Induction of tetraploidy in non-heading Chinese cabbage (Brassica campestris ssp chinensis Makino) by colchicine treatment increases the ascorbic acid concentration

Non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino) is one of the most commonly consumed vegetables in China, and has recently been introduced into other countries in Asia, North America, and Europe. In this study, we obtained tetraploid, non-heading Chinese cabbage by treating the apical portion of diploid seedlings with various concentrations of colchicine for different treatment times. Treatments included a total of two, four, or six applications of 1.5 g l(-1) or 2.0 g l(-1) colchicine, performed twice a day at 09.00 h and 15.00 h. Tetraploid plants were selected and identified based on their morphological, anatomical, agronomic, and cytological characteristics, and on their DNA content, as measured by flow cytometry. The highest rate of tetraploidy (8.6%) occurred in seedlings treated six-times with 1.5 g l(-1) colchicine. Compared to diploid plants (untreated controls), the tetraploid plants had wider leaves, larger petals, longer siliques, larger seeds, larger stomata, and fewer chloroplasts per guard cell. HPLC showed that tetraploidisation could increase the level of ascorbic acid (AsA) in this crop. Quantitative real-time PCR (qRT-PCR) showed that the levels of expression of genes encoding enzymes involved in the AsA-L-galactose biosynthetic pathway increased in tetraploid plants. This is the first study to compare levels of expression of genes involved in the biosynthetic pathway of AsA between diploid and tetraploid non-heading Chinese cabbage plants.