Regulatory mechanisms of tryptic inhibitory activity in cabbage plants

Tryptic inhibitory activity in cabbage (Brassica oleracea cv Superpack) foliage was primarily regulated by developmental factors. Low, background levels of tryptic inhibitory activity were present in the succulent foliage of the cabbage seedling. As the plant matured, all the leaves (young and mature) began to toughen. At the time of leaf toughening, the tryptic inhibitory activity significantly increased in the young foliage. After the transition from succulent to tough leaves, the level of tryptic inhibitory activity significantly increased in young and mature leaves as the plant aged, reaching a maximum in the young foliage on plants with solid cabbage heads. Environmental stresses such as pot-bound roots and acute exposure to high intensity lighting, had no significant affect on foliar tryptic inhibitory activity. Acute wounding of leaves that were succulent or in transition from succulent to tough, resulted in a significant increase in their tryptic inhibitory activity. However, wounding of one leaf did not significantly increase the tryptic inhibitory activity in adjacent leaves on the same plant.