QUOTE (grimweeder @ Aug 29 2008, 07:02 PM)
the purple/pink/blues in most strains is all natural an generally caused by a breakdown in chlorophyll, under the green pigment most cannabis plants are purple, or have purple pigment in them it is called a particular name or something but cant remember what it is
That's not quite correct....
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Plants with abnormally high anthocyanin quantities are popular as ornamental plants. Many science textbooks incompletely state that autumn coloration (including red) is the result of breakdown of green chlorophyll, which unmasks the already-present orange, yellow, and red pigments (carotenoids, xanthophylls, and anthocyanins, respectively). While this is indeed the case for the carotenoids and xanthophylls (orange and yellow pigments), anthocyanins are not present until the leaf begins breaking down the chlorophyll, during which time the plant begins to synthesize the anthocyanin, presumably for photoprotection during nitrogen translocation.
If any of you wish to understand the purpose of anthocyanins (the red/blue pigments) in plants then you might like to read this.
QUOTE
ABSTRACT
Anthocyanins are water-soluble pigments found in all plant tissues throughout the plant kingdom. Our understanding of anthocyanin biosynthesis and its molecular control has greatly improved in the last decade. The adaptive advantages of anthocyanins, especially in nonreproductive tissues, is much less clear. Anthocyanins often appear transiently at specific developmental stages and may be induced by a number of environmental factors including visible and UVB radiation, cold temperatures and water stress. The subsequent production and localization of anthocyanins in root, stem and especially leaf tissues may allow the plant to develop resistance to a number of environmental stresses. This article reviews the environmental induction of anthocyanins and their proposed importance in ameliorating environmental stresses induced by visible and UVB radiation, drought and cold temperatures.
Cold temperature induction
Induction of anthocyanins by cold temperatures has received less attention than photoinduction, even though the evidence for this process is seen in deciduous plants every fall. Low temperature has been shown to induce anthocyanin synthesis in seedlings of Arabidopsis (69,70), Sorghum (16), Poncirus (17) and Z. mays (39), leaves of Cotinus (54,71) and Pinus (18), I year-old twigs of Diospyros (14) and ray parenchyma cells of Fagus sylvatica (72). Christie et al. (39) consider the anthocyanin biosynthetic pathway to involve cor (cold-- regulation) genes but observe that very cold temperatures destroy the biosynthetic capability. McKown et al. (73) agree that there is some commonality between anthocyanin biosynthesis and freezing tolerance, in either the synthetic or regulatory pathways leading to both. It should be noted, however, that low temperatures in the absence of either visible light (23) or UVB (71) prevent anthocyanin biosynthesis. As Mol et al. (3) conclude, the mechanism of cold induction of anthocyanins and role of light is not fully understood and they again suggest separate, or perhaps overlapping, pathways.
ADAPTIVE SIGNIFICANCE OF ANTHOCYANINS
What adaptive advantages do leaf tissues containing high levels of anthocyanin have over those tissues with lower levels? To answer this question, the relative costs and benefits of anthocyanin accumulation must be compared.
Metabolic costs
Anthocyanin synthesis is metabolically expensive, requiring additional modifications of flavononal precursors. Their eventual degradation, such as that seen during maturation of red juvenile leaves of Brachystegia spp. (21), must also use energy. Another potential cost of anthocyanin accumulation is their interference with the light reactions of photosynthesis. Because of their ability to absorb blue light and reflect red wavelengths, anthocyanins in the upper epidermis or mesophyll of leaves could theoretically compete with light harvesting by chlorophyll and carotenoids. Reductions in photosynthetic rates have been noted in red-leafed varieties of Coleus (20) and pepper (99), spring flushing leaves of Brachystegia spp. (21,55) and the red juvenile leaves of several rainforest tree species (33).
Environmental strain reduction-Cold hardiness
Freezing temperatures can inflict mechanical injury on plant cells via ice crystal formation or induce dehydration as liquid water becomes extracellular ice. In nature, cold-exposed tissues take several weeks to winter harden through various mechanisms including the deposition of phenolic-rich compounds such as lignin in their cell walls. These structural changes allow cells to withstand physical damage from ice formation in extracellular spaces or on epidermal surfaces. Unlike mature tissues, expanding leaves cannot cold harden by lignifying their cell walls. Many plants avoid freeze damage to sensitive tissues through water supercooling as low as -41 C before freezing (113). Such supercooling is often induced by increasing solute levels and has been associated with xylem ray parenchyma cells, dormant flower buds ( 114) and leaf tissues (115). Anthocyanin accumulation by epidermal cells in these latter tissues would decrease the osmotic potential of the cell and delay freezing via surface nucleators, thus protecting the leaves from late spring frosts.
Decades ago, Parker (30) linked anthocyanin appearance and disappearance to cold hardiness in Hedera helix leaves. Further work (116) refuted these results, demonstrating no correlation between hardiness and anthocyanin levels in H. helix. It should be noted, however, that these latter experiments were conducted in a greenhouse and therefore the results might not be indicative of field conditions (i.e. natural UVB levels). Parker (30), on the other hand, used field-- grown leaf tissues.
More recently, Singh et al. (7) studied anthocyanin content and its relevance to cold hardiness of field-grown chickpea (Cicer arietinum). They concluded there was no association between stem anthocyanins and cold hardiness but did not report these data in the article. Furthermore, because this was not a controlled experiment (e.g. outdoor temperature fluctuations), they would not be able to assess small, but significant, differences in cold hardiness among genetic lines.
The induction of anthocyanins by chilling temperatures does suggest a protective function, and some studies are supportive of this idea. McKown et al. (73) suggest some commonality between anthocyanin biosynthesis and freezing tolerance, as four Arabidopsis mutants deficient in freezing tolerance were unable to accumulate anthocyanins. Autumn induction of anthocyanins is widely known and occurs in tandem with the onset of dormancy and cold hardiness in many woody plants. Winter-hardy tissues containing high levels of anthocyanins (14,15,71,117) generally decrease or lose these pigments the following spring. Northern ecotypes of Populus trichocarpa, which presumably survive colder winters than their southern counterparts, accumulate more anthocyanins than southern ecotypes with decreasing photoperiod (118). Krol et al. (18) believe anthocyanins protect the mesophyll of young Pinus seedlings from low-temperature photoinhibition. Anthocyanin-rich species such as Photinea have extended growing periods compared to other ornamental shrubs (119), perhaps as a result of increased tolerance of cool temperatures. A preliminary study of cold hardiness of green, UV-shielded and red, UV-exposed Cotinus leaves indicates that UV-exposure likewise increases the cold hardiness of this species (Chalker-Scott, unpublished data).
Any purported mechanism by which anthocyanins could enhance frost hardiness remains unclear. One hypothesis focuses on their ability to raise leaf temperature (120,121). This theory, however, has not been well documented (18,26) and requires further investigation. A more logical explanation might involve cold hardiness induction via osmotic control. Following a low-temperature exposure (5-10 deg C), I believe tissues will immediately show a small but significant increase in hardiness. The mechanism of this increase in frost hardiness (seen during fall and spring) is osmotic-- more solutes (e.g. anthocyanins) in the vacuole mean water freezes at a lower temperature. This small increase in hardiness would be enough to protect young tissues from frost damage in late spring. In particular, the accumulation of anthocyanins in epidermal vacuoles would prevent their freezing, especially from leaf surface nucleators. This phenomenon would also protect deciduous leaves from early fall frosts-a physiologically important time in which to mobilize substances for winter storage. Because this mobilization includes sugar transfer, anthocyanins might also facilitate this process because they exist almost exclusively as glycosides (112). Perennial tissues then show a second, more significant increase in cold hardiness (seen during the winter) several weeks postexposure that may or may not be related to anthocyanins.
An osmotically induced increase in cold hardiness could provide cross-resistance to other stresses, particularly drought. During winter freezes this could be particularly important in protecting sensitive parenchyma cells in the mesophyll or xylem rays of woody perennials from freeze-induced dehydration.
Apart from the problems of ice formation in leaf tissues, cold temperatures also decrease saturation levels of membrane lipids. Membranes with more polyunsaturated fatty acids are more sensitive to UVB damage because they are readily oxidized by radicals formed by UVB (122). Radicals are also longer-lived at lower temperatures, increasing the likelihood of membrane damage. Thus, epidermal anthocyanins are dually protective in preventing damage caused, directly or indirectly, by cold temperatures and UVB.
Cross-resistance
Many authors have commented on the similarities among the physiological and morphological responses to various abiotic stresses including UVB, cold and drought. Previous research by the author (135,136) and others (137) has demonstrated that resistance to UVB also increases cold hardiness, as does nutrient, drought and other stresses (138). Production of lignin, tannins, suberin, anthocyanins and other secondary compounds occurs in tandem with exposure to environmental stress.
While many induced cross-resistances may be due to cell wall modifications, it is more likely that developing leaves (which necessarily lack these modifications) would rely on vacuolar substances to attenuate radiation and modify water relations. Anthocyanins would seem to be good general protectors for a number of reasons:
First, anthocyanins are extremely soluble in water as they occur almost exclusively as glycosides ( 112) and would therefore readily accumulate in vacuoles. It is important to realize that osmotic stress can be induced by various environmental factors including radiation absorption, temperature extremes and relative water gradients (139), so resistance to these stresses is directly or indirectly dependent upon water relations within tissues.
Secondly, the fact that anthocyanins are glycosylated allows them to bind and transport reactive monosaccharides produced during developmentally or environmentally critical stages. The location of anthocyanins in ray parenchyma of cold-hardy trees (72) might very well serve in this capacity.
Thirdly, anthocyanins have the ability to attenuate WB if appropriately acylated with hydroxycinnamic acids. Even without acylation, anthocyanins can significantly attenuate visible radiation, which might be adaptive for young leaf tissues that lack adequate structural protection to avoid photooxidation from high levels of blue light.
I believe that anthocyanins in leaf tissues have a dual function as absorbers of harmful levels and/or wavelengths of radiation and as osmotic adjusters. This second function has at least two environmentally important consequences-- when the water potential of the epidermis is lowered, two environmental stresses can be avoided: ice nucleation via freezing events on the leaf surface and drought. Krol et al. (18) speculate that the phenomenon of anthocyanin development in young Pinus seedlings may somehow help them establish under a suite of suboptimal environmental conditions including photooxidation, low temperature, water and nutrient stress. Thus, leaf anthocyanins may be triply protective in preventing damage caused, directly or indirectly, by cold temperatures, drought and UV radiation.
.. shes a beaut!- and has been nominated loads of times for COTC. Im sure she gotta be a decent smoke with the T'wreck background.
