In situ estimation of carbon balance of in vitro sweetpotato and tomato plantlets cultured with varying initial sucrose concentrations in the medium

摘要

The effects of initial sucrose (suc) concentrations in the medium (So) on the carbon balance and growth of sweetpotato [Ipomoea batatas (L.) Lam. 'Beniazuma'] and tomato (Lycopersicon escalentum Mill. 'HanaQueen') plantlets were studied under controlled environmental conditions. Plantlets were cultured with 0, 7.5, 15, or 30 g.L-1 of S-0 under high photosynthetic photon flux (160 to 200 mumol.m(-2).S-1) and CO2 enriched (1400 to 2050 mumol.mol(-1)) conditions. Net photosynthetic rate per leaf area (P-1) decreased and dry weight per plantlet (W-d) increased with increasing S-0, but did not differ significantly between S-0 of 7.5 to 30 g.L-1 for sweetpotato or 15 to 30 g.L-1 for tomato. Carbon influxes and effluxes of the plantlets by metabolism of medium suc and/or photosynthesis, and respiration were estimated based on measurements of in situ and steady state CO2 exchange rates and sugar uptake during culture. At S-0 from 7.5 to 30 g.L-1, photosynthesis was responsible for 82 % to 92 % and 60 % to 67 % of carbohydrate assimilation for sweetpotato and tomato, respectively. Estimated carbon balances of plantlets based on the estimated and actual increases of moles of carbon in plant tissue demonstrated that in situ estimation of carbon balance was reasonably accurate for sweetpotato at S-0 of 0 to 15 g.L-1 and for tomato at S-0 of 0 g.L-1 and that the actual contribution of photosynthesis for tomato at high S-0 might be lower than the values estimated in the present experiment. Results showed that initial suc concentration affected the relative contribution of photosynthesis on their carbon balances and that the responses were species specific. The failure of validation at So in a range specific to each species suggested the need for further study on carbon metabolism of in vitro plantlets cultured with sugar in the medium.