NOTES ON THE DISTRIBUTION OF PHYTOMELANIN LAYER IN HIGHER PLANTS –A SHORT COMMUNICATION
B. Ramya Sree
Department of Biotechnology, Sree Vidyanikethan Engineering College, Tirupati
Jyothi M. Joy
Department of Pharmacognosy, Sree Vidyanikethan College of Pharmacy, Tirupati
Phytomelanin layer is constituted by a unique type of hard, black, water and acid resistant carbonized or resinous or tanniniferous or polyvinyl alcohol containing disputed phytomelanin substance usually found in the cypselar wall or pericarp of some members of the family Asteraceae belonging to the tribes Helenieae, Heliantheae, Eupatorieae, Tageteae, Millerieae, Perityleae etc. Not only in the family Asteraceae, it is also present in some other families such as Agavaceae, Aloaceae, Amaryllidaceae, Hyacinthaceae, Convolvulaceae. Indeed, the pigment was highly stable in acidic solutions, slightly soluble in dimethyl sulfoxide (DMSO), bleachable with H2O2 or NaOCl and extractable in alkaline solution, and the crude dark-brown materials were precipitated when the alkaline solution was adjusted to pH 2 by adding HCL,which are characteristics of melanins in fungi and plants. Phytomelanin develops in schizogenous spaces in the cypselar wall specially in mesocarpic region after post fertilization changes of the cypselar wall development. In case of immature cypselas, this layer is very softly developed but in mature condition, it becomes dense and rigid. According to the observation of Hanausek, this layer is exists into a space between the hypodermis and fibre layer. According to the observation of Misra, Pandey & Sing, this substance is thought to be exudates from hypodermis. According to the observation of Sarkany, this layer is appear by the hydration of carbohydrates of the cells of hypodermis. Although, the term phytomelanin is used to denote the black coloured exudates in different tissues of certain plant families, but their nature and similarity with the family Compositae is not clear, till now. It acts as a protective layer of the pericarp, which protects the developing embryo from external invasion of insects, pests and other macro - micro - organisms. Since a pairs of dominant genes or allele control distribution of phytomelanin layer, so it has significant importance in tribal and subtribal classification as well as evolutionary significance in Asteraceae. Phytomelan layer in mature pericarpic zone exists either as a continuous ring or usually found as a discrete bundles with variable thickness, depends on the maturity of cypselar wall development as well as its genetic constitution. In majority of the taxa, distribution of phytomelanin layer is noticed just below the epicarpic region. There are few other taxa, where it has been noticed in different depth of the mesocarpic region of pericarp.
4 , 3 , 2014
131 - 132