forward-looking that his model is as valid today as it was before the field of epigenetics was even established. We apply this principle when


propagating grapes. We don't use specialized cells such as a leaf blade or tendril, we use (mostly) mature woody canes, or in the tissue culture lab we use the shoot tip, a meristem. The important part of the woody cane for propagation is the cambium layer, just below the bark. The cambium is the layer that contributes


to the annual growth of a grape cane and is fairly close to the top of Waddington's Landscape. If the foot of a cane is kept warm


and moist for a few weeks, the cambium cells will divide and form a small mass of undifferentiated cells, referred to as callus. The cutting can then be planted and the callus will differentiate into roots. Buds on the cane send out shoots, and the whole process of creating cell specialization starts over.


Conrad Waddington


The new cells have the ability to be any part of the plant because the silencing genes are gone.


One of the remarkable things about grapes is that they are easily propagated from cuttings. If grapes are grown from seed, the new plants express a random assortment of genes from each parent.


Even if both parents are from the same cultivar, there is enough variation that the offspring will be quite different from the parents. On the other hand, if a part of the vine can be chosen that is not yet specialized with a lot of silenced genes then the vine can be cloned. Fifty years ago a biologist, Conrad Waddington, noted that the specialized cells of organisms went through a hierarchy of changes, starting from least specialized to more specialized (differentiated). He also observed that the more specialized a cell was, the more difficult it is to reverse that differentiation.


He likened the changes to rolling a marble down a hill. As the marble progresses down the hill, it has a choice of several pathways or gulleys, alternate courses of differentiation. The model continues its analogy in that movement from one gulley to the other is difficult and movement back up the hill becomes more difficult the further down the hill the marble progresses. The model is known as


Waddington's Landscape. He was so 20


British Columbia FRUIT GROWER • Fall 2014


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