Photosynth Res DOI 10.1007/s11120-015-0151-8


Photochemical properties in flag leaves of a super-high-yielding hybrid rice and a traditional hybrid rice (Oryza sativa L.) probed by chlorophyll a fluorescence transient Meiping Zhang1 • YongJie Shan2 • Leon Kochian3 Reto J. Strasser4 • GuoXiang Chen5

Received: 25 January 2015 / Accepted: 28 April 2015  Springer Science+Business Media Dordrecht 2015

Abstract Chlorophyll a fluorescence of flag leaves in a super-high-yielding hybrid rice (Oryza sativa L.) LYPJ, and a traditional hybrid rice SY63 cultivar with lower grain yield, which were grown in the field, were investigated from emergence through senescence of flag leaves. As the flag leaf matured, there was an increasing trend in photosynthetic parameters such as quantum efficiency of primary photochemistry (uPo) and efficiency of electron transport from PS II to PS I (WEo). The overall photosynthetic performance index (PIABS) was significantly higher in the high-yielding LYPJ compared to SY63 during the entire reproductive stage of the plant, the same to MDA content. However, uPo(=FV/FM), an indicator of the primary photochemistry of the flag leaf, did not display significant changes with leaf age and was not significantly different between the two cultivars, suggesting that PIABS is a more sensitive parameter than uPo (=FV/FM) during leaf age for distinguishing between cultivars differing in yield.

& Meiping Zhang [email protected]; [email protected] & GuoXiang Chen [email protected] 1

College of Life Sciences, ShanXi Normal University, Linfen 041004, Shanxi, People’s Republic of China


College of Geography Sciences, ShanXi Normal University, Linfen 041004, Shanxi, People’s Republic of China


USDA-ARS, Robert W. Holly Center for Agriculture and Health, Cornell University, Ithaca, USA


Bioenergetics Laboratory, University of Geneva, 1254 Jussy, Geneva, Switzerland


Key Lab of Biodiversity and Biotechnology of Jiangsu Province, College of Life Sciences, Nanjing Normal University, Nanjing 210097, People’s Republic of China

Keywords Chlorophyll a fluorescence transient  Flag leaf  JIP-test  Hybrid rice (Oryza sativa L.)  Photochemistry  Performance index

Introduction Photosynthesis is initiated when light is absorbed by the antenna pigment molecules within photosynthetic membranes. The absorbed energy is transferred as excitation energy and is either trapped at a photosynthetic reaction center and used to do chemical work, or dissipated mainly as heat and emitted fluorescence. Since photosynthesis is an essential part of the plant function and metabolism, and a number of stresses inhibit certain photosynthetic activities, in vivo chlorophyll a fluorescence has been applied extensively as a rapid and non-invasive tool for elucidating various aspects of photosynthetic performance in higher plants (Strasser et al. 2000, 2004). It is now very common to assess photosynthetic performance via fluorescence measurements associated with light utilization rather than from measurements of gas exchange, especially in the field (Osmond et al. 1999). Chlorophyll a fluorescence signals and fluorescence transients can be analyzed to provide detailed information about the structure, conformation, and function of the photosynthetic apparatus, especially for PSII (Strasser et al. 2004; Shabnam et al. 2014; Lu et al. 2003, 1999). Strasser et al. (2000) introduced a multi-parametric expression for these processes, namely the overall photosynthetic performance index (PIABS). This index takes into consideration the three main functional steps of photosynthetic activity by a PSII reaction center complex: (i) light energy absorption, (ii) trapping of excitation energy, and (iii) conversion of the excitation energy to electron transport. This


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analysis is called the JIP-test, which involves translating the fluorescence measurements of transients (O–J–I–P) into several phenomenological and biophysical expressions that evaluate PSII function (Strasser et al. 2004; Jeremy et al. 2012). A normal pattern for O–J–I–P (the fluorescence transient) includes two intermediate inflections J (at about 2 ms) and I (at about 20 ms) between the FO and FM levels. Due to the fact that the shape of the O–J–I–P fluorescence transient is sensitive to stresses caused by changes in many environmental conditions, the JIP-test is highly suited for in vivo investigations of the behavior of the plant photosynthetic apparatus in the field (Van Heerden et al. 2003; Lu and Avigad 1999a). It has been widely and successfully used for the investigation of PSII behavior in various photosynthetic organisms under different stress conditions which results in the establishment of different physiological states, as well as for the study of synergistic and antagonistic effects of different co-stressors (Lu and Avigad 1999b, 2002; Lu and Zhang 1999; Wen et al. 2005). However, the JIP-test is only rarely used for examination of dynamica photosynthetic decline during the progression of leaf senescence during the reproductive phase of crop development and yield. (Oukarroum et al. 2007; Prakash et al. 2003; Lu et al. 2002). Rice is an important crop for human survival and rice grain yield is mainly determined by leaf photosynthesis. Yoshida and Cock (1971) estimated that the potential net photosynthesis in rice leaves corresponds to 94 % of that in the whole plant, a fraction which is greater than in wheat and barley (Thorne 1965). For high yields, therefore, leaf photosynthesis needs to be enhanced and maintained for as long as possible during the reproductive stages of the plant (Makino et al. 1985). One of the primary avenues for increasing rice yields is via traditional and molecular breeding. Finding an efficient and rapid method for selection of high photosynthetic efficiency from large numbers of rice genotypes would be a very useful tool for the identification of high-yielding genotypes . However, it is unclear whether the heritability of heterotic of hybrid rice with regard to photosynthetic capacity is derived from its maternal or paternal line. Zhang et al. (2010) pointed out that the heterosis of hybrid rice was mainly from its maternal line, whereas Wang et al. (2004) stated the opposite conclusion. Therefore, more work needs to be done to elucidate the heterosis of hybrid rice. LiangYouPeiJiu (LYPJ) is a newly developed two-line intersubspecific rice hybrid (Lu and Zou 2000). Its yield is as high as 9750–10,500 kg hm-2, which is 1200–1800 kg hm-2 higher than that of ShanYou 63(SY63), a traditional cultivar that is at present cultivated in most of the rice growing areas in China (Lu and Zou 2000). Therefore, it will be very interesting to investigate the differences in fluorescence a measurements between the


super-high -yielding hybrid rice, LYPJ, and the lower yielding traditional rice cultivar, SY63 (as control). With that in mind, the objectives of this paper were (1) to demonstrate how to evaluate the photosynthetic decline in rice flag leaves during the reproductive phase of the rice plant using non-destructive, rapidly recorded measurements of OJIP fluorescence transients; (2) to examine how leaf age affects the shape of the O–J–I–P fluorescence transients; and (3) to investigate the overall photosynthetic performance index, PIABS, in the super-high-yielding hybrid rice. This research is necessary to determine which fluorescence transient parameters are sensitive to senescence, and which photosynthetic parameters might be related to the high rice yields in cultivar LYPJ. This information will be of value for further rice breeding for enhanced yield.

Materials and methods Field experiments were carried out at the Experimental Field of Jiangsu Academy of Agricultural Sciences, Nanjing, China (32030 N,118470 E). Nanjing is located in the monsoon climate area of the north subtropical zone, with four very distinctive seasons. Its annual average temperature is 15 ± 2.7 C and the annual precipitation is 989.3 ± 156 mm (Fan and Chen 1997). The soil types where the field experiments were conducted are clay loam with 1.25 g cm-1 bulk density. Temperature data were obtained from the local bureau of weather forecasting. During the period from 1 August (15 d before the first sampling) to 29 September 2010 (the last sampling date), the mean daily temperature was 25.6 ± 0.4 C (mean ± SE), the mean daily maximal temperature was 29.3 ± 0.5 C, the minimum daily temperature was 22.7 ± 0.4 C, mean daily precipitation was 44.7 ± 4.3 mm, and the mean daily relative humidity was 79.4 ± 0.8 %. A newly developed super-high-yielding hybrid rice (Oryza sativa L.), LYPJ, and a traditional hybrid rice, Shanyou63 (SY63), were grown in the field from May to October, 2010. The total N fertilizer applied was 225 kg per 667 m2, with a N–P–K ratio of 1:0.6:0.6. The plant density was 28 plants m-2. Sampling started from full expansion of the flag leaf (21 August, 2010) through advanced senescence (29 September, 2010, near grain harvesting time) on sunny days at 6–10 days intervals, depending on weather. Sampling date included the whole reproductive stage. Chlorophyll a fluorescence transients for the flag leaf on the main culm in each plant were recorded in the morning (07:30–11:30 h) in the field with a portable Plant Efficiency Analyser (PEA, Hansatech Instruments Ltd., King’s Lynn, Norfolk, PE 304NE, UK), with a data acquisition

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rate of 10 ls for the first 2 ms and every 1 ms thereafter, and 12 bit resolution (Strasser et al. 1995). Flag leaves were dark-adapted for at least 20 min before measurements and then illuminated with continuous red light (peak at 650 nm) for 1 s at 2000 mol m-2 s-1 (sufficient excitation intensity to ensure closure of all PSII reaction centers to obtain a true fluorescence intensity of FM), which was provided by an array of six light-emitting diodes focused on a 5-mm-diameter circle on the surface of the sample flag leaf. The fluorescence OJIP transients were analyzed according to the JIP-test equations (for a review, see Strasser et al. 2004). To facilitate the calculations and graphic presentations, the software Biolyzer v3.06 (developed in the Laboratory for Bioenergetics, University of Geneva, Switzerland) was used. The software is freely available by e-mail upon request from [email protected]. The JIP-test represents the translation of the original data to biophysical parameters that quantify the energy flow through PSII. The following parameters can be calculated from the original fluorescence measurements. These parameters, which all are in reference to time zero (onset of fluorescence induction) are (i) the specific energy fluxes (per reaction center) for absorption (ABS/RC) [ABS/RC = Mo(1/ VJ)(1/ uPo)], trapping (TRo/RC) [TRo/RC = Mo(1/VJ)], dissipation at the level of the antenna chlorophyll (DIo/RC)[DIo/ RC = (ABS/RC)–(TRo/RC)] and electron transport (ETo/ RC)[ETo/RC = (TRO/RC)wO]; (ii) the flux ratios or yields, i.e., the maximum quantum yield of the primary photochemistry (uPo) (uPo = TRo/ABS = FV/FM), the probability that a trapped exciton moves an electron further than QA (wEo)[wEo = ETo/TRo = 1 - VJ], the quantum yield of electron transport (uEo)[uEo = ETo/ABS = uPowO]; (iii) the phenomenological energy fluxes (per excited cross-section, CS) for absorption (ABS/CS) [ABS/CS = ABS/CSChl = Chl/CS or ABS/CSO approximated by FO], trapping (TRo/CS) [TRO/ CS = uPo(ABS/CS)], dissipation (DIo/CS)[DIO/CS = (ABS/CS) - (TRO/CS)] and electron transport (ETo/ CS)[ETo/CS = uPoWo(ABS/CS)]. The fraction of active PSII reaction centers per excited cross-section (RC/CS) [RC/ CS = (ABS/CS)(RC/ABS)] and pool size of electron carriers EC per reaction center (Sm) [Sm = EC/RC = (Area)/ (FM - FO)] are also calculated. The high sensitivity of the photosynthetic performance index PIABS {PIABS = [cRC / (1 - cRC)] [uPo /(1-uPo)][wO/(1 - wO)]} is a multi-parametric expression of these three independent steps contributing to photosynthesis. The expression cRC represents the fraction of chlorophyll a which build the reaction centers per total (RC and antenna) chlorophyll a. Malondialdehyde (MDA) was determined as an indicator of lipid peroxidation. 1.0 g fresh leaf tissue was homogenized in 10 ml of 5 % (v:v) TCA, then centrifuged at

20,0009g for 10 min. MDA in the supernatant was determined as thiobarbituric acid-reactive substances. The MDA content was expressed as nmol of MDA g-1 of fresh weight (Zhang et al. 2010). Statistical analysis Significant differences were determined by One-Way ANOVA at a probability level of p B 0.05 using Microcal Origin (version 7.0). Correlation coefficients were determined with SPSS (version 13.0), using the two-tailed test of significance of correlation coefficients.

Results As shown in Fig. 1, the diurnal mean temperature between two sampling dates (except for mean temperature for Aug. 21 which was calculated from the data measured between 14 and 21 Aug.) ranged from 22.1 to 26.8 C, with a mean value of 24.3 ± 1.0 C. The highest diurnal mean temperature ranged from 25.5 to 30.5 C, and the lowest diurnal temperature was between 19.9 and 23.5 C. The highest temperature was measured between 14 and 21 Aug, while the lowest temperatures occurred between 21 and 29 Sep. The changes in mean temperature between two sampling dates were different from that measured on the sampling date, as the temperature on the sampling date is dependent on the weather conditions for that day. The FO and FM values measured on flag leaves in the super-high-yielding hybrid rice line, LYPJ, and the traditional hybrid rice line, SY63, at different sampling dates are presented in Fig. 2. For FM, the maximum fluorescence value, all primary electron acceptors (QA) are in the reduced state (closed reaction centers), whereas minimal fluorescence in the dark-adapted state (FO) reflects a photosynthetic state with fully oxidized QA (open reaction centers). With respect to FO, there was a significant difference between LYPJ and SY63 only on Sept.29 (t = 3.032, p \ 0.05). Compared to SY63, the FM value for the LYPJ flag leaf was significantly different from emergence through senescence of flag leaves (t = 6.593, p \ 0.05). A steady decrease in FM values (p \ 0.05) and a small decrease in FO value (p [ 0.05) for LYPJ and SY63 during the whole growth period was observed. The relationship between the log function of the photosynthetic performance index (log PIABS) and the flag leaf quantum yield for electron transport is presented in Fig. 3. A clear linear relationship between these two parameters was observed, which is described by the equation [uEo = uPo. wEo = (TRo/ABS)(ETo/TRo) = ETO/ABS] with R2 = 0.9023 for LYPJ and R2 = 0.9606 for SY63.


Photosynth Res Fig. 1 Temperature at the sampling dates. a Data are the mean value during the day when sampling. b Mean temperature data were calculated from the temperature values measured between two consecutive sampling dates, except for the mean value for Aug. 21, which was calculated from the data collected between Aug. 14 and 21

Fig. 2 Dark-adapted FO and FM values measured in LYPJ and SY63; Top FM; Bottom FO; LYPJ: No. 1–8, 19–26, 37–46, 55–64; SY63: 9–18, 27–36, 47–54, 65–74; each are the average values of the sampling dates (month-day), for: a 8–21; b 8–29; c 9–05; and d 9–29. Samples no. 1–18 were taken from Aug. 14 to Aug. 21; No. 19–36 from Aug. 21 to Aug. 29; No. 37–54 from Aug. 29 to Sep. 5; and No.

55–74 from Sep. 5 to Sep. 29. Samples no. 1–8: LYPJ; No. 9–18: SY63; No. 19–26: LYPJ; No. 27–36: SY63; No. 37–46: LYPJ; No. 47–54: SY63; No. 55–64: LYPJ; and No. 65–74: SY63. First measuring day: Aug. 21; second measuring day: Aug. 29; third measuring day: Sep. 5; fourth measuring day: Sep. 29

A multi-parametric radar plot with the average for all 4 measuring days of quantification of certain selected photosynthetic parameters for LYPJ and SY63 is presented in Fig. 4. With respect to the overall photosynthetic

performance index, PIABS, as well as the other parameters that contribute to this index such as WEo,uPo, RC/ABS, the photosynthetic behavior of LYPJ was not clearly distinct from that of SY63 for several parameters. On the whole,


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Fig. 3 Correlation between the electron transport activity (ETO/ABS) and the driving force, DF = logarithm of the performance index (log PIABS), for flag leaves in the super-high-yielding hybrid rice, LYPJ, and the traditional hybrid rice, SY63, during the days from flag leaf emergence through senescence . open circle, open square: the mean value of the sampling dates (month-day), respectively, 1: 8–21; 2: 8–29; 3: 9–05; and 4: 9–29

Fig. 4 Average of selected functional and structural JIP-test parameters taken on 4 different days for variety LYPJ relative to the average analogous measurements taken on variety SY63 (radar plot center = 0.5, reference circle = 1, and maximum on the scale = 1.5)

from flag leaf emergence through senescence, the two rice hybrids displayed a similarly changing pattern for these parameters. The values of PIABS, uPo and RC/CSO were higher in LYPJ than in SY63; moreover, there were statistically significant differences between the two lines for PIABS and RC/CSO on the whole (p \ 0.05), which revealed differences in photosynthetic performance between LYPJ and SY63. Compared with SY63, LYPJ had a higher ETO/TRO = WO from Sep. 5 to 29 and on Aug. 21, but on

the whole, there was statistically no significant difference between the two lines (p = 0.283 [ 0.05). As shown in Fig. 4, when the Specific fluxes of ABS/ RC, TRO/RC, ETO/RC, DIO/RC were averaged over the four measuring days, the values from LYPJ were lower than in SY63, due to an increase in the RC density in the leaf (RC/CS). Phenomenological flux parameters for the average from all measuring days: ABS/CSO, TRO/CSO, and EIO/CSO were higher in LYPJ than in SY63, whereas DIO/CSO was lower than in SY63. Compared with SY63, LYPJ appeared to have some advantages in these parameters during the entire life span of flag leaves, especially with regard to more active reaction centers in LYPJ. The electron transport activity, ETO/CSO, was maintained at high values in LYPJ, and this difference was statistically significant (t = 3.248, p \ 0.05). The pool size of electron carriers, EC/RC = Sm, was found to be significantly higher in LYPJ than in SY63, which represents more redox energy stored in all closed reaction centers in the higher yielding line. Quantification of selected photosynthetic parameters taken on each sampling date between LYPJ and SY63 is summarized in Table 1. The specific energy fluxes per reaction center, ABS/RC, TRO/RC, ETO/RC, DIO/RC, are seen to be lower in LYPJ compared to SY63, and the phenomenological energy fluxes, TRO/CSO and EIO/CSO, were higher in LYPJ on each sampling date. ABS/CSo was lower in LYPJ on Aug. 21 but the difference was not statistically significant. The overall photosynthetic performance index, PIABS, was significantly different for LYPJ compared to SY63 on each sampling date. On the whole, the radar plot patterns for these parameters when averaged over all 4 measuring days was the same as it was for each specific sampling date. Malondialdehyde (MDA) content is used as a measure of membrane lipid peroxidation degree. As shown in Fig. 5, MDA content increased in the whole stage for LYPJ, and only decreased between September 5 and September 29 for SY63; moreover, it is significant (p \ 0.05). At the stage of full expansion, there were no significant differences among the two cultivars. LYPJ had lower MDA content than SY63 between full expansion and September 5. As shown in Table 2, there were significant differences for the correlations between specific photosynthetic parameters and temperature between the two rice hybrids. The mean temperature (Tmean) between two sampling dates had nearly the same significant effect on most of the fluorescence parameters as did the daily mean temperature (Timean) at each sampling date. There was one parameter, WO, that showed a significant correlation with temperature in both LYPJ and in SY63. Also, there were significant


Photosynth Res Table 1 Measurement of different photosynthetic parameters taken on the flag leaf of LYPJ and SY63 for each sampling date Parameter


Sampling date (month-day) 8–21






1.381 ± 0.0169**

1.451 ± 0.028**

1.637 ± 0.0456**

1.665 ± 0.0932*


1.677 ± 0.0455

1.634 ± 0.0444

1.896 ± 0.071

1.953 ± 0.0700



1.070 ± 0.0168**

1.148 ± 0.0154**

1.248 ± 0.0268

1.267 ± 0.0623


1.240 ± 0.0248

1.257 ± 0.0238

1.328 ± 0.0362

1.414 ± 0.0408



0.646 ± 0.0325

0.748 ± 0.0049**

0.679 ± 0.014

0.793 ± 0.0349


0.728 ± 0.0226

0.821 ± 0.008

0.701 ± 0.042

0.808 ± 0.0144


0.319 ± 0.0136** 0.437 ± 0.022

0.303 ± 0.014* 0.377 ± 0.021

0.389 ± 0.021** 0.567 ± 0.039

0.398 ± 0.032** 0.539 ± 0.030



307.887 ± 3.696**

269.142 ± 2.236**

258.300 ± 4.066**

241.260 ± 10.758**


258.155 ± 4.580

236.979 ± 6.137

219.006 ± 6.535

186.456 ± 4.014


424.875 ± 5.065

390.500 ± 7.201

421.300 ± 6.446

392.90 ± 4.390*


431.200 ± 5.581

385.0 ± 3.818

413.750 ± 14.749

362.800 ± 10.604



329.193 ± 5.171

308.858 ± 3.824*

321.387 ± 2.887**

299.664 ± 1.699**


319.241 ± 2.619

296.653 ± 3.595

290.088 ± 8.039

262.949 ± 6.521



198.548 ± 9.022

201.250 ± 1.309

175.226 ± 3.875*

188.207 ± 3.694**


187.547 ± 5.756

194.485 ± 4.982

153.134 ± 9.701

150.741 ± 4.275




95.681 ± 4.115* 111.959 ± 3.950

81.641 ± 3.711 88.348 ± 2.920

99.913 ± 4.451* 123.662 ± 8.126

93.236 ± 3.478 99.851 ± 4.670



25.903 ± 2.806

41.682 ± 3.472

15.551 ± 2.731

19.332 ± 2.130



88.755 ± 37.986

42.814 ± 6.548

27.791 ± 0.941

25.737 ± 1.286**



40.551 ± 4.225 0.603 ± 0.024

40.070 ± 1.353 0.652 ± 0.009

33.098 ± 1.178 0.546 ± 0.015

20.908 ± 0.666 0.628 ± 0.011*


0.587 ± 0.017

0.655 ± 0.011

0.527 ± 0.027

0.574 ± 0.011

uPo = TRo/ABS

40.792 ± 5.334*

50.489 ± 3.884*

25.529 ± 3.008*

35.023 ± 3.471**


0.775 ± 0.009**

0.791 ± 0.014

0.764 ± 0.007**

0.763 ± 0.030


0.741 ± 0.006

0.771 ± 0.008

0.703 ± 0.010

0.726 ± 0.093

* Correlation is significant at the 0.05 level (2-tailed) ** Correlation is significant at the 0.01 level (2-tailed)

correlations between leaf age and parameters as RC/CSO, TRO/RC, TRO/CSO in SY63, which indicates that photosynthetic performance in SY63 is sensitive to leaf age.

Discussion The multi-parametric radar plot (Fig. 4) was clearly able to distinguish between the two cultivars with regard to photosynthetic performance (phenotypic response). The parameters, TRO/CSO, ETO/CSO, for LYPJ when averaged over all of the measurements were higher than when measured on SY63, while DIO/CSO was higher in SY63. This indicates that the capacity for CO2 fixation is higher in super-high-yielding LYPJ rice line compared to the traditional breeding line, SY63. With regard to the energy flux parameters depicted in Table 1, electron transport per leaf cross-section


(ETO/CSO) increased late in plant development in LYPJ, suggesting that as the leaf matured there is an increased activation of reaction center complexes (activation of the oxygen-evolving system) per excited cross-section (i.e., per active measured leaf area). The distribution of the excitation energy between the photosystems is regulated by the phosphorylation of LHCII (Barber 1986; Allen 1992), which then detaches from PSII and migrates to the vicinity of PSI in the non-appressed membrane regions of the grana (Schreiber et al. 1998). Among all parameters investigated, leaf age had a significantly negative influence on RC/CSO, TRO/CSO, TRo/ RC in SY63 as shown by the correlation coefficients in Table 2. In the context of the OJIP-transient, dissipation refers to the loss of absorbed energy through heat, fluorescence, and energy transfer to other systems (Strasser et al. 2000). Therefore, dissipation can be thought of as the absorption of photons in excess of what can be trapped by

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the RC. From Table 1, it can be seen that the effective dissipation in an active RC (DIo/RC) was higher in SY63 than in LYPJ from emergence through senescence of flag leaves.

Fig. 5 Changes in malondialdehyde (MDA) in flag leaves of the super-high-yielding hybrid rice, LYPJ and a traditional hybrid rice, SY63 after full expansion of flag leaves Table 2 Correlation coefficients between fluorescence parameters, temperature, and leaf age in a high-yielding hybrid rice cultivar, LYPJ, and a traditional hybrid rice cultivar, SY63

The linear correlation between the driving forces DF and ETo/ABS suggested that changes in electron transport beyond QA determined the changes in the driving force, DF, for LYPJ and SY63. The O–J–I–P fluorescence transient is rich in information and can be used to derive a number of parameters by the so-called JIP-test that quantifies the stepwise flow of energy through PSII at the reaction center (RC) level as well as at the excited leaf cross-section (CS) level (Strasser and Strasser, 1995). Van Heerden et al. (2004) found the overall photosynthetic performance index, PIABS, is particularly useful in revealing differences in the response of PSII to dark chilling in two soybean cultivars, Maple Arrow and Java 29 (Hume and Jackson 1981; Lawn and Hume 1985). In the present work, PIABS is higher in LYPJ than in SY63 from emergence to senescence (p \ 0.05), indicating that the photosynthetic physiological activity of LYPJ was higher than SY63. Meanwhile, environmental temperature did not significantly affect LYPJ’s photosynthetic performance. Similar results were observed in the fully expanded leaves of SY63. In all genotypes that were studied by Strauss et al. (2006), the PIABS values showed a clear increase during the progression of plant development Tmin





Leaf age

































































-0.456 -0.537

-0.094 0.888

-0.033 0.869

-0.020 0.874

0.215 -0.838

0.654 -0.847

0.859 -0.763













































































































0.809 0.616

-0.456 -0.181

-0.504 -0.231

-0.499 -0.223

0.148 -0.112



-0.337 -0.579

-0.594 -0.798

* Correlation is significant at the 0.05 level (2-tailed) ** Correlation is significant at the 0.01 level (2-tailed)


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during the experimental period. This is a common phenomenon in plants; for example, in dicot species, photosynthetic activity is dependent on the stage of leaf development (Van Heerden et al. 2004). Photosynthetic activity increases during leaf development and gradually reaches a maximum in the mature fully expanded leaf (Gepstein 1988; Strauss et al. 2006. However, PIABS decreased markedly between Aug. 29 and Sep. 5 and then increased significantly on Sep. 29. Statistical analysis revealed that there was a non-significant correlation between PIABS and temperature. Relatively speaking, the minimum temperature of sampling dates (Timin) had more correlation with PIABS than the other temperature parameters (Tmax, Tmin, Timean, Timax, and Tmean, Table 2). Under natural in vivo conditions, the fluorescence behavior of any photosynthetic system changes continuously following its adaptation to a frequently changing environment (Oukarroum et al. 2012). Therefore, under normal environmental conditions, the higher PIABS value was not attributable to environmental temperature fluctuation and leaf age. It appears that the index PIABS reflects the photosynthetic performance of the rice leaf sample at the given moment. The expression FV/FM = TRo/ABS = uPo is widely used to determine the maximum quantum yield of the primary photochemistry of PSII (Kitajima and Butler 1975), or the intrinsic quantum efficiency of the PSII units (Henriques 2003). Van Heerden et al. (2004) demonstrated that the maximum uPo is not a sensitive parameter for the assessment of dark chilling stress in soybean. But what about its performance with regard to leaf maturation and senescence? In the present work, as shown in Table 2, uPo did not show a significant change with leaf age for the two cultivars, as seen from the low correlation with leaf age (r = 0.383–0.584), suggesting that FV/FM may be also insensitive to leaf age. Additionally, there was no significant difference in uPo on the sampling day between LYPJ and SY63, two cultivars with very different grain yield, indicating that uPo may lack the capacity to distinguish between the two cultivars with regard to the relationship of photosynthesis and yield. Therefore, the changes in fluorescence signal, quantified by the PIABS as an overall photosynthetic performance index, might be a useful tool for evaluating differences in grain yield between cultivars. Membrane destabilization is attributed to lipid peroxidation (zhang et al. 2010). Lipid peroxidation is an integral feature of membrane deterioration leading to cell death. Studies show that the physiological properties of membranes are deleteriously altered during senescence on cellular membranes (Dalal and Khanna-Chopra 1999). There was a steady increase in MDA content for two cultivars before Sep. 5, whereas a sudden decrease in MDA


content after Sep. 29 for SY63, which indicated that irreversible senescence took place in leaves of SY63, which is consistent with the changes of photosynthetic parameters. The difference in the type of information contained in PIABS and uPo might be responsible for the different responses of the two parameters. The overall photosynthetic performance index on an absorption basis (PIABS) is a multi-parametric expression that combines three partial responses of the photosynthetic apparatus, namely the density of operative photosystems (reaction centers per chlorophyll, RC/ABS), the ratio of the de-excitation rate constants for photochemical and non-photochemical events as kp/kN = FV/FO = uPo/(1 - uPo), and the efficiency of the conversion of red-ox energy at QA /QA to electron transport toward the plastoquinone pool WEo/(1 - WEo). The three main functional steps (light energy absorption, excitation energy trapping, and conversion of excitation energy to electron transport) are combined to describe the photosynthetic activity of a PSII reaction center complex with this multi-parametric expression (Strasser et al. 1999, 2004; Tsimilli-Michael et al. 2000). In contrast, uPo = FV/ FM contains only information about the quantum yield of primary photochemistry. In the context of the O–J–I–P fluorescence transient, the PIABS parameter is also a function of the fluorescence extremes FO (O-step) and FM (Pstep), the intermediate step J (FJ at 2 ms), and the slope at the origin of the fluorescence rise (Strauss et al. 2006), whereas the expression: uPo = FV/FM is derived only from the fluorescence extremes, FO and FM, and is independent of the trajectory which the fluorescence intensity reaches its maximal values (Van Heerden et al. 2004). An increase in FO and decrease in FM indicates a block in the electron transport to QA according to Krause and Weis 1991. Based on the basic laws of photochemistry, FO can be written as ABS. kF.(kN ? kP) and FM as ABS. kF/kN. Therefore, a constant FO for both cultivars and a higher FM for the super-high-yielding cultivar, LYPJ, means that kP is higher and kN is lower in the super-high-yielding cultivar, LYPJ, compared to the traditional hybrid, SY63 (Fig. 2). In comparison with its parents, LYPJ has a higher uPo and therefore a higher ratio of FV/FO during the entire life span of its flag leaves, indicating that the hybrid combination results in a higher activity of PSII and a higher efficiency of the primary conversion of light energy into redox-energy. Similar results were also reported with SY63 and its parents (Zhang et al. 1994). These findings further our understanding of the contribution of photosynthesis to rice heterosis and high-yielding character of hybrid rice. In conclusion, the overall photosynthetic performance index, PIABS, was found to be a very sensitive indicator with regard to distinguishing the photosynthetic performance of different cultivars. Leaf age had a high

Photosynth Res

correlation with TRO/CSO, TRo/RC, and RC/CSo in the two cultivars. These indices could possibly to some extent be of value as screening tools for the impact of leaf age on performance in different crop cultivars, and for cultivars which are not very sensitive to temperatures changes. Rice breeding has led to the development of a plant type with good light utilization, and also with less lodging, greater resistance to some environmental stresses (strong irradiation, drought, and low/high temperature), higher resistance to several major diseases caused by insects and pathogens, and effective fertilizer utilization. Our present findings also show that enhanced light utilization of a single leaf (here the flag leaf) is linked to the higher overall photosynthetic performance in the super-high-yielding rice hybrid, LYPJ, during the life of the flag leaf. This may play a role in this hybrid line’s increased grain yield. Our present findings show that the super-high-yielding hybrid rice (Oryza sativa L.), LYPJ, employs a multi-faceted strategy with regard to higher crop yield. This is a natural positive selection criterion for higher survival. In comparison to the traditional, already high-yielding hybrid rice, SY63, we found in LYPJ: •

A quantitative increase in the targets which constitute to the performance index, P, including 1. 2. 3.

Quantum yield of primary photochemistry TRo/ ABS = uPo; Efficiency of transporting electrons from Q-A toward plastoquinone as ETo/TRo = WEo; The increase in the fraction cRC of chlorophyll acting as active reaction center, relative to the total chlorophyll content.

An increase in the qualitative target due to 1. 2.


An increase in the density or the packing of active reaction centers per leaf area (RC/CS); An increase in the biochemical components, building up the total electron carrier pool per reaction center EC/RC; A decrease in the specific energy losses per active reaction center seen as a decrease in DIo/RC.

The multi-targeted hybridization strategy to generate this line seems to have an advantage compared to very specific genetic modifications, due to the fact that harmonic biological balances in the metabolism as a whole can be maintained and optimized. Fluorescence techniques such as the analysis of the fast OJIP fluorescence rise and in general opto-electronic approaches for in vivo probing of the vitality and productivity of crop plants in the field are proving to be a useful tool for helping to facilitate crop improvement.

Acknowledgments Financial support was provided by the National Natural Sciences Foundation of China (No. 31271621 and No. 31301245); Natural Sciences Foundation of Shanxi province (2009021030-2); Open project funds of State Key Laboratory of Crop Biology of Shandong Agricultural University (2014KF03); and by Shanxi Scholarship Council of China (No. 2013-067). We also want to thank Mr. Lv ChuanGen for his help with materials and Zhang ChengJun for his guide with our experiment.

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Photochemical properties in flag leaves of a super-high-yielding hybrid rice and a traditional hybrid rice (Oryza sativa L.) probed by chlorophyll a fluorescence transient.

Chlorophyll a fluorescence of flag leaves in a super-high-yielding hybrid rice (Oryza sativa L.) LYPJ, and a traditional hybrid rice SY63 cultivar wit...
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