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Anatomical features of leaf variegation in coffee plants

Two different types of leaf variegation in coffee plants are studied on the anatomical viewpoint, and their histological differences are described, when compared with normal, green leaves. In the first case, variegated leaves are normal in shape and texture, and show different variegation patterns, being histologically identical with green leaves of normal plants. The variegation seems to be due to disturbances in the chlorophyll-producing mechanism, resulting in the formation of large, green and normal chloroplasts, aad small, yellowish and abnormal chloroplasts. The distribution at random of cells having one of these two kinds of chloroplasts can be accounted for the different variegation patterns observed. In the second example, the variegation pattern is uniform throughout the entire plant, and is a more complex phenomenon, since besides being variegated the leaves present several malformations. The anatomical study has revealed that, in this case, the chloroplasts are always normal, the variegation being rather due to the presence of an 1-3-layered hialine hypodermis, which occurs right beneath the upper epidermis. The malformations, represented by abnormalities in the shape and texture of the leaf blade, are mainly due to the lackness of a true palisade parenchyma. This tissue shows all grades of disorganization in the various portions of the leaf, being sometimes present as small patches or palisade cells or lacking completely in other instances. It is suggested that disturbances of any kind should have occurred during the ontogenetical development of the leaf blade, leading the upper protoderm to divide periclinally, and thus giving origin to the 1-3-layered hypodermis, and preventing also the formation of a true palisade parenchyma. The great activity of the shoot apex of this coffee plant, as revealed by its shorter piastochron and more frequent plastochronic changes, has led the plant to a more intensive vegetative growth, and is an evidence to support the hypothesis of the disturbance occurrence during leaf development.


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