Salt-tolerant Mechanism During Post-germination Period And Photosynthetic And Chlorophyll Fluorescence Characteristic During Senescence Process Of Flag Leaf Under Heat/Darkness Stress Of 'Stay Green' Wheat

Soil salinization, high temperature and dim light are major abiotic stresses influencing wheat productivity world widely, while wheat-rye 1BL/1RS translocated chromosome has been successfully used in wheat yield improvement for growing 'stay green' wheat cultivars. To determine the salt-tolerance of them, three new 'stay green' wheat cultivars with 1BL/1RS translocated chromosome Chuannong12 (CN12), Chuannong17 (CN17) and Chuannong18 (CN18) were treated with various NaCl concentration, and Lovrin10 (LV10) also with the1BL/IRS translocated chromosome, and wheat genotypes both Mianyangll (MY11) and Chinese Spring (CS) without the translocated chromosome were used as the controls. Several morphological and physiological parameters coleoptile length, relative elongation rate(RER), fresh weight, dry weight, osmotic potential, and contents of solutes such as proline, soluble sugars, Na+ and K+ were recorded under both 0 and 100mM NaCl conditions. On the other hand, in order to illuminate the effects of heat/darkness stress on the senescence process of intact flag leaves,'stay green' wheat cultivar CN17 and normal senescence-type wheat cultivar MY11 were investigated. We studied the effects of long-time heat and darkness stress on chlorophyll content, photosynthetic characteristics and chlorophyll fluorescence of flag leaf during the senescence period for the purpose of providing theoretical evidence of super-high-yield cultivation and breeding of wheat. The main results are as follows:1. The compared percentage of coleoptile length (the coleoptile lengths of the treated to those of the control) is perhaps a more reliable index in screening salt-tolerance of wheat than coleoptile length.2. In this study,100 mM NaCl concentration showed strong ability to differentiate the salt-tolerance. Combining the different degrees of change in the physiological and morphological parameters under 100 mM NaCl condition suggested that the salt-tolerant ability from strong to weak was:LV10>CN17>CN18>CN12>CS>MY11.3. Statistical analysis showed that CN12, CN17 and CN18 had higher average compared percentages of coleoptile length than MY11 had, when under 100 mM NaCl concentration level, and the larger P value would result from the different salt-tolerant levels among the three sister lines were also obviously in this study. Together all the evidences, we can draw a conclusion IRS in certain wheat genetic background would have some contribution to salt-tolerance.4. Under salt stress conditions, the coleoptile of CN18 might have higher K+ versus Na+ selectivity that could exclude Na+ more effectively, while CN12 had stronger tolerance to high Na+ concentration conditions resulted from the reduction of cytosolic Na+ by sequestering Na+ in the vacuoles. However, the osmotic adjustment probably played an important role in the salt-tolerant mechanism of CN17.5. The different changes of Na+ contents between CN18 and both CN12 and CN17and also showed the breakpoint of the translocated chromosome influence salt-tolerance ability as well as modifying salt-tolerant response mechanisms. The different pedigree and original environment might be an important reason for salt-tolerant level of LV10 was much higher than that of CN12, CN17 and CN18.6. For 'stay-green' wheat CN17, Under CK condition, the distal parts of flag leaves were senescence earlier than veins. This phenomenon was different from flag leaves of CN17 that came from field growing conditions. The main reason was that the illumination intensity of CK condition was much lower than those of field growing conditions. Under CK condition, the sourses of CN17 were insufficient.7. Under CK condition, Pn was influenced by both the stomatal factor and photosynthetic activity for the abrupt shift of surroundings. After this time, stomatal factor is the main aspect limiting photosynthesis. At the late senescence stage of MY11, activities of the photosynthetic apparatus were the main limiting factor. During the whole process of treatment, the photosynthetic apparatus of CN17 were destroyed only a little.8. Under heat treatment condition, the senescence processes were induced in both flag leaves of CN17 and MY11. While the photochemical apparatus in CN17 had higher heat tolerance than those in MY11.9. The main reason of decrease of Pn under heat stress condition is the destruction of photosynthetic apparatus. To reply the decreasing of the efficiency of excitation capture, CN17 decreased heat dissipation rate. So the maximum photochemical efficiency of PS II and the electron transport rate were protected to a certain extent.10. Compared with flag leaves of plants under CK condition, senescence could be induced in wheat flag leaf when put the whole adult plants into continuous darkness condition.11. Under darkness condition, photosynthetic apparatus of CN17 were injured earlier than those in MY11. CN17 had lost its 'stay green' function compared with MY11. The different relationship between sources and sinks in CN17 and MY11 is the main reason for the phenomenon.