This tree (see photo) has both variegated and normal leaves, with leaves of both types on the same branch. Can anyone explain this distribution of different leaves on the same plant?
鈥� The form of variegation in this maple tree is called a periclinal chimera. Leaves consist of several layers of cells, each of which develops separately, without mixing cells between layers. In variegated leaves of this type, there is a green inner layer covered by a white outer layer, much like a green hand in a white glove.
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This entire tree is a combination of cell layers containing either the genes for normal green leaves or genes with a mutation that can鈥檛 make the green pigment chlorophyll. When leaves are very young, they consist of only a few cells in a growth tip (the meristem). The cell that will become the outer layer of the leaf comes from the outer layer of the twig, and if it contains the mutation, the layer will be white.
But in this early stage of development, cells can accidentally end up in a different layer. That way you can get solid green leaves or completely white leaves. Maple leaves have three cell layers, so even more variation is possible 鈥� if the outer layer is white it will give the leaf a narrow white edge; but if both outer layers are white the leaf will have a wide white edge.
If you want to propagate such a tree, you have to make sure you take a cutting from a twig that has variegated leaves. If you take it from a green-leaved one, the resulting tree will have only green leaves.
Seeds are formed from just one of the layers, so seedlings from these variegated trees are usually solid green. Any solid white ones won鈥檛 survive.
Margareth Hop Nursery stock breeder The Netherlands
鈥� There are two other possibilities for the outcome seen in the photo. The tree may have been infected by a virus that is causing the variegation and this virus may be affecting only parts of the tree. Or the variegated branches could be the result of grafting. Grafting is a technique commonly used by gardeners to reproduce ornamental varieties of plants that cannot be grown from seed. In such a situation, the graft is attached to root stock from a closely related plant. Without pruning, the root stock can also produce branches that appear different to the graft 鈥� in this instance the variegated branches could be from a graft and the ordinary green branches could be from the root stock.
鈥淭he tree may have been partly infected by a virus that is causing the variegation鈥�
Adrian Clayton Biology and Environmental Studies The Sixth Form College Farnborough, Hampshire, UK
鈥� Plants with variegated leaves are often special varieties bought from garden centres or plant nurseries 鈥� they have less light-energy absorbing chlorophyll than their all-green relatives and so do not compete well in the wild. A variegated form generally first occurs as a 鈥渟port鈥�, a random genetic mutation. This could be the result of a stray cosmic ray hitting the DNA of a particular cell in a particular bud, which gives rise to a leaf 鈥� and eventually a whole branch 鈥� that is variegated.
If this is a desired trait, new individuals can be propagated by taking cuttings from the sport, and then cuttings can be taken from those and so on. The result is thousands of cloned individuals all having the same mutated genetic code. This is known as a cultivar.
It is common for these variegated clones to suffer a similar fate 鈥� a random genetic mutation that leads to a reversion to an all-green leaf. Hence you often find an all-green sport on an otherwise variegated plant. It is worth noting that the all-green sport will grow faster than the rest of the plant because it has more chlorophyll.
Nicholas Hall St Just, Cornwall, UK
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