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.].
Potato tubers, Solanum tuberosum L. cv. Bintje were stored at 4 or 20 °C. A segment of parenchyma with a bud was cultívated in vitro, in order to study the growth of plantlets according to the storage temperature and the atmosphere composition in vessels. The conservation temperature had no effect on the shoot length, the leaf area and the leaf number. On the other hand, the atmosphere composition in vessels modifíed the morphology. The plantlets cultívated in non-sealed vessels were more developed than the plantlets cultívated in hermetically dosed tubes. The photosynthetic potentíals were 4.7 times higher for the plantlets coming from the tubers stored at 20 °C than for the plantlets coming from the tubers stored at 4 °C. These potentíals were 1.7 times higher when the plantlets were cultívated in non- hermetícally dosed tubes than in hermetically dosed ones. So a conservation of tubers at 20 °C and a culture in non-enclosed vessels seemed to be the suitable conditions for the micropropagation of potatoes in viiro. Moreover, this culture type could improve the acdimatízatíon.
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.].
The rooting of shoots of micropropagated Rosa hybrida cv. Madame Delbard was conducted on MS medium with 30 kg m-3 sucrose or on hydroponic medium (containing less mineral salts), under higher photosynthetic photon flux density (PPFD) (100 in comparison with 45 µmol m-2 s-1) and flushed by ambient air [AC, 340 µmol(CO2) mol-1] or by CO2-enriched air (EC, 2 500 µmol mol-1) and lower relative humidity (80-90 % vs. 96-99 %). This cultivation led to plantlets with longer roots and adventitious root formation. Net photosynthetic rate and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activities, RuBPCO/phosphoenolpyruvate carboxylase activities ratio, and starch accumulation increased under these conditions. After 14 d, plantlets had functional stomata and could be acclimated on open benches without gradual decrease in relative humidity. The percentage of survival was higher when the rooting took place in EC than in AC. However, the advantage acquired during rooting phase by plantlets cultured in liquid medium was not maintained after 4 weeks of acclimatisation. and C. Genoud ... [et al.].
During the growth cycle of micropropagated Juglans regia plantlets, phosphoenolpyruvate carboxylase (PEPC) activity was aiways higher than initial ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity. The ratio of PEPC/RuBPCO activities was higher during the first part of the exponential phase of growth and lower during the second part. The variations of PEPC activity were parallel to the soluble protein content and the variations of initial and total RuBPCO activities were parallel to the chlorophyll accumulation.