The Role of Pigments and the Putative Mechanisms Involved in Plants' Leaf Color Change and its Importance in Landscape

Plant pigments are chemical compounds that absorb or reflect light in visible spectrum. Four important plant pigments include chlorophylls, anthocyanins, carotenoids and betalains. Leaf color change is an amazing phenomenon on the earth which is spectacular especially during autumn in cool and temperate zones. Leaf color change is not merely restricted to deciduous species but also it occurs in evergreen species and new emerging shoots of both deciduous and evergreen ones. These changes are the consequence of very complex, harmonious and dynamic occurrences which are triggered by perception of some signals such as short days, low temperature and the increment of blue and violet wavelengths in autumn followed by extensive changes at cellular, molecular and ultimately gene expression. The interaction of some factors such as genetic base, growth and developmental stage, leaf life, day length, temperature, light intensity, UV, relative humidity, elevation, plant hormones, carbohydrates, minerals, pigment combination, co-pigments, metal ions, pH determine leaf color change. Reduction in auxin synthesis, the increase of ethylene and abscisic acid and the reduction of nitrogen and phosphorus are among internal changes occurring during leaf color change especially in autumn. Although, leaf color change in deciduous species is associated with senescence but this process is not necessarily related to senescence. It is generally accepted that leaf color change is closely linked with adaptation mechanisms against various stresses including light stress, UV, low and high temperature, herbivory. Color is an important element in landscape design. Therefore, plant species particularly trees and shrubs with colored leaves or elegant autumn are very important from aesthetic perspective and are extensively used for landscape purposes worldwide. Furthermore, leaf color change is significant from economic viewpoint and in some regions of temperate zones, a considerable income is obtained due to tourism importance of deciduous forests.