrida plantlets were rooted on solid sucrosed medium (MS) under an i rradiance (PPFD) of 45 mu mol m(-2) s(-1) or on liquid hydroponic solution (MH) at 100 mu mol m(-2) s(-1). Then all plantlets were acclimated without sucrose under 100 mu mol m(-2) s(-1) PPFD. After 7 d in rooting stage, the ratio of variable over maximal chlorophyll fluorescence (F-v/F-m) was signi ficantly higher for plants grown in MH than in MS and hence the higher irra diance at this stage of growth had no photoinhibitory effect. The radiant e nergy was used by the photochemical process and also by photoprotective mec hanisms of photosystem 2, expressed by increases in the rates of electron f lux, net photosynthesis, and non-photochemical quenching. This effect on F- v/F-m, was maintained during three weeks in acclimation phase. The resistan ce of plantlets increased as new leaves formed, and after six weeks in accl imation, there was no difference between the two conditions. The study unde r higher irradiance (100, 150, or 300 mu mol m(-2) s(-1)) indicated that ph otoinhibition might take place at 300 mu mol m(-2) s(-1) whatever the growt h conditions.