| Potato cultivars “Atlantic” plantlets in vitro were cultured on liquid MS medium with low-Mg2+ concentration（0,188,375,750,1 500 μmol·L-1）. Physiological and morphological indexes were determined after 20 d culture and showed that under non-Mg2+ treated condition, the total chlorophyll content, chlorophyll a content and chlorophyll b content, root/shoot ratio, total root length, root surface area, root volume, lateral root number of plantlet in vitro were the lowest. Compared with the control, the above indexes were decreased by 42.3%, 40.8%, 46.2%, 96.4%, 63.9%, 54.1%, 82.4% and 89.9%, respectively. The average root diameter and Chla/Chlb reached the maximum level under non-Mg2+ treated condition and compared with the control were increased by 16.7% and 9%, respectively. The starch content in shoots and the sucrose content, fructose content and soluble sugar content in shoots and roots were highest under non-Mg2+ treated condition, and compared with the control these indexes were increased by 58.5%, 54.8%, 59.7%, 25.9%, 22%, 46.7% and 54.7%, respectively. The starch content in roots was lowest under non-Mg2+ treated condition and compared with the control were decreased by 32.8%. The correlation analysis indicated that there existed a strong negative linear relationship between Mg2+ concentration and starch content, fructose content, soluble sugar content in shoots, respectively. These results indicated that under the treatment of Mg2+ deficiency, a large amount of carbohydrate was accumulated in shoots whereas less exported to roots. The lateral root number and root/shoot ratio were reduced, and the root system formation was totally inhibited. Under low Mg2+ concentration of 750 μmol·L-1 treatment, the chlorophyll content of plantlet in vitro increased and more carbohydrate was translocated to roots. The root/shoot ratio increased and the root system formation was promoted. These physiological and morphological indexes under 750 μmol·L-1 treatment of Mg2+ had no difference from that of normal Mg2+ treatment condition (control). The MS medium containing 750 μmol·L-1 Mg2+ was also beneficial to growth and development of potato plantlet in vitro. |