Advanced LED technology is now making it possible to control the kinds of colored light we provide plants in controlled environments. We can now design lighting to encourage flowering or to produce higher fruit yields for example.
Many plant functions can be enhanced and promoted just by knowing what light colors they react and respond to. For a hungry world just waking up to the effects of Global Warming, this is critical. It will allow us to provide environmentally friendly alternatives to help improve crop quality and growth without having to resort to powerful fertilizers and genetically modified food. Enabling Paint Shop Industry 4. Same car different color.
Blue Light Safety. Achieving a Standard Color in Cosmetic Foundations. The guard cells respond to a complex hierarchy of signals which are both intracellular and external. Light is one of the key determinants of these responses, along with [CO 2 ] and humidity, and has been shown to be dynamic in canopy conditions, with fluctuations in intensity occurring on a scale of hours to seconds and varying in magnitude Bartley and Scolnik, ; Morison, ; Pearcy and Way, ; Way and Pearcy, ; Chen et al.
There are two distinct reactions to light—the red-light response and the blue-light response Lawson, ; Chen et al. The origin and form of the signal for the guard cell response to red light is still unknown, and therefore the exact mechanism of red light-induced stomatal opening is under debate. It is uncertain whether the guard cells sense and respond to red light directly, if the signal originates from the mesophyll and is mediated via the vapour phase to the guard cells, or if the signal is produced in response to one of the products of photosynthesis itself reviewed in Lawson, ; Busch, However, it is known that the intensity of red light required for stomatal opening is much greater than that required for blue light-mediated stomatal opening Sharkey and Raschke, ; Gorton et al.
The mechanism for the blue-light response is relatively well documented Mao et al. The osmotic potential of the guard cell membranes is therefore reduced and encourages the passive movement of water into the guard cell, increasing turgor and exposing the stomatal pore for gas exchange Mao et al.
Green light deactivates cryptochromes Bouly et al. Longer-wave blue and green wavebands have been found to have a role in the modulation of stomatal aperture in a wide range of plants, including Vicia faba , Pisum sativum, Commelina communis, Nicotiana tabacum, Nicotiana glauca , and Arabidopsis thaliana Talbott et al. Frechilla et al. In both studies, under continuous irradiance the degree of reversal was irradiance-dependent, with full reversal when green light was twice that of blue light.
Further work demonstrated that the same response can be observed in intact leaves of Arabidopsis Talbott et al. Talbott et al. By contrast, green light has been found to induce a small degree of stomatal opening when it is the only source, although the response is smaller than that observed under blue or red light. Perhaps this type of stomatal response has evolved so that, in the absence of a blue-light signal, the leaf may take advantage of the green light which has penetrated through the canopy, particularly green light that has been reflected back up to illuminate the underside of the leaf, for photosynthesis.
This suggests two possibilities: first, that green light activates two photoreceptors—cryptochrome, to act antagonistically against blue light, and a putative unknown photoreceptor Zhang et al. Second, photosynthetic regulation could occur either by the photosynthate level or redox state of the chloroplast. What would be the physiological function of green light in providing a signal for such processes, in addition to existing photoreceptor- and photosynthesis-mediated sensing?
We propose that the B:G ratio has a very different profile to R:FR within plant canopies, allowing it to act as an extended and sensitive source of information for regions of the canopy.
We conducted measurements of spectral profile in UK field-grown crop species Fig. The B:G ratio would be capable of exerting specific physiological effects, such as the reversal of the blue light-induced opening discussed above.
This has some similarities to the conclusions of Sellaro et al. Roles for green-light signalling for control of stomatal aperture and the balance of water loss versus CO 2 uptake within canopies are proposed here and we suggest the following.
The proportion of red light-induced stomatal opening should decrease rapidly as overall irradiance declines through the canopy and a higher proportion of stomatal opening is caused by the more sensitive blue-light response. Although small amounts of blue light reach the bottom of the canopy, stomata are up to 10 times as sensitive to blue light than to red Sharkey and Raschke, ; Gorton et al.
It has been shown with epidermal peels and also in whole leaves that the closure of blue light-mediated stomatal opening is only completed once the intensity of green light is twice that of blue light, and the reversal of the opening response is directly proportional to the change in the B:G ratio Frechilla et al. Thus, the antagonistic property of green-light to blue-light responses means that stomata are responsive to the B:G light ratio.
The signal provided by the B:G ratio should enable fine-tuning in ways that may be beneficial to the plant in terms of balancing photosynthesis and water-use efficiency within a dense canopy.
If the same degree of canopy stomatal closure occurred concurrently with the steep decrease in the level of red light or the R:FR ratio, closure could be complete well before irradiance dropped to the light compensation point below which photosynthesis cannot take place. Responding to blue light, with its greater relative availability, enables opening within a dense canopy but response to the B:G ratio adds another layer of fine-tuning, ensuring full closure is only complete when light levels have fallen below the point at which photosynthesis cannot take place.
We therefore propose that stomatal closure with increasing canopy depth should be directly linked to the decreasing B:G gradient. It is common for leaves within plant canopies to exist in deep shade and still contribute to net plant photosynthesis close to the light compensation point Murchie and Horton, , Burgess et al.
Here, leaf conductance will not be limiting to photosynthesis but stomatal aperture should be kept low to avoid excessive water loss. We suggest that these changes in the B:G ratio, specific to these canopy regions, could stimulate further stomatal closure without loss of carbon gain, thus contributing to optimization of whole-canopy water-use efficiency.
To establish this role will require the application of specific wavelengths of light to gas exchange measurements in situ. When such signalling responses are so closely allied to empirical changes in gas exchange, it may be difficult to separate receptor-specific processes from those that are photosynthetic in origin. Green light significantly contributes to photosynthetic carbon assimilation and is crucial in promoting biomass accumulation in deeper sections of the leaf and lower canopy where blue and red light are, by comparison, severely depleted.
Green photons also provide a strong positional signal to the leaf, allowing tighter control of acclimation to a shaded or fluctuating irradiance environment, and potentially increasing water-use efficiency within canopies. Agati G Tattini M. Multiple functional roles of flavonoids in photoprotection. New Phytologist , — Google Scholar. Ultrafast excitation relaxation dynamics of lutein in solution and in the light-harvesting complexes II isolated from Arabidopsis thaliana.
The Journal of Physical Chemistry B , — High luminous efficacy green light-emitting diodes with AlGaN cap layer. Optics Express 24 , — Allen JF.
Cyclic, pseudocyclic and noncyclic photophosphorylation: new links in the chain. Trends in Plant Science 8 , 15 — The grand design of photosynthesis: acclimation of the photosynthetic apparatus to environmental cues. Photosynthesis Research 46 , — Contrasting behavior of higher plant photosystem I and II antenna systems during acclimation. The Journal of Biological Chemistry , — The signaling state of Arabidopsis cryptochrome 2 contains flavin semiquinone.
Plant carotenoids: pigments for photoprotection, visual attraction, and human health. The Plant Cell 7 , — The stomatal response to reduced relative humidity requires guard cell-autonomous ABA synthesis. Current Biology 23 , 53 — State transitions and light adaptation require chloroplast thylakoid protein kinase STN7.
Nature , — Continuous light from red, blue, and green light-emitting diodes reduces nitrate content and enhances phytochemical concentrations and antioxidant capacity in lettuce. Journal of the American Society for Horticultural Science , — Bollivar DW. Recent advances in chlorophyll biosynthesis. Photosynthesis Research 90 , — Light signaling: back to space. Trends in Plant Science 13 , — Cryptochrome blue light photoreceptors are activated through interconversion of flavin redox states.
Phototropins 1 and 2: versatile plant blue-light receptors. Trends in Plant Science 7 , — High-resolution 3D structural data quantifies the impact of photoinhibition on long term carbon gain in wheat canopies in the field. Plant Physiology , — Busch FA.
Opinion: the red-light response of stomatal movement is sensed by the redox state of the photosynthetic electron transport chain.
Photosynthesis Research , — Plant pigments: the many faces of light perception. Acta Physiologiae Plantarum 33 , — Photosynthetic light-harvesting by carotenoids: detection of an intermediate excited state. Light-regulated stomatal aperture in Arabidopsis. Molecular Plant 5 , — Adjustments of photosystem stoichiometry in chloroplasts improve the quantum efficiency of photosynthesis.
The Lhca antenna complexes of higher plants photosystem I. Biochimica et Biophysica Acta , 29 — Energy transfer pathways in the minor antenna complex CP29 of photosystem II: a femtosecond study of carotenoid to chlorophyll transfer on mutant and WT complexes.
Biophysical Journal 84 , — Photoprotective mechanisms: carotenoids. Plastid Biology. Google Preview. Depuydt S Hardtke CS. Hormone signalling crosstalk in plant growth regulation.
Current Biology 21 , R — R Despommier D. Farming up the city: the rise of urban vertical farms. Trends in Biotechnology 31 , — Dougher TA Bugbee B. Evidence for yellow light suppression of lettuce growth. Photochemistry and Photobiology 73 , — Interactions between a blue-green reversible photoreceptor and a separate UV-B receptor in stomatal guard cells.
American Journal of Botany 90 , — Absolute absorption and relative fluorescence excitation spectra of the five major chlorophyll-protein complexes from spinach thylakoid membranes. Biochimica et Biophysica Acta , 75 — Profiles of C fixation through spinach leaves in relation to light absorption and photosynthetic capacity. Plant Cell and Environment 26 , — Franklin KA.
Shade avoidance. Phytochromes and shade-avoidance responses in plants. Annals of Botany 96 , — Reversal of blue light-stimulated stomatal opening by green light. Circadian rhythms in stomatal responsiveness to red and blue light. A multicolor, femtosecond pump—probe study.
Natural and artificial light-harvesting systems utilizing the functions of carotenoids. Hillier W Babcock GT. Photosynthetic reaction centers. Plant Physiology , 33 — Structural basis of light harvesting by carotenoids: peridinin-chlorophyll-protein from Amphidinium carterae.
Science , — Blue light dose-responses of leaf photosynthesis, morphology, and chemical composition of Cucumis sativus grown under different combinations of red and blue light. Journal of Experimental Botany 61 , — Photosynthetic quantum yield dynamics: from photosystems to leaves. The Plant Cell 24 , — Introduction toPlant Physiology.
New Jersey : John Wiley and Sons. Scientific Reports 5 , Ultrafast dynamics of flavins in five redox states. Journal of the American Chemical Society , — Kasperbauer MJ. Spectral distribution of light in a tobacco canopy and effects of end-of-day light quality on growth and development.
Plant Physiology 47 , — Kim H-H. Stomatal conductance of lettuce grown under or exposed to different light qualities. Annals of Botany 94 , — Green-light supplementation for enhanced lettuce growth under red- and blue-light-emitting diodes. HortScience 39 , — Evaluation of lettuce growth using supplemental green light with red and blue light-emitting diodes in a controlled environment—a review of research at Kennedy Space Center.
Acta Horticulturae , — Physical Chemistry Chemical Physics 7 , Status and future of high-power light-emitting diodes for solid-state lighting. Lawson T. Guard cell photosynthesis and stomatal function. New Phytologist , 13 — In strong white light, therefore, the quantum yield of photosynthesis would be lower in the upper chloroplasts, located near the illuminated surface, than that in the lower chloroplasts.
Because green light can penetrate further into the leaf than red or blue light, in strong white light, any additional green light absorbed by the lower chloroplasts would increase leaf photosynthesis to a greater extent than would additional red or blue light.
Based on the assessment of effects of the additional monochromatic light on leaf photosynthesis, we developed the differential quantum yield method that quantifies efficiency of any monochromatic light in white light.
Application of this method to sunflower leaves clearly showed that, in moderate to strong white light, green light drove photosynthesis more effectively than red light. The green leaf should have a considerable volume of chloroplasts to accommodate the inefficient carboxylation enzyme, Rubisco, and deliver appropriate light to all the chloroplasts. We also discuss some serious problems that are caused by neglecting these intra-leaf profiles when estimating whole leaf electron transport rates and assessing photoinhibition by fluorescence techniques.
Absorbance spectra of chlorophylls or pigments extracted from green leaves show that green light is absorbed only weakly. Action spectra of photosynthesis for thin algal solutions, transparent thalli of ordinary green algae, and leaves of aquatic angiosperms also show that green light is less effective than red light. As has been pointed out by Nishio , these facts are often confused, and it is frequently argued that green light is inefficient for photosynthesis in green leaves.
However, many spectra of absorptance the absolute value of light absorption measured with integrating spheres have shown clearly that ordinary, green leaves of land plants absorb a substantial fraction of green light McCree , Inada , Gates On an absorbed quantum basis, the efficiency or photosynthetic quantum yield of green light is comparable with that of red light, and greater than that of blue light.
The difference between the quantum yields of green and blue light is particularly large in woody plants grown outdoors in high light.
The question of how much green light is absorbed and used in photosynthesis by the green leaves of land plants has therefore been solved. In this mini-review, however, we aim at further clarifying another important role of green light in photosynthesis, by considering the intra-leaf profiles of light absorption and photosynthetic capacity of chloroplasts. First, we briefly explain light absorption by the leaf. Secondly, we examine the light environment within the leaf.
Thirdly, we compare the vertical, intra-leaf profile of photosynthetic capacity with that of light absorption. We also discuss some serious problems with the use of pulse amplitude modulated PAM fluorometry in assessing leaf electron transport rate and photoinhibition. Fourthly, we propose a new method to measure the quantum yield of any monochromatic light in white light, and demonstrate the effectiveness of green light in strong white light.
Based on these arguments, we finally revisit the enigmatic question of why leaves are green. As an optical system, the leaf differs from a pigment solution in two aspects: the concentration of pigments into chloroplasts and the diffusive nature of plant tissues.
The first factor decreases the opportunity for light to encounter pigments and generally decreases light absorption, and has been called the sieve or flattening effect. Once light that is strongly absorbed by chlorophylls, such as blue or red, encounters a chloroplast, most of the light is absorbed.
On the other hand, for wavelengths that are weakly absorbed, such as green light, T is considerable. Using a simple model shown in Fig. In the left-hand cuvette, photosynthetic pigments are uniformly distributed, whereas the right-hand model comprises one half-cuvette with the pigments concentrated 2-fold and another half-cuvette containing only the solvent.
At wavelengths with strong absorption, the loss of absorptance by the sieve effect is large. On the other hand, at wavelengths of weak absorption such as green, the loss is marginal. The sieve effect, therefore, strongly decreases absorptance at wavelengths of strong absorption such as red and blue light.
Model explaining the sieve effect on absorptance. Left: a cuvette containing a pigment solution. Right: the pigment is concentrated in a half-cuvette, while another half-cuvette contains only the solvent. When the cuvette is uniformly irradiated with a strongly absorbed monochromatic light, the decrease in absorptance by the sieve effect was large above , while in the case of weakly absorbed monochromatic light the decrease in absorptance is small below.
The second point that distinguishes leaves from a simple pigment solution is that leaf tissues are diffusive. This is due to the fact that the leaf consists of cells and intercellular air spaces. The refractive index, which depends on both the material and wavelength of the light, of the bulk plant cells is around 1. On the other hand, the diffusive nature of the leaf tissues inevitably increases the reflectance, R , of the leaf to some extent.
Leaves appear to minimize R of the adaxial side by having a greater contact area between the adaxial epidermis and palisade tissue cells per unit leaf surface area than that between the abaxial epidermis and spongy tissue cells. In some species, palisade tissue cells are funnel-shaped, which further increases the contact area with the epidermis Haberlandt By reducing the chances of refraction at the interfaces between cells and air, R decreases to a considerable extent compare the differences in R between the adaxial and abaxial sides.
In such leaves, spongy tissues have cell surfaces facing various directions and fewer chloroplasts or chlorophyll per unit mesophyll volume. In leaves of Camellia japonica , a typical example, lengthening of the optical path is more marked in the spongy tissue than in the palisade tissue Terashima and Saeki On the other hand, in spinach, where the difference in the chlorophyll content per unit mesophyll volume between the palisade and spongy tissues use is small, the optical path length does not differ much between the tissues Vogelmann and Evans The consequence of lengthening the optical path can be shown using the same model Fig.
In this model, the path length increases by 3-fold see Vogelmann In contrast, for weakly absorbed wavelengths such as green light, the increase in absorptance is much greater. Consequently, green leaves absorb much green light. Moreover, as already mentioned above, it has been clearly shown that the quantum yield of photosynthesis based on absorbed photosynthetically active photon flux density PPFD , measured at low PPFDs, was comparable between green and red light.
Moreover, some carotenoids in thylakoid membranes do not transfer energy to reaction centers, or transfer with an efficiency significantly less than 1. For example, one of the most abundant carotenoids in thylakoids, lutein, transfers its energy to chlorophyll with an efficiency of 0.
The efficiency for neoxanthin is even less, at most 0. This probably explains to a considerable extent why the quantum yield of blue light is low. Evans and Anderson reconstructed the absorbance spectrum of thylakoid membranes from those of the chlorophyll—protein complexes and estimated the relative excitation of PSII and PSI. This might also explain why the quantum yield of blue light on an absorbed quantum basis is low.
If this effect is large, a decrease in the PSII quantum yield Genty's parameter, see below might be expected at wavelengths strongly absorbed by Chl b. However, the decreases observed were not enough to account for the large decrease in the quantum yield of blue light. Although there were some classical works, the light environment within the leaf was first intensively studied in the early s.
The micro fiberoptic method is the most efficient in measuring the flux of light within a leaf Vogelmann et al. Because the viewing angle of the optical fiber is narrow, the angular distribution of the light flux, including backward scattering, is measured by inserting the fiber into the leaf from various directions. On the other hand, it is not possible to measure the absorption profile using this method alone. Paradermal sectioning, i. This sectioning method is also used to measure the profiles of photosynthetic properties within the leaf Terashima and Hikosaka Sectioning after exposure of the leaf to 14 CO 2 has been used to reveal the photosynthetic profile in vivo across the leaf for a review, see Nishio Fukshansky and his colleagues applied the Kubelka—Munk theory to predict the light environment within the leaf and to characterize the optical properties of leaf tissues Richter and Fukshansky a , Richter and Fukshansky b.
Fluorescence techniques have also been used. Takahashi et al. To analyze the light environment within the leaf in relation to photosynthesis, it is necessary to know the light absorption profile, not the light fluxes per se.
This is because only those photons absorbed by pigments can work photochemically the law of photochemistry, see Clayton There are no straightforward methods to measure the light absorption profile, but the method of Takahashi et al. For the fitting, we used data from paradermal sections of C. The adopted k and s sufficiently describe the optical properties of these leaf tissues.
The calculated values showed abrupt changes at the interface between the palisade and spongy tissues. This is because k and s for these tissues differed. Both k and s for the spongy tissue were much greater than those for the palisade tissue see legend of Fig. Fitting of the Kubelka—Munk theory to the transmittance and reflectance data of the paradermal sections of leaves of Camellia japonica.
Although attenuance can be defined by the same mathematical equation that defines absorbance A , attenuance is used when the decrease in T due to R is substantial. Right: reflectance of the paradermal sections having the abaxial epidermes. Monochromatic light was irradiated from the cut surface. Reflectance was measured with an integrating sphere. Different symbols indicate different leaves.
The reflectance of the abaxial epidermis was assumed to be 0. The boundary between the palisade and spongy tissues was assumed to be at 0. For the unit of these numbers, see the text. The data of transmittance and reflectance were adopted from Terashima and Saeki Light environment and light absorption profile within a Camellia japonica leaf predicted by the Kubelka—Munk theory. The k and s values fitted to the data Fig. Unpublished results of I.
Our absorptance data agree well with a previous calculation of the light absorption gradient, which was based purely on the experimental data Terashima and Saeki For spinach, various estimations have been published.
Using the method of Takahashi et al. For wavelengths with strong absorption, such as red and blue, the fractions are much smaller. The profiles of photosynthetic capacity along the gradient of light absorption have been reported for Spinacia oleracea Terashima and Hikosaka , Nishio , Evans and Vogelmann and E.
The differences in photosynthetic properties found between the chloroplasts in the upper and lower parts of the leaf are essentially identical to those found between sun and shade leaves, or between sun and shade plants Terashima and Hikosaka, Thus, the formation of an intra-leaf profile of photosynthetic capacity can be regarded as an acclimation process Terashima et al. It is also worth mentioning that we verified acclimation of light sensitivity of stomatal opening to the intra-leaf light environment with Helianthus annuus leaves: stomata in the abaxial epidermis, which are located in a light environment enriched in green light, open in response to monochromatic green light, whereas those in the adaxial epidermis do not Wang et al.
Based on observations of the differences in the shape of light response curves depending on the direction of irradiation, Oja and Laisk predicted the existence of an intra-leaf gradient in photosynthetic capacity.
The profile in photosynthetic capacity and the differentiation of optical properties between palisade and spongy tissues are adaptive, because these features improve the efficiencies of both light use and nitrogen use in photosynthesis Terashima and Saeki , Farquhar , Terashima and Hikosaka The most efficient situation is realized when the profile of light absorption and the profile of photosynthetic capacity are perfectly matched, and all the chloroplasts in the leaf behave synchronously with respect to photosynthetic light saturation Farquhar , Terashima and Hikosaka , Richter and Fukshansky
0コメント