Quantification of Cry 1Ac protein in two field-grown Bt (Bacillus thuringiensis) cotton hybrids (MECH-184, RCH-2) was performed in relation to tissue maturity. Leaves of upper, middle and lower canopies and in bolls and bracts attached to the plant were chosen. Similar measurements were also made in fully mature tagged leaves attached to plants in the upper canopy and excised leaf discs. The leaf discs were incubated in the dark following the ELISA method with commercially available kits. Cry 1Ac levels declined with tissue maturity and senescence in both attached and excised plant parts of the Bt cotton hybrids examined. With advancing maturity in leaves attached to the plants till 21 days, steady increase in the levels of chlorophyll and decrease in the amounts of total protein were observed. Moreover, with increasing maturity, the concentration of reducing sugars rise in contrast to decline in total soluble amino acids. On the other hand, in case of the excised leaf discs, while total soluble amino acids exhibited an increasing trend, chlorophyll, total protein and reducing sugar contents decreased gradually.
Key words: Bt cotton, senescence, ELISA, Cry 1Ac insecticidal protein, amino acids, reducing sugars, chlorophyll.
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