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Biochemical characteristics of fresh roots of transgenic high Beta-carotene cassava
Abstract
Recent research efforts have developed high beta carotene or yellow cassava roots through genetic engineering and conventional breeding. Beta-carotene pigments are biosynthesized through a cellular isoprenoid pathway. In this study, biochemical techniques and microscopy were employed in determining beta-carotene distribution and metabolic isoprenoid pathway in fresh transgenic and conventionally bred high beta-carotene cassava roots. Transgenic high beta-carotene cassava varieties (EC20-7 and EC20-8) were compared with two conventionally bred high beta-carotene cassava varieties (UMUCASS 38 and UMUCASS 45) and an indigenous white fleshed cassava variety (TME-7). These five cassava varieties were planted in environmentally controlled greenhouse and harvested after four months. Results showed that the dry matter content of UMUCASS 38 (35.61 %) and UMUCASS 45 (36.96 %) were significantly (P<0.05) different from EC20-7 (24.23 %), and EC20-8 (23.18 %). β-carotene content on dry matter basis of the fresh yellow cassava roots (50.93 - 80.45µg/g) was not significantly (P>0.05) different between the transgenic and conventional varieties The observed carotenoids in this study were biosynthesized from isopentenyl diphosphate and its isomer dimethylallyl diphosphate. All the varieties, especially the EC20-8 transgenic variety, had appreciable levels of methyl-D-erythritol 4-phosphate. Microscopic analysis showed the distribution of carotenoids in the cortex, parenchyma and the xylem bundles. Carotenoids were not observed in the sclerenchyma, therefore, peeling of yellow cassava varieties during processing will not necessarily cause any loss in the carotenoid contents
Keywords: Cassava, Beta-carotene, fresh roots
