Fast Chlorophyll Fluorescence Induction Research Articles

Exogenous Calcium Improves Photosynthetic Capacity of Pinus sylvestris var. mongolica under Drought

Calcium (Ca), a secondary messenger, plays an essential role in improving drought resistance. We used the Fast Chlorophyll Fluorescence Induction Dynamics technique to investigate the effects of exogenous calcium on electron transport and energy fluxes in an 8-year-old Mongolian pine to investigate the mechanism of action of Ca in regulating drought adaptation in Pinus sylvestris var. mongolica. We found water stress significantly decreased Pn and Gs, but exogenous calcium significantly improved photosynthesis under water stress. The chlorophyll a fluorescence transient (OJIP) analysis revealed that water stress increased Fo and decreased Fm, inactivating reaction centers. Water stress reduced VI and VJ while increasing Mo, destroying the electron transport chain. Exogenous calcium increased Sm while decreasing VI and Mo under water stress, enhancing electron transport from QA to QB. Furthermore, 5 mM Ca2+ increased I-P phase and ψPo, δRo, and φRo, decreasing the drought-induced reduction in electron accepters of PSⅠ. The increase in ABS/RC, TRo/RC, ETo/RC, and DIo/RC caused by 5 mM Ca2+ demonstrated that calcium can regulate photoprotection to promote photosynthetic activity. Thus, exogenous calcium alleviated drought-induced reductions in photosynthetic activity by regulating photoprotection and boosting the electron transport efficiency at the acceptor side of PSⅡ and PSⅠ.

Exogenous trehalose protects photosystem II in heat-stressed wheat

Background: Photosystem II (PSII) is susceptible to heat stress. Plants naturally accumulate trehalose to improve stress tolerance. However, the mechanism by which trehalose affects PSII during heat stress is still unknown.
 Questions: How does trehalose affect PSII during heat stress?
 Studied species: Triticum aestivum L.
 Study site and dates: Shanghai, China. 2019-2021.
 Methods: Trehalose -pretreated wheat seedlings suffered from heat stress and their photosynthetic parameters were measured.
 Results: Heat stress caused a reduction in the photochemical efficiency of PSII, the electron transfer rate (ETR(II)), the quantum yield of regulated energy dissipationY(NPQ) and the coefficient of photochemical quenching (qP), but increased the quantum yield of non-regulated energy dissipation of PSII (Y[NO]). The shape of the fast chlorophyll fluorescence induction kinetics (OJIP) curve in the heat-stressed wheat was altered and the primary photochemistry maximum yield of PSII (Fv/Fo) and the PSII performance indicator PIabs were reduced. Accordingly, the activities of PSII and electron transport chain, the amount of ordered α-helix structures and the content of D1 protein also decreased. However, in trehalose-pretreated wheat, D1 protein and protein secondary structures of PSII were both protected, the electron transport activities of PSII and the whole chain were improved and greater fluorescence parameters values were maintained. Lower Y(NO) and more stable OJIP were obtained.
 Conclusions: Exogenous trehalose acted a vital role in the protection of the function of PSII, resulting in higherphotosynthetic capacity under heat stress.

Combined chlorophyll fluorescence techniques to study environmental impact on the mountain moss Polytrichum commune

Two chlorophyll fluorescence (ChlF) methods were used to study the effects of high light (photoinhibition) and dehydration, common stressors of the alpine environment, on primary photosynthetic processes in the moss Polytrichum commune from the Czech Republic, the Jeseníky Mountains. Photoinhibition (PI) was studied in fully hydrated thalli of P. commune and during the period of spontaneous desiccation. Time courses of Kautsky kinetics (KK) of ChlF and derived parameters: maximum quantum yield (FV/FM), effective quantum yeld (ΦPSII), and non-photochemical quenching parameters, were measured before and after the samples were treated with high light (1500 µmol m-2 s-1 PAR) for 60 min. Dehydration effects were tested in two sets of experiments with a Pulse-Amplitude-Modulation fluorometry (PAM) and Fast Chlorophyll Fluorescence induction curve (OJIP) techniques. In PAM tests, the desiccating samples were exposed to saturating light pulses every 10 min. in order to obtain ΦPSII and non-photochemical quenching (NPQ). In the second dehydration experiment, OJIP transients of ChlF were repeatedly recorded, OJIP-derived ChlF parameters were plotted against relative water content (RWC) monitored during desiccation. Combined ChF techniques provided insights into the mechanisms activated during P. commune desiccation, such as dissipation of excess absorbed energy through heat dissipation, and conformational changes or destructions of the light harvesting complexes. Combination of stressors resulted in amplified interference with the photosynthetic machinery, even when the added stressor (dehydration) was applied in low dose.

High nitrogen inhibits photosynthetic performance in a shade-tolerant and N-sensitive species Panax notoginseng.

Nitrogen (N) is a primary factor limiting leaf photosynthesis. However, the mechanism of high-N-driven inhibition on photosynthetic efficiency and photoprotection is still unclear in the shade-tolerant and N-sensitive species such as Panax notoginseng. Leaf chlorophyll (Chl) content, Ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) activity and content, N allocation in the photosynthetic apparatus, photosynthetic performance and Chl fluorescence were comparatively analyzed in a shade-tolerant and N-sensitive species P. notoginseng grown under the levels of moderate nitrogen (MN) and high nitrogen (HN). The results showed that Rubisco content, Chl content and specific leaf nitrogen (SLN) were greater in the HN individuals. Rubisco activity, net photosynthetic rate (Anet), photosynthetic N use efficiency (PNUE), maximum carboxylation rate (Vcmax) and maximum electron transport rate (Jmax) were lower when plants were exposed to HN as compared with ones to MN. A large proportion of leaf N was allocated to the carboxylation component under the levels of MN. More N was only served as a form of N storage and not contributed to photosynthesis in HN individuals. Compared with the MN plants, the maximum quantum yield of photosystem II (Fv/Fm), non-photochemical quenching of PSII (NPQ), effective quantum yield and electron transport rate were obviously reduced in the HN plants. Cycle electron flow (CEF) was considerably enhanced in the MN individuals. There was not a significant difference in maximum photo-oxidation P700+ (Pm) between the HN and MN individuals. Most importantly, the HN individuals showed higher K phase in the fast chlorophyll fluorescence induction kinetic curve (OJIP kinetic curve) than the MN ones. The results obtained suggest that photosynthetic capacity might be primarily inhibited by the inactivated Rubisco in the HN individuals, and HN-induced depression of photoprotection might be caused by the photodamage to the donor side of PSII oxygen-evolving complex.

Special issue in honour of Prof. Reto J. Strasser - Seasonal monitoring of PSII functionality and relative chlorophyll content on a field site in two consecutive years: A case study of different oak species

In search for practical silvicultural management tools to identify alternative tree species for predicted Central European climate conditions, a cross-species survey with five evergreen, semi-evergreen, and deciduous Quercus taxa with contrasting morphological leaf traits was performed. Fast chlorophyll fluorescence induction of PSII and relative leaf chlorophyll contents were performed to assess the overall plant vitality at any point in time during two complete vegetation periods in consecutive years (2012 and 2013). Maximum photochemical efficiency of PSII and the performance index on absorption base showed a very conservative relationship to each other and a similar intra-annual progress in all deciduous species, but with a different speed of increase and decrease during leaf development and senescence and thus a different length of vegetation period. The intra-annual variability of OJIP and chlorophyll content parameters is considered with respect to the practicability of measurements in the field for management purposes.

Effects of drought on leaf growth and chlorophyll fluorescence kinetics parameters in Cyclobalanopsis glauca seedlings of Karst areas

To uncover adaptation mechanism of Cyclobalanopsis glauca to the arid environment of Karst areas, current-year seedlings of C. glauca were potted and grown under four soil water conditions: Normal water supply (-0.1 MPa), light drought stress (-0.5 MPa), moderate drought stress (-0.9 MPa), and severe drought stress (-1.5 MPa). We measured leaf growth and parameters of fast chlorophyll fluorescence induction dynamics after treated by 15, 30, 45, 60 and 90 days. With the increase of drought stress intensity, leaf area, number of green leaves, leaf water content, the contents of chlorophyll a+b and carotenoids, the maximum fluorescence, maximum photochemical quantum yield and potential photochemical efficiency significantly decreased, while the number of dead leaves and the initial fluorescence significantly increased. There was no significant difference in these parameters between light drought and normal water treatments. There were no significant difference in the absorption flux per reaction center (ABS/RC), captured light energy used to restore qA (TRo/RC), number of active reaction centers per unit area (RC/CS), light energy captured per unit area (TRo/CS) and light energy used for electron transfer per unit area (ETo/CS) between light drought and normal water treatments. Among these parameters, RC/CS was slightly higher under light drought treatment than that of normal water treatment. TRo/CS and ETo/CS reached peaks at the 45th day, being 606.12 and 440.78, respectively. Leaf ABS/RC, TRo/RC, ETo/RC, DIRo/RC, RC/CS, TRo/CS and ETo/CS of C. glauca seedlings under mode-rate drought and severe drought treatment were lower than those of normal water treatment, and the parameters under severe drought stress decreased more significantly with the extension of drought stress time. With increasing intensity and duration of drought stress, the maximum quantum efficiency, probability of other electron acceptors, and quantum ratio of electron transfer decreased, but quantum yield for energy dissipation increased. These results demonstrated that C. glauca seedlings under light drought condition showed some degree of adaptability and resistance to drought. Mode-rate drought treatment caused a decline in chlorophyll fluorescence and photosynthetic pigments, leading to slow growth of seedlings. Severe drought had a serious impact on growth of C. glauca seedlings, but did not lead to seedling death. Therefore, C. glauca seedlings showed strong drought tolerance, which were suitable for the application of vegetation restoration and reforestation projects in Karst areas.

采煤沉陷裂缝区土壤含水量变化对柠条叶片叶绿素荧光的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 采煤沉陷裂缝区土壤含水量变化对柠条叶片叶绿素荧光的响应 DOI: 10.5846/stxb201712282341 作者: 作者单位: 中国矿业大学,中国矿业大学,中国矿业大学 环境与测绘学院,中国矿业大学 环境与测绘学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划课题（2016YFC0501107）；国家重点基础研究发展计划（973）课题（2013CB227904）；国家自然科学基金重点项目（U1361214） Effects of soil water content change on the chlorophyll fluorescence response of Caragana korshinskii leaves under the influence of coal mining subsidence cracks Author: Affiliation: China University of Mining and Technology,China University of Mining and Technology,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采煤塌陷引起的土壤环境因子的变化对矿区植物生长的影响越来越受到人们的关注，快速叶绿素荧光诱导动力学分析技术被称为植物受胁迫状态的有效探针，能够快速获取胁迫下光系统Ⅱ光化学活性和电子传递的信息。研究采煤塌陷裂缝区植物叶片叶绿素荧光的变化是揭示煤炭开采塌陷胁迫对植物个体生长影响的关键环节，能为大尺度下采煤沉陷区植物损伤机理研究提供基础。对于黄土高原半干旱矿区，土壤水分无疑是植物生长最重要的限制因素，而植物叶片叶绿素荧光变化采煤塌陷影响下土壤含水量变化的响应如何尚不清楚。为了弄清采煤沉陷裂缝影响下土壤含水量变化对柠条叶片叶绿素荧光响应的影响，选取神东煤田大柳塔矿区52302工作面为实验场地，在分析了采煤塌陷裂缝对土壤含水量的影响的基础上，以生态修复物种柠条为研究对象，对采煤塌陷裂缝区不同土壤含水量下柠条叶片快速叶绿素荧光诱导动力学曲线进行监测。结果显示：（1）由于煤炭井工开采在地表形成大量裂缝，破坏了土体结构，增加了土壤水分的蒸发面，加速了土壤水的散失。土壤水分含量随着与裂缝之间距离的增加而增加，从距离裂缝0 cm到300 cm，土壤平均含水量从5.63%增加到15.07%；（2）裂缝区土壤水分降低，柠条受到干旱胁迫程度加重，叶片快速叶绿素荧光诱导动力学曲线由O-J-I-P变形为O-K-J-I-P曲线。干旱胁迫通过干扰柠条叶片PSⅡ电子供体侧、受体侧以及电子传递链的功能，严重的损害了柠条叶片光合机构的正常功能。 Abstract:Increased attention has been given to the influence of changes in environmental factors caused by coal mining subsidence on plant physiology. Rapid chlorophyll fluorescence-induced kinetic analysis is known as an effective probe to examine the stress state of plants, using which the information of photochemical activity and electron transfer of light System Ⅱ under stress can be quickly obtained. Studying the change of chlorophyll fluorescence in plant leaves from a coal mining fractured area is a key link for revealing the effects of subsidence stress on individual plant growth, and it can provide the basis for studying the damage mechanism in plants from a mining subsidence area. Soil moisture is undoubtedly the most important limiting factor on plant growth, and the response of chlorophyll fluorescence variation in plant leaves to soil water content under the influence of coal mining subsidence is not clear. In order to ascertain the effects of soil water content on the chlorophyll fluorescence response of Caragana korshinskii under the influence of mining subsidence crack, the 52302 working face of the Daliuta mining area was selected as the experimental site with C. korshinskii as the research target. Based on an analysis of the influence of mining subsidence cracks on soil water content, the fast chlorophyll fluorescence induction kinetics curve of C. korshinskii leaves at different soil moisture contents from the coal mining subsidence fractured area was monitored. The effect of soil water content change on the chlorophyll fluorescence response of C. korshinskii leaves under the influence of coal mining subsidence cracks was studied. The results showed that (1) since coal mining destroys the soil structure, a large number of cracks formed on the surface, which increased the evaporation of surface soil moisture, accelerating the loss of soil water. The soil moisture content increased when the distance between two cracks was from 0 cm to 300 cm, and the average water content increased from 5.63% to 15.07%, respectively. (2) The soil moisture in the fractured area further decreased, and C. korshinskii faced drought stress. The rapid chlorophyll fluorescence induced kinetic curve of the leaves was deformed by O-J-I-P to O-K-J-I-P curves. Drought stress seriously interfered with the normal function of the photosynthetic organs in C. korshinskii leaves by interfering with the functions of the PSⅡ electron donor side, receptor side, and the electron transport chain. 参考文献 相似文献 引证文献

Differential ecophysiological responses to seasonal drought of three co-existing oak species in northern Greece

Oaks (Quercus spp.) represent the most important broadleaf genus with respect to forest-shaping tree species in the Mediterranean. Considering future climate scenarios (increased drought conditions), the identification of drought tolerant oak species is of great importance for future forest management in this region. The objective of the study was the comparison of physiological status of three economically and ecologically valuable oak species (Quercus ilex, Quercus frainetto and Quercus pubescens) co-existing in natural coppice stands in NE Greece, in response to seasonal drought stress. Measurements were conducted between June and September 2016, every 15–20 days until leaf falling. The parameters studied were predawn leaf water potential and fast chlorophyll fluorescence induction curves (OJIP test), chlorophyll content, and relative water content. Meteorological data from the area were also collected. Photosynthetic parameters such as performance indices (PIabs and PItot) reacted to summer drought conditions, with Q. frainetto showing the lowest values. The discrepancy between species increased with duration of drought period. Q. frainetto revealed the lowest predawn water potential values. The results indicate that Q. frainetto is less suitable for future forestry applications in the studied climate/elevation zone than Q. pubescens and Q. ilex.

Effects of four types of sodium salt stress on plant growth and photosynthetic apparatus in sorghum leaves

ABSTRACTSorghum variety Longza 17 was used as the experimental organism in a study of the effects of different types of sodium salt (two neutral salts, NaCl and Na2SO4; and two alkaline salts, NaHCO3 and Na2CO3), at an equivalent Na+ concentration (100 mmol·L−1) on leaf growth parameters and PSII and PSI function by using the Fast Chlorophyll Fluorescence Induction Dynamics technique and 820 nm light reflectance curves. The results showed that at Na+ concentration of 100 mmol·L−1, different types of sodium salt stress significantly inhibited the growth of sorghum plants. Different types of sodium salt stress showed significant inhibition on the activities of PSII and PSI in sorghum leaves, the impact of different types of sodium salt on the activities of PSII and PSI in sorghum leaves was consistent, listed from greatest to least impact as Na2CO3 > NaHCO3 > Na2SO4 > NaCl. The effects of alkaline salt stress on the growth and photosynthetic properties of sorghum were greater than those under the neutral salt stress, therefore, in addition to considering the impact of Na+ concentration in the sorghum planting area, emphasis should also be given to the influence of the degree of alkalization, especially the higher alkalinity of Na2CO3.

Pea PSII-LHCII supercomplexes form pairs by making connections across the stromal gap

In higher plant thylakoids, the heterogeneous distribution of photosynthetic protein complexes is a determinant for the formation of grana, stacks of membrane discs that are densely populated with Photosystem II (PSII) and its light harvesting complex (LHCII). PSII associates with LHCII to form the PSII-LHCII supercomplex, a crucial component for solar energy conversion. Here, we report a biochemical, structural and functional characterization of pairs of PSII-LHCII supercomplexes, which were isolated under physiologically-relevant cation concentrations. Using single-particle cryo-electron microscopy, we determined the three-dimensional structure of paired C2S2M PSII-LHCII supercomplexes at 14 Å resolution. The two supercomplexes interact on their stromal sides through a specific overlap between apposing LHCII trimers and via physical connections that span the stromal gap, one of which is likely formed by interactions between the N-terminal loops of two Lhcb4 monomeric LHCII subunits. Fast chlorophyll fluorescence induction analysis showed that paired PSII-LHCII supercomplexes are energetically coupled. Molecular dynamics simulations revealed that additional flexible physical connections may form between the apposing LHCII trimers of paired PSII-LHCII supercomplexes in appressed thylakoid membranes. Our findings provide new insights into how interactions between pairs of PSII-LHCII supercomplexes can link adjacent thylakoids to mediate the stacking of grana membranes.

Impact of Drought, Heat, and Their Combination on Chlorophyll Fluorescence and Yield of Wild Barley (Hordeum spontaneum)

The impact of (long-term) drought acclimation and (short-term) heat stress and their combination on fast chlorophyll fluorescence induction curves (OJIP) and grain yield was tested using pot-grown plants of wild barley (Hordeum spontaneum) originating from Northern Egypt. Concerning agronomic traits, the main effect of drought was decreased biomass accumulation and grain yield, while heat specifically affected floral development. The treatments caused specific inhibitions of photosystem II (PSII) functionality. While heat stressed plants showed a reduction of maximum quantum efficiency of PSII (φP0), an indication of effects on oxygen evolving complex (OEC) functionality, and the connectivity of PSII units, these features were entirely missing in drought acclimated plants. Drought caused a reduction of the Performance Index (PIabs) and of the relative amplitude of the IP-phase of the OJIP induction curve (ΔVIP). Individuals suffering from a combination of drought and heat showed a better ability to recover photosynthetic electron transport after the relief of stress in comparison to heat stressed plants. However, this improved capacity to recover was not accompanied by an increased grain yield. Thus, we conclude that chlorophyll fluorescence measurements provide valuable physiological data; however, their use in agronomic studies for the prediction of agronomic traits should be done with some precaution.

Imaging of fast chlorophyll fluorescence induction curve (OJIP) parameters, applied in a screening study with wild barley (Hordeum spontaneum) genotypes under heat stress

We quantified the influence of heat stress (HS) on PSII by imaging of parameters of the fast chlorophyll fluorescence (CF) induction (OJIP) kinetic of 20 genotypes of wild barley (Hordeum spontaneum) covering a broad geographical spectrum. We developed a standardised screening procedure, allowing a repetitive fluorescence measurement of leaf segments. The impact of HS was quantified by calculating a Heat Resistance Index (HRI), derived from the decrease of the Performance Index (PI) caused by HS treatment and following recovery. For the genotype showing the lowest HRI, reduced maximum quantum yield (φP0) and increased relative variable fluorescence of the O-J phase (K-Peak) were detected after HS, whereas the basal fluorescence (F0) remained stable. An additional feature was a lowered fraction of active (QA-reducing) reaction centres (RCs). The disturbances disappeared after one day of recovery. Spatial heterogeneities of fluorescence parameters were detected, as the negative effect of HS was stronger in the leaf areas close to the leaf tip. The results of this study prove that chlorophyll fluorescence imaging (CFI) is suitable for the detection of HS symptoms and that imaging of JIP-Test parameters should be considered in future screening and phenotyping studies aiming for the characterisation of plant genotypes.

Reduced glutamine synthetase activity plays a role in control of photosynthetic responses to high light in barley leaves

The chloroplastic glutamine synthetase (GS, EC 6.3.1.2) activity was previously shown to be the limiting step of photorespiratory pathway. In our experiment, we examined the photosynthetic high-light responses of the GS2-mutant of barley (Hordeum vulgare L.) with reduced GS activity, in comparison to wild type (WT). The biophysical methods based on slow and fast chlorophyll fluorescence induction, P700 absorbance, and gas exchange measurements were employed. Despite the GS2 plants had high basal fluorescence (F0) and low maximum quantum yield (Fv/Fm), the CO2 assimilation rate, the PSII and PSI actual quantum yields were normal. On the other hand, in high light conditions the GS2 had much higher non-photochemical quenching (NPQ), caused both by enhanced capacity of energy-dependent quenching and disconnection of PSII antennae from reaction centers (RC). GS2 leaves also maintained the PSII redox poise (QA−/QA total) at very low level; probably this was reason why the observed photoinhibitory damage was not significantly above WT. The analysis of fast chlorophyll fluorescence induction uncovered in GS2 leaves substantially lower RC to antenna ratio (RC/ABS), low PSII/PSI ratio (confirmed by P700 records) as well as low PSII excitonic connectivity.

A selection tool for freezing tolerance in common wheat using the fast chlorophyll a fluorescence transient

AbstractThe analysis of fast chlorophyll fluorescence induction kinetics in dark‐adapted leaves (JIP‐test) is proposed as a rapid method for evaluating freezing tolerance in wheat. Wheat leaves were detached from the plants of 40 cultivars grown in an open‐field in Smolice, during December and March of winters 2004/2005 and 2005/2006, transferred to laboratory in Krakow and frozen in −15°C. Next, measurements of chlorophyll fluorescence were taken. The correlation coefficients between the JIP‐test parameters with freezing tolerance data obtained in multiple field‐laboratory studies, varied between 0.58 and 0.70 depending on sampling time and parameter measured. The chlorophyll fluorescence parameter, which can always be used for the screening of freezing tolerance in the method described here, is the performance index (PI), which characterizes the overall energy flow efficiency in photosystem II (PSII). The results indicate, that the technique proposed here can be useful for freezing tolerance screening in plant breeding programmes. However, this method seems to be a more reliable tool in the selection of freezing tolerant germplasm, than for discarding freezing susceptible materials.

Electrical and chemical signals involved in short-term systemic photosynthetic responses of tobacco plants to local burning

Short-term (up to 1 h) systemic responses of tobacco (Nicotiana tabacum cv. Samsun) plants to local burning of an upper leaf were studied by measuring the following variables in a distant leaf: extracellular electrical potentials (EEPs); gas exchange parameters; fast chlorophyll fluorescence induction; and endogenous concentrations of three putative chemical signaling compounds-abscisic (ABA), jasmonic (JA), and salicylic (SA) acids. The first detected response to local burning in the distant leaves was in EEP, which started to decline within 10-20 s of the beginning of the treatment, fell sharply for ca. 1-3 min, and then tended to recover within the following hour. The measured gasometric parameters (stomatal conductance and the rates of transpiration and CO(2) assimilation) started to decrease 5-7 min after local burning, suggesting that the electrical signals may induce stomatal closure. These changes were accompanied by systemic increases in the endogenous ABA concentration followed by huge systemic rises in endogenous JA levels started after ca. 15 min, providing the first evidence of short-term systemic accumulation of these plant hormones in responses to local burning. Furthermore, JA appears to have an inhibitory effect on CO(2) assimilation. The correlations between the kinetics of the systemic EEP, stomatal, photosynthetic, ABA, and JA responses suggest that (1) electrical signals (probably induced by a propagating hydraulic signal) may trigger chemical defense-related signaling pathways in tobacco plants; (2) both electrical and chemical signals are interactively involved in the induction of short-term systemic stomatal closure and subsequent reductions in the rate of transpiration and CO(2) assimilation after local burning events.

Comparison of chlorophyll fluorescence and whole‐plant bioassays of isoproturon

Summary The response to aqueous solutions of isoproturon was examined on intact plants of Matricaria perforata, Apera spica‐venti and Sinapis alba in greenhouse tests, comparing visual estimates of shoot phytotoxicity at 30 d after application (DAA) with measurements of fast chlorophyll fluorescence induction at 10 DAA on leaves of the same treated plants. The sensitivity was greatest from pre‐emergence application to intact plants of M. perforata and A. spica‐venti, whereas post‐emergence sprays were relatively more active on S. alba. The use of fluorescence induction was investigated further in Petri‐dish experiments on excised M. perforata leaf segments. The Petri‐dish bioassay enabled detection of isoproturon at concentrations above 9 × 10−7 M within 96 h after herbicide exposure. The potential for using chlorophyll fluorescence assays for the determination of isoproturon content in soil extracts is discussed.

Effect of meta-topolin and bohemine derived from benzylaminopurine on PSII function in artificially senescing wheat leaves

Cytokinin 6-benzylaminopurine (BA) is known to slow down chlorophyll and protein degradation and decrease of photosynthetic function induced by leaf senescence. An effect of BA and its two derivatives - meta-topolin (mT; 6-(3-hydroxybenzylamino)purine, a natural derivative with cytokinin activity) and bohemine (boh; 6-benzylamino-2-(3-hydroxypropyl-amino)-9-isopropylpurine, a synthetic derivative acting as a cyclin-dependent kinase inhibitor) on photosynthetic pigment content and photosystem II (PSII) function was studied in wheat (Triticum aestivum L. cv. Hereward) leaves during artificial senescence. PSII function was evaluated using of parameters of fast chlorophyll fluorescence induction (an O-J-I-P transient). In control leaf segments (stored in distilled water), a very pronounced decrease in chlorophyll and carotenoid content was observed. An increase of the relative height of a J step (VJ) in the O-J-I-P transient and a decrease in the FV/FP ratio were observed indicating an increase in a relative content of QB-nonreducing reaction centres of PSII and an inhibition of PSII photochemistry, respectively. BA and mT slowed down the decrease in chlorophyll and carotenoid content and suppressed the changes in VJ and FV/FP which indicated their positive effect on maintenance of PSII structure and function. This effect was more pronounced in case of mT. Bohemine did not affect the decrease in photosynthetic pigment content and rather accelerated the decrease in PSII function in comparison with control.