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快速葉綠素熒光(OJIP)可作為監測植物在非生物脅迫下光合生理狀態的有效工具
歡迎點擊「漢莎科學儀器」↑關注我們! 摘要在自然條件下生活的植物會受到許多干擾光合作用過程的不利因素的影響,導致生長、發育和產量的下降。葉綠素a熒光光譜(ChlF)的研究為葉片光化學效率研究提供了一條新的途徑。具體地說,對熒光信號的分析可獲取PSII反應中心、捕光天線復合體以及PSII供體側/受體側的狀態和功能的詳細信息。在這里,我們回顧了快速ChlF技術(OJIP & JIP-test)分析光合反應對環境脅迫的相關成果,并討論了這一創新方法的潛在科學和實際應用。最近便攜式設備(Handy PEA & M-PEA, Hansatech Instruments)的出現,特別是在作物表型分型和監測方面,大大擴展了ChlF技術的潛在應用。 關鍵詞 Chlorophyll fluorescence、JIP-test、Photosynthesis、Photosystem II、Quantum efficiency、Stress detection
縮寫
| Absorption flux | 吸收通量 | | Chlorophyll | 葉綠素 | | Chlorophyll fluorescence | 葉綠素熒光 | | Cross section of the sample | 樣品橫截面 | | Cytochrome b6f | 細胞色素b6f | | Delayed (chlorophyll) fluorescence | 延遲(葉綠素)熒光 | | Drought factor index | 干旱因子指數 | | Light-harvesting complex (of PSII) | PSII捕光色素復合體 | | Oxygen-evolving complex | 放氧復合體 | | Excited PSII reaction center | 激發的PSII反應中心 | | PSI reaction center | PSI反應中心 | | Photosynthetically active radiation | 光合有效輻射 | | Plastocyanin | 質體藍素 | | Principal component analysis | 主成分分析 | | Prompt (chlorophyll) fluorescence | 瞬時(葉綠素)熒光 | | Pheophytin | 去鎂葉綠素 | | Plastoquinone | 質體醌 | | Photosystem I, II | 光系統I, II | | Primary plastoquinone electron acceptor of PSII | PSII初級質體醌電子受體 | | Secondary plastoquinone electron acceptor | 次級質體醌電子受體 | | Reaction center | 反應中心 | | Reactive oxygen species | 活性氧 | 在21世紀,全球農業必須生產更多的糧食來維持不斷增長的人口(Beddington et al. 2012)。然而,這一目標受到人為氣候變化的威脅,這種變化有可能顯著降低受影響地區的糧食產量(Lobell et al.2008)。最近的研究表明,葉綠素熒光(ChlF)測量可以為改進全球農業生產力模型提供獨特的基準,提高氣候變化情景下作物產量預測的可靠性(Guanter et al. 2014; Malaspina et al. 2014)。更廣泛地說,ChlF技術正在成為農業、環境和生態研究中的一個非常強大的工具(Gottardiniet al. 2014)。它的一個主要優點是ChlF技術是一種非侵入性的工具,允許科學家在不破壞被測樣品的情況下獲得光合過程的豐富信息。在自然條件下,植物受到許多不利的環境脅迫因子的影響。這些會破壞光合器官,導致植物生產力和總產量下降。光合作用對環境脅迫特別敏感(Kalaji et al. 2012),使光合測量成為植物脅迫研究的重要組成部分。然而,傳統的方法,甚至是技術上先進的方法,如通過氣體交換(CO2、H2O和O2)測量光合速率,需要耗費大量時間和人力,且提供的有關整體光合功能的信息并不完整。相比之下,ChlF測量是一種簡單、無損、廉價和快速的工具,可用于分析光依賴性光合反應和間接評估同一樣本組織中的葉綠素含量(Govindjee 1995; Papageorgiou & Govindjee 2011; Stirbet & Govindjee 2011, 2012)。ChlF方法的這些技術優勢使其成為植物育種家(例如作物表型和監測)、生物技術學家、植物生理學家、林業工作者、生態學家和環境學家的流行技術。
關鍵的是,從植物脅迫研究的角度來看,ChlF測量還提供了有關植物生理狀況的間接信息。通過分析葉綠素熒光(ChlF)誘導曲線,可以評估光系統II(PSII)和光合電子傳遞鏈的生理狀況。它還提供了光依賴的光化學反應和光無關的生化反應的相關信息?偟膩碚f,ChlF測量直接或間接地與依賴光的光合反應的所有階段有關,包括水的光解、電子傳遞、類囊體膜上pH梯度的形成、ATP合成以及光合機構的一般生物能條件等(Bernát et al. 2012)。 許多ChlF技術和應用現在已經開發出來,為植物光合作用研究提供了豐富的技術手段。本文綜述了連續激發式熒光儀測量的快速葉綠素熒光動力學曲線(OJIP)的相關學術成果。這些研究是通過開發一個可靠的數學模型JIP-test(Strasser et al. 2004),允許分析在不到1s內發生的熒光變化。此類分析提供了關于PSII反應中心、天線以及PSII的供體和受體側的狀態和功能的詳細信息。綜述了脅迫因子對光化學過程的影響,對快速ChlF動力學和相關生物物理參數的變化規律。暗適應葉片照光后可獲得多相葉綠素熒光誘導曲線(O–J–I–P-瞬變)(圖1)。曲線的軌跡提供了有關光合機構結構和功能的大量信息(Kautsky & Hirsch 1931; Schreiber et al. 1994)。
JIP-test是基于多相快速葉綠素熒光的上升階段,用于研究光依賴性反應與ChlF的相關性。它基于類囊體膜的“能量流”理論(Strasser et al. 2000)。這個理論可以用簡單的代數方程來計算,代表每一個被檢測的捕光復合體的總能量流入和流出之間的平衡,并提供關于吸收能量的可能分配的信息。利用這些方程,可以描述PSII復合體之間的能量通信(也稱為“聚集grouping”或“連通性connectivity”和“總體分組概率overall grouping probability”)(Stirbet 2013)。 JIP-test(OJIP)的名稱來源于ChlF信號形成的感應曲線上的特定位點(圖1):這些位點對應于PSII原初電子受體(Pheo)和QA的逐漸還原。誘導曲線的形狀取決于PSII各組分間的聚集性(L-band)(Tsimilli-Michaeland Strasser 2013)和電子供體OEC→P680+以及QA-電子的接收之間的平衡(K-band)(Strasser et al. 2005)。 O~J相的熒光上升階段與部分PSII反應中心的閉合相關,反應了QA的還原水平,其還原程度取決于捕獲速率以及QA被QB和其余電子傳遞鏈成員氧化的速率。 誘導曲線的J~I相與次級電子受體QB、PQ、Cyt b6f和PC的還原程度相關。誘導曲線的I~P相的上升通常歸因于PSI受體側電子受體(鐵氧還原蛋白、中間受體和NADP)的還原。 高溫、強光、缺氮或干旱脅迫會抑制放氧復合體OEC并阻礙OEC與酪氨酸之間的電子傳遞(Guha et al. 2013)。脅迫條件下,在ChlF誘導曲線200~300μs范圍內會出現一個波峰——K-band,表明OEC已受到破壞。
圖1:典型的植物葉綠素熒光多相動力學曲線(主圖),曲線以對數時間刻度(10μs~600s)繪制。左上部插圖顯示了按常規時間標度繪制的相同曲線。右下方插圖按常規時間標度繪制的OJIP瞬態(0-30ms)的初始部分。時間標記是指JIP-test用于計算結構和功能參數的選定時間點。 表征PAR能量吸收和電子傳遞的JIP-test參數可主要分為以下四組:(1)基本測量值和計算值[熒光(Ft)、可變熒光(Vt)值和初始斜率等];(2)量子產率和概率;(3)能量通量;和(4)性能指數。表征能量通量的生物物理參數分為specific和phenomenological兩大類。specific參數按反應中心(RC)計算,phenomenological參數按樣品截面(CS)計算。性能指數(PI)由幾個獨立參數的乘積計算得出,分別包括反應中心的密度、初級光化學反應的量子效率和電子傳遞中激發能的轉換(Strasser et al. 2000, 2004, 2010; Zushi et al. 2012)。性能指數被創建為非特定參數,主要用于實際應用,如篩選在田間條件下增強的應力耐受性(Srivastava et al. 1999; Strasser et al. 2004; Brestic & Zivcak 2013)。葉綠素熒光動力學也可以用來揭示光合機構的PSII異質性。PSII在天線色素和還原側方面具有天然異質性。天線異質性包括天線尺寸和天線色素分子組分間的連通性(或聚集性)差異。PSII反應中心基于天線尺寸可分為三類:alpha (α), beta (β)和gamma (γ) (Melis & Homann 1976),其主要區別在于天線壽命和伴生葉綠素的數量。還原側的異質性主要與從QA開始電子傳遞的能力有關?蓪㈦娮佑QA傳遞給QB的反應中心命名為可還原QB的反應中心(QB reducing centers),而不具備此能力的反應中心稱之為不可還原QB的反應中心(QB non-reducing centers)。Jajoo(2013)回顧了PSII異質性的具體特征。近期研究表明,高溫(Mathur et al. 2011b),高鹽(Mehta et al. 2010a)以及如多環芳烴(PAH)等污染物(Tomarand Jajoo 2013, 2014)脅迫下均會引起PSII異質性的變化。PSII異質性的變化可能與活躍/不活躍反應中心的數量有關,在各種脅迫條件下活躍的α反應中心轉換為非活躍的β和γ反應中心,同時不可還原QB的反應中心數量也隨之增多。在下面的章節中,我們回顧了ChlF動力學可以作為氣候變化和人類活動(如高溫和低溫、干旱、鹽分、營養缺乏和重金屬)負面影響的有效指標的證據。 圖2:不同脅迫條件下小麥(Triticum sp.L.)葉綠素熒光的O(K)JIP瞬態與非脅迫下的比較。插入顯示了O-J相(∆VOJ)、J-I相(∆VJI)、I-P相(∆VIP)的相對可變熒光振幅的變化,以及0.3 ms可變熒光(VK/VJ)與2ms可變熒光比值(VJ)的變化,作為PSII供體側限制(K-band)的指標。各圖顯示了相對于非脅迫狀態下植物(control,C)的瞬時熒光曲線:a熱脅迫(高溫脅迫8h,中度光化光照射,葉片溫度約40℃);b低溫脅迫10d(10/6℃:日間/夜間);c重度干旱脅迫(停止灌溉后12d,葉片含水量約60%);d鹽脅迫(NaCl);e氮缺乏脅迫(低氮,LN);f鉛脅迫。 氣候變化可能會增加植物的熱脅迫,限制生產力和生物量的積累。光合作用是植物細胞過程中對高溫最敏感的過程(Sharkey & Schrader 2006),高溫會導致PSII電子受體還原-氧化特性發生變化,并降低兩個光系統中光合電子傳輸的效率(Mathur et al. 2014)。熱脅迫會影響ChlF參數的值(圖2a)。例如蘋果Malus x domestica Borkh在高溫脅迫下,其QA-/RC和QB-/QA-的比率均產生下降,同時PSII最大量子產率(Fv/Fm)降低而最小熒光Fo升高(Chen et al. 2009; Brestic et al. 2013)。高溫脅迫同樣會對O-J-I-P曲線的形狀產生影響,會導致Fm的降低和Fo升高。Fo的升高可能是由于捕光色素復合體LHC II從PSII復合體上解離、PSII光化學反應的失活或還原的電子受體QA至QB電子流傳遞受到抑制而導致的(Mathur et al. 2011a)。例如,由菠菜和水稻中觀察到的Fo升高歸因于LHC II與PSII復合體的不可逆解離和PSII的部分可逆性失活(Yamane et al. 1997)。Fm的降低可能與葉綠素蛋白的變性有關(Yamane et al. 1997)。K峰(300μs)是熱應激一個極佳的指示指標,可用于指示放氧復合體OEC的解離和去鎂葉綠素Pheo與初級電子受體QA間的電子傳遞情況(Strasser et al. 2000; Lazár 2006)。在小麥中,35℃處理時對凈光合速率未產生影響,而當45℃處理時則對OEC產生了不可逆的損傷(Schreiber et al. 2012)。K峰出現的直接原因是電子由P680向PSII電子受體的流出量遠超于電子由PSII供體側向P680的流入量。同時K峰也會受到光系統II之間能量關系變化的影響。FK/FJ比率的增大表明熱脅迫抑制了OEC的電子供應(Srivastava & Strasser 1995)。快速ChlF技術也是監測PSII熱穩定性有效方法。最有效的方法是評估臨界溫度,即在臨界溫度以上觀測相應參數的快速增加或減少(Brestic & Zivcak 2013)。在作物育種中,一些基因型可以作為增強耐熱性的供體。以熱處理菜豆(Phaseolus vulgaris L.)品系為例,通過ChlF誘導的變化來監測其脅迫反應和恢復狀況,并應用JIP-test進行分析(Stefanov et al. 2011)。Brestic et al. (2012)利用快速ChlF動力學方法對30個不同地理來源冬小麥基因型的PSII熱穩定性進行了研究。Gautum et al. (2014)證明ChlF法在硬粒小麥基因型篩選中比常規方法(如收獲指數、籽粒灌漿等)更有效。在某些緯度地區,低溫是限制作物產量的主要因素(Yang et al. 2009)。在北半球冬季和早春的低溫通常伴隨著強光照現象,在這種環境條件下,會導致植物類囊體結構退化和光依賴性的光合反應的扭曲(Suzuki et al. 2011)。冷脅迫同樣會影響ChlF參數(圖2b)。例如,低溫脅迫下苦瓜(Momordica charantia L.)植株的葉綠素含量、PSII供體側OEC效率、光化學猝滅和開放的PSII反應中心效率均降低(Yang et al. 2009)。某些具有極佳低溫耐受性的物種表現出較少的PSII光抑制。例如,低溫脅迫下豌豆植株的ChlF參數只有極小的變化(Strauss et al. 2006; Strebet al. 2008)。干旱脅迫對光合器官的影響是眾所周知的。在中等干旱強度下它們通常開始主要是氣孔效應,嚴重或長期干旱脅迫最終會導致代謝和結構性變化(Jedmowski et al. 2013)。這種最終的變化也與光保護和抗氧化功能和途徑的增強有關(Chaves et al. 2009)。與PSI相比,PSII具有較高的抗缺水能力,因此只有在極端干旱的情況下才會產生負面影響(Lauriano et al. 2006)。ChlF測量表明,在干旱條件下,通過調節光系統之間的能量分布和激活交替電子流,增強了PSII和PSI光化學的保護作用(Zivcak et al. 2013)。干旱脅迫可增強PSII對熱脅迫的抗性,表現為OJIP瞬態的K峰的消失(見圖2c,Oukarroum et al. 2012)。ChlF方法可用于篩選耐旱性基因型(Guha et al. 2013)。OJIP熒光曲線上升的最初2~3ms階段與初級光化學反應相關,Oukarroum et al. (2007)建議脅迫激發出現的L-band和K-band可作為評估應對和恢復干旱脅迫潛力的有效工具。L-band受PSII各組分間激發能傳遞的影響,通常表示為連通性(connectivity)或聚集性(grouping)(Strasser & Stirbet 1998)。不論是突變(Brestic et al. 2014)或環境條件(Zivcak et al. 2014a)而引發的PSII天線色素組分的改變,同樣會使L-band受到影響。K-band的出現與放氧復合體OEC的解離有關(Guisse et al. 1995)。因此,O-L-K-J-I-P熒光瞬態的測量和利用JIP-test進行的分析可以作為干旱脅迫耐性和干旱脅迫可見癥狀出現前生理紊亂的有效指示工具。性能指數(PI)是應用最廣泛的ChlF OJIP曲線參數,為我們提供了關于植物狀態和活力的定量信息。PI由三個獨立特性的參數乘積組成:每個葉綠素分反應中心濃度、初級光化學反應相關參數和電子傳遞相關參數(Strasser et al. 2004)。因此PI對天線特性、捕獲效率或除QA外的電子傳遞的變化都很敏感。例如,冬小麥在花后長期干旱脅迫下,PI值降低。此外,根據干旱脅迫下的PI值估算的小麥基因型的耐旱性與以產量為指標的抗旱性也有很好的相關性(Zivcaket al. 2008)。PI與干旱因子指數(DFI)密切相關,DFI表示在一定的干旱脅迫時間內,PI的相對減少量。Strauss等人使用了DFI方法(Strauss et al. 2006)評估不同大豆基因型的耐暗冷性。DFI還被用于對10個大麥品種(Oukarroum et al. 2007)和21種芝麻突變體種質資源(Boureima et al. 2012)的耐旱性進行排序。利用PI參數和ChlF快速誘導曲線成功篩選了來自埃及的**耐性和最敏感的大麥和高粱品種(Jedmowskiet al. 2013)。這些研究表明,在PSII水平上可以區分耐旱性和敏感性品種。在干旱脅迫下同樣觀察到ABS/RC的增大(Van Heerden et al. 2007; Gomeset al. 2012),這可能是由于部分PSIIRCs失活或天線尺寸增大而導致的。干旱脅迫也會影響OJIP曲線I~P相的相對振幅。I~P相是熒光曲線上升的最慢階段(約30~200ms),與質體籃素PC和PSI中P700+的再還原有關(Schreiber et al. 1989; Schansker et al. 2003)。I~P相似乎與PSI反應中心的含量(Ceppiet al. 2012)或由820nm透射測量得到的線性電子傳遞活性(Zivcak et al. 2014a)有關。例如,不同大麥品種的I~P損失程度取決于它們的耐旱性(Oukarroum et al. 2009; Ceppi et al. 2012)。ChlF是在光合樣品在暗到光轉換之后發射的,而延遲熒光(DF)的發射發生在光到暗的轉換過程中(Goltsev et al. 2009; Strasser et al. 2010; Kalaji et al. 2012)。DF被認為反映了還原的初級電子受體QA-和光誘導電荷分離形成的PSII氧化供體P680+的在黑暗狀態下的再復合。DF誘導曲線的形狀取決于樣品材料類型和其生理狀態。使用Hansatech公司M-PEA多功能植物效率分析儀同時測量ChlF 瞬時熒光OJIP曲線和DF曲線,目前被用于獲取不同光合反映的速率常數(Strasser et al. 2010)。使用此技術Goltsev et al. (2012)觀察到在干旱脅迫下QA-的再氧化受到抑制,PSII反應中心光誘導電子傳遞量子產率被抑制,調制反射信號(820nm)的光誘導動力學快速相降低。 植物對鹽脅迫的反應是由多個方面決定的,如特定基因的表達、植物的發育階段、甜菜堿的積累,這些甜菜堿通過穩定PSII復合體的外部蛋白質來保護光合機構(Murata et al. 1992)。鹽分脅迫干擾了從RCs至質體醌庫的電子傳遞(Strasser et al. 2000; 圖2d)。Schreiber et al. (1994)鑒定出OEC是光合電子傳遞鏈中最敏感的組分之一。OEC性能的下降通常是由于電子傳遞紊亂引起的。鹽脅迫下同樣可觀察到ChlF參數和PSII功能性的改變。在高鹽脅迫下,由于LHC II和PSII解離導致了PSII反映中心捕獲電子效率的下降(Havaux 1993)。在許多物種中,如大麥(Kalaji & Rutkowska 2004)、煙草Nicotiana tobacum L. (Yang et al. 2008)、甚至某些鹽生植物如草珊瑚Sarcocorniafruticosa L中,均觀察到了PSII最大量子效率(Fv/Fm)的降低和非光化學淬滅(NPQ或qN)的增加。此外,番茄和黃瓜幼苗在鹽分脅迫下,光下PSII光化學效率(ΦPSII)、電子傳遞效率(ETR)和光照下PSII開放反應中心的效率均受影響而降低(He et al. 2009; Zhang & Sharkey 2009)。鹽脅迫對小麥的傷害主要表現在供體側,而非受體側,這種損傷在PSII受體側是完全可逆的(約100%),而供體側的恢復率小于85%(Mehta et al. 2010b)。鹽脅迫的滲透和離子效應也通過ChlF測量得到了有效區分(Singh-Tomar et al. 2012)。特定營養元素(N、P、K、Ca、Mg、S或Fe)的缺乏會破壞光合器官的功能,降低PSII光化學效率并改變ChlF參數的值(Smethurst et al. 2005)。氮素(N)缺乏是限制植物生長的關鍵因素,是所有蛋白質、核酸和其他有機化合物的組成部分。氮素缺乏導致類囊體膜的改變并擾亂其功能(圖2e),并進一步加速葉綠體衰老和質體小球的形成(Wu et al. 2006)。氮也是RuBisCO光合復合物、卡爾文循環酶、葉綠素和類胡蘿卜素中的重要元素(Correia et al. 2005)。氮缺乏會導致蒸騰作用、氣孔導度、葉綠素和類胡蘿卜素含量以及可溶性糖濃度的降低(Huang et al. 2004)。氮攝取不足也會降低PSII中的電子受體庫,降低RuBisCO和磷酸烯醇式丙酮酸羧化酶(PEPCase)的活性(Correia et al. 2005)。JIP-test分析已經在處理氮缺乏的研究中多次應用,并且已經很好地描述了氮供應不足對PSII的影響(Redillas et al. 2011, Li et al. 2012)。特別是,氮素缺乏導致的反應中心密度顯著降低(Dudeja & Chaudhary 2005)。同時,高氮處理對大豆(Van Heerden et al. 2004)、玉米(Li et al. 2012)和小麥(Zivcak et Val. 2014b)中PI值的積極影響已經得到了證明。磷對植物的生長發育也是必不可少的。磷缺乏將主要導致籽粒和類囊體膜結構改變、捕光復合體吸收PAR的下降,從而導致PSII活性的降低(Foyer & Spencer 1986)。磷缺乏還對NADPH的再生過程產生不利影響,降低光合作用的量子產率、羧化效率和電子傳遞效率(Wu et al. 2006)。JIP-test已成功應用于磷缺乏脅迫下植物PSII活性或效率的評估(Kruger et al. 1997; Tsimilli-Michael & Strasser 2008)。此外各種研究證明,JIP-test參數和氣體交換或植物生長參數具有高度相關性(Strasser et al. 2000)。鉀(K)在細胞滲透調節中起著關鍵作用:鉀離子是保持類囊體膜上的pH梯度所必需的(Rampino et al. 2006)。鉀缺乏會導致氣孔導度阻力增加,限制二氧化碳通過氣孔的擴散。在光合作用中,鉀在許多酶的激活和ATP合成中的重要作用可能比它在調控氣孔功能中的作用重要的多。然而鉀缺乏對光合組織效率和PSII功能的影響知之甚少。然而,在缺鉀條件下,一些光合參數如電子傳遞效率(ETR)和最大量子產率(Fv/Fm)都會降低(Schweiger et al. 1996)。有許多研究使用快速ChlF參數來分析其他礦物質缺乏對光化學功能的影響,例如鈣(Liu et al. 2009; Lauriano et al. 2006)、鎂(Smethurst et al. 2005)和鐵(Molassiotis et al. 2006)。由于許多營養物質對PSII光化學反應有特殊的影響,這里的問題是是否有可能利用葉綠素熒光動力學來識別營養缺乏。盡管這一問題仍然懸而未決,Kalaji et al. (2014a, b)能夠利用JIP-test參數的主成分分析(PCA)來識別番茄和玉米的主要營養素的缺乏情況。高濃度的重金屬脅迫會破壞光合作用進程,但特定重金屬離子的影響可能是物種特異性的(Antosiewicz 2005; Mishra & Dubey 2005)。PSI被認為比PSII更能耐受重金屬的脅迫(Romanowska et al. 2006; Tuba et al. 2010)。鎘(Cd)是毒性最大的重金屬之一,可在生物體內富集。環境中鎘的來源包括磷肥和工業廢料(Romanowska et al. 2006; Kalaji & Łoboda 2007)。然而,鎘似乎不會影響光合色素的含量。對油菜幼苗的研究表明,在Cd存在下生長2周后,葉綠素a、葉綠素b和類胡蘿卜素的含量沒有顯著變化(Janeczko et al. 2005)。然而,Cd確實對光合過程的光化學效率有負面影響。PSII比PSI對鎘的影響更敏感,表明Cd以更大的強度破壞PSII功能(Mallick & Mohn 2003)。Cd同時影響PSII的供體和受體側。在供體側,它抑制OEC,而在受體側,由于LHCII復合體的解離導致電子傳遞紊亂,抑制了QA-和QB-之間的電子傳遞(Sigfridsson et al. 2004)。Cd脅迫同樣會引發非光學淬滅或熱耗散的升高(Janeczko et al. 2005)。對油菜JIP-test參數的分析表明,Cd引起了油菜葉片橫截面比能流如RC/CS、ETo/CS和OEC活性的降低(Janeczko et al. 2005)。PSII最大量子效率Fv/Fm是Cd脅迫影響最不敏感的參數。植物對鎘的抗性與“清除”活性氧的能力、激活抗氧化酶[特別是過氧化物酶(Ekmekci et al. 2008)]以及合成抗氧化化合物[如谷胱甘肽(Streb et al. 2008)]等保護機制的啟動有關。鉛對植物也有有害影響。土壤和植物中鉛的主要源頭來自于燃煤發電廠、汽車尾氣和工業廢棄物(Mishra & Dubey 2005)。鉛會引起呼吸代謝的改變,導致線粒體產生高能化合物,使ATP含量和ATP/ADP比值升高(Romanowska et al. 2002)。鉛脅迫下植物光合作用效率的降低是由于葉綠體超微結構和類囊體膜脂成分的破壞,以及葉綠素和類胡蘿卜素合成的減少造成的(Sharma & Dubey 2005)。鉛脅迫會阻斷如鎂和鐵等營養元素的吸收,而鎂和鐵是光合作用所必需的。此外鉛還會導致OEC復合體的解離,并將Ca,Cl,Mn化合物從OEC復合體中分離去除(Sharma & Dubey 2005; Romanowska et al. 2006)。與對照組相比,暴露于鉛脅迫的植物的O–J–I–P誘導曲線中I和P階的熒光強度降低(圖2f),并出現K峰(Kalaji & Łoboda 2007)。ChlF誘導曲線上出現以上變化可能與OEC和PSII反應中心之間的電子傳遞抑制有關(Strasser et al. 2004; Wu et al. 2008)。鉛脅迫模型表明,PSII內的能量吸收和耗散很高,而電子捕獲和電子傳遞則大幅減少(Lazár & Jablonsky 2009)。用于快速ChlF動力學分析的數學模型,如JIP-test,是專門用來評估微秒級或毫秒級葉綠體氧化還原反應級聯反應的生物物理工具。盡管如此,早期的研究即已經獲取了很多關于葉片生理狀態和熒光瞬態曲線形狀之間關系的有趣的經驗理論(Strasser et al. 2000)。隨后又有許多文獻報道了葉片生理狀態與ChlF瞬變之間的直接關系。而常被忽略的一個事實是測量得到的信號是一個復合信號(見上文關于PSII異質性的討論),而該信號是與樣品測定時的生理狀態和環境條件高度相關的。因此,需要我們多方考慮各種因素的綜合作用,以避免錯誤地或過度簡化的得出結論(Evans 2009)。快速葉綠素熒光技術操作簡單、快速,但如對其基本理論原理了解不深,很容易造成對該技術的不當應用。綜合參數的使用,如性能指數(PI)可能比復雜的特定生物物理參數更有用,后者需要對光化學過程有更深入的理解才能正確地解釋數據。Stirbet & Govindjee (2011)深入探討了JIP-test在分析OJIP曲線中的各方利弊。為了避免ChlF應用中的錯誤,強烈建議所有用戶熟悉該技術的各種理論細節(見Kalaji et al. 2014a綜述文章)。本文介紹了葉綠素熒光技術在植物科學、農業和生態研究中應用的**信息。葉綠素熒光的測量信號及其統計分析(如JIP-test)可用于預測、監測和識別植物的脅迫。因此,它可以作為一種生物指示劑應用于幾乎所有的植物生態學研究中。ChlF測量的多功能性意味著它們可以在單一植物的水平上應用于草原、農田甚至海洋生態系統。然而,這種潛在的多功能性強調了需要進行更實際和概念性的研究,使科學家能夠獲得有關植物生長和健康的可靠信息。這樣一種方法不僅將使我們對光合作用的生理基礎的理解得到改善,而且還將有助于了解和補救氣候變化對作物產量和糧食安全的影響。- AntosiewiczDM (2005) Study of calcium-dependent lead-tolerance on plants differing intheir level of Ca-deficiency tolerance. 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