Fig. 1.

Axenic H. actites and A. thaliana use external protein for growth. (A and B) Root and shoot dry weight and nitrogen content of Hakea seedlings grown without nitrogen, with protein, or with inorganic nitrogen; 30 mg of nitrogen was supplied to each plant as protein or inorganic nitrogen (17 mM protein nitrogen as BSA or 17 mM inorganic nitrogen as NH₄NO₃). (C and D) Arabidopsis dry weight and nitrogen content grown without nitrogen or with nitrogen supplied as protein (1.5 or 6 mg BSA per ml), inorganic nitrogen (0.04 or 0.4 mg NH₄NO₃ per ml), or protein and inorganic nitrogen combined (5.4 mg BSA per ml and 0.04 mg NH₄NO₃ per ml). Bars represent averages and SD of five to eight Hakea plants and 7–10 plates with ≈80 Arabidopsis plants per plate (see also Fig. 2). Different letters indicate significant differences at P < 0.05 (Hakea) and P < 0.01 or P < 0.001 (Arabidopsis) (ANOVA, Neuman–Keuls post hoc test; data were log-transformed before analysis to account for different variances between groups).