Abstract:
 For better understand the differences of drought tolerance among Brassica species, 3 materials from
Brassica napus (Q2), B. juncea (Xinyou 9) and B. rapa (L14) were used to investigated the physiological and bio⁃
chemical changes. Photosynthesis parameters, chlorophyll fluorescence parameters and water content of their leaves
under drought stress were measured by pot experiments. Results showed that with the aggravation of drought stress,
drought resistance indexes of 3 materials were different. Total biomass, water loss rate of leaf, leaf relative water con⁃
tent, chlorophyll fluorescence parameters and gas exchange parameters had decreasing trend, among which photo⁃
synthetic system of Xinyou 9 was the least affected, Q2 was the most severely damaged. All the root-shoot ratio and
malondialdehyde content increased, and their superoxide dismutase and peroxidase activities increased also. But
the superoxide dismutase and peroxidase activities increased the most, which were 2.92 and 4.14 times respectively
than normal control. In addition, more differences were found in organic solutes accumulation. Proline was the most
accumulated protein in Q2 and Xinyou 9, which increased to 12.37 and 6.60 times of the originals, while soluble
protein in L14 increased to 6.55 times of the original. By subordinate function values analysis, capability of drought
resistant was in the order of B. juncea Xinyou 9 > B. rapa L14 > B. napus Q2. In conclusion, 3 Brassica species as
B. juncea, B napus and B. rapa could respond to drought by 4 main strategies: growth regulation, photosynthesis inhi⁃
bition aadjustment, active oxygen metabolism system and osmotic adjustment.

Key words: drought stress, Brassica juncea, Brassica napus, Brassica rapa, physiological response, drought resistant mechanism