| To clarify the effects of drought stress on potato leaf subcellular structure and physiological indexes, plantlets of three potato varieties with different drought-resistance capabilities were selected as materials to be cultured in MS liquid medium with 20% PEG-6000. Favorita was sensitive to drought, Dongnong 308 possessed relatively stronger drought tolerance, and Jinshu 2 was a drought-tolerant variety. The results showed that the most serious damage by drought stress occurred in chloroplast, and then mitochondria, while damage on nucleus was not obvious. Chloroplast morphology turned to be wavelike or swollen. Chloroplast lamellae became loosened, and the interspaces between lamellar structures became large, exhibiting some holes sometimes. The membrane of mitochondria was disrupted, and the cristae was partially degraded. Ultrastructure of Favorita was damaged most seriously, followed by Dongnong 308, and Jinshu 2 was the least. With the changes in ultrastructure after drought stress, the physiological indexes also displayed changes. The contents of malondialdehyde (MDA) in plantlets of three varieties under in vitro stress were increased by 48.89%～243.27%, significantly different from the control with water treatment. The activities of peroxidase (POD) ascended by 2.06%～32.98%. Favorita and Jinshu 2 reached highly significant and significant levels, respectively. The superoxide dismutase (SOD) activities and chlorophyll contents in all three varieties displayed varying treads. In summary, after drought stress, the contents of MDA and the chloroplast ultrastructure of plantlets in vitro were changed significantly, reflecting variances in drought resistance capabilities of different varieties. |