Samara is the generative organ ( seed ) for many tree species in the waterless land of northwesterly China. It is ecologically of import in population development due to its dispersion map. However, information on its photosynthesis and consequence of environmental emphasiss on its photosynthesis is still really limited. In the present survey, comparative responses of photosystem II ( PSII ) activity in key fruit and foliage of Siberian maple to short-run chilling/freezing and subsequent recovery potency were relatively investigated by utilizing polyphasic fluorescence trial. The key fruit had more efficient photosynthesis ( Fv/Fm and PIABS ) and more efficient negatron conveyance (degree FahrenheitEo ) but lower energy dissipation ( DIo/RC ) than foliage. By and large, the PSII public presentation and the negatron conveyance for both key fruit and foliage were inhibited under low temperature emphasis, accompanied by an addition of energy dissipation in PSII reaction centres ( RCs ) . PSII of both key fruit and foliage was non markedly affected by chilling and can acclimatize to chilling emphasis. Short-run freeze could wholly suppress PSII activity in both key fruit and foliage, indicated by the bead of values of Fv/Fm, PIABS,degree FahrenheitEo to nothing. PSII functional parametric quantities of short-run dark frozen key fruit could be mostly cured whereas those of frozen foliage could non be recovered. The higher tolerance of key fruit to short-run low temperature emphasis than foliage is of great ecological significance for seed development, population constitution of Siberian maple.
Keywords:key fruit ; photosystem II ; JIP-test analysis ; chlorophyll fluorescence
Samara has an evolutionary advantage because the seed can be dispersed to a long distance through wings by air current ( Osada et al. 2001 ) . Samara wing was reported to hold photosynthetic activity to back up its ain development ( Ashton 1989 ) . Evidences from anatomy and physiology show that green key fruits photosynthesize and contribute to the C balance and growing of the fruit ( Bazzaz and others 1979 ; Peck and Lersten 1991 ) . Since the seed is embedded in the wings, the quality of the seed should be partially dependent on the photosynthetic public presentation of key fruit. However, information on photosynthetic procedure in key fruit is still really limited.
Siberian maple (Acer ginnala) is widely present in the waterless land of northwesterly China. Its fruit is a v-shape key fruit composed of a seed embedded in two membranous wings. The Siberian maple key fruit appears in late March and early April. At the same clip ( from March to April ) , the air temperature in northwesterly China frequently drastically fell to chilling temperature or freezing temperature. Therefore the key fruit frequently encounters chilling or stop deading emphasis during its development. The consequence of low temperature ( chilling and stop deading ) on the photosynthesis of key fruit is still unknown.
The fast rise Chlafluorescence ( O-J-I-P ) rise transient was believed to supply of import information on the photochemical activity of photosystme II ( PSII ) and the associated filling of the plastoquinone pool ( Krause and Weis, 1991 ) . Strasser and Strasser ( 1995 ) established a process for quantitatively ciphering several phenomenological and biophysical parametric quantities on the footing of O-J-I-P curve, known as the JIP-test. The fast rise Chlafluorescence and the JIP-test has been proved to be a utile tool for probe of PSII map under assorted environmental emphasiss ( Strasser and Strasser, 1995 ; Eullaffroy et al. , 2007 ; Pan et al. , 2008 ; Pan et al. , 2009 ) .A
In the present survey, comparative consequence of short-run cooling and freeze emphasiss on PSII activity in key fruit and foliage of Siberian maple and subsequent recovery were investigated by utilizing polyphasic rise Chlafluorescence and JIP-test analysis. The aims of this survey were to: ( 1 ) compare the responses of PSII activity between key fruit and foliage to low temperature emphasiss ; ( 2 ) elucidate the mechanisms involved in the consequence of low temperature on PSII in key fruit and foliage ; and ( 3 ) assess the recovery potency of key fruit and foliage from the suppression induced by low temperature emphasis.
2 Materials and methods
2.1 Plant stuff
On April 20, 2009, Siberian maple (Acer ginnala) shoot film editings with about four-week old key fruit and foliages were obtained from Xinjiang Branch of Chinese Academy of Sciences, Urumqi, China. The film editings were grown in glassy containers incorporating tap H2O in a growing chamber with 12 h photoperiod and photosynthetic photon flux denseness ( PPFD ) of 200 Aµmol m-2 S-1 at 22-25? . The chlorophyll fluorescence of key fruit and foliage were monitored sporadically. The JIP-test parametric quantities for key fruit and foliage of film editings grown in tap H2O are stable for at least two yearss. Therefore, tap H2O was used as the back uping medium for film editings.
2.2 Treatment with low temperature
The film editings were incubated in the dark at 4? for chilling experiment and -4? for stop deading experiment, severally. After 12-hour chilling/freezing intervention, the film editings were returned to normal conditions ( photosynthetic photon flux denseness ( PPFD ) of 200 Aµmol m-2 S-1 and temperature of 22-25? ) . In order to measure their recovery potency from the harm, induced by low temperature emphasis, the film editings without low temperature intervention were kept under normal conditions all the clip and were used as the control. A
2.3 Polyphasic fast fluorescence initiation and JIP trial
When illuminated with high strength actinic visible radiation, dark-adapted oxygenic photosynthetic being shows the polyphasic rise with the basic stairss from the ‘origin ‘ ( O ) through two ‘inflections ‘ ( J and I ) to a ‘peak ‘ fluorescence degree ( P ) ( Strasser and Strasser 1995 ) . The polyphasic fast-phase fluorescence initiation curve provides valuable information on the magnitude of emphasis effects on photosystem II ( PSII ) map. Strasser and Strasser ( 1995 ) has developed the JIP-test for quantifying PSII map by the biophysical parametric quantities calculated from the O-J-I-P fluorescence transient informations. The JIP-test has been proved to be a valid tool for investigation of the behaviour of the photosynthetic setup under assorted environmental emphasiss ( e.g. , Nussbaum et al. , 2001 ) . In the present survey, samples ( key fruit and foliage ) were adapted in the dark for 5 min before measuring of chlorophyll fluorescence. The chlorophyll fluorescence transient was recorded up to 1 s on a logarithmic clip graduated table, with a information acquisition every 10 Aµs for the first 2 MS and every 1ms thenceforth, by a handheld fluorometer ( Fluopen-100, Brno, Czech ) . Each measured O-J-I-P initiation curve was analyzed harmonizing to the JIP-test ( Strasser and Strasser, 1995 ) . The undermentioned informations were straight obtained from the fast rise kinetic curves: Fo, the initial fluorescence, was measured at 50 Aµs, at this clip all reaction centres ( RCs ) are unfastened ; FJ and FI are the fluorescence strength at J measure ( at 2 MS ) and I step at 30ms ) ; FM, the maximum fluorescence, was the peak fluorescence at P measure when all RCs were closed after light ; F300Aµs was the fluorescence at 300 Aµs. Selected JIP-test parametric quantities quantifying PSII behaviour were calculated from the above original informations as the expression in Table 1 ( Strasser et al. , 2000 ) .
Each experiment was at least triplicated and the consequences were presented as mean.
Table 1 Formulae and footings used in the JIP-test ( Strasser et al. , 2000 )
Formulae and footings IllustrationsVJ = ( F2ms - Field-grade officer ) / ( Fm - Field-grade officer ) A Relative variable fluorescence strength at the J-step Mo = 4 ( F300 Aµs - Field-grade officer ) / ( Fm - Field-grade officer ) Approximated initial incline of the fluorescence transientdegree FahrenheitPo = TRo/ABS = [ 1- ( Fo/Fm ) ] = FV/Fm Maximum quantum output for primary photochemistry ( atT=0 )degree FahrenheitEo = ETo/ABS = [ 1- ( Fo/Fm ) ] aˆ??O Quantum output for negatron conveyance ( atT=0 )?o =A ETo/TRo = ( 1-VJ ) Probability that a at bay exciton moves an negatron into the negatron conveyance concatenation beyond QA ( atT=0 ) ABS/RC =Mo aˆ? ( 1/VJ ) aˆ? ( 1/degree FahrenheitPo ) Absorption flux per reaction centerA A A A A A TRo/RC =Mo aˆ? ( 1/VJ ) Trapped energy flux per reaction centre ( atT=0 ) DIo/RC = ( ABS/RC ) - ( TRo/RC ) Dissipated energy flux per reaction centre ( atT=0 ) PIABS = ( RC/ABS ) aˆ? [degree FahrenheitPo / ( 1-degree FahrenheitPo ) ] aˆ? Performance index on soaking up footing [?O / ( 1-?O ) ]
Table 1 selected JIP-test parametric quantities for key fruit and foliage. Each information represents the average value of at least three pieces of key fruits or foliages.
Fv/Fm PIABS? O fEo ABS/RC TRo/RC DIo/RC leaf 0.798 1.433 0.45 0.359 2.263 1.807 0.456 key fruit 0.826 3.987 0.627 0.518 2.006 1.658 0.349
3.1 PSII activities in key fruit and foliage
Typical OJIP fluorescence transient curves for key fruit and foliage were shown in Fig. 1. Selected JIP-test parametric quantities for key fruit and foliage were presented in table 1. Samara had higher negatron conveyance flux (degree FahrenheitEo and?O ) and higher photosynthetic efficiency ( Fv/Fm and PIABS ) than foliage. In the instance of energy flux, key fruit had lower value of ABS/RC and lower value of TRo/RC than those for foliage, ensuing in lower dissipated energy flux ( DIo/RC ) in key fruit than in foliage. The difference of JIP-test parametric quantities between foliage and key fruit proposing that key fruit had more efficient photosynthetic procedure with more efficient negatron conveyance and energy ordinance.
Fig. 2 JIP-test parametric quantities for key fruit and foliage during chilling intervention and their recovery: the key fruits and foliages were dark chilled at 4? for 12 H ; After 12-hour cooling intervention, the key fruits and foliages were returned to the normal conditions ( at 22-25? with 200 Aµmol m-2 S-1 PPFD ) to retrieve from chilling emphasis ; Chlorophyll fluorescence of the key fruits and foliages were measured sporadically during their cooling and recovery period. Each information point represents the average value of at least three pieces of key fruits or foliages.
3.2 Effect of chilling on PSII activity and recovery
Selected JIP-test parametric quantities for key fruit and foliage during their 12-hour cooling and subsequent two-hour recovery are presented in Fig. 2. The maximal PSII photochemical quantum output ( Fv/Fm ) for key fruit and foliage declined somewhat during the first 2-hour cooling and so bit by bit regained to the normal degree during the subsequent 4-hour cooling. The values of Fv/Fm for key fruit and foliage changed small during the following 6-hour cooling, bespeaking the acclimatization of the key fruit and foliage to chilling emphasis. The values of Fv/Fm fell within the scope from 0.816 to 0.830 for key fruit and 0.783-0.804 for foliage, severally over the scarey period. The photosynthesis public presentation ( PIABS ) for key fruit decreased during the first one-hour cooling and regained somewhat during the following hr and so remained changeless. PIABS for foliage by and large showed a diminishing tendency during the first six-hour cooling and so changed small. Electron conveyance flux (degree FahrenheitEo and?O ) changed somewhat under chilling emphasis. For foliage,degree FahrenheitEo and?O declined with increasing chilling clip during the first six hours and so was kept about a changeless value. Absorption flux per RC ( ABS/RC ) and trapped energy flux per RC ( TRo/RC ) for foliage increased during the first 6-hour cooling and so remained changeless. In the instance of key fruit, ABS/RC and TRo/RC increased during the first 4 H, decreased a small during the following 2 hours and so changed small. The alteration forms of ABS/RC and TRo/RC resulted in the similar alteration form of debauched energy flux per RC ( DIo/RC ) .
After the key fruit and foliage were exposed to dark chilling emphasis for 12 Hs, they were transferred to the normal conditions for recovery. Fv/Fm, PIABS,degree FahrenheitEo and?O for key fruit changed small during recovery whereas these parametric quantities for foliage quickly returned to normal after surcease of chilling intervention. The energy flux ( ABS/RC, TRo/RC and DIo/RC ) for both key fruit and foliage quickly decreased to the normal values during the 2-hour recovery.A
3.3 Effect of stop deading on PSII activity and recovery
JIP-test parametric quantities for key fruit and foliage after exposed to dark stop deading at -4? for 12 Hs and their recovery are presented in Fig. 3. Photosynthetic public presentation ( Fv/Fm and PIABS ) and electron conveyance per RC (degree FahrenheitEo ) were wholly inhibited after the key fruit and foliage were exposed to stop deading emphasis for 1h. Electron conveyance beyond QA for key fruit and foliage was reduced by 70.3 % and 15.3 % , severally. On the contrary, energy flux per RC ( ABS/RC, TRo/RC and DIo/RC ) in key fruit and foliage increased drastically. The JIP-test parametric quantities changed small during farther 11-hour exposure to stop deading emphasis. However, recovery potency of key fruit differed greatly from that of foliage. Photosynthesis efficiency and negatron conveyance in 12-h frozen foliage could non retrieve. The values of energy flux parametric quantities for foliage still remained at high degree. For 12-h frozen key fruit, photosynthesis and electron conveyance activity significantly recovered during 3-hour recovery. The energy flux decreased to the values near to those of the control after 3-hour recovery. After 12-hour recovery, Fv/Fm for key fruit to the full recovered to normal whereas PIABS anddegree FahrenheitEo merely recovered to 20.8 % and 57.6 % of the control, respectively.A
Fig. 3 Recovery of the JIP-test parametric quantities for key fruit and foliage after exposed to -4? in the dark for 12 H: the key fruits and foliages were exposed to -4? in the dark for 12 H and so were returned to the normal conditions ( at 22-25? with 200 Aµmol m-2 S-1 PPFD ) in order to retrieve from stop deading emphasis ; Chlorophyll fluorescence of the key fruits and foliages were measured sporadically during their recovery period. Each information point represents the average value of at least three pieces of key fruits or foliages.
Our survey revealed that there is pronounced difference of PSII activity between the key fruit and the foliage ( Fig. 1 ) . The key fruit has higher photosynthetic efficiency ( Fv/Fm and PIABS ) and higher negatron conveyance flux (degree FahrenheitEo ) than foliage ( table 2 ) . The higher value of?O means that negatron conveyance beyond QA- in key fruit was more efficient than foliage ( Strauss et al. 2006 ) . The higher Fv in key fruit farther indicates the higher PSII capacity to cut down plastoquinone in key fruit ( Bukhovet al. , 1987 ) . The differences in?O and Fv resulted in higher negatron conveyance flux (degree FahrenheitEo ) on the whole. The lower values of ABS/RC, TRo/RC and DIo/RC in key fruit than foliage shows that samara has more efficient energy ordinance mechanisms than foliage.
PSII has been demonstrated to be one of the sensitive mark sites for low temperature emphasis ( Demmig-Adams and Adams, 1992 ; Jung and Steffen, 1997 ; Strauss et al. , 2006 ; 2007 ; Pagter et al. , 2008 ) . In our survey, OJIP fluorescence transient and the JIP-test analysis clearly showed that PSII map in key fruit and foliage of Siberian maple was affected by short-run cooling or freezing temperature intervention.
Similar to a figure of old surveies ( Demmig-Adams and Adams, 1992 ; Li et Al. 2004 ; Jung and Steffen, 1997 ; Strauss et al. , 2006 ; 2007 ; Pagter et al. , 2008 ) , the maximal primary PSII photochemical quantum output ( Fv/Fm ) for key fruit and foliage declined under low temperature emphasis. Fv/Fm for key fruit and leaf responds to chilling emphasis in a different manner to stop deading emphasis. Chilling at 5? merely somewhat reduces Fv/Fm foremost and so returned to normal ( Fig. 2-a ) , proposing that PSII of both key fruit and foliage is non significantly affected and can acclimatize to sudden chilling emphasis. However, stop deading intervention at -4? decreased Fv/Fm for both key fruit and foliage to zero ( Fig. 3-a ) , bespeaking that photochemical activity was wholly suppressed by stop deading intervention. PIABS for seems to be a more sensitive index under chilling emphasis than Fv/Fm ( Fig. 2-a, B ) . Marked lessenings in PIABS for both key fruit and foliage induced by chilling were observed. Several earlier surveies besides reported that PIABS was a much more sensitive parametric quantity for separating differences in dark chilling response than Fv/Fm ( Strauss et al. , 2006 ; 2007 ; Pagter et al. , 2008 ) . However, Pagter et Al. ( 2008 ) pointed out that PIABS may non be more suited than Fv/Fm if the differences in chilling sensitiveness were non important. Under stop deading emphasis, PIABS responds in the similar form as Fv/Fm ( Fig. 3-a, B ) , that is, PIABS for both key fruit and foliage was quickly reduced to zero after one-hour freeze intervention.
Under chilling emphasis, negatron conveyance (degree FahrenheitEo and?O ) for foliage was markedly decreased but somewhat altered for key fruit ( Fig. 2-c ) . This consequence suggested that negatron conveyance, particularly beyond QA in foliage, was more susceptible to chilling emphasis than in key fruit. Electron conveyance in both key fruit and foliage was wholly blocked under stop deading emphasis ( Fig. 3-c ) . Since from O to J in the reflects decrease of QA to QA- and J to I to P decrease of the PQ pool ( Strasser et al. , 1995 ) , lessening in?O could be attributed to the diminishing PQ pool size in response to low temperature emphasis ( Martin et al. , 1978 ; A-quist and A-gren, 1985 ) . A-quist and A-gren ( 1985 ) reported that the considerable lessening in the ratio of PQ pool size to the primary negatron acceptor ( Q ) under winter emphasis corresponded to the suppression of whole concatenation negatron conveyance.
An addition in evident aerial size ( ABS/RC ) was induced by low temperature emphasis ( Fig. 2-d, vitamin E, degree Fahrenheit and Fig. 3-d, vitamin E, degree Fahrenheit ) , bespeaking that some of RCs were inactivated ( Kruger et al. , 1997 ) . The at bay energy flux per RC ( TRo/RC ) besides increased but of much smaller magnitude. The big addition in ABS/RC accompanied with little addition in TRo/RC resulted in pronounced debauched energy flux per RC ( DIo/RC ) . The increased dissipation of energy flux led to diminish in efficiency for transition of excitement energy flux to electron flux (?O ) . Similar response of energy flux through PSII in soya bean to dark cooling was observed ( van Heerden et al. , 2003 ) . Taking the alterations of these parametric quantities together, it can be concluded that the repressive consequence of chilling temperature on photosynthetic public presentation ( PIABS ) was chiefly resulted from the decelerating down of negatron conveyance beyond QA and an addition in thermic energy dissipation.
All the PSII functional parametric quantities of chilled key fruit and foliage can quickly retrieve to normal ( Fig. 2 ) . However, the PSII functional parametric quantities of short-run dark frozen key fruit can be mostly cured whereas those of frozen foliage can non be recovered ( Fig. 3 ) . Since key fruit is the generative organ, the higher tolerance of key fruit to short-run freeze and its better recovery potency from stop deading emphasis than foliage was of great ecological significance for population constitution of Siberian maple and its northern distribution bound in northern hemisphere.
( 1 ) There is marked difference of PSII activity between the key fruit and the foliage of Siberian maple. The key fruit has more efficient negatron conveyance flux (degree FahrenheitEo ) and photosynthetic efficiency ( Fv/Fm and PIABS ) but lower energy dissipation ( DIo/RC ) than foliage.
( 2 ) By and large, the PSII public presentation and negatron for both key fruit and foliage were reduced under low temperature emphasis accompanied by increasing of energy dissipation in PSII reaction centres ( RCs ) .
( 3 ) PSII of both key fruit and foliage is non significantly affected and can acclimatize to sudden chilling emphasis. Short-run freezing intervention can wholly suppress PSII activity in both key fruit and foliage. PSII functional parametric quantities of short-run dark frozen key fruit can be mostly cured whereas those of frozen foliage can non be recovered.
( 4 ) Samara is more tolerant to short-run low temperature emphasis and has better recovery potency than foliage.
This work was supported by Knowledge Innovation Program of Chinese Academy of Sciences ( kzcx2-yw-335 ) , the Program of 100 Distinguished Young Scientists of the Chinese Academy of Sciences, and the National Natural Science Foundation of China ( 40673070, 40872169 ) .
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