| Each spring when the colorful mosaic of flowers | | | | sustain its metabolism. |
| comes to a close, red-leafed plants stand out in | | | | Numerous studies have shown that anthocyanins |
| the sea of green. While green- and red-leafed | | | | can effectively “reduce both the frequency |
| trees, bushes, and flora consist of chloroplasts to | | | | and severity of photoinhibition [and] expedite |
| undertake photosynthesis, the latter utilize | | | | photosynthetic recovery. [For example] in |
| anthocyanins to provide added benefits and to | | | | red-osier dogwood (Cornus stolonifera), a |
| differentiate themselves. The question is, with the | | | | 30-minute exposure to strong white light [was |
| continued ozone depletion that allows harmful | | | | found to have reduced] the quantum efficiency of |
| ultraviolet (UV) rays to penetrate the atmosphere | | | | photosynthesis by 60% in red leaves [and] by |
| at greater levels and intensity and subtle changes | | | | almost 100% in acyanic leaves (those without |
| in sunlight ranging from brightness to the way it is | | | | anthocyanins). [Then] when the plants were |
| refracted due to the continued buildup of | | | | returned to darkness, the red leaves recovered |
| emissions and pollutants, is the existence of | | | | to their maximum [photosynthetic] potential |
| red-leafed plants evidence of evolution in | | | | after… 80 minutes [while] their acyanic |
| progress? Is a transformation underway in which | | | | counterparts [still had not fully recovered] after |
| they will become the dominant type? | | | | six hours.”[25] |
| While these questions cannot be readily answered, | | | | Another study involving the Setcreasea purpurea, |
| it appears that red-leafed plants hold several | | | | a plant that can grow well under both extremely |
| advantages. They absorb green and yellow | | | | low light and high light conditions also illustrated this. |
| wavelengths (two dominant colors of the | | | | When Setcreasea purpurea plants were kept in |
| spectrum), they attract “friendly” | | | | low light conditions, they did not synthesize |
| insects to assist with pollination, they repel | | | | anthocyanins. Accordingly their leaves were green. |
| “hostile” pests that would exploit | | | | However, when these same plants were exposed |
| them, and they can tolerate environmental stress | | | | to bright light conditions, they defensively |
| better than green-leafed plants because of their | | | | accumulated anthocyanins in the epidermal layer |
| slower metabolism. However, to gain these | | | | of their leaves, transforming the color of their |
| advantages, red-leafed plants must expend | | | | leaves to red. Accordingly, when the epidermal |
| energy and utilize nutrients to produce the | | | | layer consisting of anthocyanins in the red leaves |
| pigmentation responsible for their color. | | | | was removed, they exhibited a photoinhibitory |
| Red-leafed plants “are common throughout | | | | effect similar to that experienced by green |
| all orders of the plant kingdom, from… basal | | | | leaves, in which their photosynthetic yield was |
| liverworts [mosses, ferns, gymnosperms (cycads | | | | reduced by between 2-4 times from that of |
| or conifers)][1] to the most advanced | | | | leaves where anthocyanins were present in their |
| angiosperms (flowering plants with ovaries). They | | | | epidermal layer.[26] |
| [exist] in habitats as diverse as the Antarctic | | | | Second, because of their ability “to absorb |
| shoreline and the tropical rainforests, are as | | | | strongly in the UV region [of the |
| abundant in arid deserts as in freshwater lakes, | | | | spectrum]” anthocyanins have been proven |
| and seem equally at home in the light-starved | | | | to protect critical structures from |
| forest understorey (ground-lower level) as in the | | | | “potentially damaging [amounts of] UV-B |
| sun-drenched canopy (upper level-top).”[2] | | | | radiation – red-leafed Coleus varieties [were |
| While the existence of red leaves is transient in | | | | found to have retained] higher photosynthetic |
| some plants (e.g. deciduous plants that change | | | | efficiencies… than green-leafed |
| colors in the fall, others that start out with red | | | | varieties” after exposure to UV |
| hues in the spring), it is permanent in other | | | | radiation.[27] However, anthocyanins’ ability |
| species. The focus of this article is on the plants | | | | to absorb UV radiation is also a double-edged |
| with red leaf pigments that exist for the duration | | | | sword since if damage occurs, such absorption |
| of their lives. | | | | impairs DNA repair. |
| The “Red” in Leaves | | | | Third, since red-leafed plants have slower rates of |
| Anthocyanins (mainly cyanidin-3-O-glucoside)[3], | | | | photosynthesis and metabolism, they can also |
| which belong to the flavonoid family are the key | | | | thrive well in low-light, high or low temperatures |
| water-soluble pigment responsible for giving a | | | | (anthocyanins “function as antifreeze by |
| plant its red color. They are synthesized in the | | | | protecting leaves during a frost”[28] and |
| cytoplasm[4] and reside in the vacuole of leaf | | | | from extreme heat) as well as from drought and |
| cells. Other contributing pigments or photoreceptor | | | | desiccation (severe drying of tissues). For |
| chemicals that emit “reddish” colors | | | | example, “New Zealand’s liverworts, |
| are thiarubrine A, the 3-deoxyanthocyanins, the | | | | [a primitive and simple land species] are |
| betalains, some terpenoids, and certain | | | | remarkably resilient to environmental stresses |
| carotenoids. These pigments too, may perform | | | | such as intense sunlight, high temperatures, UV-B |
| similar functions and provide similar benefits as | | | | radiation, and desiccation.”[29] |
| anthocyanins. | | | | In addition to protecting against harmful lighting, |
| Based on their properties, anthocyanins absorb | | | | UV radiation, temperature extremes, droughts |
| the green and yellow wavebands of light, | | | | and desiccation, anthocyanins have been found to |
| commonly between 500 and 600 nanometers | | | | enhance plant resistance to heavy metal |
| (nm)[5] (each nonmeter is equal to one billionth | | | | contamination (e.g. mercury) and wounds (e.g. leaf |
| (10-9) of a meter), making leaves appear red to | | | | punctures). |
| purple as they “reflect the red to blue | | | | Protection of Photolabile (Light-Sensitive) Defense |
| range of the visible spectrum”[6] of light. In | | | | Compounds and against Herbivory |
| addition, flavins absorb blue wavelengths of light | | | | Anthocyanins because of their absorptive qualities |
| [to some degree], also contributing to a | | | | also play an important role in protecting photolabile |
| “reddish” color in leaves.[7] | | | | (light-sensitive) molecules from degradation and |
| “Interestingly [though], the amount of red | | | | damage caused by exposure to bright light and |
| light that is reflected from red leaves | | | | UV radiation. An example of this is illustrated in |
| often… correlates [poorly] to anthocyanin | | | | the silver beachweed (Ambrosia chamissonis), a |
| content; leaf morphology (structure and form) | | | | plant that grows in sunny areas and contains large |
| and the amount and distribution of chlorophyll | | | | amounts of thiarubrine A, “a potent |
| are… stronger determinants of red | | | | defense compound that is toxic to insects, |
| reflectance.”[8] Although chlorophyll is the | | | | bacteria, and fungi.” Without protection |
| pigment responsible for giving most plants their | | | | from two anthocyanic pigments – |
| green color, an experiment showed that it can | | | | cyaniding-3-O-glucose and |
| play a role in red reflectance. When a transparent | | | | cyaniding-3-O-(6’-O-malonylglucoside) |
| pure chlorophyll solution was created from ground | | | | – this plant’s defenses would be |
| up spinach leaves mixed with acetone to dissolve | | | | rendered impotent since thiarubrine A is |
| chloroplasts and their membranes, it reflected a | | | | photolabile; even short exposures to visible light |
| “reddish glow/flourescence” when a | | | | and/or [UV] radiation render it inactive.”[30] |
| beam of light was directed at it.[9] | | | | Second, red color alone has also been found to |
| When it comes to Rhodophyta (Red Algae), | | | | protect plants from herbivory (harmful insects |
| phycoerythrin, a pigment belonging to the | | | | and organisms that feed on them). For example, |
| phycobilin family found in its chloroplasts is | | | | “California maple aphids… readily [and |
| responsible for its color. Phycoerythrins absorb | | | | harmfully] colonize [and exploit] yellow-orange |
| (between 500 and 650 nm. of)[10] blue | | | | leaves of Japanese maples [while ignoring] |
| wavelengths of light and reflect red wavelengths | | | | red-leafed [Japanese maples]. Similarily, leaf-cutting |
| as Rhodophyta engage in photosynthesis. | | | | ants from tropical forests… browse |
| Photosynthesis | | | | significantly less on red leaves than on green |
| Photosynthesis is the process that plants and | | | | leaves, [indicative that] athocyanins may serve as |
| some bacteria use to convert energy from | | | | aposematic signals (warning of a special defense |
| sunlight into sugar (glucose); which cellular | | | | against enemies such as poison and toxins), |
| respiration converts into ATP (adenosine | | | | [mimick the appearance of dead, inedible foliage |
| triphosphate), chemical energy or the | | | | and/or] simply render the leaves |
| “fuel” used by all living organisms. | | | | unpalatable.”[31] |
| Photosynthesis uses six molecules of water | | | | Attraction of “Friendly” Creatures |
| (transported through the stem from the roots) | | | | While serving as a potent repellant to herbivores |
| and six molecules of carbon dioxide (that enter | | | | that could potentially cause serious or mortal |
| through a leaf’s stomata or openings) to | | | | harm through ingestion of plant foliage and |
| produce one molecule of sugar (glucose) and six | | | | compounds, anthocyanins also play the opposite |
| molecules of oxygen (6H2O + 6CO2 -> | | | | role when it comes to “friendly” |
| C6H12O6+ 6O2), the latter, which is released into | | | | creatures. “The red colors of anthocyanic |
| the air (also through the leaf’s stomata). | | | | leaves”[32] also serve as a means to |
| Although “sugar (glucose) molecules formed | | | | attract “birds, insects and mammals… |
| during photosynthesis serve as… the | | | | for pollination and reproduction |
| primary source of food”[11] for plants, | | | | [purposes].”[33] When the fruit and |
| excess sugar (glucose) molecules are converted | | | | background foliage of a Canadian shrub were |
| into starch, “a polymer… to store | | | | manipulated, it was found that “red-orange |
| energy”[12] for use at a later time when | | | | [coloring accentuated] the conspicuousness of [its] |
| photosynthetic sources of energy are lacking. | | | | black-colored fruits to birds [enabling them to |
| While chlorophyll (green) is the best-known | | | | remove the fruits at a higher rate, accordingly |
| photosynthetic pigment, other pigments also play | | | | enhancing the plants’ reproductive efforts |
| a role in converting sunlight into useable energy. | | | | since when the fruits were consumed, their |
| They include carotenoids such as carotene | | | | inedible seeds fell to the ground for possible |
| (orange), xanthophylls (yellow), and phycoerythrin | | | | germination].[34] |
| (red). When engaging in photosynthesis, chlorophyll | | | | Antioxidants and Scavenging Free Radicals |
| “absorbs its energy from the Violet-Blue | | | | Another important role of anthocyanins is that |
| and Reddish orange-Red wavelengths, and little | | | | they serve as antioxidants to scavenge free |
| from the intermediate (Green-Yellow-Orange) | | | | radicals (highly oxidized compounds that could |
| wavelengths,”[13] while carotenoids and | | | | damage proteins, membrane lipids, DNA and other |
| xanthophylls absorb some energy from the green | | | | botanic structures) for salvageable compounds |
| wavelength, and phycoerythrin absorbs a | | | | and diffuse their harmful energy. They reduce the |
| significant amount of its energy from the blue | | | | amount of oxidized compounds by filtering out |
| wavelength. Many plants use multiple pigments for | | | | yellow-green light since “the majority of |
| photosynthetic purposes, enabling them to | | | | reactive oxygen in plant cells is derived from the |
| maximize use of sunlight that falls on their leaves. | | | | excitation of chlorophyll.”[35] In one study, |
| When comparing photosynthesis that occurs | | | | anthocyanins were found “to have the |
| within red and green leaves, the latter, which | | | | strongest antioxidizing power of [a group] of 150 |
| have greater concentrations of chloroplasts, | | | | flavonoids.” In another study, conducted by |
| scientific studies have shown that the rate of | | | | the USDA, anthocyanins in blackberries were |
| photosynthesis is higher in green-leafed plants. In | | | | found to have a potent antioxidant capacity |
| one experiment, green and red leaves were | | | | against “superoxide radicals, hydrogen |
| collected from the same deciduous tree and | | | | peroxide, and other oxidants.”[36] A third |
| exposed to 5-10 minutes of light and another 5-10 | | | | study, involving Arabidopsis plants (a species |
| minutes of darkness. Afterwards the change in | | | | belonging to the mustard family that have white, |
| Carbon Dioxide (CO2) levels was measured to | | | | yellow or purplish flowers) found that exposure |
| determine the rate of photosynthesis. The | | | | “to strong light and low temperatures |
| “results showed that green leaves [had] a | | | | caused more lipid peroxidation in |
| higher mean rate of photosynthesis (-.5855 parts | | | | anthocyanin-deficient [plants]… Similarly, upon |
| per million (ppm) CO2/minute/gram) than red | | | | gamma irradiation, only those Arabidopsis plants |
| leaves (-0.200 ppm CO2/minute/gram). [However] | | | | that contained both anthocyanin and ascorbic acid |
| the differences in [the] average rates of | | | | were able to grow and flower |
| photosynthesis were not significantly | | | | normally.”[37] |
| different.”[14] | | | | Likewise, in a study involving Elatostema rugosum |
| Another experiment compared the photoperiodic | | | | plants it was “established that red-leaved |
| sensitivity of green-leafed (Perilla frutescens) and | | | | morphs held a significant antioxidant advantage |
| red-leafed (Perilla crispa) Perilla (flowering Asian | | | | over green morphs.”[38] |
| annuals) or how long it took each of the Perilla | | | | In addition a study reported by Kevin S. Gould |
| plants to reach the same level of growth or | | | | also showed that anthocyanins served as a |
| flowering based on exposure to different light | | | | chemical remedy to repair damage caused by |
| conditions. When exposed to 8 hours of light, | | | | oxidation and free radicals. “Microscopic |
| red-leafed Perilla took 4 days longer to reach the | | | | examinations of wounded leaf peels have shown |
| same growth stage as green-leafed Perilla. The | | | | that red-pigmented cells eliminate Hydrogen |
| results were more dramatic when each plant was | | | | Peroxide (H2O2) significantly faster than… |
| exposed to continuous light – red-leafed | | | | green cells.”[39] |
| Perilla took between 47 to 55 days longer to | | | | Conclusion |
| reach the same growth stage as green-leafed | | | | While it appears red-leafed plants with their slower |
| Perilla.[15] | | | | metabolic rate (to compensate for the edge |
| A third experiment involved an in-depth study of | | | | green-leafed plants hold regarding photosynthesis) |
| photosynthesis in red- and green-leafed Quintinia | | | | have an advantage because of the powerful |
| serrata, a tree native to New Zealand. When the | | | | presence of anthocyanins that give them an edge |
| rate of photosynthesis was measured at the | | | | in hostile environments and assist with healing, the |
| “cellular, tissue, and whole leaf levels to | | | | case cannot be made that “red” is |
| understand the role of anthocyanin pigments on | | | | biologically superior to “green.” Many |
| patterns of light utilization” of red- and | | | | green-leafed plants also utilize anthocyanins to |
| green-leafed Quintinia serrata, it was found that | | | | reduce climactic stress – the only difference |
| “anthocyanins in the mesophyll | | | | being is that they only expend energy to produce |
| (photosynthetic tissue between the upper and | | | | this pigment when most needed – spring to |
| lower epidermis of a leaf) restricted absorption of | | | | resist freezes and in autumn against heightened |
| green light to the uppermost [section of the] | | | | sensitivity to light exposure, thus ensuring that |
| mesophyll [and that] distribution was further | | | | their leaves can “function long enough to |
| restricted when anthocyanins were also present in | | | | unload nutrients and sugars” to store for |
| the upper epidermis.”[16] | | | | the approaching winter and to give them a |
| Accordingly, “mesophyll cells located | | | | “head start for the next growing |
| beneath a cyanic (blue or bluish) light filter | | | | season.”[40] Last, if advantages of |
| assumed the characteristic features of | | | | red-leafed plants were materially overwhelming |
| shade-adapted cells, [with red leaves showing] a | | | | (which, if their presence constitutes evolution in |
| 23% reduction in CO2 assimilation under | | | | progress, could some day be the case depending |
| light-saturating conditions, and a lower threshold of | | | | on global warming, ozone depletion, and other |
| irradiance (density of radiation occurrence) for | | | | adverse ecological changes), the vast majority of |
| light-saturation, relative to those of green | | | | the Earth’s land would not be clothed in |
| leaves.”[17] In short, the findings were | | | | green. |
| consistent with the previous two experiments in | | | | ________________________________ |
| which red leaves displayed slower rates of | | | | [1]Kevin S. Gould. Plant ecophysiology research. |
| photosynthesis, exhibiting photosynthetic | | | | (Otago, New Zealand: Department of Botany, |
| characteristics of “shade-acclimated | | | | University of Otago). 19 May 2006. [ |
| plants.”[18] | | | | [2]Kevin S. Gould. Nature’s Swiss Army |
| Although green-leaves appear to hold the | | | | Knife: The Diverse Protective Role of |
| advantage when it comes to photosynthesis, this | | | | Anthocyanins in Leaves. Biomedicine and |
| advantage should not be overstated since to | | | | Biotechnology. 15 July 2004. 19 May 2006. |
| compensate for their slower rate of | | | | [3]Kevin S. Gould. Nature’s Swiss Army |
| photosynthesis, red-leafed plants exhibit slower | | | | Knife: The Diverse Protective Role of |
| metabolism as established by an experiment using | | | | Anthocyanins in Leaves. |
| Iodine to test for the presence of starch. When I | | | | [4]Kevin S. Gould, et. al. Functional role of |
| tested red leaves of an Acer Palmatum Japanese | | | | anthocyanins in the leaves of Quintinia serrata A. |
| Maple and Acer Rubrum Red Maple in May 2006 | | | | Cunn. Journal of Experimental Botany, Vol. 51, No. |
| (when the leaves were young and after the | | | | 347 (June 2000). 22 May 2006. |
| respective trees had expended most of their | | | | [5] Kevin S. Gould. Nature’s Swiss Army |
| excess reserves over the winter), red Iodine | | | | Knife… |
| turned a dark blue when placed on their | | | | [6]Anthocyanin. 13 May 2006. 19 May 2006. |
| sub-epidermal tissue, indicating that each leaf | | | | [7]Seeing Red. 29 October 1994. 22 May 2006. [ |
| tested held this polymer. Thus, their | | | | [8]Kevin S. Gould. Nature’s Swiss Army |
| photosynthetic activities were not only producing | | | | Knife… |
| sufficient amounts of sugar (glucose) but excess | | | | [9]W.P. Armstrong. Photosynthesis & Cellular |
| reserve amounts. Had the metabolic rate of | | | | Respiration: Supplements To Biology 101 Cell Unit. |
| red-leafed plants been comparable, the same, or | | | | 2001. 19 May 2006. |
| faster than that of green-leafed plants, when their | | | | [10]Lecture 5 Photosynthesis I: Light, Pigments, |
| rate of photosynthesis is slower as established by | | | | and Leaves. 22 May 2006. [ |
| the above three experiments, it is unlikely that | | | | [11]Karin Tanino. Photosynthesis: Leaf Coloration. |
| they would have been able to produce excess | | | | 19 May 2006. |
| sugar (glucose) as evidenced by the presence of | | | | [12]Starch. Polymer Science Learning Center, |
| starch. | | | | Department of Polymer Science, University of |
| In addition, the presence of anthocyanins, which | | | | Southern Mississippi. 2003. 22 May 2006. |
| slow photosynthetic rates also provide an | | | | [13]M.J. Farabee. Photosynthesis. 2001. 19 May |
| advantage. They give red-leafed plants a higher | | | | 2006. [ |
| tolerance for harmful UV rays, which can reduce | | | | [14]Courtney Marne et. al.. The Effects of Leaf |
| photosynthetic productivity in green-leafed plants. | | | | Color on Rates of Photosynthesis. Colorado |
| This is especially important when considering the | | | | University Boulder (Boulder, CO. 2004). 19 May |
| ongoing depletion of the stratospheric ozone layer | | | | 2006. |
| that filters harmful UV rays, minimizing the level | | | | [15]William P. Jacobs. Comparison of Photoperiodic |
| that reaches the earth’s surface. | | | | Sensitivity of Green-Leafed and Red-Leafed Perilla. |
| Anthocyanins | | | | Plant Physiology Vol. 70. July 1982. 19 May 2006. |
| The presence of anthocyanins provide important | | | | [16]Kevin S. Gould et al. Profiles of photosynthesis |
| benefits (which are discussed below) to red-leafed | | | | within red and green leaves of Quintinia serrata. |
| plants. Had their presence been for mere | | | | Plant Sciences Group, School of Biological Sciences, |
| extravagance (e.g. solely to provide color – | | | | University of Auckland (Auckland, New Zealand: |
| red, pink, purple, and blue hues to enable these | | | | September 2002). 19 May 2006. |
| plants to stand out from the sea of green) it is | | | | [17]Kevin S. Gould et. al. Profiles of |
| unlikely that red-leafed plants would make | | | | photosynthesis… |
| “the considerable metabolic | | | | [18]Kevin S. Gould et al. Profiles of |
| investment” and expend energy to | | | | photosynthesis… |
| synthesize and accumulate the pigment in their | | | | [19] Kevin S. Gould. Nature’s Swiss Army |
| leaf cells. As Kevin S. Gould, one of the | | | | Knife… |
| world’s leading botanists and researchers | | | | [20] Kevin S. Gould. Nature’s Swiss Army |
| wrote, “…a wealth of… | | | | Knife… |
| evidence, ascribes a remarkable diversity of | | | | [21]Glenn Rosenholm. Maples gamble on |
| functions to anthocyanins… many of them | | | | antioxidant’s value, says New England |
| associated with stress responses and some | | | | researcher. News Release USDA Forest Service |
| potentially critical to a plant’s | | | | Northeastern Area. 18 October 2005. 24 May |
| survival.”[19] In his words, | | | | 2006. |
| “Anthocyanins are arguably the most | | | | [22] Kevin S. Gould. Nature’s Swiss Army |
| versatile of all [plant] pigments, their multifarious | | | | Knife… |
| (diverse) roles in plant stress responses stemming | | | | [23]Anthocyanin. 13 May 2006. 19 May 2006. |
| as much from the physicochemical property of | | | | [24] Kevin S. Gould. Nature’s Swiss Army |
| light absorption as from their unique combination | | | | Knife… |
| of biochemical reactivities.”[20] | | | | [25] Kevin S. Gould. Nature’s Swiss Army |
| U.S. Department of Agriculture (USDA) Forest | | | | Knife… |
| Service Researcher Paul Schaberg, a plant | | | | [26]David Dewez et. al. Photorotective role of |
| physiologist agrees. “There are all kinds of | | | | anthocyanins regulating PSII activity |
| strategies that [plants] have to protect | | | | [27] Kevin S. Gould. Nature’s Swiss Army |
| themselves and increase their chance of survival. | | | | Knife… |
| …some trees have deep roots to get extra | | | | [28]Glenn Rosenholm. Maples gamble on |
| water and survive droughts. Others survive by | | | | antioxidant’s value, says New England |
| just using less of the water they get. …red | | | | researcher. [29]Kevin S. Gould. Plant ecophysiology |
| leaf coloration may be one of those specialized | | | | research. Department of Botany, University of |
| adaptive traits…”[21] | | | | Otago (Dunedin, New Zealand). 19 May 2006. [ |
| Protection from Hostile Environments | | | | [30] Kevin S. Gould. Nature’s Swiss Army |
| “When leaves receive more light energy | | | | Knife… |
| than can be used in photochemistry, they show a | | | | [31] Kevin S. Gould. Nature’s Swiss Army |
| characteristic decline in the quantum efficiency of | | | | Knife… |
| photosynthesis, termed photoinhibition. Under | | | | [32] Kevin S. Gould. Nature’s Swiss Army |
| severe conditions [critical leaf structures such as | | | | Knife… |
| chloroplasts, thylakoid membranes (the area | | | | |
| where photons from sunlight initiate | | | | [33]Sean Henahan. Time to Leave. The National |
| photosynthesis), DNA, and proteins essential for | | | | Health Museum. 19 May 2006. |
| photosynthetic activities can be harmed or | | | | [34] Kevin S. Gould. Nature’s Swiss Army |
| destroyed].”[22] | | | | Knife… |
| Anthocyanins, through their absorption of | | | | [35] Kevin S. Gould. Nature’s Swiss Army |
| blue-green light, “have been shown to | | | | Knife… |
| protect plants from excess light during periods of | | | | [36]Marilyn Sterling, R.D. Got Anthocyanins? |
| high light stress (as occurs when plants are | | | | Nutrition Science News. (Penton Media, Inc. 2006). |
| exposed to high light in combination with drought | | | | 19 May 2006. [ |
| or cold temperatures)”[23] by providing a | | | | [37] Kevin S. Gould. Nature’s Swiss Army |
| physicochemical barrier to protect a leaf’s | | | | Knife… |
| chloroplasts and other critical structures. | | | | [38]Samuel O. Neill et. al. Antioxidant capacities of |
| “Chloroplasts irradiated with light that has | | | | green and cyanic leaves in the sun species, |
| first passed through a red filter have been shown | | | | Quintinia serrata. Functional Plant Biology. Abstract. |
| to generate fewer superoxide radicals (highly | | | | 19 May 2006. |
| oxidized compounds)” that could damage a | | | | [39] Kevin S. Gould. Nature’s Swiss Army |
| plant’s “photosystems (group of | | | | Knife… |
| structures that perform | | | | [40]Glenn Rosenholm. Maples gamble on |
| photosynthesis)”[24] and impair its ability to | | | | antioxidant’s value, says New England |
| transfer and use necessary sugar (glucose) to | | | | researcher. |