Short single node cuttings of tissue-cultured potato plantlets (
Solanum tuberosum L. cv. Benimaru) were placed onto the culture media with three different sucrose concentrations (5g·
l-1 (S
5), 15g·
l-1(S
15) and 25g·
l-1(S
25)) to follow the time course of CO
2 exchange of potato cultures for 30 days. Moreover, how the CO
2 balance of the cultures changes during the growth and development phases from short single node cuttings (length: 5mm; dry weight: 1mg) to plantlets (dry weight: >10mg) large enough to transfer to
ex vitro conditions was investigated. The CO
2 exchange was calculated from the time course of the difference (Δ
C) between CO
2 concentrations of inflow and outflow air (flow rate: 2.1
l·h
-1) through the culture vessel.
On day 3 Δ
C for all sucrose concentrations showed tendencies to decrease by photosynthesis after the beginning of photoperiod. Cyclic changes in Δ
C for all sucrose concentrations according to 8 hours-dark/16 hours-photoperiod cycles were clearly observed after day 5. The difference between maximum and minimum Δ
C on the same day in each sucrose concentration increased as the day proceeded, and the difference on day 30 was in the order: S
15>S
25>S
5. The CO
2 exchange during photoperiod and daily CO
2 exchange for all sucrose concentrations continuously increased as the day proceeded. The daily CO
2 exchange was found to turn to positive values from negative ones around day 16 for S
5, and day 10 for S
15 and S
25: the cultures turned into positive CO
2 balances. These results indicate that the cultures have grown and developed dominantly depending on sucrose in the culture medium before the CO
2 balance turned to positive, even having contained chlorophyll and been under appropriate CO
2 (880±50μmol·mol
-1 for inflow air) and light (120μmol·m
-2·s
-1 during photoperiod) conditions for photosynthesis. The dry weight increase and net production by photosynthesis for 30 days were in the order: S
15>S
25>S
5.
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