Plant material and photosynthesis
Sunflower (Helianthus annuus L.) var. XRQ was sown directly in sand (washed with distilled water) in the greenhouse, using 7-L pots. Growth conditions were: 12/12 h photoperiod, 25/18°C air temperature, 70/60% relative humidity day/night. Photosynthetic parameters were measured using a portable open system Li-Cor 6400 XT. Net assimilation (A ) and conductance reported in Fig. 2 was obtained under saturating light (1500 µmol m-2 s-1PAR) at 400 µmol mol-1 CO2 and 21% O2. Night respiration (R n) was measured after photosynthesis measurements on dark-adapted leaves (30 min) at 400 µmol mol-1 CO2, 21% O2 and 25°C.