밀 耐凍性 染色體置換系統에서 光合成의 光沮害現象 差異

Differences in photoinhibition of photosynthesis in wheat chromosome substitution lines for freezing resistance

In order to evaluate the relationship between low temperature-induced photoinhibition and winter survival in wheat, seeds of 20 chromosome substitution lines and their parents, Chinese Spring and Cheyenne were germinated at 20℃ and were transferred to 5/2℃ and 20/16℃ growth chambers to obtain cold-acclimated (CA) and nonacclimated (NA) plants, respectively. For photoinhibition and recovery experiments, 7 to 8cm long leaf portions were placed on moist filter paper and placed in trays at 5℃ cold room with 1,100 μmol m⁻² s⁻¹ PPFD. Room temperature chlorophyll fluorescence was measured with a PAM system after 50 minute dark adaptation. Instantaneous Fo, Fv, and Fm were determined and the Fv/Fm, was calculated. Fv/Fm of CA plants were reduced from 0.81 in control leaves to 0.33 following photoinhibition of 8h and the CVs were increased from 1% to 19%. Fv/Fm of NA plants were reduced from 0.82 in control leaves to 0.39 in leaves exposed to 5℃ for 6h, and the CVs were increased from 0.5% to 15%. Thus, photoinhibition of CA plants was less than that of NA plants. Fv/Fm of freezing tolerant Cheyenne grown under either CA and NA conditions, were higher than those of freezing-sensitive Chinese Spring. Chinese Spring lines substituted with Cheyenne chromosome 5(5A, 5B and 5D) showed relatively higher resistance to photoinhibition. A series of studies suggests that the chromosomes of homologous group 5 of Cheyenne have major genes controlling freezing tolerance, expression of antifreeze proteins and factors resistant to low temperature-induced photoinhibition. Winter survival in wheat was positively correlated with resistance to photoinhibition of PSⅡ and significantly fitted by multple linear regression(R²=0.75∗∗). Also, winter survival in wheat was positively correlated with resistance to photoinhibition of PSⅡ and expression of antifreeze proteins, and significantly fitted by multple linear regression (R²=0.76∗∗). Variable chlorophyll fluorescence measured by Fv/Fm has been found to be very useful in evaluating relative levels of freezing tolerance in wheat.