Difference In Growth And Physiology-Biochemistry Between Two Maize Inbred Lines With Different Drought Tolerance During Seedlings Under Drought Stress

Drought is one of the main limiting factors for crop yield forming. It is one of the effective approaches to develop drought-tolerant maize hybrids. Due to the difference of drought-tolerance among various inbred lines, it is necessary to further study on the physiological foundation to develop drought-tolerant hybrids and to improve crop cultivated technology. Two inbred lines of different drought-tolerance were selected to use in this study. The drought stress simulation was used with PEG-6000 at different stress levels. The objectives were to research the differences on plant morphology, physiological characteristics, micro-structure and WUE during seedlings in Maize inbred lines. The results were as follows:1. Differences in growth and development between two maize inbred lines under drought stressDrought limited the above-ground growth and development of maize inbred lines. Under drought stress, the plant height and leaf area were decreased, and the above-ground dry matters were limited to different extents. The limiting degree was increased with the stress time extending and the stress degree increasing. The effects in drought-tolerant inbred line were less than those in drought-susceptible inbred lines.Drought affected the growth and development of root system between two maize inbred lines. Comparing with the CK, the total length, surface area, mean diameter of roots of two inbred lines were increased at 5mmol/L, but those of drought-tolerant inbred line were significance increased than drought-susceptible inbred lines. As the concentration of PEG-6000 was 10mmol/L and 15mmol/L, the total length, surface area, and mean diameter of roots were decreased with the increase of treatment contents. When the drought stress occurred, the above-ground parts were damaged first, but the roots were still growing. As stress prolonged, the root growth was inhibited.2. Differences in osmotic adjustment matters between two maize inbred lines under drought stressUnder drought stress, the soluble carbohydrate and proline in leaf and root of two inbred lines were increased with the interments of drought severity and stress time. The increasing range of drought-tolerant line was much more than those of drought-susceptible line, and the contents of soluble carbohydrate, proline and soluble protein in root were more than those in leaf.3. Differences in lipid membrane permeability, lipid peroxidation and protective enzyme between two maize inbred lines under drought stressThe relative conductivity value and MDA content were increased with the increment of stress under drought stress, especially in root. The activities of three protective enzymes SOD, POD and CAT under drought were higher than under normal growing condition. This showed the tendency as’up to down’with the interment of stress severity and time. The increasing range of drought-tolerant inbred line was more than that of drought-susceptible line, but the decreased range was less than drought-susceptible line. The activities of SOD, POD and CAT in root were higher than in leaf.4. Differences in photosynthetic physiological characteristics between two maize inbred lines under drought stressUnder drought stress, the intercellular CO2 content in leaf was increased, but the net photosynthetic rate, stoma conductivity and transpiration rate were decreased, which was indicating that the no-stoma factors were maybe the main reason for the reduction of photosynthetic rate.The contents of chlorophyll a, chlorophyll b, and chlorophyll a+b were increased with the increments of stress due to the increase of cell wall thickness, as well as the inhibition of cell elongation which increased the amount of chlorophyll per unit area; another reason was that the decrease of relative water in leaf led to increase of content in unit weight.The initial Florence Fo in leaf of two inbred lines were increased with the stress increased, but the Fv, Fv/Fo, Fv/Fm, and PI value were decreased. The decreased range of drought-tolerant inbred line was less than that of drought-susceptible line. The Fm was increased in drought-tolerant line, but it was decreased in drought-susceptible inbred line. The area of drought-susceptible line was increased but the area of resistant line was decreased with the increment of drought stress. The PSⅡof drought-tolerant inbred line maintained higher electron transportation ability and photosynthesis. 5. Differences in micro-structure between two maize inbred linesThe drought-tolerant inbred line was characterized with thick leaf, developed mesophyll cell and bundle sheath cell under drought stress. Furthermore, the decreasing ranges of leaf thickness, mesophyll cell and bundle sheath cell areas were not obvious with the increase of drought, but the drought-susceptible line were significantly decreased.The vessel diameter and cortex thickness were decreased with the increment of stress, and the decreased range of drought-tolerant line was greater than that of drought-susceptible line. For the drought-tolerant line, the cortex thickness took less portion of root diameter, but it was on the contrary for drought-susceptible line.6. Differences in ability of water absorption and WUE between two maize inbred linesThe ability of water absorption and WUE were decreased with the increment of stress, and decreasing range of drought-tolerant maize inbred line was less than that of drought-susceptible line.