Environmental and developmental regulation of trypsin inhibitor activity in Brassica napus

We examined several environmental and developmental influences on trypsin i nhibitor (TI) activity in leaves of young Brassica napus seedlings in a ser ies of greenhouse experiments. In seedlings of B. napus cv. Westar, TI acti vity is constitutively present and exhibits a rise then fall through time i n the first true leaves of young plants. TI activity is induced by wounding in the first true leaves, but the degree of induction is relatively insens itive to the degree of wounding over a gradient of 5-15% of leaf area damag e. TI activity is enhanced in first true leaves of plants in which the coty ledons have been wounded relative to plants in which the cotyledons have no t been wounded. TI activity is also enhanced in the second true leaves on p lants in which the first true leaves have been wounded. The degree of syste mic induction in second true leaves declines additively with plant age, bur local induction in the first true leaves is not affected by age. In B. nap us cv. Gido, TI activity is constitutively present but is not locally wound -inducible in first true leaves of young plants exposed to the same woundin g gradient as cv. Westar. In unwounded plants at the six-leaf stage, TI act ivity is higher in second true leaves than in fifth true leaves, indicating that TI activity is developmentally regulated in this cultivar.