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ABSTRACT Chlorophyll serves as a crucial pigment in plants, essential for photosynthesis, growth, and development. Our previous study has shown that PpnCCT39 can increase leaf chlorophyll content and photosynthesis rate in poplar. However, the underlying molecular mechanisms remain unknown. In this study, we observed that overexpression of PpnCCT39 not only elevates chlorophyll content and photosynthesis, but also induces alterations in leaf morphology, basal diameter, and chloroplast structure. By performing RNA‐seq on terminal buds and leaves at leaf positions 1, 3, 5, and 10, we determined that PpnCCT39 predominantly exerts its effects in young leaves. Chromatin Immunoprecipitation Sequencing (ChIP‐seq) performed on PpnCCT39‐overexpressing poplars identified 17 194 potential regulatory target genes. By integrating RNA‐seq and ChIP‐seq datasets along with validation assays for protein‐DNA interactions, we determined that PpnCCT39 directly stimulated the transcription of three key genes involved in the chlorophyll biosynthesis and photosynthesis pathways: PagHO1, PagLIL3, and PagPYG7. Furthermore, protein interaction assays revealed that PpnCCT39 interacts with PagRD19 and PagATP2, localized in vesicles and mitochondria respectively, with these interactions occurring within chloroplasts. This study elucidates the molecular mechanism by which the PpnCCT39 transcription factor in poplar promotes chlorophyll biosynthesis and photosynthesis. It also highlights the critical role of PpnCCT39 in nucleocytoplasmic interactions. These findings underscore the significance of PpnCCT39 in regulating chlorophyll biosynthesis and enhancing photosynthesis through molecular design. [ABSTRACT FROM AUTHOR] more...

Chlorophyll is the major light‐absorbing pigment for plant photosynthesis. While evolution has been selected for high chlorophyll content in leaves, previous work suggests that domesticated crops grown in modern high‐density agricultural environments overinvest in chlorophyll production, thereby lowering light use and nitrogen use efficiency. To investigate the potential benefits of reducing chlorophyll levels, we created ethanol‐inducible RNAi tobacco mutants that suppress Mg‐chelatase subunit I (CHLI) with small RNA within 3 h of induction and reduce chlorophyll within 5 days in field conditions. We initiated chlorophyll reduction later in plant development to avoid the highly sensitive seedling stage and to allow young plants to have full green leaves to maximise light interception before canopy formation. This study demonstrated that leaf chlorophyll reduction >60% during seed‐filling stages increased tobacco seed nitrogen concentration by as much as 17% while canopy photosynthesis, biomass and seed yields were maintained. These results indicate that time‐specific reduction of chlorophyll could be a novel strategy that decouples the inverse relationship between yield and seed nitrogen by utilising saved nitrogen from the reduction of chlorophyll while maintaining full carbon assimilation capacity. Summary statement: Reducing chlorophyll levels in tobacco plants during seed filling stages, without compromising canopy carbon assimilation, increased seed nitrogen concentration by up to 17%, suggesting a potential strategy to improve yield and seed nitrogen content simultaneously. [ABSTRACT FROM AUTHOR] more...

Chlorophyll is one of the primary pigments of plant leaves, and changes in its content can be used to characterize the physiological status of plants. Spectral indices have been devised and validated for estimating leaf chlorophyll content (LCC). However, most of the existing spectral indices do not consider the influence of angular reflection on the accuracy of the LCC estimation. In this study, the spectral reflectance factors of leaves from three plant species were measured from several observations in the principal plane. The relationship between the existing spectral indices and the LCC from different directions suggests that the directional reflection of a leaf surface impacts the accuracy of its LCC estimation. Subsequently, the ratio of reflectance differences, that is, the modified Datt index, was tested to reduce the directional reflection effect when predicting LCC. Our results indicated that the modified Datt index not only estimated LCC with high accuracy for all observation directions and plant species but also consistently predicted the LCC of each species in individual observation directions. Our method opens the possibility for optical detection of LCC using multiangular spectral reflection, which is convenient for plant science studies focused on the variation in LCC. Existing spectral indices are angular sensitive when estimating leaf chlorophyll content. A spectral index, which can estimate leaf chlorophyll content from arbitrary measurement directions, was optimized. This index provides a highly effective, reliable, and convenient method for estimating plant biochemical properties. [ABSTRACT FROM AUTHOR] more...

Abstract: Deep‐shade plants have adapted to low‐light conditions by varying morphology and physiology of cells and chloroplasts, but it still remains unclear, if prolonged periods of high‐light or darkness induce additional modifications in chloroplasts' anatomy and pigment patterns. We studied giant chloroplasts (bizonoplasts) of the deep‐shade lycopod Selaginella erythropus in epidermal cells of mature fully developed microphylls and subjected them to prolonged darkness and high‐light conditions. Chloroplast size and ultrastructure were investigated by light and electron microscopy. Physiological traits were studied by pigment analyses, photosynthetic performance of photosystem II, and formation of reactive oxygen species. Results show that (a) thylakoid patterns and shape of mature bizonoplasts vary in response to light and dark conditions. (b) Prolonged darkness induces transitory formation of prolamellar bodies, which so far have not been described in mature chloroplasts. (c) Photosynthetic activity is linked to structural responses of chloroplasts. (d) Photosystem II is less active in the upper zone of bizonoplasts and more efficient in the grana region. (e) Formation of reactive oxygen species reflects the stress level caused by high‐light. We conclude that during prolonged darkness, chlorophyll persists and even increases; prolamellar bodies form de novo in mature chloroplasts; bizonoplasts have spatial heterogeneity of photosynthetic performance. [ABSTRACT FROM AUTHOR] more...

UVB radiation is biologically active; in plants, it can induce a range of molecular, biochemical, morphological and developmental responses. Although much progress has been made in elucidating UVB perception and signalling pathways under controlled laboratory conditions, understanding of the adaptive, ecological role of UVB responses is still very limited. In this study, we looked at the functional role of UVR8 under outdoor light conditions, by studying growth, photosynthetic competence and accumulation of UV absorbing pigments in a mutant lacking functional UVR8 protein. It was found that the influence of UVB on morphology is restricted to summer and is independent of UVR8. In contrast, UVB had an effect on the content of UV-absorbing pigments and the maximal efficiency of photosystem II of photosynthesis in the uvr8-1 mutant throughout the year. It is concluded that the UVR8 photoreceptor plays a role throughout the year, in the temperate climate zone, even when UVB levels are relatively low. [ABSTRACT FROM AUTHOR] more...

We investigated the response to increasing intensity of red (R) and far-R (FR) light and to a decrease in R:FR ratio in Pinus sylvestris L. (Scots pine) seedling. The results showed that FR high-irradiance response for hypocotyl elongation may be present in Scots pine and that this response is enhanced by increasing light intensity. However, both hypocotyl inhibition and pigment accumulation were more strongly affected by the R light compared with FR light. This is in contrast to previous reports in Arabidopsis thaliana (L.) Heynh. In the angiosperm, A. thaliana R light shows an overall milder effect on inhibition of hypocotyl elongation and on pigment biosynthesis compared with FR suggesting conifers and angiosperms respond very differently to the different light regimes. Scots pine shade avoidance syndrome with longer hypocotyls, shorter cotyledons and lower chlorophyll content in response to shade conditions resembles the response observed in A. thaliana. However, anthocyanin accumulation increased with shade in Scots pine, which again differs from what is known in angiosperms. Overall, the response of seedling development and physiology to R and FR light in Scots pine indicates that the regulatory mechanism for light response may differ between gymnosperms and angiosperms. [ABSTRACT FROM AUTHOR] more...

The sensitivity of the photochemical reflectance index ( PRI) to leaf pigmentation and its impacts on its potential as a proxy for light-use efficiency ( LUE) have recently been shown to be problematic at the leaf scale. Most leaf-to-leaf and seasonal variability can be explained by such a confounding effect. This study relies on the analysis of PRI light curves that were generated at the canopy scale under natural conditions to derive a precise deconvolution of pigment-related and physiologically related variability in the PRI. These sources of variability were explained by measured or estimated physiologically relevant variables, such as soil water content, that can be used as indicators of water availability and canopy chlorophyll content. The PRI mainly reflected the variability in the pigment content of the canopy. However, the corrected PRI, which was obtained by subtracting the pigment-related seasonal variability from the PRI measurement, was highly correlated with the upscaled LUE measurements. Moreover, the sensitivity of the PRI to the leaf pigment content may mask the PRI versus LUE relationship or result in an artificial relationship that reflects the relationship of chlorophyll versus LUE, depending on the species phenology. [ABSTRACT FROM AUTHOR] more...

There is a need to reappraise the effects of UV- B radiation on plant morphology in light of improved mechanistic understanding of UV- B effects, particularly elucidation of the UV RESISTANCE LOCUS 8 ( UVR8) photoreceptor. We review responses at cell and organismal levels, and explore their underlying regulatory mechanisms, function in UV protection and consequences for plant fitness. UV-induced morphological changes include thicker leaves, shorter petioles, shorter stems, increased axillary branching and altered root:shoot ratios. At the cellular level, UV- B morphogenesis comprises changes in cell division, elongation and/or differentiation. However, notwithstanding substantial new knowledge of molecular, cellular and organismal UV- B responses, there remains a clear gap in our understanding of the interactions between these organizational levels, and how they control plant architecture. Furthermore, despite a broad consensus that UV- B induces relatively compact architecture, we note substantial diversity in reported phenotypes. This may relate to UV-induced morphological changes being underpinned by different mechanisms at high and low UV- B doses. It remains unproven whether UV-induced morphological changes have a protective function involving shading and decreased leaf penetration of UV- B, counterbalancing trade-offs such as decreased photosynthetic light capture and plant-competitive abilities. Future research will need to disentangle seemingly contradictory interactions occurring at the threshold UV dose where regulation and stress-induced morphogenesis overlap. [ABSTRACT FROM AUTHOR] more...

In growing leaves, lack of isoprene synthase ( IspS) is considered responsible for delayed isoprene emission, but competition for dimethylallyl diphosphate ( DMADP), the substrate for both isoprene synthesis and prenyltransferase reactions in photosynthetic pigment and phytohormone synthesis, can also play a role. We used a kinetic approach based on post-illumination isoprene decay and modelling DMADP consumption to estimate in vivo kinetic characteristics of IspS and prenyltransferase reactions, and to determine the share of DMADP use by different processes through leaf development in Populus tremula. Pigment synthesis rate was also estimated from pigment accumulation data and distribution of DMADP use from isoprene emission changes due to alendronate, a selective inhibitor of prenyltransferases. Development of photosynthetic activity and pigment synthesis occurred with the greatest rate in 1- to 5-day-old leaves when isoprene emission was absent. Isoprene emission commenced on days 5 and 6 and increased simultaneously with slowing down of pigment synthesis. In vivo Michaelis- Menten constant ( Km) values obtained were 265 nmol m−2 (20 μ m) for DMADP-consuming prenyltransferase reactions and 2560 nmol m−2 (190 μ m) for IspS. Thus, despite decelerating pigment synthesis reactions in maturing leaves, isoprene emission in young leaves was limited by both IspS activity and competition for DMADP by prenyltransferase reactions. [ABSTRACT FROM AUTHOR] more...

The influence of internal (genetic and developmental) and external (environmental) factors on levels of flavonoid gene transcripts, enzyme activity and metabolites was studied in fruit of six cultivated strawberry ( Fragaria × ananassa Duch.) genotypes grown at two Italian locations. Gene expression and enzyme activity showed development- and genotype-associated patterns, revealing gene coordination. Analysis clarified the regulation mechanism of the hydroxylation status of the B-ring of the major flavonoid pools and pointed out examples of genotype-specific post-transcriptional regulation mechanisms and key steps of pathway regulation in strawberry fruits. Metabolite profiles were strongly affected by development and genotype. Flavan-3-ols, their proanthocyanidin (PA) derivatives and anthocyanins were the most abundant metabolites. Flavonol levels and PA-associated traits (epicatechin/catechin ratio and mean degree of polymerization) showed significant environmental effects. Multivariate and correlation analyses determined the relationships among genes, enzymes and metabolites. The combined molecular and biochemical information elucidated more in depth the role of genetic and environmental factors on flavonoid metabolism during strawberry fruit development, highlighting the major impact of developmental processes, and revealing genotype-dependent differences and environmental effects on PA-related traits. [ABSTRACT FROM AUTHOR] more...

We report here on the characterization of a putative Dof transcription factor gene in rice ( Oryza sativa) – rice Dof daily fluctuations 1 ( Rdd1). Daily oscillations in Rdd1 expression were retained after transferring to continuous dark (DD) or light (LL) conditions, indicating circadian regulation. However, Rdd1 showed arrhythmic expression in etiolated coleoptiles. Experiments revealed that the Rdd1 transcript accumulated up to 1 h after transferring from DD to LL conditions and decreased thereafter. We examined Rdd1 expression using phytochrome (phy)-deficient mutants, and the results showed that phyA and most likely phyB contributed to the regulation of Rdd1 expression. To further examine the role of Rdd1, transgenic rice plants were produced that carried Rdd1 in either a sense (RDD1-S) or antisense (RDD1-AS) orientation, driven by a constitutive promoter. The expression of endogenous Rdd1 in response to far-red light was found to be modified in RDD1-AS plants compared with wild-type (WT) or RDD1-S plants. In addition, RDD1-AS plants were smaller and flowered later than WT or RDD1-S plants; decreases in grain length, width and 1000-grain weight were also recorded. This study demonstrates that Rdd1 is a circadian clock and phy-regulated gene, which is associated with grain size in rice. [ABSTRACT FROM AUTHOR] more...

Jasmonic acid (JA) is an important negative regulator of light-regulated coleoptile elongation in rice. We isolated rice JASMONATE RESISTANT 1 ( osjar1) mutants from the Tos17 mutant panel by BLAST search. In far-red and blue lights, osjar1 coleoptiles were longer if compared with the wild type (WT), indicating that OsJar1 participates in the suppression of coleoptile elongation in these light conditions, while the mutant did not show a clear phenotype in red light. The analysis of OsJar1 expression in phytochrome ( phy) mutants revealed that phytochrome A (phyA) and phytochrome B (phyB) act redundantly to induce this gene by red light, presumably. Unexpectedly, blue light-induced expression of OsJar1 gene was impaired in phyA-deficient mutants, indicating the involvement of phyA in the blue light signalling. In WT seedlings, OsJar1 transcripts were up-regulated transiently in response to treatment with exogenous methyl-jasmonic acid (MeJA). The dose–response curve of the MeJA treatment showed a characteristic pattern: concentrations as low as 4.5 nm could induce OsJar1 transcription, while the gene was superinduced at a concentration of 450 µm MeJA. In summary, this paper demonstrated that OsJar1 modulates light and JA signalling in the photomorphogenesis of rice. [ABSTRACT FROM AUTHOR] more...

Labelling of plastids with fluorescent proteins has revealed the diversity of their sizes and shapes in different tissues of vascular plants. Stromules, stroma-filled tubules comprising thin extensions of the stroma surrounded by the double envelope membrane, have been observed to emanate from all major types of plastid, though less common on chloroplasts. In some tissue types, stromules are highly dynamic, forming, shrinking, attaching, releasing and fragmenting. Stromule formation is negatively affected by treatment of tissue with cytoskeletal inhibitors. Plastids can be connected by stromules, through which green fluorescent protein (GFP) and fluorescently tagged chloroplast protein complexes have been observed to flow. Within the highly viscous stroma, proteins traffic by diffusion as well as by an active process of directional travel, whose mechanism is unknown. In addition to exchanging materials between plastids, stromules may also serve to increase the surface area of the envelope for import and export, reduce diffusion distance between plastids and other organelles for exchange of materials, and anchor the plastid onto attachment points for proper positioning with the plant cell. Future studies should reveal how these functions may affect plants in adapting to the challenges of a changing environment. [ABSTRACT FROM AUTHOR] more...

Plant growth and development are coordinately controlled by environmental signals and internal factors. Light signals, mediated by phytochromes, regulate photomorphogenesis by interacting with endogenous programmes that involve multiple phytohormones. Brassinosteroids (BRs) are a group of growth-promoting phytohormones with a crucial role in the light-dependent development of plants. However, the interaction between light-signalling pathways and BR signalling is not well understood. Here, we examined the responses of lamina joint inclination and coleoptile elongation to exogenous brassinolide (BL) under light or dark conditions. Both responses were more pronounced under darkness, implying that BR signalling is inhibited by light. To elucidate which phytochrome is involved in this interaction, we isolated rice phytochrome-deficient mutants ( osphyA, osphyB and osphyC) from a T-DNA insertional population. Whereas the osphyA and osphyC knockout mutants did not differ from the wild-type plants in their BL responses, osphyB mutants were more sensitive. In addition, RT-PCR analysis revealed enhanced expression of BR-inducible genes and decreased transcript levels of BR-biosynthetic genes in osphyB plants. These results suggest that Phytochrome B acts as a negative regulator of BL-regulated growth and development processes in rice. [ABSTRACT FROM AUTHOR] more...

A novel A- Ci curve (net CO2 assimilation rate of a leaf – An– as a function of its intercellular CO2 concentration – Ci) analysis method (Plant, Cell & Environment 27, 137–153, 2004) was used to estimate the CO2 transfer conductance ( gi) and the maximal carboxylation ( Vcmax) and electron transport ( Jmax) potentials of ageing, non-senescing Pseudotsuga menziesii leaves in relation to their nitrogen (N) content and protein and pigment composition. Both gi and the stomatal conductance ( gsc) of leaves were closely coupled to Vcmax, Jmax and An with all variables decreasing with increasing leaf age. Consequently, both Ci and Cc (chloroplastic CO2 concentration) remained largely conserved through successive growing seasons. The N content of leaves, as well as the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and other sodium dodecyl sulfate-soluble proteins, increased during the first three growing seasons, then stabilized or decreased only slightly afterwards. Thus, the age-related photosynthetic nitrogen use efficiency (PNUE) decline of leaves was not a consequence of decreased allocation of N towards Rubisco and other proteins involved in bioenergetics and light harvesting. Rather, loss of photosynthetic capacity was the result of the decreased activation state of Rubisco and proportional down-regulation of electron transport towards the photosynthetic carbon reduction (PCR) and photorespiratory (PCO) cycles in response to a reduction of CO2 supply to the chloroplasts’ stroma. This study emphasizes the regulatory potential and homeostaticity of Cc– rather than photosynthetic metabolites or Ci– in relation to the commonly observed correlation between photosynthesis and gsc. [ABSTRACT FROM AUTHOR] more...

Carotenoids are plant pigments that function as antioxidants, hormone precursors, colourants and essential components of the photosynthetic apparatus. Carotenoids accumulate in nearly all types of plastids, not just the chloroplast, and are thus found in most plant organs and tissues, albeit at trace levels in some tissues. In this review we summarise the current knowledge of the carotenoid content of non-green plastids and discuss what is known about the regulation of their biosynthesis in roots, fruits, flowers, tubers and seeds. The emphasis is on food crops as carotenoids are essential components of human diets, primarily as some are precursors of vitamin A. The low carotenoid content of many staple foods, such as cereals, can exacerbate dietary deficiencies. The World Health Organisation has estimated that more than 100 million children are vitamin A-deficient and up to 500,000 of these children become blind each year. Many of these children die within 12 months of going blind. Thus, understanding the regulation of carotenoid accumulation in food crops, especially tubers and cereals, should facilitate improvements to nutritional value with potentially significant health benefits. [ABSTRACT FROM AUTHOR] more...

Juvenile trees of temperate and boreal regions cease growth and set buds in autumn in response to short day-lengths (SD) detected by phytochrome. Growth cessation and bud set are prerequisites for the development of winter dormancy and full cold hardiness. In this study we show that the SD-requirement for bud set and cold hardening can be overcome in hybrid aspen ( Populus tremula L. × tremuloides Michx.) by low night temperature and inhibition of gibberellin (GA) biosynthesis. Bud set and increased cold hardiness were observed under normally non-inductive long day-length (LD) in wild-type plants, when exposed to low night temperature and paclobutrazol. In addition, the effect of PHYA overexpression could be overcome in transgenic plants, producing bud set and cold acclimation by treatment with: SD, low night temperature and paclobutrazol. After cold acclimation, the degree of bud dormancy was lower for wild-type plants prior treated with LD and transgenic plants (overexpressing PHYA), than SD-treated, wild-type plants. Thus, low night temperature in combination with reduced GA content induced bud set and promoted cold hardiness under normally non-inductive photoperiods in hybrid aspen, but was unable to affect development of dormancy. This might suggest separate signalling pathways from phytochrome regulating the induction of cold/cold hardiness and bud dormancy in hybrid aspen or alternatively, there might be one pathway that fails to complete its action in the transgenic and paclobutrazol treated plants. [ABSTRACT FROM AUTHOR] more...

Many cyanobacteria are highly adaptable to light quality, and many species undergo a complex life cycle. In this study we show that adaptive changes in the photosynthetic apparatus of cyanobacteria are not only caused by environmental, but also by developmental factors. Spectral confocal laser scanning microscopy (CLSM) was used to analysein vivothe fluorescence spectra of the photosynthetic pigments chlorophylla(Chl a), allophycocyanin (APC), phycocyanin (PC) and phycoerythrin (PE) of twoNostoc punctiformestrains. Changes in pigment fluorescence emission occurred in different developmental stages. Strain 1:1-26 showed an emission maximum at 674 nm in motile hormogonia stages, whereas vegetative stages showed maxima at 658 and 575 nm. These changes were not caused by chromatic adaptation. In contrast, the second strain (1:1-26lg) showed distinct fluorescence spectra, pigment localization and clear chromatic adaptation in red light. When these properties are known, both strains can be easily distinguished by the spectral CLSM method, which also allows the localization of the pigments within single cells. To calculate the contribution of individual phycobiliproteins to the observed changes, fluorescence spectra were analysed by spectral unmixing. This allowed the mathematical estimation of fluorescence shares for the individual phycobiliproteins in different developmental stages and both before and after chromatic adaptation. It is concluded that care should be taken when characterizing cyanobacteria by differences in pigment fluorescence, because these differences are influenced not only by chromatic adaptation, but also developmental stages. Spectral CLSM offers a powerful method to study the phycobiliprotein compositionin vivo. [ABSTRACT FROM AUTHOR] more...

The natural variation in quantity and quality of light modifies plant morphology, growth rate and concentration of biochemicals. The aim of two growth-room experiments was to study the combined effects of red (R) and far-red (FR) light and ultraviolet-B (UV-B) radiation on the concentrations of leaf phenolics and growth and morphology of silver birch ( Betula pendula Roth) seedlings. Analysis by high-performance liquid chromatography showed that the leaves exposed to supplemental FR relative to R contained higher concentrations of total chlorogenic acids and a cinnamic acid derivative than the leaves treated with supplemental R relative to FR. In contrast, concentration of a flavonoid, quercetin 3-galactoside, was higher in the R + UV-B leaves than in the FR + UV-B leaves. The UV-B induced production of kaempferols, chlorogenic acids and most quercetins were not modified by the R : FR ratio. Growth measurements showed that the leaf petioles and stems of FR seedlings were clearly longer than those of R seedlings, but leaf area was reduced by UV-B radiation. Results of these experiments show that exposure of silver birch seedlings to supplemental FR compared to R leads to fast elongation growth and accumulation of phenolic acids in the leaves. [ABSTRACT FROM AUTHOR] more...

Abstract In this study the variations in surface reflectance properties and pigment concentrations of Antarctic moss over species, sites, microtopography and with water content were investigated. It was found that species had significantly different surface reflectance properties, particularly in the region of the red edge (approximately 700 nm), but this did not correlate strongly with pigment concentrations. Surface reflectance of moss also varied in the visible region and in the characteristics of the red edge over different sites. Reflectance parameters, such as the photochemical reflectance index (PRI) and cold hard band were useful discriminators of site, microtopographic position and water content. The PRI was correlated both with the concentrations of active xanthophyll-cycle pigments and the photosynthetic light use efficiency, F v /F m , measured using chlorophyll fluorescence. Water content of moss strongly influenced the amplitude and position of the red-edge as well as the PRI, and may be responsible for observed differences in reflectance properties for different species and sites. All moss showed sustained high levels of photoprotective xanthophyll pigments, especially at exposed sites, indicating moss is experiencing continual high levels of photochemical stress. [ABSTRACT FROM AUTHOR] more...

ABSTRACT Studies of pollination ecology have been hindered by an absence of biochemical information about the basis of polymorphism. Using model plants and mutant lines described by molecular genetics may circumvent this difficulty. Mutation of genes controlling petal colour and petal epidermal cell shape in Antirrhinum majus was previously shown to influence fruit set. White flowers set less fruit than magenta flowers and mutants with flat petal epidermal cells set less fruit than flowers with conical cells. Here we analyse the causal pathway underlying this phenomenon through a study of floral characteristics and bee behaviour. Results indicate that bees recognized plants with magenta conical-celled flowers at a distance and did not approach white flowers or magenta flat-celled flowers so frequently. Petal cell shape interacted with colour in determining whether an approaching bee landed on a flower within a plot and whether a bee landing on a flower would probe it. The intrafloral temperature of flowers with conical petal cells was shown to increase with solar irradiance, unlike the intrafloral temperature of flowers with flat petal cells. The difference in fruit set may reflect pollinator discrimination between genotypes as a consequence of the effect of intrafloral temperature on nectar quality and quantity. [ABSTRACT FROM AUTHOR] more...

The effects on pigment composition and photosynthesis of low temperature during growth were examined in the third leaf of three chilling-tolerant and three chilling-sensitive genotypes of Zea mays L. The plants were grown under a controlled environment at 24 or 14 °C at a photon flux density (PFD) of 200 or 600 μmol m–2 s–1. At 24 °C, the two classes of genotypes showed little differences in their photosynthetic activity and their composition of pigments. At 14 °C, photosynthetic activity was considerably reduced but the chilling-tolerant genotypes displayed higher photosynthetic rates than the chilling-sensitive ones. Plants grown at 14 °C showed a reduced chlorophyll (Chl) a + b content and a reduced Chl a/b ratio but an increased ratio of total carotenoids to Chl a + b. These changes in pigment composition in plants grown at low temperature were generally more pronounced in the chilling-sensitive genotypes than in the tolerant ones, particularly at high PFD. Furthermore, at 14 °C, all the genotypes showed increased ratios of lutein, neoxanthin and xanthophyll-cycle carotenoids to Chl a + b but a reduced ratio of β-carotene to Chl a + b, especially at high PFD. At 14 °C, the chilling-tolerant genotypes, when compared with the sensitive ones, were characterized by higher contents of β-carotene and neoxanthin, a lower content of xanthophyll-cycle carotenoids, a lower ratio of xanthophylls to β-carotene, and less of their xanthophyll-cycle carotenoid pool in the form of zeaxanthin. These differences between the two classes of genotypes were more pronounced at high PFD than at low PFD. The results are discussed in terms of the relationship that may exist in maize between pigment composition and the capacity to form an efficient photosynthetic apparatus at low growth temperature. [ABSTRACT FROM AUTHOR] more...

The quality and quantity of light reflected from Nicotinia tabacum L. internodes was monitored as the angle of incidence was varied. Reflectance of incident light, which was either normal or longitudinal to the lnternode axis, was investigated. Increasing the angle of incidence caused a greater proportion of incident light to be reflected. Light striking N. tabacum internodes was always modified prior to reflection, and smaller incident angles produced greater modification of the reflected light quality. At larger angles, interactions with the internode were reduced. As a parallel investigation, the extension growth rate of light-grown Sinapis alba L. seedlings was monitored continuously using sensitive linear displacement transducers. When the angle of illumination by fibre-optic probes, presenting far-red light to the growing internode, was changed from 0° to 45°, an increase was observed in stem extension rate. There is a possibility that this rate increase was the result of a fall in the red:far-red ratio (R:FR) present inside the plant internode as the angle of incidence was altered. However, it is more likely that it was due to the larger surface area of stem being illuminated. The consequences of these observations are discussed in relation to the potential influence of such modified reflections on canopy light environments and resultant shade responses which may occur when light of known R:FR impinges on plant internodes at angles other than 0% The possibility is discussed that plants may perceive the quality of reflected radiation from neighbouring plants to be substantially different dependent upon the angle at which it is reflected. [ABSTRACT FROM AUTHOR] more...

The role of phytochrome A in the control of hypocotyl growth under continuous red light (Rc) was investigated using phyA and phyB mutants of Arabidopsis thaliana, which lack phytochrome A (phyA) or phytochrome B (phyB), respectively, and transgenic seedlings of Nicotiana tabacum overexpressing Avena phyA, compared to the corresponding wild type (WT). In WT seedlings of A. thaliana, hypocotyl growth inhibition showed a biphasic response to the fluence rate of Rc, with a brake at 10.2 μmol m-2 s-1. At equal total fluence rate, hourly pulses of red light caused slightly more inhibition than Rc.The response to very low fluences of continuous or pulsed red light was absent in the phyA and phyA phyB mutants and present in the phyB mutant. The second part of the response was steeper in the phyA mutant than in the WT but was absent in the phyB mutant. In WT tobacco the response to Rc was biphasic. Overexpression of Avena phyA enhanced the response only at very low fluence rates of Rc (less than 10.2 μmol m-2 s-1). In both species, the effect of hourly pulses of far-red light was similar to the maximum inhibition observed in the first phase of the response to Rc. Using reciprocity failure (i.e. higher inhibition under continuous than pulsed light) as the operational criterion, a 'true' high-irradiance reaction occurred under continuous far-red light but not under Rc or red plus far-red light mixtures. Native and overexpressed phyA are proposed to mediate very low fluence responses under Rc. In WT A. thaliana, this effect is counteracted by a negative action of phyA on phyB-mediated low-fluence responses. [ABSTRACT FROM AUTHOR] more...

Dark-adapted coleoptiles of maize (Zea mays L.) were treated with red light (3 hain at 10.5 μmol m-2s-1) and were stimulated, after a dark interval, with a pulse of unilateral blue light to induce phototropism. Phototropic fluence-response curves were obtained in this way for different dark intervals. It was confirmed that the bell-shaped fluence--response curve for the first pulse-induced positive photutropism (PIPP) shifts to higher fluences following the red-light treatment, the maximal shift being achieved at a dark interval of 2 h. We found, however, that the two arms of the fluence-response curve do not shift synchronously. The shift of the descending arm to higher fiuences hegan at 15 min. The ascending arm showed a slight shift to lower fluences before a greater shift to higher flueuces, the change of the shift direction occurring at 30--40 min. Accordingly, thc fluenct,-response curve obtained for a 30 min dark interval was comparatively wide. Although dark-adapted colenptiles showed only fPIPP, another bell-shaped fluence-response curve, representing the second pulse-induced positive phototropism (sPIPP), appeared gradually after the red-light treatment. These changes of the phototropic flueuct-respnse curve following exposure to red light are likely to have adaptive values because they favour phutotropism under brighter light. [ABSTRACT FROM AUTHOR] more...

Photosynthetic performance, mineral content and chloroplast pigments were investigated in August-September 1988 and 1989 in Norway spruce trees (Picea abies (L.) Karst.) exposed to SO2 and O3 in an open-air fumigation facility at Liphook, England. The data do not suggest a treatment effect on the mineral content of the needles in terms of nutrient leaching from the foliage. In addition, there were no direct SO2 and/or O3 effects on the content and/or composition of the chloroplast pigments. However, the long-term application of SO2 resulted in a depression of net photosynthesis under light saturation and ambient CO2 (A340) which was probably caused by a treatment-related depression of the carboxylation efficiency (CE). In 1989, the supposed treatment effects were apparently masked by an insufficient N-supply and probably also by low water availability during summer. However, fumigation appeared to accelerate an N-deficiency-related decrease of CE, stomatal closure and the age-dependent development of the chlorophyll content of the needles. In 1989, an observed depression of the photosynthetic capacity (A2500) was in part accompanied by a decrease in light use efficiency (α), suggesting an enhanced photosensitivity resulting from the impact of several possible interacting stresses (drought, N deficiency and fumigation). The results support the general conclusion that long-term low-level SO2 dosage adversely affects the photosynthetic performance of the needle, whether directly or indirectly, and may also interact with other environmental stresses. The findings of our investigations are discussed with regard to the hypothesis of forest decline in the mountain regions of teh Fichtelgebirge (north-eastern Bavaria, Germany). [ABSTRACT FROM AUTHOR] more...

The effects of overexpression of oat phytochrome A on neighbour detection and on stem-growth responses to changes in red light (R), far-red light (FR) and blue light (B) simulating neighbours were investigated in transgenic tobacco seedlings grown under natural radiation, In wild-type (WT) seedlings, stem extension growth was promoted: (1) by lowering the R:FR by means of daytime supplementary FR, end-of-day FR, neighbours reflecting FR, or selective light filters placed around the base of the shoot to reduce R without affecting FR; and (2) by lowering phytochrome-absorbable radiation (R+FR) reaching the stems Transgenic seedlings only responded to reductions in R:FR involving no significant changes in FR irradiance, i.e. end-of-day FR and filters placed around the stem to reduce R. Neither daytime supplementary R nor selective filters placed around the stem to reduce B affected stem growth in any genotype. In growing canopies, WT seedlings responded to the reduction of R:FR caused by FR reflected in neighbour plants. Transgenic seedlings responded to plant density about a week Later, when mutual plant shading reduced R and (to a lesser extent) FR below sunlight levels, Overexpression of phytochrome A impaired early neighbour detection. [ABSTRACT FROM AUTHOR] more...

The effect of ultraviolet-B radiation (UV-B: 280-320nm) on gene expression and pigment composition has been investigated in pea tissue at different stages of development. Pea (Pisum sativum L., cv. Feltham First) seedlings were grown for 17d and then exposed to supplementary UV-B radiation. Chlorophyll a per unit fresh weight decreased by more than 20% compared with control levels after exposure to UV-B radiation for 7d. In contrast, chlorophyll bcontent remained the same or increased slightly. Leaf protein biosynthesis, as determined by 35S-methionine incorporation, was rapidly inhibited by UV-B radiation, although the steady-state levels of proteins were either unchanged or only slightly altered. RNA transcripts for the chlorophyll a/b binding protein (cab) were also rapidly reduced to low or even undetectable levels in the expanded third leaf or younger leaf bud tissue after exposure to UV-B radiation. In contrast, cab RNA transcripts were either low or undetectable in etiolated pea tissue, but increased substantially in light and during exposure in UV-B radiation. The cab RNA transcripts were still present at control levels in pea plants after 7d of greening under supplementary UV-B radiation or UV-B alone. The protein composition changed significantly over the 7d of greening, but no differences could be detected between the light treatments. The increase in chlorophyll content was slightly greater during de-etiolation under supplementary UV-B radiation than under control irradiance. Under UV-B radiation alone, chlorophyll was synthesized at a greatly reduced rate. Changes in protective pigments were also determined. Anthocyanins did not change in either etiolated or green tissue exposed to UV-B radiation. The RNA levels for chalcone synthase were measured in green and etiolated tissues exposed to UV-B radiation. The chs RNA transcripts were present in low or undetectable amounts in control tissues. In green leaf tissue exposed in supplementary UV-B, a transient increase was detected. The transcripts for chs reached a maximum level after approximately 8 h UV-B exposure, and then declined to lower levels over subsequent days of diurnal photoperiods. However. a constant increase in chs was found after continuous exposure to UV-B for up to 30 h. In etiolated tissue, either white-light supplementary UV-B or UV-B alone gave small increases in chs, only 8 h of UV-B radiation alone gave any substantial increased in chs expression. Overall, these results clearly demonstrate that the response to increased levels of UV-B radiation is dependent upon the developmental stage of the tissue and involves complex changes in gene expression. [ABSTRACT FROM AUTHOR] more...

The pigment composition of leaves from a number of different plant species collected from field sites in the region of Sheffield, UK, have been compared using high-performance liquid chromatography. Expression of pigment content per unit leaf area was dominated by variation in the total leaf chlorophyll Neither chlorophyll per unit area nor the chlorophyll a/b ratio were found to be correlated with the habitat from which the plants or iginated. When the amounts of different carotenoids were expressed relative to the total carotenoid pool, it was found that whilst neither total carotene (α- + β-carotene) nor neoxanthin correlated with ability to grow in shade, the leaf content of both lutein and the total xanthophyll cycle carotenoids (zeaxanthin, antheraxanthin and violaxanthin) did, with lutein content being high in shade species and xanthophyll cycle intermediates low, There was a strong negative correlation between the relative amounts of each of these groups of carotenoids, The ratio of lutein to xanthophyll cycle carotenoids was strongly correlated to an index of shade tolerance. [ABSTRACT FROM AUTHOR] more...

One short red (R) irradiation increases the ATP content of Kalanchoë blossfeldiana Poelln. cv Feuerblüte seeds before onset of germination. Phytochrome control is demonstrated by the full R/far-red light (FR) reversibility of the effect in water Imbibed seeds. In seeds imbibed in the presence of gibberellin A3 (GA3), one short R exposure already increases the ATP content when given 2h after start of imbibition, showing phytochrome control at the energy-metabolic level when one R pulse cannot yet induce germination. After longer imbibition periods in the presence of GA3, one short FR irradiation also increases the ATP of ungerminated Kalanchoë seeds. The time of course of the ATP levels after a R or FR germination irradiation shows an initial increase that clearly preceeds germination. A second increase starts about 15h after irradiation and is most probably the consequence of the germination itself. The results suggest that, in Kalanchoë seeds, the increase in ATP levels, induced by irradiation(s) and preceding germination, is a phytochrome-mediated process, supplying energy, required for germination. [ABSTRACT FROM AUTHOR] more...

Glycine max (L.) Merr. was grown under several light conditions to determine the role of red and far-red radiation in plant adaptation to vegetation shade. Neutral density, 'neutral' density with elevated far-red radiation, anti green shade treatments were used in a greenhouse. producing calculated phytochrome photostationary state (Pfr/Pr + Pfr) values of (0.68, 0.63 and 0.51, respectively. Cool-white fluorescent lamps either alone or in conjunction with far-red fluorescent lamps were used in a growth chamber, providing Pfr/Pr + Pfr of 0.79 and 0.61, respectively. Daily photosynthetically active radiation was about 25% of daylight and was approximately equal for both greenhouse 2.15 MJ m-2) and growth chamber (2.57 MJ m-2). Developmental stage 4 weeks after sowing was similar for all treatments, but axillary growth and rates of leaf area and dry matter accretion differed between plants from greenhouse and growth chamber. Light conditions simulating vegetation shade (i e. a low ratio of red to far-red radiation) significantly promoted petiole elongation and retarded the tat of stem elongation in both greenhouse and growth chamber experiments. Other aspects of growth either were not significantly altered by spectral quality or were not modified consistently in both greenhouse and growth chamber environments. Net photosynthetic rates measured under growth conditions for unifoliate anti first trifoliolate (TF1) leaves of growth chamber plants between 9 and 21 d after sowing were generally unaffected by spectral quality, but supplemental FR enhanced TF1 leaf area expansion The latter effect was not correlated with increased thy matter accumulation. The significance of spectral quality tot adaptation of soybeans to canopy closure and intercropping is discussed, [ABSTRACT FROM AUTHOR] more...

It has previously been proposed that the fundamental function of phytochrome in the natural environment is the perception of the relative proportions of red and far-red light, i.e. the red:far-red fatio. This paper re-evaluates this hypothesis, for vegetative green plants, in the light of recent findings. Essentially, three issues are considered: (a) the modulation of the response to red: far-red by fluence rate; (b) the anticipation of competition for light by perception of changes in red:far-red that precede actual shading; and (c) characteristics of phytochrome that may be important in the mechanism of photoperception (i.e. the accumulation of photoconversion intermediates, and the stability of Pfr). We conclude: (a) the red: far-red ratio provides a reliable signal of plant density, even before shading by neighbours occurs; (b) plants are able to perceive and respond to these signals, and that possible ambiguities due to low red: far-red at low solar angles may be avoided by modulation of the perception process by fluence-rate dependent mechanisms; (c) although direct experimental evidence does not yet exist, circumstantial evidence suggests that the perception of red: far-red may confer positive adaptive advantage; and (d) plants of certain species perceive and respond to fluence rate changes, mediated perhaps by a blue-light absorbing photoreceptor or by phytochrome, but that these responses do not necessarily lead to shade avoidance reactions and their ecological relevance is not fully understood. [ABSTRACT FROM AUTHOR] more...

Changes in the phytochrome status at the end of the daily photosynthetic period result in several plant responses. To understand the causal relations among these responses it is useful to investigate species or experimental conditions where the most common correlations among responses are broken. A step in this direction is presented here with Petunia axilaris, where FR-treated plants showed low chlorophyll content and erect leaves, but-contrary to other species--higher leaf area and plant dry weight. Differences in area expansion were related to the late phase of leaf growth and were due, at least in part, to larger ceils in FR-treated plants. Effects on length/width ratio, specific leaf area, net assimilation rate, shoot/root ratio and leaf number were small or non-existent. It is suggested that the lower chlorophyll content in FR-treated plants was not a consequence of scarcity of assimilates. [ABSTRACT FROM AUTHOR] more...

It is well established that phytochrome exists as a dimer in vitro. A comparison of the relative photoequilibrium concentrations of PrPr, PrP∞r and P∞rP∞r, with the relative sizes of the P∞r- pools which undergo dark reversion in the intact plant, leads to the hypothesis that phytochrome also exists as a dimer in vivo. This hypothesis is in accordance with kinetic properties of the phytochrome system under continuous irradiation. Additional support for this view is provided by the observation that P∞r-destruction after a red light flash, which should favour the formation of PrP∞r dimers, is paralleled by a decay of Pr, even if the presence of Pr cycled through P∞r can be excluded. Preliminary observations could indicate an interaction of the subunits of a phytochrome dimer during the process of phototransformation. [ABSTRACT FROM AUTHOR] more...

A brief high temperature treatment (45°C) promoted anthocyanin synthesis in 2-d-old darkgrown red cabbage seedlings. The increased effectiveness of a temperature/red light treatment as opposed to the reverse sequence suggests that an elevated temperature 'induces' some component which facilitates the phytochrome response. [ABSTRACT FROM AUTHOR] more...

The effects of norflurazon (San 9789) on light-increased extractable NADH nitrate reductase activity (NRA) in soybean seedlings were studied. Continuous white light (W) increased NRA steadily in root and cotyledonary tissues over a 5 d period. Norflurazon, a pyridazinone herbicide which causes chlorophyll bleaching in W, reduced the initial NRA induction rate in roots and cotyledons. However, in cotyledons of norflurazon-treated plants NRA increased at a more rapid rate than in the control after 24 h of W, with activity levels reaching three times those of control seedlings alter 5 d. NRA induced by W in control and norflurazon-treated cotyledons was fluence-rate dependent. Continuous FR induced equal amounts of NRA in control and norflurazon-treated tissues, suggesting that the superinduceable NRA of norflurazon-treated plants under W is not phytochrome induced. The FR-induced NRA of control and norflurazon-treated cotyledons had pH optima of 6.6, but during development under W the pH optimum of control cotyledons changed from 6.3 to between 6.6 and 7.1. The pH optimum of the norflurazon-induced NRA of the cotyledon under W was about 7.5. The NADH/NADPH NRA ratio after 4 d of W was 1.3 in control and 2.5 in norflurazon-treated cotyledons. These data indicate that photosynthetic pigments are involved only secondarily in light-induction of NRA in this system. [ABSTRACT FROM AUTHOR] more...

We measured phytochrome content by radiommunoassay in green, light-grow oats (Avena sativa L., cv. Garry) grown under several light regimes. Phytochrome content increased linearly to six times the light-grown level during a 24-h dark incubation and to fifty times the light-grown level after 48 h darkness. Phytochrome content, in response to a cycle of 12-h light, 12-h dark photoperiods, increased to three times the light-grown level in darkness and returned to the light-grown level during the subsequent light period. Plants given far-red light immediately prior to a 12-h dark period contained about four-fold more phytochrome than light-grown oats, compared with a three-fold increase in plants treated identically except given no far-red light. We also attempted, unsuccessfully, to eliminate a general nonspecific interference by crude plant extracts with the radioimmunoassay. [ABSTRACT FROM AUTHOR] more...

A scheme to account for the phytochrome responses of dark grown and green plants is presented. In contrast to some other models (e.g. Smith, 1970; Schäfer, 1975) it is proposed that both Pfr and the photoconversions of phytochrome are effectors of phytochrome action and interact to promote the observed responses. Under conditions where Ptot is not strongly wavelength dependent (e.g. with short pulses of light and in plants grown for prolonged periods in the light), responses will be predominantly related to Pfr concentration. Where Ptot is the major wavelength dependent variable (e.g. in the 'high irradiance reaction' of etiolated seedlings) it is proposed that the photoconversion process itself predominates in controlling the ultimate response. Some responses predicted by the scheme are compared with relevant published data. [ABSTRACT FROM AUTHOR] more...

Two phytochrome-dependent processes are compared in Anagallis arvensis, an absolute long-day plant: flowering and internode elongation. The effectiveness of red or far red radiation is different according to the length of the treatment and its position within the photoperiodic cycle: for both flowering and internode elongation, 15 h treatments with wavelengths above 700 nm are promotive, whilst wavelengths below 700 nm are inhibitory. In contrast, night breaks of 3 h red light (λ < 700 nm), given after the middle of the dark period, are promotive for flowering and inhibitory for internode elongation. These results are discussed in context with data reported in the literature on photoperiodic control of long-day plants. [ABSTRACT FROM AUTHOR] more...

Phytochrome photoequilibria within a model green leaf have been calculated. The results show a gradient in photoequilibria within the leaf lamina due to selective attenuation of incident light by the leaf tissue. Large differences were observed between photoequilibria calculated for a leaf under natural daylight and photoequilibria calculated for a leaf receiving daylight filtered through a vegetation canopy. [ABSTRACT FROM AUTHOR] more...

Changes in the bioelectric field potential at the apical end of dark-grown soybean (Glycine max) hypocotyls after exposure to several wavelengths of light have been monitored with an electrometer. A small dose of 660 mn radiation brings about a rapid positive rise in the potential. A following small dose ar 760nm prevents the increase, suggesting a phytochrome action. Pre-irradiation with 660 nm enables a subsequent larger dose of 760 nm, which by itself is without effect, to elicit a delayed rise in the potential. A large dose at 710 nm induces a delayed increase in the field potential. The increase is prevented by a following dose at 550 nm, bur not at 660 nm. [ABSTRACT FROM AUTHOR] more...

Presents a correction to the article "The Effect of Red and Far-Red Light in the High Irradiance Reaction of Phytochrome" that was previously published in an issue of the periodical "Plant, Cell and Environment." more...