Neil R. Baker's research while affiliated with University of Essex and other places
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Publications (210)
Oxygen is both product and substrate of photosynthesis and metabolism in plants, by oxygen evolution through water splitting and uptake by photorespiration and respiration. It is important to investigate these processes simultaneously in leaves, especially in response to environmental variables, such as light and temperature. To distinguish between...
Fig. S1 Response of stomatal conductance to water vapour (g
s) of 15 species to an increase in irradiance from 100 to 1000 μmol m−2 s−1 PPFD.
Fig. S2 Response of net CO2 assimilation (A) of 15 species to an increase in irradiance from 100 to 1000 μmol m−2 s−1 PPFD.
Fig. S3 The relationship between 95% maximum net CO2 assimilation (A
95) and stead...
Both photosynthesis (A) and stomatal conductance (g s) respond to changing irradiance, yet stomatal responses are an order of magnitude slower than photosynthesis, resulting in noncoordination between A and g s in dynamic light environments.
Infrared gas exchange analysis was used to examine the temporal responses and coordination of A and g s to a...
Water availability is the biggest single limitation on plant productivity worldwide. In Arabidopsis, changes in metabolism and gene expression drive increased drought tolerance and initiate diverse drought avoidance and escape responses. To address regulatory processes that link these responses together, we set out to identify novel genes that gove...
Water availability is a major limitation for agricultural productivity. Plants growing in severe arid climates such as deserts provide tools for studying plant growth and performance under extreme drought conditions. The perennial species Calotropis procera used in this study is a shrub growing in many arid areas which has an exceptional ability to...
The C3 plant Rhazya stricta is native to arid desert environment zones, where it experiences daily extremes of heat, light intensity (PAR) and high vapour pressure deficit (VPD). We measured the photosynthetic parameters in R. stricta in its native environment to assess the mechanisms that permit it to survive in these extreme conditions. Infrared...
Instrumentation and methods for rapid screening and selection of plants with improved water use efficiency are essential to address current issues of global food and fuel security. A new imaging system that combines chlorophyll fluorescence and thermal imaging has been developed to generate images of assimilation rate (A), stomatal conductance (g
s...
Heat-stressed crops suffer dehydration, depressed growth, and a consequent decline in water productivity, which is the yield
of harvestable product as a function of lifetime water consumption and is a trait associated with plant growth and development.
Heat shock transcription factor (HSF) genes have been implicated not only in thermotolerance but...
Light absorbed by photosystems I and II is used to drive linear electron transport, and associated proton transport, in the thylakoid membranes of leaves. In healthy leaves operating under non-stressful conditions and in which photorespiration is inhibited, photosynthetic electron transport is used primarily to reduce NADP+ to NADPH, which is then...
Electron flux from water via photosystem II (PSII) and PSI to oxygen (water-water cycle) may provide a mechanism for dissipation of excess excitation energy in leaves when CO(2) assimilation is restricted. Mass spectrometry was used to measure O(2) uptake and evolution together with CO(2) uptake in leaves of French bean and maize at CO(2) concentra...
Diatoms are frequently exposed to high light (HL) levels, which can result in photoinhibition and damage to PSII. Many microalgae can photoreduce oxygen using the Mehler reaction driven by PSI, which could protect PSII. The ability of Nitzschia epithemioides Grunow and Thalassiosira pseudonana Hasle et Heimdal grown at 50 and 300 μmol photons · m−2...
Severe environmental stress imposed on plant tissues induces changes in oxygen (O 2) metabolism that cause oxidative stress. Oxidative stress occurs when reactive oxygen species (ROS) are not rapidly scav-enged and the rate of repair of damaged cell components fails to keep pace with the rate of damage. If this situation persists, irreversible dama...
Previously, it has been shown that Arabidopsis thaliana leaves exposed to high light accumulate hydrogen peroxide (H2O2) in bundle sheath cell (BSC) chloroplasts as part of a retrograde signaling network that induces ASCORBATE PEROXIDASE2 (APX2). Abscisic acid (ABA) signaling has been postulated to be involved in this network. To investigate the pr...
Reactive oxygen species (ROS) are involved in many signalling pathways and numerous stress responses in plants. Consequently, it is important to be able to identify and localize ROS in vivo to evaluate their roles in signalling. A number of probes that have a high affinity for specific ROS and that are effectively taken up by cells and tissues are...
Occurrences whereby cnidaria lose their symbiotic dinoflagellate microalgae (Symbiodinium spp.) are increasing in frequency and intensity. These so-called bleaching events are most often related to an increase in water temperature, which is thought to limit certain Symbiodinium phylotypes from effectively dissipating absorbed excitation energy that...
A brief review of the photosynthetic apparatus of higher plants is given, followed by a consideration of the modifications induced in this apparatus by changes in light intensity and light quality. Possible strategies by which plants may optimize photosynthetic activity by both long- and short-term modifications of their photosynthetic apparatus in...
Apex and Bristol cultivars of oilseed rape (Brassica napus) were irradiated with 0.63 W m−2 of UV-B over 5 d. Analyses of the response of net leaf carbon assimilation to intercellular CO2 concentration were used to examine the potential limitations imposed by stomata, carboxylation velocity and capacity for regeneration of ribulose 1,5-bis-phosphat...
When plants of Zea mays L. cv. LG11 that have been grown at optimal temperatures are transferred to chilling temperatures (0–12°C) photoinhibition of photosynthetic CO2 assimilation can occur. This study examines how growth at sub-optimal temperatures alters both photosynthetic capacity and resistance to chilling-dependent photoinhibition. Plants o...
An instrument capable of imaging chlorophyll a fluorescence, from intact leaves, and generating images of widely used fluorescence parameters is described. This instrument, which is based around a fluorescence microscope and a Peltier-cooled charge-coupled device (CCD) camera, differs from those described previously in two important ways. First, th...
Globally, agriculture accounts for 80-90% of all freshwater used by humans, and most of that is in crop production. In many areas, this water use is unsustainable; water supplies are also under pressure from other users and are being affected by climate change. Much effort is being made to reduce water use by crops and produce 'more crop per drop'....
Transgenic antisense tobacco plants with a range of reductions in sedoheptulose-1,7-bisphosphatase (SBPase) activity were
used to investigate the role of photosynthesis in stomatal opening responses. High resolution chlorophyll a fluorescence imaging showed that the quantum efficiency of photosystem II electron transport (Fq′/Fm′) was decreased sim...
The use of chlorophyll fluorescence to monitor photosynthetic performance in algae and plants is now widespread. This review examines how fluorescence parameters can be used to evaluate changes in photosystem II (PSII) photochemistry, linear electron flux, and CO(2) assimilation in vivo, and outlines the theoretical bases for the use of specific fl...
The light-dependent production of ATP and reductants by the photosynthetic apparatus in vivo involves a series of electron and proton transfers. Consideration is given as to how electron fluxes through photosystem I (PSI), using absorption spectroscopy, and through photosystem II (PSII), using chlorophyll fluorescence analyses, can be estimated in...
As a result of ozone depletion, ground doses of ultraviolet B (UVB) radiation in the mid latitudes of the Northern Hemisphere have increased since the 1980s, and current predictions indicate no possible alleviation until at least post 2020. Mudflats and sandflats are important coastal-zone habitats, and support extensive biofilms of benthic microal...
The effects of UV-B radiation on photosynthesis and photosynthetic productivity of higher plants are reviewed. When plants
were exposed to large UV-B doses in a glasshouse in order to study the mechanistic basis of UV-B-induced inhibition of photosynthesis,
direct effects on stomata and on Calvin cycle enzymes (i.e. large decreases in ribulose-1,5-...
A rapid and sensitive technique, involving analysis of chlorophyll a fluorescence induction kinetics, for the study of the penetration of photosynthetically active herbicides into leaves is described. A range of chlorophyll fluorescence parameters are examined for wheat leaves treated with diuron in order to determine the most appropriate parameter...
An overview of some of the major issues that emerge from the book is presented. Consideration is given to possible future
developments in studies of the impact of environmental changes on photosynthesis and the role that these may play in predictive
modeling of the effects of global climate change on plant productivity.
In this article, the role of the reactive oxygen species (ROS) hydrogen peroxide (H2O2) as a signaling molecule involved in plant response to a sudden change in light intensity will be considered in a spatial context. The relatively low reactivity of H2O2 compared with other ROS (Halliwell and Gutteridge, 1985) might suggest that it could diffuse f...
Two C4 plants, Miscanthus x giganteus and Cyperus longus L., were grown at suboptimal growth temperatures and the relationships between the quantum efficiencies of photosynthetic electron transport through photosystem II (PSII) (PSII operating efficiency; Fq'/Fm') and CO2 assimilation (phiCO2) in leaves were examined. When M. x giganteus was grown...
Epipelic diatoms are important components of microphytobenthic biofilms. Cultures of four diatom species (Amphora coffeaeformis, Cylindrotheca closterium, Navicula perminuta and Nitzschia epithemioides) and assemblages of mixed diatom species collected from an estuary were exposed to elevated levels of ultraviolet-B (UV-B) radiation. Short exposure...
Photosystem II plays an especially important role in the response of photosynthesis in higher plants to environmental perturbations and stresses. The relationship between photosystem II and photosynthetic CO2 assimilation is examined and factors identified that may modulate photosystem II activity in vivo. Particular attention is given to non-photo...
The effect of growth temperatures on quantum yield (φ) was examined for leaves at different stages of development within the immature canopies of two crops of field grown maize (Zea mays cv. LG11) sown on 3 May and 20 June 1990. During the period of 23 to 49d after sowing, the crop sown on the 3 May experienced temperatures below 10°C on 19 occasio...
The effects of zinc concentrations up to 400 μM were examined on three photosynthetic electron transport reactions of thylakoids isolated from Pisum sativum L. cv. Meteor. Zinc (400 μM) had no effect on photosystem I mediated electron transport from reduced N,N,N′,N′-tetramethyl-p-phenylenediamine to methyl viologen, but inhibited uncoupled electro...
Abstract Photosynthetic electron transport activities and the ability to generate and maintain a trans-thylakoid proton electrochemical gradient were examined during chloroplast development in 4-day-old wheat leaves grown under a diurnal light regime. Polarographic and spectropholometric studies on leaf tissue demonstrated that poorly developed chl...
A portable apparatus has been constructed to measure simultaneously the quantum yield of CO2 assimilation, light absorption, chlorophyll fluorescence emission and water vapour exchange of attached intact leaves in the field. The core of the instrument is a light-integrating spherical leaf chamber which includes ports for a light source, photosynthe...
Chlorophyll fluorescence emission spectra and the kinetics of 685 mm fluorescence emission from wheat leaf tissue and thylakoids isolated from such tissue were examined as a function of excitation wavelength. A considerable enhancement of fluorescence emission above 700 nm relative to that at 685 nm was observed from leaf tissue when it was excited...
A comparative study was made of the effects of high concentrations of NaCl, KCl and MgCl2 on two electron transport reactions of thylakoids isolated from a mesophyte, Pisum sativum and a halophyte, Aster tripolium. The rate of photosystem I mediated electron transport from reduced N, N, N′, N′-tetramethyl-p-phenylenediamine (TMPD) to methyl viologe...
When maize (Zea mays L. cv. LG11) leaves are exposed to low temperatures and high light modifications to both photosystem 2 (PS2) and the light-harvesting chlorophyll a/b protein complex associated with photosystem 2 (LHC2) occur. This study examines the consequences of these modifications for phosphorylation of LHC2 and PS2 polypeptides and the as...
Leaves of Triticum aestivum cv. Avalon were grown in an atmosphere that contained 150 nmole mol-1 ozone for 7h each day. After leaves had reached maximum size, the leaf blade was divided into three sections to provide tissue of different age, the youngest at the base of the blade and the oldest at the leaf tip. The ozone treatment was found to decr...
The effects of a wide concentration range of NaCl and sorbitol on three photosynthetic electron transport reactions of Pisum sativum L. cv. Feltham First chloroplasts were examined as a function of time from thylakoid membrane isolation. Rates of electron flow from water to diaminodurene (DAD) and ferricyanide were determined polarographically, whi...
The physiological characteristics and photo-system composition of the photosynthetic apparatus of Silene dioica, a woodland plant, grown in sun and natural shade are examined. As expected, shade leaves exhibited lower chlorophyll a/b ratios, light saturated rates of CO2 assimilation (Asat), dark respiration (Rd,) and light compensation points (Г),...
Tissue-specific effects of low growth temperature on maize chloroplast thylakoid protein accumulation were analysed using immunocytology. Sections of leaves from plants grown at 25 and 14°C were probed with antibodies to specific chloroplast thylakoid proteins from the four major protein multisubunit complexes of the thylakoid membrane followed by...
Low temperatures are known to restrict chloroplast development and prevent the attainment of photosynthetic competence in maize leaves. The responses of the photosynthetic apparatus of mature maize leaves grown at 14°C on transfer of the plants to 25°C are examined. The synthesis of thylakoid proteins increased immediately on transfer of leaves fro...
Abstract An instrument for the generation and measurement of modulated chlorophyll fluorescence signals from leaves exposed to continuous, highintensity white light is described. Modulated fluorescence is generated in the leaf by pulsed diodes emitting low-intensity yellow radiation and is detected with a photodiode whose output is fed to an amplif...
A new modulated lamp system is described. This system has successfully provided an ultraviolet-B (UV-B) supplement in proportion to ambient UV-B. The modulated system was used to simulate the UV-B environment resulting from an annual mean reduction of 15% in the stratospheric ozone under UK field conditions, but taking account of seasonal variation...
Singlet oxygen is known to be produced by cells in response to photo-oxidative stresses and wounding. Due to singlet oxygen being highly reactive, it is thought to have a very short half-life in biological systems and, consequently, it is difficult to detect. A new commercially available reagent (singlet oxygen sensor green, SOSG), which is highly...
Chlorophyll a fluorescence induction (FI) is widely used as a probe for studying photosynthesis. On illumination, fluorescence emission rises from an initial level O to a maximum P through transient steps, termed J and I. FI kinetics reflect the overall performance of photosystem II (PSII). Although FI kinetics are commonly and easily measured, the...
Lateral diffusion of CO(2) was investigated in photosynthesizing leaves with different anatomy by gas exchange and chlorophyll a fluorescence imaging using grease to block stomata. When one-half of the leaf surface of the heterobaric species Helianthus annuus was covered by 4-mm-diameter patches of grease, the response of net CO(2) assimilation rat...
The importance of temporal changes in the vertical distribution of microphytobenthic algae on the overall functioning of intertidal biofilms were investigated with low-temperature scanning electron microscopy and high-resolution single-cell fluorescence imaging of photosystem II efficiency (estimated by the fluorescence parameter $F_{q}^{\prime}/F_...
The bleaching of corals in response to increases in temperature has resulted in significant coral reef degradation in many tropical marine ecosystems. This bleaching has frequently been attributed to photoinhibition of photosynthetic electron transport and the consequent photodamage to photosystem II (PSII) and the production of damaging reactive o...
Chlorophyll fluorescence has been routinely used for many years to monitor the photosynthetic performance of plants non-invasively.
The relationships between chlorophyll fluorescence parameters and leaf photosynthetic performance are reviewed in the context
of applications of fluorescence measurements to screening programmes which seek to identify...
We have quantitatively measured nitric oxide production in the leaves of Arabidopsis thaliana and Vicia faba by adapting ferrous dithiocarbamate spin tapping methods previously used in animal systems. Hydrophobic diethyldithiocarbamate
complexes were used to measure NO interacting with membranes, and hydrophilic N-methyl-d-glucamine dithiocarbamate...
ASCORBATE PEROXIDASE 2 (APX2) encodes a key enzyme of the antioxidant network. In excess light-stressed Arabidopsis leaves, photosynthetic electron transport (PET), hydrogen peroxide (H(2)O(2)) and abscisic acid (ABA) regulate APX2 expression. Wounded leaves showed low induction of APX2 expression, and when exposed to excess light, APX2 expression...
Plastids are vital plant organelles involved in many essential biological processes. Plastids are not created de novo but divide by binary fission mediated by nuclear-encoded proteins of both prokaryotic and eukaryotic origin. Although several plastid division proteins have been identified in plants, limited information exists regarding possible di...
High‐resolution imaging of chlorophyll a fluorescence from intact tobacco leaves was used to compare the quantum yield of PSII electron transport in the chloroplasts
of guard cells with that in the underlying mesophyll cells. Transgenic tobacco plants with reduced amounts of Rubisco (anti‐Rubisco
plants) were compared with wild‐type tobacco plants....
Chlorophyll fluorescence is now widely employed to investigate electron transport and C02 assimilation in leaves and algae. A brief description of how the application of fluorescence parameters has developed for
the investigation of electron transport, and C02 assimilation in situ, is initially presented and followed by a consideration of the curre...
Development of photosynthetically competent thylakoid membranes requires the coordinated synthesis and assembly of a large
number of polypeptides of both cytoplasmic and chloroplast origins. Chloroplast and nuclear gene expression has been the subject
of intensive research in recent years and has led to detailed understanding of molecular aspects o...
A great deal is now understood about the photosynthetic reactions and processes occurring within chloroplasts that use light
energy to convert inorganic molecules into organic compounds. From this knowledge base about chloroplast function is emerging
an understanding of how chloroplasts operate within, and interact with, the environment of a leaf....
Photosynthesis is highly responsive to environmental changes. Even so, fundamental modifications of the photosynthetic processes
during the evolution of plant life have been relatively limited in comparison to the enormous variations in climatic conditions
that have occurred during this period. This is evidence of the remarkable plasticity within t...
Pulse amplitude modulation (PAM) and fast repetition rate (FRR) fluorescence are currently used to estimate photosynthetic quantum yields and photosynthetic rates in aquatic systems. Here we compare simultaneous measurements of the photochemical efficiency of photosystem II obtained from the two techniques and independent estimates of the rate of l...
High resolution chlorophyll a fluorescence imaging was used to compare the photosynthetic efficiency of PSII electron transport (estimated by Fq′/Fm′) in guard cell chloroplasts and the underlying mesophyll in intact leaves of six different species: Commelina communis, Vicia faba, Amaranthus caudatus, Polypodium vulgare, Nicotiana tabacum, and Trad...
A rapid, noninvasive technique involving imaging of chlorophyll fluorescence parameters for detecting perturbations of leaf metabolism and growth in seedlings is described. Arabidopsis seedlings were grown in 96-well microtitre plates for 4 d and then treated with eight herbicides with differing modes of action to induce perturbations in a range of...
In Arabidopsis leaves, high light stress induces rapid expression of a gene encoding a cytosolic ascorbate peroxidase (APX2), whose expression is restricted to bundle sheath cells of the vascular tissue. Imaging of chlorophyll fluorescence and the production of reactive oxygen species (ROS) indicated that APX2 expression followed a localised increa...
Laboratory studies and field trials were conducted to investigate the role of herbicides on saltmarsh vegetation, and their possible significance to saltmarsh erosion. Herbicide concentrations within the ranges present in the aquatic environment were found to reduce the photosynthetic efficiency and growth of both epipelic diatoms and higher saltma...
Photoprotection of the photosynthetic apparatus has two essential elements: first, the thermal dissipation of excess excitation energy in the photosystem II antennae (i.e. non-photochemical quenching), and second, the ability of photosystem II to transfer electrons to acceptors within the chloroplast (i.e. photochemical quenching). Recent studies i...
High resolution digital imaging was used to identify sites of photo‐oxidative stress responses in Arabidopsis leaves non‐invasively, and to demonstrate the potential of using a suite of imaging techniques for the study of oxidative
metabolism in planta. Tissue‐specific photoinhibition of photosynthesis in individual chloroplasts in leaves was image...
High resolution digital imaging was used to identify sites of photo‐oxidative stress responses in Arabidopsis leaves non‐invasively, and to demonstrate the potential of using a suite of imaging techniques for the study of oxidative metabolism in planta . Tissue‐specific photoinhibition of photosynthesis in individual chloroplasts in leaves was imag...
Chlorophyll fluorometry has frequently been used to estimate the photosynthetic elec- tron transport rate (ETR) within oxygenic organisms. One of the requirements of this method is that the absorptivity of the photosynthetic system is known. In the specific case of microphytobenthos within biofilms, it is known that cells migrate vertically over re...
High-resolution images of the chlorophyll fluorescence parameter Fq'/Fm' from attached leaves of commelina (Commelina communis) and tradescantia (Tradescantia albiflora) were used to compare the responses of photosynthetic electron transport in stomatal guard cell chloroplasts and underlying mesophyll cells to key environmental variables. Fq'/Fm' e...
The tropical wetland legume, Sesbania rostrata Brem. forms N2-fixing nodules along its stem and on its roots after infection by Azorhizobium caulinodans. The N2-fixing tissue is surrounded by a cortex of uninfected cells which, in the stem nodules (but not the root nodules), contain chloroplasts. The photosynthetic competence of these chloroplasts...
High-resolution images of the chlorophyll fluorescence parameter Fq′/Fm′ from attached leaves of commelina (Commelina communis) and tradescantia (Tradescantia albiflora) were used to compare the responses of photosynthetic electron transport in stomatal guard cell chloroplasts and underlying mesophyll cells to key environmental variables. Fq′/Fm′ e...
It has been suggested that field experiments which increase UV-B irradiation by a fixed amount irrespective of ambient light conditions (‘square-wave’), may overestimate the response of photosynthesis to UV-B irradiation. In this study, pea (Pisum sativum L.) plants were grown in the field and subjected to a modulated 30% increase in ambient UK sum...
Over a large part of the photoperiod, light energy absorbed by upper canopy leaves saturates photosynthesis and exceeds the energetic requirements for light-saturated linear electron flow through photosystem II (JPSII), so that photoinhibition results. From a theoretical consideration of the response of light-saturated photosynthesis to elevated at...
Biochemically based models of C(3) photosynthesis can be used to predict that when photosynthesis is limited by the amount of Rubisco, increasing atmospheric CO(2) partial pressure (pCO(2)) will increase light-saturated linear electron flow through photosystem II (J(t)). This is because the stimulation of electron flow to the photosynthetic carbon...
High resolution imaging of chlorophyll a fluorescence was used to identify the sites at which ozone initially induces perturbations of photosynthesis in leaves of
Phaseolus vulgaris. Leaves were exposed to 250 and 500 nmol mol−1 ozone at a photosynthetically active photon flux density of 300 μmol m−2 s−1 for 3 h. Images of fluorescence parameters i...
High resolution imaging of chlorophyll a fluorescence was used to identify the sites at which ozone initially induces perturbations of photosynthesis in leaves of Phaseolus vulgaris . Leaves were exposed to 250 and 500 nmol mol ⁻¹ ozone at a photosynthetically active photon flux density of 300 μmol m ⁻² s ⁻¹ for 3 h. Images of fluorescence paramete...
