珊瑚树叶片叶绿素荧光非光化学猝灭的日变化和季节变化

用脉冲调制荧光仪观测了珊瑚树叶片叶绿素荧光化学猝灭的日变化和季节变化后发现：在晴天,ｑＥ及慢弛豫组分随着光强的增加而升高,中午达最高值,之后随光强的减弱而下降,阴天时,这两个指标的日变化不明显。在不同季节,相同日时间和同一光照强度下测定瑚叶片的ｑＥ和ｑＥ－ｓｌｏｗ,两个指标在冬季明显高于春,秋两季;在短时间内改变强光下的叶片周围的温度,叶片的ｑＥ和ｑｅ－ＳＫＯＷ在高温和低温下均高于适温下测定的结果     

几种常绿植物光合特性的季节变化

在上海自然条件下生长的珊瑚树、女贞、孝顺竹和棕榈等四种常绿植物为材料,在春、夏、秋、冬四个季节测定了它们的叶片在不同温度时的光饱和光合速率;用ＣＦ－１０００荧光仪测定了叶片的初始荧光（Ｆ０）、最大荧光（Ｆｍ）和可变荧光（ＦＶ）等特征值。结果表明,珊瑚树和女贞适应环境温度变化的能力较强,它们的光合最适温度（Ｔｏｐｔ）的变化范围比较大,在四季均保持较高的光合活力,光合量子效率和Ｆｖ／Ｆｍ值较高,而孝顺     

珊瑚树和大豆叶片叶绿素荧光的非光化学猝灭

用ＰＡＭ２０００ 型荧光仪和７５４ 型分光光度计观测了珊瑚树和大豆叶片叶绿素荧光的非光化学猝灭快、中和慢３ 个组分（ｑＮｆ,ｑＮｍ 与ｑＮｓ） 和５０５ ｎｍ 光吸收的日变化。主要结果如下：（１） 中午,珊瑚树叶片的ｑＮｓ 比ｑＮｆ 大得多,而大豆叶片的这两个参数却几乎处于同一水平。它们的ｑＮｍ 虽然也随光强变化,但与ｑＮｓ 和ｑＮｆ 相比,除早晨和傍晚以外全天的水平都是最低的。（２） 珊瑚树叶片的初始荧光水平（Ｆｏ） 中午最低,而大豆叶片的Ｆｏ 中午最高。（３） 饱和光照射引起的珊瑚树叶片５０５ ｎｍ 光吸收的增加比大豆叶片大得多。（４） 珊瑚树叶片５０５ ｎｍ 光吸收的日变化方式与ｑＮｓ 的相类似。（５） 叶黄素循环的抑制剂ＤＴＴ对珊瑚树叶片ｑＮｓ 的抑制（５７ ％ ） 比对大豆叶片ｑＮｓ 的抑制（２３ ％ ） 严重。     

珊瑚树和大豆叶片叶绿素荧光的非光化学猝灭

用ＰＡＭ－２０００型荧光仪和７５４型分光光度计观测了珊瑚树和大豆叶片叶绿素荧光的非光化学猝灭性,中和慢３个组分和５０５ｎｍ光吸收的日变化。主要结果如下：（１）中午,珊瑚树叶片的ｑＮ８比ｑＮｆ大得多,而大豆叶片的这两个参数却几乎处于同一水平。它们的ｑＮｍ虽然也随光强变化,但与ｑＮ８和ｑＮｍ相比,除早期和傍晚以外全天的水平都是最低的。     

西宁和海北麻花艽净光合速率和叶绿素荧光参数的日变化比较

以青藏高原药用植物麻花艽为材料,研究了西宁和海北两个地区麻花艽叶片的净光合速率和叶绿素荧光参数的日变化进程。结果表明：在中午太阳辐射较强时两地麻花艽叶片的净光合速率（Pn）均下降,下午随日间光强的减弱逐渐上升,形成双峰曲线;海北麻花艽叶片的净光合速率（Pn）及其日变幅均低于西宁。随日间光强的增加麻花艽叶片的PSⅡ最大光化学效率（Fv／Fm）、PSⅡ的潜在活性（Fv/Fo）下降,非光化学猝灭系数（NPQ）则上升,黄昏各参数都恢复到接近早晨的水平,表明未发生光合机构的破坏;一天中海北麻花艽叶片的Pn、Fv／Fm、Fv／Fo均低于西宁,表明随海拔的升高、光强的增加,海北麻花艽热耗散增多,午间光抑制加重。     

C_3植物光合效率的日变化

多种田间C_3植物在晴天的光合效率常有明显的日变化,中午前后光合效率降低。C_3植物大豆叶片光合效率中午降低的主要原因,不是空气CO_2浓度和气孔导度及光呼吸的变化,而可能是光抑制。因为:1.在饱和CO_2中测定仍可观测到这种中午降低;2.光合作用的饱和光强远低于晴天中午的太阳光强;3.用纱布预遮阴可以提高叶片的光合效率;4.阴天时叶片光合效率不发生中午降低。     

自然条件下珊瑚树（Viburnum odoratissimum）叶片光合作用的光抑制

利用气体交换观察、叶绿素荧光分析和ＱＢ蛋白含量的测定３种方法,研究了常绿灌木珊瑚树叶片的光合作用在上海深秋初冬自然条件下的光抑制,以便确定在除光以外不存在其它环境胁迫的自然条件下光合机构的破坏是否是引起光抑制的主要原因。经过中午３ｈ左右的强光照射以后,珊瑚树叶片的表观量子效率（ＡＱＹ）和ＰＳⅡ光化学效率（Ｆｖ／Ｆｍ）明显下降,表明珊瑚树叶在自然条件下经常发生光抑制。而且,经中午强光照射以后,叶片的初始荧光（Ｆ０）下降;非光化学荧光猝灭的慢弛豫成分（ｑＥｓｌｏｗ）上升;光饱和的光合速率略有下降;中午光照后降低了的ＡＱＹ和Ｆｖ／Ｆｍ在叶片离开强光１ｈ以后基本恢复;模拟中午光照的强光处理对叶片的ＱＢ蛋白含量没有明显的影响。这些事实都说明这种光抑制发生的主要原因是非光辐射能量耗散的增加,光合机构的破坏即使发生,也是很轻微的。     

草莓叶绿素荧光参数日变化的研究

以草莓（Fragaria ananassa Duch）为材料,研究其叶片叶绿素荧光参数的日变化。在自然光下,草莓叶片的最大荧光（Fm）、PSⅡ光化学效率（Fv／Fm）、PSⅡ光量子效率（Yield）和光化学猝灭系数（qP）从6：00-18：00均先下降后上升,其中在下午14：00最低;而非光化学猝灭系数（qN）先上升后下降,其中在下午14：00最高。表明在中午强光下,草莓叶片遭受了强烈的光抑制,而热耗散是其主要的光保护机制。     

EFFECTS OF TEMPERATURE AND LIGHT TREATMENT ON VIOLAXANTHIN DE-EPOXIDASE ACTIVITY AND XANTHOPHYLL CYCLE-DEPENDENT ENERGY DISSIPATION IN WHEAT LEAVES

 为了探讨温度和光强是如何影响离体紫黄质脱环氧化酶(VDE)活性, 阐明依赖叶黄素循环的热耗散与VDE活性关系, 该文以小麦(Triticum aestivum)为材料, 研究了不同光强(200、500、900和1 200 μmol&;#8226;m^–2&;#8226;s^–1)和不同温度(4、25、38和45 ℃) 交叉处理对小麦叶片VDE活性以及依赖叶黄素循环热耗散能力的影响。结果表明: 小麦叶片VDE活性在30 ℃最高, 说明30 ℃是小麦叶片VDE体外条件下的最适温度; 不同光强处理下小麦叶片VDE活性基本一致。与室温(25 ℃)处理的叶片相比, 低温(4 ℃)处理的叶片VDE活力没有明显下降, 而高温(45 ℃)处理则导致了叶片VDE活性急剧下降。小麦叶片热耗散(NPQ)以及依赖叶黄素循环的热耗散(qE)均随着处理光强的增加不断上升, 而qE/NPQ则随光强增加略微下降, 在1 200 μmol&;#8226;m^–2&;#8226;s^–1光强条件下qE/NPQ则急剧下降。该研究揭示VDE活性与依赖叶黄素循环热耗散能力的指标qE/NPQ的变化有一定的相关性, 但不完全一致。并针对此问题进行了讨论。     

几种常绿植物光合特性的季节变化

以在上海自然条件下生长的瑚瑚树、女贞、孝顺竹和棕榈等四种常绿植物为材料,在春、夏、秋、冬四个季节测定了它们的叶片在不同温度时的光饱和光合速率;用ＣＦ１０００荧光仪测定了叶片的初始光（Ｆｏ）、最大荧光（Ｆｍ）和可变荧光（Ｆｖ）等特征值．结果表明．瑚瑚树和女贞适应环境温度变化的能力较强,它们的光合最适温度（Ｔｏｐｔ）的变化范围比较大,在四季均保持较高的光合活力,光合量子效率和Ｆｖ／Ｆｍ值较高,而孝顺竹和棕榈适应环境温度变化的能力较差,只在春秋两季有较高的光合活力．这些差别和它们的自然分布有联系．     

Alteration of photosystem II properties with non-photochemical excitation quenching

Oxygen yield from single turnover flashes and multiple turnover pulses was measured in sunflower leaves differently pre-illuminated to induce either 'energy-dependent type' non-photochemical excitation quenching (qE) or reversible, inhibitory type non-photochemical quenching (qI). A zirconium O2 analyser, combined with a flexible gas system, was used for these measurements. Oxygen yield from saturating single turnover flashes was the equivalent of 1.3-2.0 micromole(-) m(-2) in leaves pre-adapted to low light. It did not decrease when qE quenching was induced by a 1 min exposure to saturating light, but it decreased when pre-illumination was extended to 30-60 min. Oxygen evolution from saturating multiple turnover pulses behaved similarly: it did not decrease with the rapidly induced qE but decreased considerably when exposure to saturating light was extended or O2 concentration was decreased to 0.4%. Parallel recording of chlorophyll fluorescence and O2 evolution during multiple turnover pulses, interpreted with the help of a mathematical model of photosystem II (PS II) electron transport, revealed PS II donor and acceptor side resistances. These experiments showed that PS II properties depend on the type of non-photochemical quenching present. The rapidly induced and rapidly reversible qE type (photoprotective) quenching does not induce changes in the number of active PS II or in the PS II maximum turnover rate, thus confirming the antenna mechanism of qE. The more slowly induced but still reversible qE type quenching (photoinactivation) induced a decrease in the number of active PS II and in the maximum PS II turnover rate. Modelling showed that, mainly, the acceptor side resistance of PS II increased in parallel with the reversible qI.     

Non-photochemical quenching of chlorophyll fluorescence in the green alga Dunaliella

The relaxation of the non-photochemical quenching of chlorophyll fluorescence has been investigated in cells of the green alga Dunaliella following illumination. The relaxation after the addition of DCMU or darkening was strongly biphasic. The uncoupler NH₄Cl induced rapid relaxation of both phases, which were therefore both energy-dependent quenching, qE. The proportion of the slow phase of qE increased at increasing light intensity. In the presence of the inhibitors rotenone and antimycin the slow phase of qE was stabilised for in excess of 15 min. NaN₃ inhibited the relaxation of almost all the qE. The implications of these results are discussed in terms of the interpretation of the non-photochemical quenching of chlorophyll fluorescence in vivo and the mechanism of qE.Abbreviations PS II Photosystem II - qQ photochemical quenching of chlorophyll fluorescence - qNP non-photochemical quenching of chlorophyll fluorescence - qE energy-dependent quenching of chlorophyll fluorescence - F _m maximum level of chlorophyll fluorescence for dark adapted cells - F _m level of fluorescence at any time when qQ is zero     

Characterization of the fast and slow reversible components of non-photochemical quenching in isolated pea thylakoids by picosecond time-resolved chlorophyll fluorescence analysis.

The fast and slow reversible components of non-photochemical chlorophyll fluorescence quenching commonly assigned to the qE and the qI mechanism have been studied in isolated pea thylakoids which were prepared from leaves after a moderate photoinhibitory treatment. Chlorophyll fluorescence decays were measured at picosecond resolution and analyzed on the basis of the heterogeneous exciton/radical pair equilibrium model. Our results show that the fast reversible non-photochemical quenching is completely assigned to the PS II antenna and is related to zeaxanthin. The slow reversible qI type quenching is located at the PS II reaction center and involves enhanced nonradiative decay of the primary charge separated state to its ground state and/or triplet excited state. Apart from its independence from the proton gradient, the qI quenching shows striking similarities to a particular form of qE quenching which is also located at the PS II reaction center and has resently been resolved in isolated thylakoids from dark-adapted leaves [Wagner, B., et al. (1996) J. Photochem. Photobiol., B 36, 339-350]. Our data suggest that during exposure to the supersaturating light the reaction center qE component was replaced by qI quenching. This qE to qI transition is supposed to be part of the mechanism of the long-term downregulation of PS II during photoinhibition. It is also evident that under the conditions used in our study zeaxanthin-dependent antenna quenching is not involved in the slow reversible downregulation of PS II but that it retains its dependence on the proton gradient during exposure to strong light.     

Polyamines induce aggregation of LHC II and quenching of fluorescence in vitro

Dissipation of excess excitation energy within the light-harvesting complex of Photosystem II (LHC II) is a main process in plants, which is measured as the non-photochemical quenching of chlorophyll fluorescence or qE. We showed in previous works that polyamines stimulate qE in higher plants in vivo and in eukaryotic algae in vitro. In the present contribution we have tested whether polyamines can stimulate quenching in trimeric LHC II and monomeric light-harvesting complex b proteins from higher plants. The tetramine spermine was the most potent quencher and induced aggregation of LHC II trimers, due to its highly cationic character. Two transients are evident at 100μM and 350μM for the fluorescence and absorbance signals of LHC II respectively. On the basis of observations within this work, some links between polyamines and the activation of qE in vivo is discussed.     

Is PsbS the site of non-photochemical quenching in photosynthesis?

The PsbS protein of photosystem II functions in the regulation of photosynthetic light harvesting. Along with a low thylakoid lumen pH and the presence of de-epoxidized xanthophylls, PsbS is necessary for photoprotective thermal dissipation (qE) of excess absorbed light energy in plants, measured as non-photochemical quenching of chlorophyll fluorescence. What is known about PsbS in relation to the hypothesis that this protein is the site of qE is reviewed here.     

PSII supercomplex disassembly is not needed for the induction of energy quenching (qE)

Photoprotection by non-photochemical quenching is important for optimal growth and development, especially during dynamic changes of the light intensity. The main component responsible for energy dissipation is called qE. It has been proposed that qE involves the reorganization of the photosynthetic complexes and especially of Photosystem II. However, despite a number of studies, there are still contradictory results concerning the structural changes in PSII during qE induction. The main limitation in addressing this point is the very fast nature of the off switch of qE, since the illumination is usually performed in folio and the preparation of the thylakoids requires a dark period. To avoid qE relaxation during thylakoid isolation, in this work quenching was induced directly on isolated and functional thylakoids that were then solubilized in the light. The analysis of the quenched thylakoids in native gel showed only a small decrease in the large PSII supercomplexes (C₂S₂M₂/C₂S₂M) which is most likely due to photoinhibition/light acclimation since it does not recover in the dark. This result indicates that qE rise is not accompanied by a structural disassembly of the PSII supercomplexes.

     

Xanthophyll cycle and energy-dependent fluorescence quenching in leaves from pea plants grown under intermittent light

The possible role of zeaxanthin formation and antenna proteins in energy-dependent chlorophyll fluorescence quenching (qE) has been investigated. Intermittent-light-grown pea (Pisum sativum L.) plants that lack most of the chlorophyll a/b antenna proteins exhibited a significantly reduced qE upon illumination with respect to control plants. On the other hand, the violaxanthin content related to the number of reaction centers and to xanthophyll cycle activity, i.e. the conversion of violaxanthin into zeaxanthin, was found to be increased in the antenna-protein-depleted plants. Western blot analyses indicated that, with the exception of CP 26, the content of all chlorophyll a/b-binding proteins in these plants is reduced to less than 10% of control values. The results indicate that chlorophyll a/b-binding antenna proteins are involved in the energy-dependent fluorescence quenching but that only a part of qE can be attributed to quenching by chlorophyll a/b-binding proteins. It seems very unlikely that xanthophylls are exclusively responsible for the qE mechanism.Abbreviations CAB chlorophyll a/b-binding - Chl chlorophyll - F_V variable fluorescence - IML intermittent light - LHC light harvesting complex - PFD photon flux density - qP photochemical quenching of chlorophyll fluoresence - qN non-photochemical quenching - qE energy-dependent quenching - qI photoinhibitory quenching - qT quenching by state transition     

不同品种美国山核桃叶绿素荧光参数日变化的研究

以湖南省永州市冷水滩采穗圃中的美国山核桃为试材,研究了叶绿素荧光参数的日变化规律。结果表明:初始荧光(Fo)、最大荧光(Fm)、PSII原初光能转化效率(Fv/Fm)、光合量子产额(Yield)、光化学猝灭系数(qP)、非光化学猝灭系数(qN)和表观电子传递速率(ETR)均存在着明显的日变化。其中Fv/Fm、Fm、Yield、qP均呈先下降后上升的趋势,在中午强光下降低到最低值;qN则呈先上升后下降的趋势,在中午时分达到峰值;Fo呈下降趋势,部分品种傍晚稍有回升,但仍比早晨低;ETR日变化呈双峰曲线。不同品种间Fv/Fm、Yield、ETR、qP、qN对光强和温度的响应也存在着明显差异,可作为鉴定品种耐光抑制能力大小的指标。