Abstract: Low temperature stress is an important factor affecting plant growth and benefit in southwest Karst. In order to explore whether there were differences in physiological structure of different varieties of Passiflora caerulea L. and their differences in adaptability under low temperature stress, the morphological structures of the roots, stems, leaves, flowers, fruits and seeds of 2 varieties and 4 genotypes were dissected and observed at normal temperature, and the anatomical structures of 2 varieties leaves under different low temperature stress was observed, the relationship between morphologic structure and cold resistance of Passiflora caerulea L. varieties was studied. The results showed that the anatomical structures of cold resistant varieties (Ping Tang 1) and genotypes (Qian Xiang Xiang 1, 2, 3, 4) and non-cold resistant varieties (Zi Xiang 1) were only distinctions in the morphology of vascular bundles in leave's xylem. After treatment with different low temperatures (5.0, 2.5, 0, -2.5℃), leaf length, width and thickness of Ping Tang 1 were significant smaller than Zi Xiang 1 before freezing injury (5.0, 2.5, 0 ℃). There were no significant differences in wax thickness of 2 varieties when Zi Xiang 1 was not damaged. There were no significant changes in length and width of vascular bundles in 2 varieties. There were no significant differences in thickness of vein and length of palisade tissue in 2 varieties at 5.0 ℃, but at 2.5 ℃, 0 ℃ and -2.5℃, leaf vein thickness and palisade tissue length of Ping Tang 1 were significant larger than those in Zi Xiang 1. Sponge tissue thickness in 2 varieties increased with the decrease of temperature, thickness of the sponge tissue of Ping Tang 1 was always less than that of Zi Xiang 1. Cell tense ratio and vein protuberant degree of the 2 varieties were significantly different, with the constant decrease of temperature, the proportion of cell tense ratio and vein protuberant degree of Ping Tang 1 were greater than those in Zi Xiang 1. The spongy ratio of the 2 varieties showed significant differences before Zi Xiang 1 was obviously frozen, influenced by size and thickness of leaves, the spongy ratio of Ping Tang 1 was greater than Zi Xiang 1. In summary, leaf length and width of the Ping Tang 1 which was cold resistance varieties were smaller, leaves were thinner, leaf veins were thicker, palisade tissue/spongy tissue ratio was higher, cell tense ratio and vein protuberant degree were greater, and Zi Xiang 1 was the opposite.

Key words: Passiflora caerulea L., anatomical structure, low temperature stress, cold resistance