水稻的光合作用

1、Response of Photosynthesis, Growth, Carbon Isotope Discrimination and Osmotic Tolerance of Rice to Elevated CO2PENG Chang_Lian, DUAN Jun, LIN Gui_Zhu, CHENYi_Zhu, PENG Shao_Lin (South China Institute ofBotany,The Chinese Academy ofSciences, Guangzhou 510650, China)Abstract: Four rice (Oryza sativaL.

2、) cultivars IR72”，“Tesanai 2”，“Guichao 2” and “IIyou 4480” were grown in two plastic house (15 m X 3 m) with 35 p mol/mol and 60 p mol/mol CO2concentration which was controlled by computer. As comparedwith rice at ambient 35p mol/mol CO2, the changes in photosynthetic rate at elevated CO2showed up_r

3、egulation ( IR72 ” and “Tesanai 2 ” ), stable (unchanged) in “Guichao 2” and down_regulation type ( “IIyou 4480” ). Growth rate, panicleweight, integrated water use efficiency (WUE) calculated from 13C and the capacity of scavengingDPPH (1,1_diphenyl_2_picrylhydrazyl) free radical were increased at

4、elevated CO2. An increment in total biomass was observed in three cultivars by elevated CO2, with the exception of “IIyou 4480 ” . Ratios of panicleweight/total biomasswere altered to different extents in tested cultivars by elevated CO2. When leaf segments were subjected to PEG osmotic stress, the

5、electrolyte leakage rate from leaves grown at elevated CO2was less than that at 35 p mol/mol CO2. Those intraspecific variations of rice imply a possibility for selecting cultivarswith maximal productivity and high tolerance to stresses adapted to elevated CO2in the future.Key words: rice cultivars;

6、 elevated CO2; photosynthesis; water use efficiency;13C discrimination; osmotic toleranceThe continuous increase in CO2concentration in atmosphere has been proved and predicted that itwill reach up to 60p mol/mol by the year of 20501. The possible effect and its mechanism by elevated CO2on global cl

7、imate, ecological environment, biological diversity and agriculture production have become the hot point in the concerned researches. For the C3plants, the present ambient CO2concentration is limiting to photosynthesis, growth and production. Increase in CO2concentration leads to higher photosynthet

8、ic rate and yield inmostofthe C3crop plants2,3, but an acclimation of growth, photosynthesis and rubisco activity in a number of species to long_termexposure to elevated CO2has been reported4,5.The significant difference in the response to elevated CO2 existed among different species2,6. Whereas onl

9、y a few studies deal with the intraspecific variation in this case- 7,8. On the other hand, many of the studies are performed with potted plant or small chamber, which differs fromthe field conditions andmay limitthe potential application in practice.Rice is an importantfood crop providingthe main d

10、iet of about50% human population in theworld9. As the improvement of social economy and life level, the breeding aim of rice in future may request to select the cultivar not onlywith maximumyield, good quality, but alsowith high tolerance to the unfavorable stress. Our previous works showed that the

11、re was a more significant reduction of lipid peroxidation and photooxidative damage in rice leaves of six cultivars grown at elevated CO2than at ambient CO210. It implies that less potential oxidative stress might exist in rice leaves as CO2concentration increases. In the present study, the photosyn

12、thetic rate, growth rate, carbon isotope discrimination, electrolyte leakage rate and the scavenging capacity fororganic free radical in four rice cultivars grown under two different CO2concen- trations in the field were detected. Specifically the purpose of this studywere: (1) to further examine th

13、e possible differences among some local tropical rice cultivars in response to elevated CO2in the field conditions on a relative large_scale experimental area; (2) to know whether the water use efficiency (WUE) and osmotic stress tolerance are altered by elevated CO2. How is WUE related to the toler

14、ance to water stress in rice? The results may be useful as the primary information for future search of the genotype variation/diversity and the optimum rice cultivar responded to elevated CO2.1 Materials and MethodsPlant materials and growth conditions Rice (Oryza sativaL.) cultivars “Tesanai 2” ，“

15、Guichao 2” and hybrid rice “IIyou 4480” ， which are the commonly used cultivars in Guangdong Province, were obtained from The Rice Research Institute, Guangdong AgriculturalAcademy, and IR72” was provided by International Rice Research Institute (IRRI) ofPhilippines. Seeds were sown on 4, March and

16、the seedlings were transplanted on 1, April by 18 cmX15 cm in the rice field. Two plastic houses (15 mX 3 mX 1. 5 m)structured by stainless steel frame were covered with clear cellulose acetate membrane.The houseswere equipedwith automatically controlled system which consisted of two Received: 2000-

17、08-08 Accepted: 2001-03-02Supported by the State Key Basic and Development Plan (G1998010100), the National Natural Science Foundation of China (39899370) and Natural Science Foundation of Guangdong (970653).植物學(xué)報Acta Botanica Sinica 2002,44(1): 76-81fans and Infrared CO2Analyzer connecting to a comp

18、uterfor maintaining CO2level in the houses at 35p mol/mol or 60p mol/mol during the growth of rice. The management of irrigation and fertilization was as the routine process. Eight individual plantswere harvested for dryweightmeasurement at each sampling time.Determination of photosynthesis Photosyn

19、thetic rate of flag leafwas determined underthe given CO2concentration in the house by a portable Li- cor 6200 system at the heading stage of rice. Each determination was performed with four replications.Determination of6 13CFlag leaves collected after photosynthesis measurements were oven_dried, gr

20、ound and sieved. 6 13C value was detected by MAT_251 Isotope Mass Spectrometer according to the method described previously11.Calculation ofA 13C and water use efficiency (WUE)A 13C (carbon isotope discrimination) and integrated WUE were calculated bythe following equations according to Farquhar and

21、 Richards12, Beerling and Woodwa- rd13.A 13C=(6 13Ca-6 13Cp)/(1+6 13Cp/1 000) (1) Pi/Pa= (6 13Ca-6 13Cp-a)/(b-a) (2) WUE=PaX (1-Pi/Pa)/1.6A W(3) Where6 13Ca and6 13Cp are the carbon isotope compositions of air CO2and of leaves, respectively,ais the13C fractionation due to diffusion (0.44%),bis the f

22、ractionation during rubisco carboxylation (2.7% or 2.8%). Pi/Pais the ratio of intercellular CO2to atmospheric CO2 concentration. 6 13Ca is given by -0.931% (in 35 p mol/mol CO2) and -1.554% (60p mol/mol CO2) recorded by Beerling and Woodward13and Zhuet al14. A Wis water vapor gradient between leaf

23、and air during rice growth.Scavenging capacity to organic free radicalDPPH Dry leaf powderwas extractedwith 50% ethanol and the reduction in the absorption of solution with stable organic free radical DPPH , (1,1_diphenyl_2_picrylhydrazyl) by leaf extract at 525 nmwas detected and the scavenging cap

24、acity15was expressed as scavenging mg DPPH or p mol DPPH per gram dayweight.PEG osmotic treatment and measurement of tissue electrolyte leakage rateLeaf segments were floated on solution of 20% PEG 6000 or H2O for 32 h, then the electrolyte leakage rate was detected in distilled water before and aft

25、er boiling. 2 ResultsChanges in photosynthetic rate and growth In comparison with ambient CO2concentration (35 p mol/mol), the photosynthetic rates (Pn) in flag leaf of four cultivars at elevated CO2(60p mol/mol) showed three patterns (Fig.1A). At 60p mol/mol CO2,Pnin “IR72” and “Tesanai 2” was incr

26、eased by 42% and 19%, respectively, however, “Guichao 2” showed a similarPn with that at ambient CO2, whilePnin “IIyou 4480” was decreased by 39%, indicating a down_regulation to long term treatment of high CO2concentration. The reduction in stomata conductance in response to elevated CO2in “IR72” ，

27、 “Tesanai 2” and “Guichao 2” was significant but not in “IIyou 4480” .The analysis for growth rate calculated from the linear regression slope of biomassvstime (r=0.91- 0.98) indicated that rice growth rate during 10-80 d after transplanting was stimulated by elevated CO2(Table 1). Except the “IIyou

28、 4480” ， the differences of growth rate between ambient and elevated CO2were significant in other three cultivars. It means that the growth stimulation by elevated CO2was continuous from early growth stage to maturation stage. Low growth rate and lower correlation coefficient (r) in “IIyou 4480” at

29、elevated CO2were accordantwith its lowPnshown in Fig.1.Fig.1. Effect of CO2enhancement on photosynthetic rate (A) and stomatal conductance (B) in leaves of different rice cultivars. Under elevated CO2condition, total biomass per plant (with tillers) increased by 35%-40% in “IR 72”,“Tesanai 2”and“Gui

30、chao 2”at mature stage, but decreased by about 9% in “IIyou 4480” (Table 2). Dry weight of panicle increased significantly at elevated CO2in all four cultivars by 20% - 53%. The trend in the change in shootweightwas similarwith total biomass. On the contrary, the ratio of panicle DW to total DW decr

31、eased slightly at high CO2in IR72” and “Guichao 2” ， but an increase in this ratio was found in both “Tesanai 2” (1.09) and “IIyou 4480” (1.31), Thus, the allocation of assimilate between vegetative and reproductive growthwas affected by elevated CO2for rice cultivarswith intraspecific variation.PEN

32、G Chang_Lianet al: Response of rice grown in the field to elevated CO277 Table 1 Effect of elevated CO2on growth rate of rice Cultivar Growth rate(g DW plant-1 d-1) A B Correlation coefficient (r) A B IR72 0.271 0 0.422 1 0.930 4 0.951 4 Tesanai 2 0.278 8 0.441 9 0.979 9 0.962 5 Guichao 2 0.194 0 0.

33、512 9 0.937 6 0.962 5 Ilyou 4480 0.362 9 0.385 6 0.980 3 0.913 7 The slope of the linear regression equation calculated fromthe total dryweight per plant at 10, 20, 29, 36, 42, 49, 57 and 80 d after transplanting, respectively, was expressed asgrowth rate. A, 35p mol/mol CO2; B, 60p mol/ mol CO2.Lea

34、f。 13C,A 13C value and WUE Stable carbon isotope composition (6 13C) in leaves is in relation to atmospheric CO2concentration and plant species, reflectingthe integrated ecophysiological processes, especially the response of photosynthesis, to environmental change during the life span of leaf13.A 13

35、C (13C discrimination) is an important, convenient, and available measure for leafWUE,Pi/Pa, and even the plant productivity, as evidenced by a large number of studie- s16,17. There were a few reports concerning carbon isotope discrimination and water_use efficiency (only expressed by mg DW/g H2O or

36、 instantaneousPn/Tr) in common rice or upland rice16,18subjected to drought. However, little is known aboutWUEof rice grown at elevated CO2and estimated byA 13C technique. Our results in Table 3 indicated that in the open field,6 13C and A 13C values were in the range of -2.922% to -2.712% and 1.734

37、% to 1.934%, respectively, forfour rice cultivars. The intraspecific variation is about 0.20%o. In two plastic houses, the variation inb 13C and 13C between cultivars was less than 0.10%. Average ofb 13C in rice was -2.66% at 35p mol/mol CO2and -3.438% at 60p mol/mol CO2, close to -2.69% and -3. 30%

38、 in wheat grown at 32p mol/mol and 64 p mol/mol of CO2reported by Wong and Osmond19. As expected, elevated CO2caused the marked decrease inb 13C by 0.778% and increase inA 13C by 0.170% in rice. It is suggested thatthe affinityof rubisco to12CO2or its discrimination to13CO2during carboxylation were

39、raised at high CO2.Leaf integratedWUEcalculated from isotope data (Fig.2) showed thatWUEwas 2.28-2.56p mol CO2/ mmolH2O at 35p mol/mol CO2and 3.24-3.55p mol CO2/mmol H2O at 60p mol/mol CO2. The mean percentage of increase inWUEfor tested cultivars was ca. 38%, demonstrating that although with suffic

40、ient water, high CO2level was still favourable for highWUEof rice. In order to knowwhether increased leafWUEcould potentially lead to increase in the tolerance of rice towater stress, rice leaf segments sampled from plants at two CO2 concentrations were treated with PEG 6000 and then their relative

41、electrolyte leakage rate (ELR) was detected. As shown in Fig.3, osmotic effect of PEGresulted in the obvious electrolyte leakage in three rice cultivarsgrown at35 p mol/mol CO2. However, at elevated CO2, reduced ELR in all leaves treated withH2O (control) or 20% PEG so- lutionwas found except that o

42、f “Guichao 2” (no PEG). The results suggested that rice with highWUEat high CO2concentration displayed a high stability of membrane system in response to osmotic stress. Variations in electrolyte leakage rate caused by PEGosmosiswere negatively correlated with variations inWUE(Fig.4B). Moreover, the

43、re was a significant positive correlation between WUEand growth rate at different CO2concentrations (Fig.4A).Changes in scavenging capacity to DPPH free radical (SCDR)The formation of free radicals (oxygen free radical and organic free radical) occurs duringmetabolic processes and is enhanced by str

44、ess condition. The tolerance of plant to oxidative stress resulted from the accumulation of toxic free radical, usually depends on its scavenging capacity to free radicals20. It is proposed that the determination of scavenging capacity to organic free radical DP- PH (SCDR) is a simple, sensitive and

45、 direct assay for evaluation of antioxidative capacity in plants15. Fig.5 showed an increment in SCDR in rice flag leaves grown at 60p mol/mol CO2compared with that at 35p mol/mol CO2. The increment in SCDR was found either with the expression in scavenging DPPH of mg orp mol per g of leaf powder, a

46、nd the order of SCDR in tested cultivares was “IR72” “Guichao 2” “Tesanai 2” “IIyou 4480” .Fig.2. The integrated water use efficiency (WUE) in rice leaves grown at different CO2concentrations.Fig.3. Effect of CO2enhancement on the electrolyte leakage rate of rice leaves treated with PEG.A, IR72; B,

47、Tesanai 2; C, Guichao 2; D, IIyou 4480.78 植物學(xué)報 Acta Botanica Sinica Vol.44 No.1 2002Table 2 Effect of elevated CO2on total dry weight (DW) and panicle dry weightCultivars CO2conc (p mol/mol) Stem and leaf DW (g/plant) Panicle DW (g/plant) Total DW (g/plant) Panicle DW/total DWIR72 35 13.63+1.68 8.25

48、+1.37 21.88 + 2.66 0.370 60 19.57 + 0.84 11.06 + 0.31 30.63 + 0.61 0.361 60/35 1.436 1.341 1.40 0.958Guichao 2 35 12.02+1.87 9.04+0.69 21.06+1.56 0.429 60 17.04 + 0.84 11.49 + 0.56 28.53+1.90 0.403 60/35 1.417 1.272 1.355 0.939Tesanai 2 35 14.12+1.89 11.53 + 0.88 25.65 + 2.25 0.450 60 18.29+1.08 17.

49、69 + 0.76 35.98 + 2.03 0.492 60/35 1.295 1.534 1.403 1.093 IIyou4480 35 16.00+2.95 9.09 + 3.13 25.09+2.81 0.362 60 12.08 + 3.86 10.86+1.91 22.94+5.21 0.473 60/35 0.755 1.195 0.914 1.306Table 3 Effect of elevated CO2on6 13C value and13C discrimination ( 13C) in leaves of rice plants Cultivars Open fi

50、eld 6 13C (%) 13C (%) In the plastic house 35p mol/mol CO2 6 13C (%) 13C (%) 60p mol/mol CO2 6 13C (%) 13C (%)IR72 -2.922 + 0.020 1.934+0.013 -2.640 + 0.020 1.665 + 0.013 -3.497 + 0.022 1.877 + 0.011Guichao 2 -2.866 + 0.020 1.881 + 0.014 -2.750 + 0.023 1.770 + 0.014 -3.427 + 0.023 1.8110.012Tesanai

51、2 -2.7970.021 1.8150.012 -2.6640.018 1.6680.011 -3.401 0.024 1.881 0.011Ilyou 4480 -2.712 0.022 1.734 0.015 -2.636 0.021 1.661 0.012 -3.429 0.021 1.8310.012Table 4 The intraspecific variation of relative percentage in several parameters calculated at 60p mol/mol CO2comparedwith that at 35p mol/ mol

52、CO2Cultivar WUE Electrolyte leakage rate Scavenging DPPH capacity Growth rate IR72 127.430.80 93.852.33 131.750.59 175.14Tesanai 2 130.361.95 60.060.25 103.301.72 158.50 Guichao 2 155.805.05 74.831.65 114.083.21 264.38 Ilyou 4480 138.300.35 87.960.76 108.142.04 106.25Fig.4. Water use efficiency (WUE

53、) in relation to growth rate (A) and electrolyte leakage rate (B) under PEG osmosis in rice leaves grown at two CO2concentrotions.Intraspecific variation of some parameters at elevated CO2The relative percentage of the parameters calculated at 60p mol/mol CO2to that at 35p mol/mol CO2fromTa- ble 1 a

54、nd Figs.2,3,5 were a significantly various among the four cultivars (Table 4). In general, “Guichao” showed the highest relative increase inWUEand growth rate but a mild response of SCDR and electrolyte leakage rate upon PEG osmosis. The growth rate of “IIyou 4480” was lower and with a mild enhancem

55、ent of SCDR,ELR andWUE.Fig.5. Changes in scavenging capacity to organic free radical (DPPH) in rice leaves grown under different CO2concentrations.PENG Chang_Lianet al: Response of rice grown in the field to elevated CO2793DiscussionIn the previous study performed in green house, intraspecific varia

56、tion of rice in response to elevated CO2 was found in reproductive characters between “IR36” and“Fujiyama 5” 21, and also among other 17 cultivars7.Ziska and Teramura21reported that photosynthetic rate and biomass in response to 66p mol/mol CO2were not much different between “IR36” and “Fujiyama 5”

57、. The rapid loss ofPnenhancement was not observed. Row- land_Bamfordet al4found thatPnin “IR30” increased just from 16p mol/mol CO2to 50p mol/mol CO2, then it decreased slightly with the increasing CO2concentration. The changes inPnin the range of 16-90p mol/mol CO2 were accompanied with the obvious

58、 reduction of rubiscoactivity and content of rubisco protein. Tanget al22 proved that double atmospheric CO2concentration resulted in the decrease ofPn, rubisco activity and itsmRNAlev- el of rice. In the present study, the decrease ofPnin “IIyou 4480” at 60p mol/mol CO2was consistentwith the result

59、s of Rowland_Bamfordet al4and Tanget al22. Therefore, the loss ofPnenhancement in flag leaf of “IIyou 4480” (Fig.1A) mightbe caused bythe decreased rubisco activity and content through the inhibition of rubi- sco expression at translation level, and might be also due to the feedback inhibition of hi

60、gh carbohydrate content in the leaves grown at elevated CO2. It is interesting that a lowPnin “IIyou 4480” at elevated CO2did not limit the allocation of assimilate to panicle (Table 2). The panicle weight and panicle/total dryweightratiowere increased by 20% and 30%, respectively, at 60p mol/mol CO