Action potential in a plant cell lowers the light requirement for non-photochemical energy-dependent quenching of chlorophyll fluorescence

This study deals with effects of membrane excitation on photosynthesis and cell protection against excessive light, manifested in non-photochemical quenching (NPQ). In Chara corallina cells, NPQ and pericellular pH displayed coordinated spatial patterns along the length of the cell. The NPQ values were lower in H⁺-extruding cell regions (external pH ∼ 6.5) than in high pH regions (pH ∼ 9.5). Generation of an action potential by applying a pulse of electric current caused NPQ to increase within 30-60 s. This effect, manifested as a long-lived drop of maximum chlorophyll fluorescence (F_m′), occurred at lower photosynthetic flux densities (PFD) in the alkaline as compared to acidic cell regions. The light response curve of NPQ shifted, after generation of an action potential, towards lower PFD. The release of NPQ by nigericin and the rapid reversal of action potential-triggered NPQ in darkness indicate its relation to thylakoid ΔpH. Generation of an action potential shortly after darkening converted the chloroplasts into a latent state with the F_m identical to that of unexcited cells. This state transformed to the quenched state after turning on weak light that was insufficient for NPQ prior to membrane excitation of the cells. The ionophore, A23187, shifted NPQ plots similarly to the action potential effect, consistent with a likely role of a rise in the cytosolic Ca²⁺ level in the action potential-induced quenching. The results suggest that a rapid electric signal, across the plasma membrane, might exert long-lived effects on photosynthesis and chlorophyll fluorescence through ion flux-mediated pathways.     

Effect of action potential on photosynthesis and spatially distributed H+ fluxes in cells and Chloroplasts of Chara corallina

When exposed to light, the cells of characean algae produce intermittent regions of H⁺ extrusion and H⁺ absorption, featuring different photosynthetic activities. Methods for local measurements of outer pH, O₂ content, and photochemical activity of photosystem II (PSII) were applied to examine microscopic regions of Chara coralline Klein ex Willd. internodes. The results show that the functional spatial heterogeneity of these excitable cells is controlled not only by light but also by electric excitation of the plasma membrane. Generation of a single action potential (AP) induced a reversible transition to the state with homogenous pH distribution and had different effects on photosynthesis in cell regions producing alkaline and acid zones. The effective quantum yield of PSII primary processes and the maximal chlorophyll fluorescence decreased after AP in the alkaline cell regions but were almost unaffected in the acidic cell regions. The suppression of photosynthesis after AP was also evident in the decrease of photosynthetic O₂ evolution. The results provide evidence that electric signals arising at the plasmalemma are transmitted to the level of thylakoid membranes. The effects of electric excitation on fluorescence and the quantum yield of PSII photochemistry were best pronounced at low light intensities and low level of nonphotochemical quenching. The sensitivity of chlorophyll fluorescence in resting and excited cells to light intensity and protonophores indicates that the AP-induced fluorescence changes derive from the increase in pH gradient at the thylakoid membrane. The temporal elimination of alkaline zones and inhibition of photosynthesis apparently arise from parallel operational sequences that have a common initial stage. A possible role of cytosolic Ca²⁺ rise in the mechanism of photosynthesis suppression after electric excitation of the plasma membrane is discussed.     

Effect of a Single Excitation Stimulus on Photosynthetic Activity and Light-dependent pH Banding in <Emphasis Type="Italic">Chara</Emphasis> Cells

Using pH microelectrodes and a Micro-scopy PAM (pulse-amplitude modulated) chlorophyll fluorometer, it is shown that a propagation of an action potential in Chara corallina leads to transient suppression of spatially periodic pH profiles along the illuminated cell. The suppression was manifested as a large pH decrease in the alkaline zones and a slight pH increase in the acid zones. The propagating action potential diminished the maximum yield of chlorophyll fluorescence (F_m′) in the alkaline cell regions, as well as the quantum yield of photosystem II photochemistry, without affecting F_m′ in the acid cell regions. The results indicate an interference of membrane excitation in the mechanisms responsible for pH banding patterns in Characean algae. Apparently, the electrical excitation of the plasma membrane in the alkaline cell regions initiates a pathway that can modulate membrane events at the thylakoid membrane.     

Action potential in Chara cells intensifies spatial patterns of photosynthetic electron flow and non-photochemical quenching in parallel with inhibition of pH banding

Characean cells exposed to illumination arrange plasma-membrane H(+) fluxes and photosynthesis in coordinated spatial patterns. The limited availability of CO(2) in alkaline bands accounts for the lower effective quantum yield of photosystem II (DeltaF/F(m)') in chloroplasts of these bands compared to acidic zones. The effect of electrically triggered action potential on the spatial distribution of photosynthetic parameters (DeltaF/F(m)' and non-photochemical quenching, NPQ) and extracellular pH was studied with fluorescence imaging and pH microelectrodes. In the resting cell at a range of light intensities, the periodic profile of extracellular pH is parallel to the profile of NPQ and antiparallel to that of DeltaF/F(m)'. After triggering the action potential, the pH banding temporarily disappeared, but in contrast, the differences in effective quantum yield and NPQ patterns became more apparent. The transient changes in pH-banding, effective quantum yield and non-photochemical quenching are discussed in relation to alterations in intracellular Ca(2+) and H(+) concentrations during and after the action potential.     

Short-term acclimation of the photosynthetic electron transfer chain to changing light: a mathematical model

Photosynthetic eukaryotes house two photosystems with distinct light absorption spectra. Natural fluctuations in light quality and quantity can lead to unbalanced or excess excitation, compromising photosynthetic efficiency and causing photodamage. Consequently, these organisms have acquired several distinct adaptive mechanisms, collectively referred to as non-photochemical quenching (NPQ) of chlorophyll fluorescence, which modulates the organization and function of the photosynthetic apparatus. The ability to monitor NPQ processes fluorometrically has led to substantial progress in elucidating the underlying molecular mechanisms. However, the relative contribution of distinct NPQ mechanisms to variable light conditions in different photosynthetic eukaryotes remains unclear. Here, we present a mathematical model of the dynamic regulation of eukaryotic photosynthesis using ordinary differential equations. We demonstrate that, for Chlamydomonas, our model recapitulates the basic fluorescence features of short-term light acclimation known as state transitions and discuss how the model can be iteratively refined by comparison with physiological experiments to further our understanding of light acclimation in different species.     

Molecular genetics of xanthophyll-dependent photoprotection in green algae and plants

The involvement of excited and highly reactive intermediates in oxygenic photosynthesis inevitably results in the generation of reactive oxygen species. To protect the photosynthetic apparatus from oxidative damage, xanthophyll pigments are involved in the quenching of excited chlorophyll and reactive oxygen species, namely 1Chl*, 3Chl*, and 1O2*. Quenching of 1Chl* results in harmless dissipation of excitation energy as heat and is measured as non-photochemical quenching (NPQ) of chlorophyll fluorescence. The multiple roles of xanthophylls in photoprotection are being addressed by characterizing mutants of Chlarnydomonas reinhardtii and Arabidopsis thaliana. Analysis of Arabidopsis mutants that are defective in 1Chl* quenching has shown that, in addition to specific xanthophylls, the psbS gene is necessary for NPQ. Double mutants of Chlamydomonas and Arabidopsis that are deficient in zeaxanthin, lutein and NPQ undergo photo-oxidative bleaching in high light. Extragenic suppressors of the Chlamydomonas npq1 lor1 double mutant identify new mutations that restore varying levels of zeaxanthin accumulation and allow survival in high light.     

Mechanistic aspects of xanthophyll cycle-dependent photoprotection in higher plant chloroplasts and leaves

Higher plants must dissipate absorbed light energy that exceeds the photosynthetic capacity to avoid molecular damage to the pigments and proteins that comprise the photosynthetic apparatus. Described in this minireview is a current view of the biochemical, biophysical and bioenergetic aspects of the primary photoprotective mechanism responsible for dissipating excess excitation energy as heat from photosystem II (PSII). The photoprotective heat dissipation is measured as nonphotochemical quenching (NPQ) of the PSII chlorophyll a (Chl a) fluorescence. The NPQ mechanism is controlled by the trans-thylakoid membrane pH gradient (ΔpH) and the special xanthophyll cycle pigments. In the NPQ mechanism, the de-epoxidized endgroup moieties and the trans-thylakoid membrane orientations of antheraxanthin (A) and zeaxanthin (Z) strongly affect their interactions with protonated chlorophyll binding proteins (CPs) of the PSII inner antenna. The CP protonation sites and steps are influenced by proton domains sequestered within the proteo-lipid core of the thylakoid membrane. Xanthophyll cycle enrichment around the CPs may explain why changes in the peripheral PSII antenna size do not necessarily affect either the concentration of the xanthophyll cycle pigments on a per PSII unit basis or the NPQ mechanism. Recent time-resolved PSII Chi a fluorescence studies suggest the NPQ mechanism switches PSII units to an increased rate constant of heat dissipation in a series of steps that include xanthophyll de-epoxidation, CP-protonation and binding of the xanthophylls to the protonated CPs; the concerted process can be described with a simple two-step, pH-activation model. The xanthophyll cycle-dependent NPQ mechanism is profoundly influenced by temperatures suboptimal for photosynthesis via their effects on the trans-thylakoid membrane energy coupling system. Further, low temperature effects can be grouped into either short term (minutes to hours) or long term (days to seasonal) series of changes in the content and composition of the PSII pigment-proteins. This minireview concludes by briefly highlighting primary areas of future research interest regarding the NPQ mechanism.     

The causes of altered chlorophyll fluorescence quenching induction in the Arabidopsis mutant lacking all minor antenna complexes

Non-photochemical quenching (NPQ) of chlorophyll fluorescence is the process by which excess light energy is harmlessly dissipated within the photosynthetic membrane. The fastest component of NPQ, known as energy-dependent quenching (qE), occurs within minutes, but the site and mechanism of qE remain of great debate. Here, the chlorophyll fluorescence of Arabidopsis thaliana wild type (WT) plants was compared to mutants lacking all minor antenna complexes (NoM). Upon illumination, NoM exhibits altered chlorophyll fluorescence quenching induction (i.e. from the dark-adapted state) characterised by three different stages: (i) a fast quenching component, (ii) transient fluorescence recovery and (iii) a second quenching component. The initial fast quenching component originates in light harvesting complex II (LHCII) trimers and is dependent upon PsbS and the formation of a proton gradient across the thylakoid membrane (ΔpH). Transient fluorescence recovery is likely to occur in both WT and NoM plants, but it cannot be overcome in NoM due to impaired ΔpH formation and a reduced zeaxanthin synthesis rate. Moreover, an enhanced fluorescence emission peak at ~679?nm in NoM plants indicates detachment of LHCII trimers from the bulk antenna system, which could also contribute to the transient fluorescence recovery. Finally, the second quenching component is triggered by both ΔpH and PsbS and enhanced by zeaxanthin synthesis. This study indicates that minor antenna complexes are not essential for qE, but reveals their importance in electron stransport, ΔpH formation and zeaxanthin synthesis.     

The site of regulation of light capture in Symbiodinium: Does the peridinin–chlorophyll a–protein detach to regulate light capture?

Dinoflagellates from the genus Symbiodinium form symbiotic associations with cnidarians including corals and anemones. The photosynthetic apparatuses of these dinoflagellates possess a unique photosynthetic antenna system incorporating the peridinin–chlorophyll a–protein (PCP). It has been proposed that the appearance of a PCP-specific 77 K fluorescence emission band around 672–675 nm indicates that high light treatment results in PCP dissociation from intrinsic membrane antenna complexes, blocking excitation transfer to the intrinsic membrane-bound antenna complexes, chlorophyll a–chlorophyll c₂–peridinin–protein-complex (acpPC) and associated photosystems (Reynolds et al., 2008 Proc Natl Acad Sci USA 105:13674–13678).We have tested this model using time-resolved fluorescence decay kinetics in conjunction with global fitting to compare the time-evolution of the PCP spectral bands before and after high light exposure. Our results show that no long-lived PCP fluorescence emission components appear either before or after high light treatment, indicating that the efficiency of excitation transfer from PCP to membrane antenna systems remains efficient and rapid even after exposure to high light. The apparent increased relative emission at around 675 nm was, instead, caused by strong preferential exciton quenching of the membrane antenna complexes associated with acpPC and reaction centers. This strong non-photochemical quenching (NPQ) is consistent with the activation of xanthophyll-associated quenching mechanisms and the generally-observed avoidance in nature of long-lived photoexcited states that can lead to oxidative damage. The acpPC component appears to be the most strongly quenched under high light exposure suggesting that it houses the photoprotective exciton quencher.     

Changes in the condition of photosynthetic apparatus of a diatom alga <Emphasis Type="Italic">Thallassiosira weisflogii</Emphasis> during photoadaptation and photodamage

Two populations of a diatom alga Thallassiosira weisflogii were grown at photon flux densities (PFD) of 0.8 and 8 μmol/(m² s). For both diatom populations, the recovery of chlorophyll fluorescence parameters (F ₀, F _m, F _v/F _m, and NPQ) was monitored after nondestructive irradiation by visible light at PFD of 40 μmol/(m² s) and after high-intensity irradiation by visible light (1000–4000 μmol/(m² s)). The exposure of diatoms to PFD of 40 μmol/(m² s)—higher than PFD used for algal growth but still nondamaging to photosynthetic apparatus—induced nonphotochemical quenching (NPQ), which was stronger in algae grown at higher PFD (8 μmol/(m² s)) than in algae grown at low light. After irradiation with high-intensity light, the recovery of chlorophyll fluorescence parameters was more pronounced in algae grown at elevated PFD level. During short-term irradiation of diatoms with high-intensity visible light (1000 μmol/(m² s)), a stronger NPQ was observed in the culture adapted to high irradiance. After the treatment of algae with dithiothreitol (an inhibitor of carotenoid deepoxidase in the diadinoxanthin cycle) or NH₄Cl (an agent abolishing the proton gradient at thylakoid membranes), a short exposure of algae to PFD of 40 μmol/(m² s) induced hardly any nonphotochemical quenching. The results indicate the dominant contribution of xanthophyll cycle carotenoids to energy-dependent quenching.     

两种杂交杨叶绿素荧光特性及光能利用

比较研究了伊犁地区两种杂交杨伊犁杨1号(Populus deltaids‘cv-64’ (P64))和伊犁杨小叶杨(P. simonii canaden×P. russkii-9(Jia))对太阳辐射光能的利用和耗散特性。两种杂交杨光合速率(P_n)的日变化均呈现双峰型, 高光量子通量密度(PFD)阶段P_n达到20.1%的差距; 实际最大光化学猝灭ΦPSII日变化均呈“U”型, 于16:30时, P64的ΦPSII达到最低值, 而Jia的值于14:30时达到最低(Jia>P64); 光合系统的闭合程度(L)在14:30时均出现一个短暂回落, 全天平均闭合程度无显著差异(p>0.05)。非光化学猝灭系数(NPQ)在16:30同时达到最大值(Jia>P64), 两者NPQ全天相差31.7%。叶片转化吸收太阳能热能耗散(E.D)和光化学反应转化的光能量(E.P)进行估算表明: 在PFD较低的环境条件下, 两种杂交杨将吸收的光能50%以上用于光化学猝灭; 在PFD较高的环境条件下, P64的E.P值比例大于Jia, 两者全天的E.P值没有太大的差异, P64的E.D值显著大于Jia的E.D值(p>0.01), 而P64的E.D值占全天转化能量的比例小于Jia。P64和Jia的E.P达到最大的估算值时, 其E.D也达到了最大。分析结果表明: 两种杂交杨对高光能形成不同的适应机制, P64利用更多的太阳能进行光化学猝灭反应, 而Jia利用更多的太阳能进行非光化学猝灭反应, 减缓强太阳辐射伤害; 两种杂交杨用于光化学能量分配的比例P64大于Jia, 而P_n值在强辐射阶段和全天平均值、累积值均出现Jia>P64。结果证明, 仅通过杂交杨本身叶绿体对光的荧光特性反应计算接收到的光能中有多少能量被利用与实际植物光合速率的转化的干物质存在一定的差异, 两种杂交杨光化学实际固定碳和转化光能的多少的内在关系需进一步的研究。     

氯化胆碱对低温弱光下黄瓜幼苗叶片细胞膜和光合机构的保护作用

1.07mmol／L氯化胆碱处理降低了低温弱光（6℃．PFD100μmol m^-2s^-1）下黄瓜幼苗叶片膜脂组分中主要是磷脂酰甘油（PG）的饱和脂肪酸含量,增加了膜脂不饱和度：减缓了膜透性的下降、MDA的产生速率、叶绿素的降解及PSII最大量子效率（Fv/Fm）、捕光效率（Fv＇／Fm＇）、光化学猝灭系数（qp）、实际光化学效率（ФPSII）和抗氧化酶POD、APX及CAT活性的下降;提高了非光化学猝灭系数（NPQ）和脯氨酸的含量。以上结果表明氯化胆碱处理保护了低温弱光对黄瓜叶片细胞膜和光合机构的伤害。     

In diatoms, the transthylakoid proton gradient regulates the photoprotective non-photochemical fluorescence quenching beyond its control on the xanthophyll cycle

In diatoms, the non-photochemical fluorescence quenching (NPQ) regulates photosynthesis during light fluctuations. NPQ is associated with an enzymatic xanthophyll cycle (XC) which is controlled by the light-driven transthylakoid proton gradient (delta pH). In this report, special illumination conditions and chemicals were used to perturb the kinetics of the delta pH build-up, of the XC and of NPQ. We found that the delta pH-related acidification of the lumen is also needed for NPQ to develop by switching the xanthophylls to an 'activated' state, probably via the protonation of light-harvesting antenna proteins. It confirms the NPQ model previously proposed for diatoms.     

Light-induced isomerization of the LHCII-bound xanthophyll neoxanthin: possible implications for photoprotection in plants

Light-harvesting pigment-protein complex of Photosystem II (LHCII) is the largest photosynthetic antenna complex of plants and the most abundant membrane protein in the biosphere. Plant fitness and productivity depend directly on a balance between excitations in the photosynthetic apparatus, generated by captured light quanta, and the rate of photochemical processes. Excess excitation energy leads to oxidative damage of the photosynthetic apparatus and entire organism and therefore the balance between the excitation density and photosynthesis requires precise and efficient regulation, operating also at the level of antenna complexes. We show that illumination of the isolated LHCII leads to isomerization of the protein-bound neoxanthin from conformation 9'-cis to 9',13- and 9',13'-dicis forms. At the same time light-driven excitation quenching is observed, manifested by a decrease in chlorophyll a fluorescence intensity and shortened fluorescence lifetimes. Both processes, the neoxanthin isomerization and the chlorophyll excitation quenching, are reversible in dim light. The results of the 77K florescence measurements of LHCII show that illumination is associated with appearance of the low-energy states, which can serve as energy traps in the pigment-protein complex subjected to excess excitation. Possible sequence of the molecular events is proposed, leading to a protective excess excitation energy quenching: neoxanthin photo-isomerization→formation of LHCII supramolecular structures which potentiate creation of energy traps→excitation quenching.     

Effects of cyclosis on chloroplast-cytoplasm interactions revealed with localized lighting in Characean cells at rest and after electrical excitation

Cytoplasmic streaming in Characean internodes enables rapid intracellular transport and facilitates interactions between spatially remote cell regions. Cyclosis-mediated distant interactions might be particularly noticeable under nonuniform illumination, in the vicinity of light-shade borders where metabolites are transported between functionally distinct cell regions. In support of this notion, chlorophyll fluorescence parameters assessed on a microscopic area of Chara corallina internodal cells (area of inspection, AOI) responded to illumination of nearby regions in asymmetric manner depending on the vector of cytoplasmic streaming. When a beam of white light was applied through a 400-μm optic fiber upstream of AOI with regard to the direction of cytoplasmic streaming, non-photochemical quenching (NPQ) developed after a lag period in AOI exposed to moderate intensity light. Conversely, no NPQ was induced in the same cell area when the beam position was shifted to an equal distance downstream of AOI. Light-response curves for the efficiency of photosystem II electron transport in chloroplasts differed markedly depending on the illumination pattern (whole-cell versus small area illumination) but these differences were eliminated after the inhibition of cytoplasmic streaming with cytochalasin B. Localized illumination promoted chloroplast fluorescence responses to electrical plasmalemma excitation at high light intensities, which contrasts to the requirement of low to moderate irradiances for observation of the stimulus-response coupling under whole-cell illumination. The results indicate that different photosynthetic capacities of chloroplasts under general and localized illumination are related to lateral transport of nonevenly distributed cytoplasmic components between the cell parts with dominant photosynthetic and respiratory metabolism.     

Disentangling two non-photochemical quenching processes in Cyclotella meneghiniana by spectrally-resolved picosecond fluorescence at 77 K

Diatoms, which are primary producers in the oceans, can rapidly switch on/off efficient photoprotection to respond to fast light-intensity changes in moving waters. The corresponding thermal dissipation of excess-absorbed-light energy can be observed as non-photochemical quenching (NPQ) of chlorophyll a fluorescence. Fluorescence-induction measurements on Cyclotella meneghiniana diatoms show two NPQ processes: qE₁ relaxes rapidly in the dark while qE₂ remains present upon switching to darkness and is related to the presence of the xanthophyll-cycle pigment diatoxanthin (Dtx). We performed picosecond fluorescence measurements on cells locked in different (quenching) states, revealing the following sequence of events during full development of NPQ. At first, trimers of light-harvesting complexes (fucoxanthin–chlorophyll a/c proteins), or FCPa, become quenched, while being part of photosystem II (PSII), due to the induced pH gradient across the thylakoid membrane. This is followed by (partial) detachment of FCPa from PSII after which quenching persists. The pH gradient also causes the formation of Dtx which leads to further quenching of isolated PSII cores and some aggregated FCPa. In subsequent darkness, the pH gradient disappears but Dtx remains present and quenching partly pertains. Only in the presence of some light the system completely recovers to the unquenched state.     

Photoprotection in plants involves a change in lutein 1 binding domain in the major light-harvesting complex of photosystem II

Nonphotochemical quenching (NPQ) is the fundamental process by which plants exposed to high light intensities dissipate the potentially harmful excess energy as heat. Recently, it has been shown that efficient energy dissipation can be induced in the major light-harvesting complexes of photosystem II (LHCII) in the absence of protein-protein interactions. Spectroscopic measurements on these samples (LHCII gels) in the quenched state revealed specific alterations in the absorption and circular dichroism bands assigned to neoxanthin and lutein 1 molecules. In this work, we investigate the changes in conformation of the pigments involved in NPQ using resonance Raman spectroscopy. By selective excitation we show that, as well as the twisting of neoxanthin that has been reported previously, the lutein 1 pigment also undergoes a significant change in conformation when LHCII switches to the energy dissipative state. Selective two-photon excitation of carotenoid (Car) dark states (Car S(1)) performed on LHCII gels shows that the extent of electronic interactions between Car S(1) and chlorophyll states correlates linearly with chlorophyll fluorescence quenching, as observed previously for isolated LHCII (aggregated versus trimeric) and whole plants (with versus without NPQ).     

Spectral Radiation Dependent Photoprotective Mechanism in the Diatom Pseudo-nitzschia multistriata

Phytoplankton, such as diatoms, experience great variations of photon flux density (PFD) and light spectrum along the marine water column. Diatoms have developed some rapidly-regulated photoprotective mechanisms, such as the xanthophyll cycle activation (XC) and the non-photochemical chlorophyll fluorescence quenching (NPQ), to protect themselves from photooxidative damages caused by excess PFD. In this study, we investigate the role of blue fluence rate in combination with red radiation in shaping photoacclimative and protective responses in the coastal diatom Pseudo-nitzschia multistriata. This diatom was acclimated to four spectral light conditions (blue, red, blue-red, blue-red-green), each of them provided with low and high PFD. Our results reveal that the increase in the XC pool size and the amplitude of NPQ is determined by the blue fluence rate experienced by cells, while cells require sensing red radiation to allow the development of these processes. Variations in the light spectrum and in the blue versus red radiation modulate either the photoprotective capacity, such as the activation of the diadinoxanthin-diatoxanthin xanthophyll cycle, the diadinoxanthin de-epoxidation rate and the capacity of non-photochemical quenching, or the pigment composition of this diatom. We propose that spectral composition of light has a key role on the ability of diatoms to finely balance light harvesting and photoprotective capacity.     

外源6-BA对低温胁迫下茄子幼苗光合作用、叶绿素荧光参数及光能分配的影响

本文研究了外源6-BA对低温胁迫下茄子幼苗光合作用、叶绿素荧光参数和能量分配的影响。结果表明,外源6．BA显著增加了低温胁迫下茄子叶绿素含量、净光合速率（Pn）、蒸腾速率（t）、气孔导度（Gs）和胞间CO2浓度（c1）;同时外源6-BA明显提高了低温胁迫下茄子幼苗叶片的PSⅡ最大光化学效率（Fv/Fm）、PSⅡ潜在活性（R／Fo）、PSII天线转化效率（FvFm）、实际光化学效率（φpsⅡ）、光化学猝灭系数（g,）和光化学反应能量（P）,降低了非光化学猝灭系数（NPQ）、天线热耗散能量（D）,对非光化学反应耗散能量（E）无明显影响。表明外源6-BA处理通过促进低温胁迫下茄子幼苗光合作用,提高光合电子传递效率,从而保护光合系统,降低低温胁迫对植物的损伤。