No abstract

Growth characteristics, oxygen exchange, and carbohydrate and chlorophyll contents were determined 30 days after subculturing of single node-derived plantlets of Solanum tuberosum cv Haig cultivated in vitro. Cultivation conditions were: (a) photomixotrophy in closed vessel, (b) photomixotrophy in closed vessel on medium supplemented with silver thiosulfate, (c) photomixotrophy in aerated vessel, (d) photoautotrophy in air, (e) photoautotrophy in C02-enriched air. In photomixotrophic conditions, aeration of the vessel enhanced sucrose utilization and had a positive effect on plantlet growth. In photoautotrophic conditions, growth of the plantlets was slow in air and was strongly enhanced by CO2 enrichment of the atmosphere. Starch to sucrose ratios were higher in plants grown photoautotrophically than in plants grown with sucrose in the medium. Oxygen exchange characteristics on a chlorophyll basis were similar between the plantlets when measured under moderate light, and resembled those of greenhouse plant leaves. In high light, however, plantlets grown photoautotrophically in a C02-enriched atmosphere had higher oxygen exchange rates. We concluded from these results that potato plantlets in vitro in conditions (c), (d), and (e) developed C3-plant photosynthetic characteristics, which were in photoautotrophically grown plantlets comparable to those of field-grown plants.and could be a cause of growth abnormalities during the in vitro stage or during acclimatization.One can expect that achievement of photoautotrophic plant growth or aeration in photomixotrophic culture systems will improve in vitro cultivation efficiency, as well as plantlet behavior (8,14). Nevertheless, information is scarce on the effects of such culture conditions on plantlet physiology. We therefore investigated how culture conditions, i.e. different carbon sources (photomixotrophy and photoautotrophy at two CO2 levels) and confinement status (photomixotrophy with or without gas exchange with the atmosphere), could affect the growth, photosynthetic characteristics, and carbon metabolism of white potato (Solanum tuberosum) plantlets cultivated in vitro. MATERIALS AND METHODS Plant MaterialStock plantlets of Solanum tuberosum cv Haig were routinely subcultured from stem axillary buds on a medium containing Murashige and Skoog (18)

A factorial analysis was conducted to investigate the effects of different levels of photosynthetic photon flux (PPF) and CO2 concentration on the interactions between the vesicular–arbuscular endomycorrhizal fungus Glomus intraradices and potato plantlets (Solanum tuberosum) cultured in an in vitro tripartite system. We observed that CO2 enrichment from 350 to 10000 ppm stimulated root colonization by the fungus, and that this stimulation was more pronounced under high PPF (300 μmol m−2 s−1) than low PPF (60 μmol m−2 s−1). Consistent with these observations, the effects of G. intraradices on dry matter production in potato plantlets were strongly dependent on the CO2 and PPF levels during cultivation. There was no significant effect of the mycorrhizal fungus on dry matter production at 350 ppm of CO2. However, under the high CO2 concentration, mycorrhiza had opposite effects on dry matter production depending on the PPF: a decrease (−21%) and a stimulation (+25%) of dry matter production after 2 wk of growth under low and high PPF, respectively, were observed in presence of G. intraradices relative to plantlets grown in its absence. Furthermore, in mycorrhizal plantlets grown under high levels of both PPF and CO2, the chlorophyll and carotenoid contents as well as the quantum yields of photosynthetic electron transport and the photochemical quenching qP of the chlorophyll‐a fluorescence measured near the PPF during growth were all higher than in non‐infected plantlets. Our results therefore indicate that mycorrhizal G. intraradices can alleviate the down regulation of photosynthesis related to sink limitation, and its effect on dry matter production is strongly dependent on the levels of CO2 and PPF during growth which determine the balance between the photosynthetic carbon uptake by the plantlets and the carbon cost by the fungus.