Effects of sugar concentration in the medium on photosynthesis

When roses are grown on a medium with a lower amount of sugar (1 and 3%), a higher maximum net photosynthesis value and a lower light compensation point is found compared to plantlets treated with 5% sucrose.

Exogenous sugars in the medium tend to reduce net photosynthesis of tissue cultured plants. Fig. 1

Rosa multiflora

Fig. 1. Light response curves of in vitro cultured

Rosa multiflora with three different concentrations of sucrose

In Spathiphyllum cultured on a medium containing 3% sucrose, a positive net photosynthesis is measured at the end of the in vitro culture (Fig. 2, day 0). When the sucrose concentration was doubled (6%) plants became more mixotrophic as is shown by a decrease in net photosynthesis, lower F_v/F_m and a very low photochemical quenching (q_p) (Figs. 2 and 3). During acclimatization it takes about two weeks before those mixotrophic cultures become fully autotrophic and reach the same photosynthetic rates as the 3% cultures.

Fig. 2. Dark respiration and net photosynthesis measured

at 100 µmol m^-2 s^-1, during acclimatization of Spathiphyllum

plantlets micropropagated on 3 (circles) or 6 (squares) %

sucrose containing medium.

Fig. 3. Fluorescence parameters (A) F_v/F_m and (B) photochemical quenching

during acclimatization of Spathiphyllum plantlets micropropagated on 3

(circles) or 6 (squares) % sucrose containing medium.