| The purpose of this study was to explore the response of photosynthesis and the regulation of fatty acid on it under low temperature in chrysanthemum,which provided a theoretical basis for cold breeding.Autumn chrysanthemum cultivar ‘Tangyujinqiu' was chosen as the experimental material,and three processing temperatures of 26 ?(CK),4 ? and-4 ? were set with each sustaining for 72 h.Physiological indicators such as relative electrical conductivity,activity of antioxidant enzyme(SOD and POD),chlorophyll fluorescence and membranous fatty acid content were determined,and relative expression of chrysanthemum fatty acid desaturase(Cm SAD,Cm FAD2 and Cm FAD7)and light-harvesting chlorophyll a-b binding protein(Cm CAB and Cm Lhca2)genes were analysed.The results are listed as follows.(1)The relative electrical conductivity of chrysanthemum leaves increased with the stress temperature by 42.5%(4 ?)and 80.2%(-4 ?),respectively.The content of soluble sugar,soluble protein and proline decreased with temperature dropping.The proline was the most obvious at-4 ?,which was 95% lower than the control.(2)The activities of antioxidant enzymes in chrysanthemum leaves were significantly lesser than those in the control under low temperature.The SOD and POD decreased by 11.6% and 97.1% at4 ?,and by 26.4% and 62.3% at-4 ?,respectively.(3)The chlorophyll content first rose and then fell with the decrease of temperature.The chlorophyll a+b increased by 23.8% at 4 ? and declined by 21.8% at-4 ? compared with the control;PSII related parameters RC/CSo rose by 3.2% at 4 ? and fell by 38.9% at-4 ? while DIo/RC increased by 0.7%(4 ?)and 152.8%(-4 ?).Vj went up when temperature dropping,which reached its maximum at-4 ? and 1.3 times the control.?(Ft-Fo)/(Fk-Fo)>0 at-4 ?;PSI related parameters REo/CSo,REo/RC,?Ro amd ?Ro reduced by 26.6%,17.6%,25.3% and 20.4% at4 ?and by 67.7%,33.2%,51.1% and 22.7% at-4 ?,respectively.Furthermore,the OJIP curve,MR/MRo curve and other photochemical reaction parameters changed significantly;Light-harvesting chlorophyll a-b binding protein genes were down-regulated with decreasing temperature,in which the Cm CAB was only 9.0% of the control and the Cm Lhca2 declined by68.3%(4 ?)and 92.3%(-4 ?),respectively.(4)In the aspect of fatty acid content in chrysanthemum leaves,there was a escalating trend of the content of stearic acid and linolenic acid,which increased 1.7% and 3.8% at 4 ? while 9.2% and6.8% at-4 ?,respectively.The oleic acid fell by 34.9% and 17.6% at 4 ? and-4 ?,respectively;IUFA had an indistinctive variation at 4 ?,and rose by 3.7% at-4 ?;In the aspect of fatty acid content in the thylakoid membrane,the stearic acid content decreased by 6.4% and 16.2% at 4 ?and-4 ?,respectively;the trend of oleic acid content fell before rose,which decreased by 28.3%at 4 ? and increased 16.7% at-4 ?;the content of linoleic acid and linolenic acid went up by8.4% and 63.2% at 4 ? before going down by 52.4% and 132.6% at-4 ?;IUFA rose by 31.1% at4 ?,which was 1.9 times of the control at-4 ?;there were rising trends in the expression quantity of Cm SAD and Cm FAD7 genes with the decrease of stressing temperature,which increased by 17.0% and 76.7% at 4 ? while 340.5% and 136.3% at-4 ?,respectively;the Cm FAD2 decreased by 15.5% at 4 ? and went up by 145.2% at-4 ?.The fall of chlorophyll content and photosynthetic electron transfer rate(TRo/RC and ETo/RC,et al)and the rise of thermal dissipation(DIo/RC)under low temperature stress indicated that the photosystem was damaged.The expression quantity of light-harvesting chlorophyll a-b binding protein(Cm CAB and Cm Lhca2)gene lowered the amount of pigment-protein complex,which reduced the damage of low temperature to photosystem to some extent.Osmotic adjustment substances(SS,SP and Pro)were mainly used for respiration and antioxidant enzyme(SOD and POD)activity were gradually reduced with dropping temperature,which lowered the cell metabolism levels and increased the damage of cytomembrane.The fatty acid desaturase genes expression were up-regulated to increase the fatty acid unsaturation degree in order to maintain the stability of biomembrane system. |
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