From leaf explants to rooted plantlets in a mist reactor

The medicinally important plant Artemisia annua was used as an example to study the effect of mist reactor conditions on shooting, rooting, and in vitro acclimatization. During all three stages, plants grown in the mist reactor yielded more shoot biomass than corresponding gelled medium controls. During shoot development, shooting percentage and shoot multiplication increased with increased light intensity and CO2. Shooting percentage and shoot multiplication were also better under a once vs. twice per hour misting frequency. Hyperhydricity was lowest under light and CO2 enrichment and with less frequent misting. Compared to unhyperhydric shoots, hyperhydric shoots showed significantly greater water content. Hyperhydric shoots also produced fewer glandular trichomes and artemisinin and flavonoids were 3 and 14.5%, respectively, compared to unhyperhydric shoots. During root development, all aspects of root growth, including rooting percentage, number of primary roots and secondary roots, and length of the latter, improved with more frequent misting cycles and light and CO2 enrichment. Although plants grown in the mist reactor did not yield a better rooting percentage than gelled medium controls, new roots formed in the reactor were thicker than those grown on gelled medium. During in vitro acclimatization, reducing the relative humidity of the ventilating air from similar to 50 to similar to 10% improved stomatal closure and subsequent ex vitro survival. Plantlets acclimatized in unventilated reactors had broken stems with less lignin. Together, these results showed that compared to traditional methods using gelled medium, the mist reactor can be used to improve micropropagation.