William Sutherland Protection from Hostile Environments
“When leaves receive more light energy than can be used in photochemistry, they show a characteristic decline in the quantum efficiency of photosynthesis, termed photoinhibition. Under severe conditions [critical leaf structures such as chloroplasts, thylakoid membranes (the area where photons from sunlight initiate photosynthesis), DNA, and proteins essential for photosynthetic activities can be harmed or destroyed].”23
Anthocyanins, through their absorption of blue-green light, “have been shown to protect plants from excess light during periods of high light stress (as occurs when plants are exposed to high light in combination with drought or cold temperatures)”24 by providing a physicochemical barrier to protect a leaf’s chloroplasts and other critical structures. “Chloroplasts irradiated with light that has first passed through a red filter have been shown to generate fewer superoxide radicals (highly oxidized compounds)” that could damage a plant’s “photosystems (group of structures that perform photosynthesis)” 25 and impair its ability to transfer and use necessary sugar (glucose) to sustain its metabolism.
Numerous studies have shown that anthocyanins can effectively “reduce both the frequency and severity of photoinhibition [and] expedite photosynthetic recovery. [For example] in red-osier dogwood (Cornus stolonifera), a 30-minute exposure to strong white light [was found to have reduced] the quantum efficiency of photosynthesis by 60% in red leaves [and] by almost 100% in acyanic leaves (those without anthocyanins). [Then] when the plants were returned to darkness, the red leaves recovered to their maximum [photosynthetic] potential after… 80 minutes [while] their acyanic counterparts [still had not fully recovered] after six hours.”26
Another study involving the Setcreasea purpurea, a plant that can grow well under both extremely low light and high light conditions also illustrated anthocyanins’ ability to provide protection from extreme or high light conditions. When Setcreasea purpurea plants were kept in low light conditions, they did not synthesize anthocyanins. Accordingly their leaves were green. However, when these same plants were exposed to bright light conditions, they defensively accumulated anthocyanins in the epidermal layer of their leaves, transforming their color of their leaves to red. Accordingly, when the epidermal layer
7
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149