Effects of the Natural Ventilation and Light Intensity on the Growth, Photosynthesis and Acclimation of in Vitro Cultured Cauliflower Plantlets under Photomixotrophic Conditions

Abstract

Growth and photosynthesis of the photomixotrophically grown cauliflower plantlets (Brassica oleracea L.) were investigated during a 1-week in vitro culture under naturally ventilated conditions followed by a 2-week ex vitro acclimating period. The in vitro generated leaves in a ventilated vessel had higher rates of photosynthesis than those in an airtight vessel. The enhanced rates of photosynthesis in those leaves, which contained both increased amounts of chlorophyll and total soluble protein, contributed to promote the growth in vitro and the acclimation of plantlets to ex vitro. A nearly half concentration of ambient CO₂ was kept in a naturally ventilated vessel, in which the plantlets grew well by positive photosynthesis during the photoperiods. Both the leaf expansion and the shoot and root dry weight increased under higher photosynthetic photon flux density (PPFD, 50 vs. 100μmol m^-2 s^-1) during the ventilated in vitro culture period. In the first two weeks after transplanting the cauliflower plantlets, the high photosynthetic capacity of in vitro generated leaves had an important contribution to the unfolding of acclimating leaves and the successful acclimation of the whole plantlets.