The importance of being red
Ursula Buchan
Hooray for anthocyanin. Where would we be without it? It has long been my favourite water-soluble, vacuolar, glucosidic pigment, and I feel that this autumn has justified my preference. True, chlorophyll is more important until then, being essential for photosynthesis, so we should all be in dead trouble without it; and the carotenoids, carotene and xanthophyll, are often more obvious to us, because of the delicious golden yellow to which many native shrubs — field maple, elm suckers, and blackthorn — turn in autumn. However, even at that time of year, anthocyanin just gets my vote, because it produces the most beautiful of crimson-lake and purple tints in aging leaves. My paperbark maple, Acer griseum (see picture), was remarkable for the depth and warmth of its leaf colour — until the gales in the second weekend in November stripped it almost bare, that is.
We gardeners talk of anthocyanin in the singular but, in truth, there are more than 300 different anthocyanin compounds. The distinctions matter only to scientists; we need only know that they occur in the tissues of a wide range of plants, and are responsible for purple and deep red colours in stem, leaf and fruit. It is thought that anthocyanins are ‘photo-protective’, in other words, they shield plant tissue from strong sunlight.
That is not the half of it, however, for it is now well-established that anthocyanins are powerful antioxidants, and that fruits and vegetables, which are high in them, help mammals to fight aggressive tumours, such as colon cancer, as well as heart conditions, diabetes and degenerative conditions associated with old age. What is more, you don’t have to be a plant scientist to work out which these fruit and vegetables might be: the deep-coloured ones like blackcurrants, blueberries, bilberries, cranberries, blackberries, raspberries, red grapes, purple-sprouting broccoli and red cabbage. (Beetroot, strangely, contains betanin rather than anthocyanin, but that is a distinction without a difference to us, since it is also an antioxidant.) Much of the research work on the cancerclobbering properties of anthocyanins has been done in the United States on a native plant called Aronia melanocarpa, or chokeberry. Melanocarpa means ‘black fruit’, although, as you would expect, they are actually deep purple.
It’s a mild mystery to me why aronias are not more commonly grown in British gardens, since they are hardy, not fussy as to soil, tolerate some shade, have very pretty white flowers in clusters in late spring, above oval leaves, on an erect plant growing six to ten feet tall. The shoots are thin and whippy, so they don’t make very dense shrubs, which can be handy. They all produce ample quantities of deep red (Aronia arbutifolia) or purple-black (Aronia melanocarpa) fruits in autumn, at the same time as reliable and impressive crimson, purple or scarlet autumn leaf colour. What is more, although tart when unripe (the reason why they are called chokeberries), the fruits can be eaten after cooking. A couple of aronias in the garden, together with a blackcurrant bush and two blueberry varieties in large pots filled with acid compost, constitute your own personal antioxidant manufactory.
Tomatoes, already important to human health because of their concentrations of the carotenoid, lycopene, could soon be even more valuable. Scientists at the John Innes Centre in Norwich have removed anthocyanin pigments from deep-red flowered snapdragons and implanted them into tomato plants, producing purple tomatoes thereby. These have concentrations of anthocyanins as high as anything that blackcurrants or blueberries can boast, it would seem. Look out, in future, for tomato varieties with names like — let us imagine — ‘Cardinal’ or ‘Deep Purple’.
All this is excellent news, but there is more, since anthocyanins contribute hugely to the aesthetics of gardening as well. I cannot imagine making a garden without deep red, purple or blue flowers, all of which contain these pigments; one without Dahlia ‘Arabian Nights’, Viola ‘Jackanapes’, Delphinium ‘Black Knight’ or Pelargonium ‘Lord Bute’, say. Can you?
In all honesty, however, I must admit that my attitude is not entirely positive. This is because the leaves of a substantial number of plants refuse to lose their springtime purpleness as the season wears on. By the end of summer, therefore, it is hard not to weary of the matt, stygian gloominess of the purple beech, Prunus cerasifera ‘Nigra’ or even Cotinus ‘Grace’. Fortunately, just when I have really had enough, carotenoids come to my rescue, combining with the anthocyanins to turn these leaves from deep, dead purple to invigorating, enlivening scarlet and bloodred. So all’s well that ends well. ❑
Previous page
