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1.
J Exp Bot ; 64(16): 4993-5007, 2013 Nov.
Article in English | MEDLINE | ID: mdl-24043857

ABSTRACT

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 (gs), and intrinsic water use efficiency (WUEi) from whole plants or leaves under controlled environmental conditions. This is the first demonstration of the production of images of WUEi and the first to determine images of g s from themography at the whole-plant scale. Data are presented illustrating the use of this system for rapidly and non-destructively screening plants for alterations in WUEi by comparing Arabidopsis thaliana mutants (OST1-1) that have altered WUEi driven by open stomata, with wild-type plants. This novel instrument not only provides the potential to monitor multiple plants simultaneously, but enables intra- and interspecies variation to be taken into account both spatially and temporally. The ability to measure A, gs, and WUEi progressively was developed to facilitate and encourage the development of new dynamic protocols. Images illustrating the instrument's dynamic capabilities are demonstrated by analysing plant responses to changing photosynthetic photon flux density (PPFD). Applications of this system will augment the research community's need for novel screening methods to identify rapidly novel lines, cultivars, or species with improved A and WUEi in order to meet the current demands on modern agriculture and food production.


Subject(s)
Arabidopsis/metabolism , Water/metabolism , Arabidopsis/genetics , Arabidopsis/growth & development , Carbon Dioxide/metabolism , Optical Imaging , Plant Leaves/genetics , Plant Leaves/metabolism
2.
Diabetologia ; 51(6): 1085-6; author reply 1087, 2008 Jun.
Article in English | MEDLINE | ID: mdl-18330542
3.
Philos Trans R Soc Lond B Biol Sci ; 363(1491): 639-58, 2008 Feb 12.
Article in English | MEDLINE | ID: mdl-17652070

ABSTRACT

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'. This paper examines water use by crops, taking particularly a physiological viewpoint, examining the underlying relationships between carbon uptake, growth and water loss. Key examples of recent progress in both assessing and improving crop water productivity are described. It is clear that improvements in both agronomic and physiological understanding have led to recent increases in water productivity in some crops. We believe that there is substantial potential for further improvements owing to the progress in understanding the physiological responses of plants to water supply, and there is considerable promise within the latest molecular genetic approaches, if linked to the appropriate environmental physiology. We conclude that the interactions between plant and environment require a team approach looking across the disciplines from genes to plants to crops in their particular environments to deliver improved water productivity and contribute to sustainability.


Subject(s)
Adaptation, Physiological , Agriculture/methods , Crops, Agricultural/physiology , Plants/metabolism , Water/metabolism , Carbon/metabolism , Conservation of Natural Resources , Crops, Agricultural/metabolism , Plant Physiological Phenomena , Plants, Genetically Modified , Water Supply
4.
Br J Nurs ; 14(2): 109-14, 2005.
Article in English | MEDLINE | ID: mdl-15750513

ABSTRACT

This study investigated the clinical performance and safety of a sustained silver-releasing foam dressing, Contreet Foam, in the treatment of diabetic foot ulcers. Twenty-seven patients with diabetic foot ulcers of grade I or II (Wagner's classification) were followed for six weeks: one week run-in using Biatain dressings, four weeks' treatment with Contreet dressings. Four ulcers healed during the four-week treatment with Contreet 56% in average. Contreet Foam showed good exudate management properties and was considered easy to use. Only two infections occurred showed that all six of the non-study ulcers developed an infection during the study. All ulcers (study ulcers as well as non-study ulcers) were treated according to good practice of diabetic wound care. There were no directions for the treatment of secondary wounds. No device-related adverse events were observed. This study demonstrated that Contreet Foam is safe and easy to use and effectively supports healing and good wound progress of diabetic foot ulcers.


Subject(s)
Bandages, Hydrocolloid , Diabetic Foot/drug therapy , Silver/administration & dosage , Adult , Aged , Aged, 80 and over , Delayed-Action Preparations , Diabetic Foot/pathology , Female , Humans , Male , Middle Aged , Silver/analysis , Wound Healing
5.
Environ Pollut ; 122(1): 41-9, 2003.
Article in English | MEDLINE | ID: mdl-12535594

ABSTRACT

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 saltmarsh plants in the laboratory and in situ. The addition of sublethal concentrations of herbicides resulted in decreased growth rates and photosynthetic efficiency of diatoms and photosynthetic efficiency of higher plants. Sediment stability also decreased due to a reduction in diatom EPS production. There was qualitative evidence that diatoms migrated deeper into the sediment when the surface was exposed to simazine, reducing surface sediment stability by the absence of a cohesive biofilm. Sediment loads on leaves severely reduced photosynthesis in Limonium vulgare. This, coupled with reduced carbon assimilation from the effects of herbicides, could have large negative consequences for plant productivity and over winter survival of saltmarsh plants. The data support the hypothesis that sublethal herbicide concentrations could be playing a role in the increased erosion of salt marshes that has occurred over the past 40 years.


Subject(s)
Chenopodiaceae/drug effects , Diatoms/drug effects , Herbicides/adverse effects , Plumbaginaceae/drug effects , Water Pollutants, Chemical/adverse effects , Analysis of Variance , Chenopodiaceae/growth & development , Diatoms/growth & development , Dose-Response Relationship, Drug , England , Geologic Sediments , Herbicides/analysis , Photosynthesis/drug effects , Plumbaginaceae/growth & development , Seawater/analysis , Simazine/adverse effects , Simazine/analysis , Soil/analysis , Water Pollutants, Chemical/analysis
6.
Plant Physiol ; 127(3): 1204-11, 2001 Nov.
Article in English | MEDLINE | ID: mdl-11706199

ABSTRACT

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 reduction cycle (J(c)) will be greater than the competitive suppression of electron flow to the photorespiratory carbon oxidation cycle (J(o)). Where elevated pCO(2) increases J(t), then the ratio of absorbed energy dissipated photochemically to that dissipated non-photochemically will rise. These predictions were tested on Dactylis glomerata grown in fully controlled environments, at either ambient (35 Pa) or elevated (65 Pa) pCO(2), and at two levels of nitrogen nutrition. As was predicted, for D. glomerata grown in high nitrogen, J(t) was significantly higher in plants grown and measured at elevated pCO(2) than for plants grown and measured at ambient pCO(2). This was due to a significant increase in J(c) exceeding any suppression of J(o). This increase in photochemistry at elevated pCO(2) protected against photoinhibition at high light. For plants grown at low nitrogen, J(t) was significantly lower in plants grown and measured at elevated pCO(2) than for plants grown and measured at ambient pCO(2). Elevated pCO(2) again suppressed J(o); however growth in elevated pCO(2) resulted in an acclimatory decrease in leaf Rubisco content that removed any stimulation of J(c). Consistent with decreased photochemistry, for leaves grown at low nitrogen, the recovery from a 3-h photoinhibitory treatment was slower at elevated pCO(2).


Subject(s)
Carbon Dioxide/physiology , Nitrogen/metabolism , Photosynthesis/physiology , Poaceae/growth & development , Acclimatization/radiation effects , Carbon/metabolism , Electron Transport , Light , Oxidation-Reduction , Photochemistry , Photosynthesis/drug effects , Photosynthesis/radiation effects , Photosynthetic Reaction Center Complex Proteins , Photosystem II Protein Complex , Poaceae/physiology , Ribulose-Bisphosphate Carboxylase/metabolism
7.
J Exp Bot ; 52(361): 1689-96, 2001 Aug.
Article in English | MEDLINE | ID: mdl-11479334

ABSTRACT

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 micromol m(-2) s(-1) for 3 h. Images of fluorescence parameters indicated that large decreases in both the maximum and operating quantum efficiencies of photosystem II had occurred in cells adjacent to stomata in the upper, but not lower, leaf surfaces. However, this treatment did not produce any significant changes in the maximum or operating quantum efficiencies of photosystem II in the leaves when estimated from fluorescence parameters measured with a conventional, integrating fluorometer. The localized decreases in photosystem II photochemical efficiencies were accompanied by an increase in the minimal fluorescence level, which is indicative of photoinactivation of photosystem II complexes and a decrease in stomatal conductance. Perturbations of photochemical efficiencies were not observed in cells associated with all of the stomata on the upper leaf surface or within cells distant from the upper leaf surface. It is concluded that ozone penetrates the leaf through stomata and initially damages only cells close to stomatal pores.


Subject(s)
Fabaceae/drug effects , Ozone/pharmacology , Photosynthesis/drug effects , Plants, Medicinal , Chlorophyll/metabolism , Diagnostic Imaging/methods , Fabaceae/cytology , Fabaceae/metabolism , Fluorescence , Light-Harvesting Protein Complexes , Photosynthesis/radiation effects , Photosynthetic Reaction Center Complex Proteins/drug effects , Photosynthetic Reaction Center Complex Proteins/metabolism , Photosystem II Protein Complex , Plant Epidermis/cytology , Plant Epidermis/drug effects , Plant Epidermis/metabolism , Plant Leaves/cytology , Plant Leaves/drug effects , Plant Leaves/metabolism , Quantum Theory
8.
J Exp Bot ; 52(356): 615-21, 2001 Apr.
Article in English | MEDLINE | ID: mdl-11373309

ABSTRACT

Through imaging of chlorophyll fluorescence, it is possible to produce parameterized fluorescence images that estimate the operating quantum efficiency of photosystem II (PSII) photochemistry and which can be used to reveal heterogeneous patterns of photosynthetic performance within leaves. The operating quantum efficiency of PSII photochemistry is dependent upon the effective absorption cross-section of the light-harvesting system of PSII and the photochemical capacity of PSII. The effective absorption cross-section is decreased by the process of down-regulation, which is widely thought to operate within the pigment matrices of PSII and which results in non-photochemical quenching of chlorophyll fluorescence. The photochemical capacity is non-linearly related to the proportion of PSII centres in the 'open' state and results in photochemical quenching of chlorophyll fluorescence. Examples of heterogeneity of the operating quantum efficiency of PSII photochemistry during the induction of photosynthesis in maize leaves and in the chloroplast populations of stomatal guard cells of a leaf of Tradescantia albifora are presented, together with analyses of the factors determining this heterogeneity. A comparison of the operating quantum efficiency of PSII photochemistry within guard cells and adjacent mesophyll cells of Commelina communis is also made, before and after stomatal closure through a change in ambient humidity.


Subject(s)
Diagnostic Imaging/methods , Fluorescence , Photosynthesis , Photosynthetic Reaction Center Complex Proteins/metabolism , Chlorophyll/metabolism , Chloroplasts/physiology , Diagnostic Imaging/instrumentation , Light , Light-Harvesting Protein Complexes , Luciferases/pharmacology , Models, Theoretical , Photosystem II Protein Complex , Plant Cells , Plant Leaves/cytology , Plant Leaves/drug effects , Plant Leaves/metabolism , Plants/drug effects , Plants/metabolism , Spectrum Analysis
9.
Infect Immun ; 69(5): 3510-5, 2001 May.
Article in English | MEDLINE | ID: mdl-11292786

ABSTRACT

The Pseudomonas aeruginosa major constitutive outer membrane porin protein OprF, which has previously been shown to be a protective antigen, was targeted as a DNA vaccine candidate. The oprF gene was cloned into plasmid vector pVR1020, and the plasmid vaccines were delivered to mice by biolistic (gene gun) intradermal inoculation. Antibody titers in antisera from immunized mice were determined by enzyme-linked immunosorbent assay, and the elicited antibodies were shown to be specifically reactive to OprF by immunoblotting. The immunoglobulin G (IgG) immune response was predominantly of the IgG1 isotype. Sera from DNA vaccine-immunized mice had significantly greater opsonic activity in opsonophagocytic assays than did sera from control mice. Following the initial immunization and two consecutive boosts, each at 2-week intervals, protection was demonstrated in a mouse model of chronic pulmonary infection by P. aeruginosa. Eight days postchallenge, both lungs were removed and examined. A significant reduction in the presence of severe macroscopic lesions, as well as in the number of bacteria present in the lungs, was seen. Based on these findings, genetic immunization with oprF has potential for development as a vaccine to protect humans against infection by P. aeruginosa.


Subject(s)
Bacterial Vaccines/immunology , Lung Diseases/prevention & control , Porins/immunology , Pseudomonas Infections/prevention & control , Pseudomonas aeruginosa/immunology , Vaccines, DNA/immunology , Animals , Chronic Disease , Female , Humans , Immunization , Mice , Mice, Inbred ICR , Porins/genetics
10.
Philos Trans R Soc Lond B Biol Sci ; 355(1402): 1489-98, 2000 Oct 29.
Article in English | MEDLINE | ID: mdl-11128002

ABSTRACT

Photoinactivation of photosystem II (PS II) is a light-dependent process that frequently leads to break-down and replacement of the D1 polypeptide. Photoinhibition occurs when the rate of photoinactivation is greater than the rate at which D1 is replaced and results in a decrease in the maximum efficiency of PS II photochemistry. Downregulation, which increases non-radiative decay within PS II, also decreases the maximum efficiency of PS II photochemistry and plays an important role in protecting against photoinhibition by reducing the yield of photoinactivation. The yield of photoinactivation has been shown to be relatively insensitive to photosynthetically active photon flux density (PPFD). Formation of the P680 radical (P680+), through charge separation at PS II, generation of triplet-state P680 (3P680*), through intersystem crossing and charge recombination, and double reduction of the primary stable electron acceptor of PS II (the plastoquinone, Q(A)) are all potentially critical steps in the triggering of photoinactivation. In this paper, these processes are assessed using fluorescence data from attached leaves of higher plant species, in the context of a Stern-Volmer model for downregulation and the reversible radical pair equilibrium model. It is shown that the yield of P680+ is very sensitive to PPFD and that downregulation has very little effect on its production. Consequently, it is unlikely to be the trigger for photoinactivation. The yields of 3P680* generated through charge recombination or intersystem crossing are both less sensitive to PPFD than the yield of P680+ and are both decreased by down regulation. The yield of doubly reduced Q(A) increases with incident photon flux density at low levels, but is relatively insensitive at moderate to high levels, and is greatly decreased by downregulation. Consequently, 3P680* and doubly reduced Q(A) are both viable as triggers of photoinactivation.


Subject(s)
Down-Regulation , Photosynthesis/physiology , Photosynthetic Reaction Center Complex Proteins/metabolism , Signal Transduction/physiology , Energy Metabolism , Fabaceae , Models, Biological , Photosynthetic Reaction Center Complex Proteins/radiation effects , Photosystem II Protein Complex , Plants, Medicinal , Zea mays
11.
Diabet Med ; 17(7): 546-9, 2000 Jul.
Article in English | MEDLINE | ID: mdl-10972587

ABSTRACT

AIMS: The 'eye-foot syndrome' was initially described by Walsh et al. to highlight the important association of foot lesions in patients with diabetic retinopathy. We present a case of a 58-year-old patient with Type 2 diabetes mellitus who developed blindness following endogenous staphylococcal endophthalmitis from an infected foot ulcer. RESULTS: Our case describes the link between the eye and the foot but is somewhat different to the association as described by Walsh et al. Endogenous endophthalmitis is rare with diabetic patients being especially at risk, and we report the first case of endogenous staphylococcal endophthalmitis related to a diabetic foot lesion. CONCLUSIONS: Our case illustrates several important issues in the management of diabetic patients admitted to hospital with infection; the need to thoroughly examine the feet to ascertain any foot lesions and any underlying peripheral vascular disease or peripheral neuropathy, to treat aggressively any infected foot lesions to prevent serious complications of septicaemia and to consider rare conditions like endogenous endophthalmitis in any diabetic patient presenting with acute visual impairment and septicaemia.


Subject(s)
Blindness/etiology , Diabetes Mellitus, Type 2/physiopathology , Diabetic Foot/complications , Eye Infections, Bacterial/complications , Staphylococcal Infections/complications , Humans , Male , Middle Aged , Staphylococcus aureus/isolation & purification , Visual Acuity
12.
J Exp Bot ; 51(348): 1309-17, 2000 Jul.
Article in English | MEDLINE | ID: mdl-10937707

ABSTRACT

The effects of drought on the photosynthetic characteristics of three Mediterranean plants (olive, Olea europea L.; rosemary, Rosmarinus officinalis L.; lavender, Lavandula stoechas L.) exposed to elevated UV-B irradiation in a glasshouse were investigated over a period of weeks. Drought conditions were imposed on 2-year-old plants by withholding water. During the onset of water stress, analyses of the response of net carbon assimilation of leaves to their intercellular CO2 concentration were used to examine the potential limitations imposed by stomata, carboxylation velocity and capacity for regeneration of ribulose 1,5-bisphosphate on photosynthesis. Measurements of chlorophyll fluorescence were used to determine changes in the efficiency of light utilization for electron transport, the occurrence of photoinhibition of photosystem II photochemistry and the possibility of stomatal patchiness across leaves. The first stages of water stress produced decreases in the light-saturated rate of CO2 assimilation which were accompanied by decreases in the maximum carboxylation velocity and the capacity for regeneration of ribulose 1,5-bisphosphate in the absence of any significant photodamage to photosystem II. Leaves of rosemary and lavender were more sensitive than those of olive during the first stages of the drought treatment and also exhibited increases in stomatal limitation. With increasing water stress, significant decreases in the maximum quantum efficiency of photosystem II photochemistry occurred in lavender and rosemary, and stomatal limitation was increased in olive. No indication of any heterogeneity of photosynthesis was found in any leaves. Drought treatment significantly decreased leaf area in all species, an important factor in drought-induced decreases in photosynthetic productivity. Exposure of plants to elevated UV-B radiation (0.47 W m(-2)) prior to and during the drought treatment had no significant effects on the growth or photosynthetic activities of the plants. Consequently, it is predicted that increasing UV-B due to future stratospheric ozone depletion is unlikely to have any significant impact on the photosynthetic productivity of olive, lavender and rosemary in the field.


Subject(s)
Disasters , Magnoliopsida/physiology , Photosynthesis/physiology , Ultraviolet Rays , Water/physiology , Carbon Dioxide/metabolism , Fluorometry , Lamiaceae/physiology
13.
FEMS Immunol Med Microbiol ; 27(2): 147-54, 2000 Feb.
Article in English | MEDLINE | ID: mdl-10640610

ABSTRACT

The promising arena of DNA-based vaccines has led us to investigate possible candidates for immunization against bacterial pathogens. One such target is the opportunistic pathogen Pseudomonas aeruginosa which produces exotoxin A (PE), a well-characterized virulence factor encoded by the toxA gene. In its native protein form, PE is highly cytotoxic for susceptible eukaryotic cells through ADP-ribosylation of elongation factor-2 following internalization and processing of the toxin. To study the biologic and immunological effects of PE following in situ expression, we have constructed eukaryotic plasmid expression vectors containing either the wild-type or a mutated, non-cytotoxic toxA gene. In vitro analysis by transfection of UM449 cells suggests that expression of the wild-type toxA gene is lethal for transfected cells whereas transfection with a mutated toxA gene results in the production of inactive PE which can be readily detected by immunoblot analysis of cell lysates. To investigate the effects resulting from the intracellular expression of potentially cytotoxic gene products in DNA vaccine constructs, we immunized mice with both the wild-type and mutant toxA plasmid constructs and analyzed the resulting humoral and cellular immune responses. Immunization with the mutated toxA gene results in production of neutralizing antibodies against native PE and potentiates a T(H)1-type response, whereas only a minimal humoral response can be detected in mice immunized with wild-type toxA. DNA-based vaccination with the non-cytotoxic toxA(mut) gene confers complete protection against challenge with the wild-type PE. Therefore, genetic immunization with genes encoding potentially cytotoxic gene products raises concern with regard to the selection of feasible gene targets for DNA vaccine development.


Subject(s)
ADP Ribose Transferases , Antibodies, Bacterial/biosynthesis , Bacterial Toxins , Exotoxins/genetics , Exotoxins/immunology , Pseudomonas Infections/immunology , Th1 Cells/immunology , Vaccines, DNA/immunology , Virulence Factors , Animals , Antibodies, Bacterial/blood , Exotoxins/toxicity , Female , Humans , Male , Melanoma , Mice , Mice, Inbred BALB C , Neutralization Tests , Plasmids/genetics , Pseudomonas aeruginosa/genetics , Pseudomonas aeruginosa/immunology , Pseudomonas aeruginosa/metabolism , Transfection , Tumor Cells, Cultured , Vaccination , Vaccines, DNA/administration & dosage , Pseudomonas aeruginosa Exotoxin A
14.
J Wound Care ; 6(Sup4): 9-16, 1997 Apr.
Article in English | MEDLINE | ID: mdl-27967540

ABSTRACT

It has been suggested that 45% of lower limb amputations occur in patients with diabetes1. Yet, in areas where there are specialist diabetic foot clinics, amputation rates fall. This was initially demonstrated by Edmonds et al2 and is now becoming the experience of many such clinics around the UK. The successful management of foot ulcers is dependent upon a multidisciplinary team approach, which must include both nuclear and peripheral health-care professionals, utilising a wide range of experience, skills and resources.

15.
Plant Physiol ; 108(2): 761-767, 1995 Jun.
Article in English | MEDLINE | ID: mdl-12228508

ABSTRACT

The photosynthetic productivity of maize (Zea mays) in temperate regions is often limited by low temperatures. The factors responsible for the sensitivity of photosynthesis in maize to growth at suboptimal temperature were investigated by measuring (a) the quantum yields of CO2 fixation and photosystem II (PSII) photochemistry, (b) the pigments of the xanthophyll cycle, (c) the concentrations of active and inactive PSII reaction centers, and (d) the synthesis of core components of PSII reaction centers. Measurements were made on fully expanded leaves grown at 14[deg]C, both before and during the first 48 h after transfer of these plants to 25[deg]C. Our findings indicate that zeaxanthin-related quenching of absorbed excitation energy at PSII is, quantitatively, the most important factor determining the depressed photosynthetic efficiency in 14[deg]C-grown plants. Despite the photoprotection afforded by zeaxanthin-related quenching of absorbed excitation energy, a significant and more persistent depression of photosynthetic efficiency appears to result from low temperature-induced inhibition of the rate at which damaged PSII centers can be replaced.

16.
Chem Pharm Bull (Tokyo) ; 43(6): 1045-8, 1995 Jun.
Article in English | MEDLINE | ID: mdl-7641304

ABSTRACT

A series of 1-(2,3-epoxypropoxy)-2(4)-fluorobenzenes and their corresponding 1-(2-hydroxy-3-morpholinopropoxy and piperazino)fluorobenzene derivatives (8a--f) were synthesised via a short synthetic route in good chemical yields and were evaluated for inotropic and chronotropic activity in isolated guinea-pig atria preparation. The compounds act as potential phosphodiesterase (PDE) inhibitors with desirable biological activity and have considerable promise in heart therapy.


Subject(s)
Epoxy Compounds/chemical synthesis , Fluorobenzenes/chemical synthesis , Morpholines/chemical synthesis , Myocardial Contraction/drug effects , Phosphodiesterase Inhibitors/chemical synthesis , Piperazines/chemical synthesis , Animals , Epoxy Compounds/pharmacology , Fluorobenzenes/pharmacology , Guinea Pigs , Heart Rate/drug effects , In Vitro Techniques , Morpholines/pharmacology , Papillary Muscles/drug effects , Phosphodiesterase Inhibitors/pharmacology , Piperazines/pharmacology , Ventricular Pressure/drug effects
17.
Photosynth Res ; 44(1-2): 81-91, 1995 May.
Article in English | MEDLINE | ID: mdl-24307028

ABSTRACT

The light-harvesting chlorophyll a/b proteins associated with PS II (LHC II) are often considered to have a regulatory role in photosynthesis. The photosynthetic responses of four chlorina mutants of barley, which are deficient in LHC II to varying degrees, are examined to evaluate whether LHC II plays a regulatory role in photosynthesis. The efficiencies of light use for PS I and PS II photochemistry and for CO2 assimilation in leaves of the mutants were monitored simultaneously over a wide range of photon flux densities of white light in the presence and absence of supplementary red light. It is demonstrated that the depletions of LHC II in these mutants results in a severe imbalance in the relative rates of excitation of PS I and PS II in favour of PS I, which cannot be alleviated by preferential excitation of PS II. Analyses of xanthophyll cycle pigments and fluorescence quenching in leaves of the mutants indicated that the major LHC II components are not required to facilitate the light-induced quenching associated with zeaxanthin formation. It is concluded that LHC II is important to balance the distribution of excitation energy between PS I and PS II populations over a wide range of photon flux densities. It appears that LHC II may also be important in determining the quantum efficiency of PS II photochemistry by reducing the rate of quenching of excitation energy in the PS II primary antennae.

18.
Photosynth Res ; 42(3): 217-25, 1994 Dec.
Article in English | MEDLINE | ID: mdl-24306563

ABSTRACT

Changes in the photosynthetic light-response curve during leaf development were determined for the fourth leaf of maize crops sown on 23 April and 10 June. Temperatures were unusually mild during late spring/early summer and neither crop experienced chilling damage. The concept of thermal time was used to take into account the effects of different temperature regimes on developmental stage, thereby enabling photosynthetic light-response data to be combined for both crops to describe the general response. Large variations in the upper asymptote (Asat) and convexity (Θ) of the light-response curve occurred during leaf development, but the maximum quantum yield of CO2 assimilation remained relatively constant throughout. Dark respiration rates showed a small but significant decrease with leaf age and generally ranged between 5 and 10% of Asat. A simple mathematical model was developed to assess the sensitivity of daily leaf photosynthesis (AL) to reductions in the Asat, Θ and the initial slope (Φ) of the light-response curve at different stages of leaf development. On bright sunny days, and at all developmental stages, AL was ca. twice as sensitive to reductions in Asat than to reductions in Φ and Θ. In overcast conditions, however, all three parameters contributed significantly to reductions in leaf photosynthesis, although the contribution of Φ was greatest during early leaf growth, while older leaves were most sensitive to depressions in Asat. The implications of these results for modelling the sensitivity of canopy photosynthesis to chill-induced photoinhibition of the light-response curve are discussed.

19.
Photosynth Res ; 42(1): 17-25, 1994 Oct.
Article in English | MEDLINE | ID: mdl-24307464

ABSTRACT

The light harvesting and photosynthetic characteristics of a chlorophyll-deficient mutant of cowpea (Vigna unguilata), resulting from a single nuclear gene mutation, are examined. The 40% reduction in total chlorophyll content per leaf area in the mutant is associated with a 55% reduction in pigment-proteins of the light harvesting complex associated with Photosystem II (LHC II), and to a lesser extent (35%) in the light harvesting complex associated with Photosystem I (LHC I). No significant differences were found in the Photosystem I (PS I) and Photosystem II (PS II) contents per leaf area of the mutant compared to the wildtype parent. The decreases in the PS I and PS II antennae sizes in the mutant were not accompanied by any major changes in quantum efficiencies of PS I and PS II in leaves at non-saturating light levels for CO2 assimilation. Although the chlorophyll deficiency resulted in an 11% decrease in light absorption by mutant leaves, their maximum quantum yield and light saturated rate of CO2 assimilation were similar to those of wildtype leaves. Consequently, the large and different decreases in the antennae of PS II and PS I in the mutant are not associated with any loss of light use efficiency in photosynthesis.

20.
Photosynth Res ; 37(2): 89-102, 1993 Aug.
Article in English | MEDLINE | ID: mdl-24317706

ABSTRACT

Analysis is made of the energetics of CO2 fixation, the photochemical quantum requirement per CO2 fixed, and sinks for utilising reductive power in the C4 plant maize. CO2 assimilation is the primary sink for energy derived from photochemistry, whereas photorespiration and nitrogen assimilation are relatively small sinks, particularly in developed leaves. Measurement of O2 exchange by mass spectrometry and CO2 exchange by infrared gas analysis under varying levels of CO2 indicate that there is a very close relationship between the true rate of O2 evolution from PS II and the net rate of CO2 fixation. Consideration is given to measurements of the quantum yields of PS II (φ PS II) from fluorescence analysis and of CO2 assimilation ([Formula: see text]) in maize over a wide range of conditions. The[Formula: see text] ratio was found to remain reasonably constant (ca. 12) over a range of physiological conditions in developed leaves, with varying temperature, CO2 concentrations, light intensities (from 5% to 100% of full sunlight), and following photoinhibition under high light and low temperature. A simple model for predicting CO2 assimilation from fluorescence parameters is presented and evaluated. It is concluded that under a wide range of conditions fluorescence parameters can be used to predict accurately and rapidly CO2 assimilation rates in maize.

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