Journal of Experimental Botany, Vol. 52, No. 356, pp. 615-621,
April 2001
© 2001 Oxford University Press
High resolution imaging of photosynthetic activities of tissues, cells and chloroplasts in leaves
Department of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, UK
Received 31 March 2000; Accepted 19 October 2000
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Abstract |
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 Top Abstract IntroductionMaterials and methodsExamples of imaging and...Concluding remarksReferences |
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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.
Key words: Chlorophyll fluorescence, chloroplasts, down-regulation, imaging, leaves, photosynthesis, photosystem II photochemistry, stomata.
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Introduction |
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TopAbstractIntroductionMaterials and methodsExamples of imaging and...Concluding remarksReferences |
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Chlorophyll fluorescence has long been an important tool for the estimation of a range of photosynthetic parameters in leaves. The development and commercial availability of modulated fluorometers, together with an increased understanding of the factors that determine the yield of chlorophyll fluorescence, has led to the widespread use of chlorophyll fluorometry as a non-invasive method for assessing photosynthetic performance in leaves. Perhaps the single most useful fluorescence parameter is (
, which is theoretically proportional to the operating quantum efficiency of PSII photochemistry and which frequently exhibits a strong, quantitative relationship with the quantum yield of CO2 assimilation (
) (Genty et al., 1989
, 1990; Di Marco et al., 1990; Krall and Edwards, 1990; Edwards and Baker, 1993; Cornic, 1994). Since the light-driven oxidation of water by PSII ultimately provides the reducing power for CO2 assimilation, it is not too surprising that such a relationship exists in many situations.
It is well established that changes in photosynthetic activity within leaves can be heterogeneous. Imaging of chlorophyll fluorescence from leaves has revealed heterogeneous responses to changing CO2 concentration (Genty and Meyer, 1995; Siebke and Weis, 1995a, b; Bro et al., 1996), changing photon flux density (Eckstein et al., 1996), low growth temperature (Oxborough and Baker, 1997a), treatment with abscisic acid (Daley et al., 1989), in regions of fungal infection (Scholes and Rolfe, 1996) and during induction of photosynthesis (Oxborough and Baker, 1997b). It is now possible to generate images of chlorophyll fluorescence, under very low light and at the cellular and subcellular levels of organization. This allows for a detailed assessment of the differences in photosynthetic activities between cells to be made and has the potential to provide an understanding of the reasons for the heterogeneity in photosynthetic metabolism across leaves. In this article, the fluorescence parameters that are required to carry out such analyses are reviewed and examples are provided of how the technique has been used, with intact leaves, to estimate and analyse the photosynthetic performances of different cell types and individual chloroplasts within cells.
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Materials and methods |
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TopAbstractIntroductionMaterials and methodsExamples of imaging and...Concluding remarksReferences |
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Hardware
The instrument used in these experiments is essentially the same as that described previously (Oxborough and Baker, 1997
a). One important change to the instrument has been modification of the lower light source (which is used to illuminate the opposite side of the leaf to the one being imaged) so that a much larger area of leaf (a circle of 2.5 cm diameter) is illuminated. This was required in studies of stomatal regulation because only a small area is illuminated by the upper light source (through the lens) and this can result in the internal CO2 concentration (ci) being determined by diffusion within the leaf, from the surrounding (non-illuminated) tissue, rather than by changes in stomatal aperture. With most leaves, very little of the light from the lower light source is transmitted through to the upper surface. However, the system has been designed in such a way that the upper and lower light sources are under independent computer control. This allows the change in light output from the upper and lower light sources during a saturating pulse to be matched or for the lower light source to be shuttered out completely while imaging is taking place.
Fluorescence terminology
The calculation of useful fluorescence parameters, irrespective of whether fluorescence measurements are made with conventional modulated fluorometers or imaging systems, requires that the fluorescence signal is recorded while the photosynthetic system is in known states. With dark-adapted material, the 
level of fluorescence is recorded at very low PPFD (generally less than 1 µmol m-2 s-1), which leaves virtually all PSII centres in the ‘open’ state (capable of photochemistry). The 
level of fluorescence is recorded during a short pulse at very high PPFD (typically less than 1 s at several thousand µmol m-2 s-1), which transiently drives a very high proportion of PSII centres into the ‘closed’ state (making the capacity for photochemistry close to zero). With light-adapted material, the equivalent terms are 
and 
At any point between and 
(where a variable proportion of PSII centres are in the ‘open’ state), the fluorescence signal is termed F'. The difference between and is termed 
and the difference between and is termed 
While and 
have been widely used for a number of years, there is no equivalent specific term, in general usage, to quantify the difference between and 
(although 
F has been used in this context, this is actually a general term denoting the difference in the fluorescence signal measured at two points that has been used in many other contexts). The specific term 
has recently been introduced to denote the difference between and F' measured immediately before application of the saturating pulse used to measure (Oxborough and Baker, 2000; Oxborough et al., 2000). The diagram in Fig. 1 illustrates this terminology and shows the sequence of events leading to the acquisition of the fluorescence images required for construction of parameterized images.
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As noted above,
is theoretically proportional to the operating quantum efficiency of PSII photochemistry (hereafter referred to as PSII operating efficiency). On the same theoretical basis, is actually the product of two other useful parameters, 
and 
as shown by Equation 1.
 | (1) |
provides an estimate of the maximum quantum efficiency of PSII photochemistry (hereafter referred to as PSII maximum efficiency), i.e. the PSII operating efficiency if all PSII centres were in the ‘open’ state at the point of measurement. In most situations, its value is largely determined by down-regulation, which appears to involve the operation of one or more processes that increase the rate constant for non-radiative decay of excitation energy within the pigment matrix associated with PSII. The remaining parameter, , is a factor (hereafter referred to as the PSII efficiency factor) that relates the PSII maximum efficiency to the PSII operating efficiency. Its value is non-linearly related to the proportion of PSII centres in the open state.
The term 
PSII has often been used to denote in the literature and, in this context, has generally been used as a proxy for the quantum yield of electron transfer from water, through PSII and into the plastoquinone pool. One reason for not using PSII is that the symbol is already employed in the widely used term, CO2, which denotes the quantum yield of CO2 assimilation. In the case of CO2, refers to the quantum yield of photosynthetically-active photons that are absorbed by a leaf, while the in PSII refers to the quantum yield of photosynthetically-active photons that are absorbed only by PSII. Consequently, CO2 and PSII refer to the quantum yields of two different quantities and their use in the same context is potentially confusing.
The PSII efficiency factor, , is mathematically the same as the widely used coefficient of photochemical quenching, qP. One reason for not using qP is that, in the theoretical context of the relationship described by Equation 1, is a factor, not a coefficient. Another reason for avoiding the use of qP is that it has been very widely used as an estimate for the proportion of PSII centres in the ‘open’ state. While this would be reasonable if there were little or no connectivity among PSII centres, current evidence suggests that the level of connectivity between PSII centres is actually quite high, which makes the relationship between the closure of PSII centres and the fluorescence signal curvilinear (Joliot and Joliot, 1969). The theoretical relationship between and the concentration of open PSII centres (determined from the concentration of the primary quinone acceptor, QA) is shown in Fig. 2 and illustrates how this curvilinearity decreases as down-regulation increases.
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In order to calculate the parameters
and , it is required that the value of is known (because 
). Images of cannot be taken with the imaging system used here (or with any other imaging system that we are aware of). However, can be calculated using Equation 2 (Oxborough and Baker, 1997b).; images of and were constructed in this way.
 | (2) |
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Examples of imaging and analyses of photosynthetic activities in leaves |
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TopAbstractIntroductionMaterials and methodsExamples of imaging and...Concluding remarksReferences |
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Induction of photosynthesis in dark-adapted leaves
It is well established that oscillations in fluorescence can occur during the induction of photosynthesis when dark-adapted leaves are illuminated (Peterson et al., 1988
; Keiller and Walker, 1990). Images of a dark-adapted maize leaf were taken at the and levels of fluorescence, after which the leaf was exposed to a PPFD of 815 µmol m-2 s-1. Images at F' and were taken at intervals during the induction of CO2 assimilation over a period of 1 h and images of , and constructed (Fig. 3). It should be noted that although the resolution of these images is relatively low, in the context of this microscope-based system, it is approximately 1000 times higher (on an area basis) than whole-leaf imaging systems previously reported. After 2 min exposure to light, the PSII operating efficiency () was low, and little heterogeneity was observed within the images of , or 
an apparently normal distribution of values within a narrow band about the mean being evident for all three parameters. After 8 min in the light, the mean value of had increased from c. 0.07 to 0.35, and similar patterns of heterogeneity were observed in the images of and , but not in the image of 
The pixel values for the images of and exhibited a clear bimodal distribution, with the pixel values for the image showing a more normal distribution. It can also be seen that the large increase in that occurred between 2–8 min was accompanied by a large increase in , but only a very small increase in Clearly, this increase in the PSII operating efficiency was due to an increase in the capacity for electron transfer on the reducing side of PSII, rather than a decrease in the level of down-regulation. In the context of photosynthetic metabolism, the increase in between 2 and 8 min, in the absence of any significant change in over the same period, is indicative of an increase in the electron flux through PSII, due to an increased rate of utilization of the products of non-cyclic electron transport (NADPH and ATP). After 1 h, the heterogeneity had all but disappeared and a reasonably uniform distribution across the leaf was again observed for all three parameters.
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Photosynthesis in stomatal guard cells and adjacent mesophyll tissue
The imaging system (described by Oxborough and Baker, 1997a) allows for images of reflected light and chlorophyll fluorescence at and to be taken from the same area of leaf within a short time frame (<10 s). A potentially useful application of this feature is in the study of the relationship between changes in stomatal aperture and photosynthetic efficiency within the chloroplasts of guard and mesophyll cells. The images in Fig. 4 are from a region around a pair of guard cells of an attached leaf of Tradescantia albifora. The mean values of for the chloroplasts within these guard cells range between 0.27 and 0.43, indicating a wide range of PSII operating efficiencies within the chloroplast populations of the cells. Two chloroplasts, with values of 0.40 and 0.31, have been isolated in Fig. 4. Mean values of , and were also calculated. What these values reveal is that, as was the case for the induction of photosynthesis in maize leaves (Fig. 3
), the heterogeneity observed in the PSII operating efficiency () is largely attributable to differences in the capacity for electron flux on the reducing side of PSII, rather than down-regulation, since most of the difference in PSII operating efficiency is due to a difference in the PSII efficiency factor () rather than the PSII maximum efficiency ().
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The third example compares the photosynthetic activities within guard cells chloroplasts and adjacent mesophyll cells (Fig. 5
), before and after the induction of stomatal closure through a decrease in relative humidity. Before the humidity was decreased, the mean PSII operating efficiency () within the guard cell chloroplasts was 0.42, while the equivalent value within the adjacent mesophyll cells was significantly higher at 0.53. Decreasing the relative humidity from 56% to 9% resulted in closure of the stoma within the field of view (and presumably a decrease in cI) and resulted in a substantial decrease in the mean values of , to 0.30 within the guard cells and 0.41 within adjacent mesophyll cells. Although there was no clear difference in the way that the guard cell and mesophyll cell chloroplasts responded to closure of the stoma, these data clearly illustrate the way in which high resolution imaging of chlorophyll fluorescence can be used to distinguish the photosynthetic performance of closely adjacent cells.
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Concluding remarks |
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TopAbstractIntroductionMaterials and methodsExamples of imaging and...Concluding remarksReferences |
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It is clear, from the examples presented above, that high-resolution imaging of PSII operating efficiency, through the fluorescence parameter
, provides a powerful tool for identifying differences in the photosynthetic performance of different plant tissues, cells and individual chloroplasts within intact leaves. Also, analyses of images of and allow for an evaluation of the extent to which differences in among samples are due to differences in the maximum efficiency of PSII photochemistry and/or differences in the capacity for photochemistry. In the two examples shown in Figs 3 and 4, most of the heterogeneity observed in the images of could be attributed to differences in the capacity for photochemistry at PSII (which is reflected in the images of ). In most situations, the assimilation of CO2 is the main sink for the reducing power that is provided by PSII photochemistry. It therefore seems likely that the differences in PSII operating efficiencies and PSII efficiency factors that are evident within Figs 3 and 4 are related to the supply of CO2 to different areas of the leaf (Fig. 3) or different chloroplasts within closely adjacent cells (Fig. 4).
A potentially important application of fluorescence imaging is in understanding the response of plants to various types of stress. It is well established that many abiotic and biotic stresses result in a rapid modification of chlorophyll fluorescence characteristics of leaves associated with the inhibition of photosynthetic metabolism and the development of photo-oxidative perturbations of the photosynthetic apparatus. Consequently, fluorescence imaging offers a non-intrusive method for the identification of sites of stress in leaves. High-resolution fluorescence imaging provides the additional benefit of allowing for the detection of the early onset of stresses, when very few cells (or even chloroplasts within individual cells) are affected. Coupling of this technique with methods for studying gene expression in individual cells within leaves, such as single cell sampling and message amplification, should allow identification of changes in gene expression that result from the onset of stress in leaf cells. A particularly striking example of the potential of fluorescence imaging to examine the molecular bases of photo-oxidative stress in leaves comes from studies of expression of a peroxidase (APX2) gene in Arabidopsis. This gene is expressed rapidly after the onset of severe photoinhibitory stress in the leaves (Karpinski et al., 1997). The promoter of APX2 has been fused to the firefly luciferase reporter gene (LUC) and has been used to transform Arabidopsis (Karpinski et al., 1999). The APX2-LUC fusion gene is induced in parallel with the native APX2 gene during photoinhibitory stress and this expression has been imaged after painting leaves with luciferin to elicit luminescence (Fig. 6; M Fryer, K Oxborough, PM Mullineaux, NR Baker, unpublished data). It is most striking that the gene expression in response to the high light stress is only associated with the major veins of the leaf. Currently, the relationships between the photosynthetic responses of the mesophyll cells and the induction of APX2 gene expression is being investigated by parallel imaging of the chlorophyll fluorescence parameters, described above, and the luminescence associated with LUC gene expression from the same leaves. Such studies will help to resolve the signalling pathways involved in triggering gene expression in response to photo-oxidative stresses.
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Acknowledgments |
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The imaging studies presented were supported by grants to NRB and JILM from the Biotechnology and Biological Sciences Research Council. We are grateful to Mike Fryer and Phil Mullineaux for assistance with generating the images presented in Fig. 6
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Notes |
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1 To whom correspondence should be addressed. Fax: +44 1206 873416. E-mail: baken{at}essex.ac.uk
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Abbreviations |
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cI, intercellular CO2 concentration; F', fluorescence level at any point between F'o and F'm; Fm, maximal fluorescence level from dark-adapted leaves;
, maximal fluorescence level from leaves in light; 
, minimal fluorescence level from dark-adapted leaves; 
, minimal fluorescence level of leaves in light; 
, difference in fluorescence between and F (
; Fv, variable fluorescence level from dark-adapted leaves 
; 
, variable fluorescence level of leaves in light (
). |
References |
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TopAbstractIntroductionMaterials and methodsExamples of imaging and...Concluding remarksReferences |
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Bro E, Meyer S, Genty B. 1996. Heterogeneity of leaf CO2 assimilation during photosynthetic induction. Plant, Cell and Environment 19, 1349–1358.
Cornic G. 1994. Drought stress and high light effects on leaf photosynthesis. In: Baker NR, Boyer JR, eds. Photoinhibition of photosynthesis: from molecular mechanisms to the field. Oxford: Bios Scientific Publishers, 297–313.
Daley PF, Rashke K, Ball JT, Berry JA. 1989. Topography of photosynthetic activity of leaves obtained from video images of chlorophyll fluorescence. Plant Physiology 90, 1233–1238.
Di Marco G, Manes FS, Tricoli D, Vitale E. 1990. Fluorescence parameters measured concurrently with net photosynthesis to investigate chloroplastic CO2 concentration in leaves of Quercus silex L. Journal of Plant Physiology 136, 538–543.[Web of Science]
Edwards GE, Baker NR. 1993. Can CO2 assimilation in maize leaves be predicted accurately from chlorophyll fluorescence analysis? Photosynthesis Research 37, 89–102.
Eckstein J, Beyschlag W, Mot KA, Ryel RJ. 1996. Changes in photon flux can induce stomatal patchiness. Plant, Cell and Environment 19, 1066–1074.
Genty B, Briantais J-M, Baker NR. 1989. The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence. Biochimica et Biophysica Acta 990, 87–92.[Web of Science]
Genty B, Harbinson J, Baker NR. 1990. Relative quantum efficiencies of the two photosystems of leaves in photorespiratory and non-photorespiratory conditions. Plant Physiology and Biochemistry 28, 1–10.
Genty B, Meyer S. 1995. Quantitative mapping of leaf photosynthesis using chlorophyll fluorescence imaging. Australian Journal of Plant Physiology 22, 277–284.[Web of Science]
Joliot P, Joliot A. 1964. Études cinétiques de la réaction photochimique libérant l'oxygene au cours de la photosynthese. Compte Rendue Academie Sciences Paris 258, 4622–4625.
Karpinski S, Escobar C, Karpinska B, Creissen G, Mullineaux PM. 1997. Photosynthetic electron transport regulates the expression of cytosolic ascorbate peroxidase genes in Arabidopsis during excess light stress. The Plant Cell 9, 627–640.[Abstract]
Karpinski S, Reynolds H, Karpinska B, Wingsle G, Creissen G, Mullineaux PM. 1999. Systemic signaling and acclimation in response to excess excitation energy in Arabidopsis. Science 284, 654–657.
Keiller DR, Walker DA. 1990. The use of chlorophyll fluorescence to predict CO2 fixation during photosynthetic oscillations. Proceedings of the Royal Society London B 241, 59–64.
Krall JP, Edwards GE. 1990. Quantum yields of photosystem II electron transport and CO2 fixation in C4 plants. Australian Journal of Plant Physiology 17, 579–588.[Web of Science]
Oxborough K, Baker NR. 1997a. An instrument capable of imaging cholorophyll a fluorescence from intact leaves at very low irradiance and at cellular and subcellular levels. Plant, Cell and Environment 20, 1473–1483.
Oxborough K, Baker NR. 1997b. Resolving chlorophyll a fluorescence images of photosynthetic efficiency into photochemical and non-photochemical components–calculation of qP and without measuring . Photosynthesis Research 54, 135–142.
Oxborough K, Baker NR. 2000. An evaluation of the potential triggers of photoinactivation of photosystem II in the context of a Stern-Volmer model for down-regulation and the reversible radical pair equilibrium model. Proceedings of Royal Society London B (in press).
Oxborough K, Hanlon ARM, Underwood GJC, Baker NR. 2000. In vivo estimation of the photosystem II photochemical efficiency of individual microphytobenthic cells using high-resolution imaging of chlorophyll a fluorescence. Limnology and Oceanography 45, 1420–1425.[Web of Science]
Peterson RB, Sivak MN, Walker DA. 1988. Carbon dioxide-induced oscillations in fluorescence and photosynthesis— role of thylakoid membrane energization in regulation of photosystem II activity. Plant Physiology 88, 1125–1130.
Scholes JD, Rolfe SA. 1996. Photosynthesis in localized regions of oat leaves infected with crown rust (Puccinia coronata): quantitative imaging of chlorophyll fluorescence. Planta 199, 573–582.[Web of Science]
Siebke K, Weis E. 1995a. Imaging of chlorophyll a fluorescence in leaves: topography of photosynthetic oscillations in leaves of Glechoma hederacea. Photosynthesis Research45, 225–237.
Siebke K, Weis E. 1995b. Assimilation images of leaves of Glechoma hederacea: analysis of non-synchronous stomata related oscillations. Planta196, 225–237.[Web of Science]
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