Analysis of Chlorophyll Fluorescence Characteristics in Winter Turnip Rape(Brassica rapa L.)Under Natural Low Temperature Conditions
This study investigates the relationship between chlorophyll fluorescence characteristics and cold resistance in winter turnip rape(Brassica rapa L.)at low temperatures.Under field conditions,winter rapeseed varieties Longyou 7,Longyou 8,and Tianyou 4 were selected to determine the chlorophyll fluorescence characteristics of winter rapeseed seedlings during the natural cooling process before winter.The results showed that as the temperature decreased from October 7(6.7℃)to November 25(-8.3℃),the initial fluorescence content(Fo)of the leaves of the three winter turnip rape varieties exhibited an increasing trend,with the order being Fo for Longyou 8>Longyou 7>Tianyou 4.The maximum fluorescence(Fm),PSII electron transfer(Fm/Fo),variable fluorescence yield(Fv),maximum photochemical efficiency(Fv/Fm),and PSII receptor library size(Area)in the leaves of Tianyou 4 demonstrated a decreasing trend.The order for Fm,Fm/Fo,and Fv was Tianyou 4>Longyou 8>Longyou 7,while for Fv/Fm and Area,the order was Tianyou 4>Longyou 7>Longyou 8.Additionally,the activity state of the oxygen-re-leasing complex(Fo-k),the ability of QA to be reduced(Fk-j),the ability of QB(including fast reduction PQ library)to be re-duced(Fj-i),and the ability of QB(slow reduction PQ library)to be reduced(Fi-p)all showed a decreasing trend.The perfor-mance for Fo-k,Fk-j,and Fi-p was Longyou 8>Tianyou 4>Longyou 7,while Fj-i showed the order Tianyou 4>Longyou 8>Longyou 7.The light energy absorbed per unit reaction center(ABS/RC)and the closing degree of the reaction center(Vj)ex-hibited an increasing trend,with ABS/RC being Longyou 7>Tianyou 4>Longyou 8 and Vj being Longyou 8>Longyou 7>Tianyou 4.The potential photochemical activity(Fv/Fo)and photosynthetic performance index(PI)of PSII showed a decreasing trend,with Fv/Fo as Longyou 8>Tianyou 4>Longyou 7 and PI as Tianyou 4>Longyou 8>Longyou 7.Canonical correlation analysis indicated that Fo was positively correlated with ABS/RC and Vj,while it was significantly negatively correlated with Fm,Fm/Fo,Fv,Fv/Fm,Area,Fo-k,Fk-j,Fj-i,Fi-p,Fv/Fo,and PI.Based on a multivariate evaluation using membership function analysis,the order of cold tolerance was determined to be Longyou 8>Longyou 7>Tianyou 4.These results provide an experi-mental basis for the innovation of cold-resistant germplasm in winter turnip rape(B.rapa L.)in cold arid regions.
brassica rapa L.low temperaturechlorophyll fluorescence characteristicscorrelation coefficientmember-ship function valu
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