Rosa hybrida plantlets were rooted on solid sucrosed medium (MS) under an irradiance (PPFD) of 45 μmol m-2 s-1 or on liquid hydroponic solution (MH) at 100 μmol m-2 s-1. Then all plantlets were acclimated without sucrose under 100 μmol m-2 s-1 PPFD. After 7 d in rooting stage, the ratio of variable over maximal chlorophyll fluorescence (Fv/Fm) was significantly higher for plants grown in MH than in MS and hence the higher irradiance at this stage of growth had no photoinhibitory effect. The radiant energy was used by the photochemical process and also by photoprotective mechanisms of photosystem 2, expressed by increases in the rates of electron flux, net photosynthesis, and non-photochemical quenching. This effect on Fv/Fm was maintained during three weeks in acclimation phase. The resistance of plantlets increased as new leaves formed, and after six weeks in acclimation, there was no difference between the two conditions. The study under higher irradiance (100, 150, or 300 μmol m-2 s-1) indicated that photoinhibition might take place at 300 μmol m-2 s-1 whatever the growth conditions. and C. Genoud ... [et al.].
The symbiotic association of endophyte fungus, Neotyphodium lolii, and ryegrass improves the ryegrass resistance to drought. This is shown by a 30 % increase in the number of suckers in infected plants (E+), compared to plants lacking endophyte (E-), and by a higher water potential in the E+ than E- plants. The E+ plants have higher stomatal conductance (gs), transpiration rate, net photosynthetic rate (PN), and photorespiratory electron transport rate than the E- plants. The maximal photochemical efficiency (Fv/Fm) and the actual photochemical efficiency (ΦPS2) are not affected by the endophyte fungus. The increase in PN of the E+ plants subjected to water stress was independent from internal CO2 concentration. An increased PN was observed in E+ plants also in optimal water supply. Hence the drought resistance of E+ plants results in increased gs, PN, and photorespiratory electron transport rate. and C. Amalric ... [et al.].