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The present article reviews various evolutionary events that resulted in skin color variation among humans. Skin of the early man is presumed to be colorless as that of the chimpanzees. During the course of evolution, hairless state of skin with sweat glands would have occurred for the purpose of thermoregulation. Thermoregulation was very important for brain development and function. In due course, pigmentation occurred in the naked skin of man in order to offer photo-protection. The physiological demand of vitamin D3 and folate in human system and the effect of sun-light in their synthesis and metabolism would have further established some changes in the skin color of man in various geographic locations. Although genetics and physiological adaptations have determined human skin color in different groups/races, during the course of civilization, humans have developed a deep desire to change skin color. Current scientific research on development of novel agents for modulation of skin color is likely to benefit in pigmentary disorders and also in psychological well being through the use of cosmetics. [ABSTRACT FROM AUTHOR]

For successful transformation of a plant by Agrobacterium tumefaciens it is essential that the explant used in cocultivation has the ability to induce Agrobacterium tumour-inducing (Ti) plasmid virulence ( vir) genes. Here we report a significant variation in different tissues of Indica rice ( Oryza sativa L. cv. Co43) in their ability to induce Agrobacterium tumefaciens vir genes and T-strand generation, using explants preincubated in liquid Murashige and Skoog (MS) medium. An analysis of rice leaf segments revealed that they neither induced vir genes nor inhibited vir gene induction. Of different parts of rice plants of different ages analysed only scutellum from four-day old rice seedlings induced vir genes and generation of T-strands. We observed that the physical presence of preincubated scutella is required for vir gene induction. Conditioned medium from which preincubated scutella were removed did not induce the vir genes. Scutellum-derived calli, cultured for 25 days on medium containing 2,4-D, also induced virE to an appreciable level. These results suggest that scutellum and scutellum-derived calli may be the most susceptible tissues of rice for Agrobacterium-mediated transformation. [ABSTRACT FROM AUTHOR]