ALLOCATION OF NITROGEN TO AN INDUCIBLE DEFENSE AND SEED PRODUCTION INNICOTIANA-ATTENUATA

Resource-based tradeoffs in the allocation of a limiting resource are commonly invoked to explain negative correlations between growth and d efense in plants, but critical examinations of these tradeoffs are lac king. To rigorously quantify tradeoffs in a common currency, we grew N icotiana attenuata plants in individual hydroponic chambers, induced n icotine production by treating roots with methyl jasmonate (MJ) and st andardized leaf puncturing, and used N-15 to determine whether nitroge n-based tradeoffs among nicotine production, growth, and seed producti on could be detected. Plants were treated with a range of MJ quantitie s (5, 45 or 250 mu g plant(-1)) to effect a physiologically realistic range of changes in endogenous jasmonic acid levels and increases in n icotine production and accumulation; MJ treatments were applied to the roots to target JA-induced nicotine production, since nicotine biosyn thesis is restricted to the roots. Leaf puncturing and 5 mu g MJ treat ments increased de novo nicotine synthesis and whole-plant (WP) nicoti ne pools by 93 and 66%, while 250 mu g MJ treatments increased these v alues 3.1 and 2.5-fold. At these high rates of nicotine production, pl ants incorporated 5.7% of current nitrogen uptake and 6.0% of their WP nitrogen pools into nicotine. The N-15-labeled nicotine pools were st able or increased for the duration of vegetative growth, indicating th at the N-nicotine was not metabolized and re-used for growth. Plants w ith elevated nicotine production grew more slowly and the differences in plant biomass gain between MJ-treated plants and controls were line arly related to the differences in nicotine accumulation. Despite the reductions in rosette-stage growth associated with nicotine production , estimates of lifetime fitness (cumulative lifetime seed production, mass/seed, seed viability) were not affected by any treatment. Only tw o treatments (leaf puncturing and 250 mu g MJ) increased the allocatio ns of N-15 acquired at the time of induction to seed production. On av erage, plants used only 14.9% of their WP nitrogen pool for seed produ ction, indicating that either the nitrogen requirements for seed produ ction or the reproductive effort of these hydroponically-grown plants are low. To determine if seed production is strongly influenced by the amount of vegetative biomass attained before reproduction, the experi ment was repeated with plants that had 44% of their leaf area (or 29% of their WP biomass) removed before MJ treatments with a removal techn ique that minimized the nicotine response. MJ treatments of these plan ts dramatically increased nicotine production and accumulation, but th ese plants also suffered no measurable fitness consequences from eithe r the leaf removal or MJ treatments. We conclude that when N. attenuat a plants are grown in these individual hydroponic chambers, their allo cation to reproduction is sufficiently buffered to obscure the large i ncreases in nitrogen allocations to an inducible defense. To determine whether soil-grown plants are similarly buffered, we grew two genotyp es of plants in the high-nutrient soil from a 1-year-old burn in a pin yon-juniper forest (the plants' natural habitat) and in low-nutrient s oil from an adjacent unburned area, and induced nicotine production in half of the plants with a 500 mu g root MJ treatment. Plants grown in burned soils had an estimated lifetime fitness that was on average 2. 8-fold greater than that of plants grown in unburned soils. MJ treatme nt reduced fitness estimates by 43% and 71% in the burned and unburned soils, respectively. We conclude that while hydroponic culture allows one to rigorously quantitate nitrogen allocation to growth, reproduct ion and defense, the allocation patterns of plants grown in hydroponic culture differ from those of plants grown in soil. Under hydroponic c onditions, plants have low reproductive allocations and reproductive-d efense tradeoffs are not detected. Reproductive-defense tradeoffs are readily discernible in soil-grown plants, but under these growing cond itions, the nitrogen-basis for the tradeoff is difficult to quantify.