Plant density and nutrient availability constrain constitutive and wound-induced expression of trypsin inhibitors in Brassica napus

We investigated the effects of plant density on plant size, leaf total solu ble protein content, and constitutive and wound-induced levels of proteinac eous trypsin inhibitors in pot-grown Brassica napus seedlings in two greenh ouse studies. We manipulated plant density by varying the number of intrasp ecific neighbors surrounding a target plant in the center of each pet. In g eneral, constitutive and induced levels of trypsin inhibitors were signific antly reduced by competition in a density-dependent manner, to the extent t hat induction was greatly reduced or abolished in target plants surrounded by six neighbors. To investigate whether the effects of plant density on in hibitor production were mediated by nutrient availability, we manipulated t he concentration of a complete fertilizer applied to target plants surround ed by six neighbors in two greenhouse studies. In general, constitutive and wound-induced levels of inhibitors in plants surrounded by six neighbors w ere increased by nutrient addition in a dose-dependent manner, such that wo und-induction was completely restored in competing plants under conditions of high nutrient availability. Leaf total soluble protein content, measured only in the second trial of each experiment, was not affected by any of th e treatments. The effects of plant density, nutrient addition, and wounding on inhibitor levels in all experiments were independent of their effecs on above-ground plant size at the time of wounding. Overall, our results sugg est that decreasing nutrient availability mediates the density-dependent re ductions in inhibitor levels in B. napus seedings.