WOUND-INDUCED CHANGES IN ROOT AND SHOOT JASMONIC ACID POOLS CORRELATEWITH INDUCED NICOTINE SYNTHESIS IN NICOTIANA-SYLVESTRIS SPEGAZZINI AND COMES

Leaf damage by herbivores in Nicotiana sylvestris Spegazzini and Comes (Solanaceae) produces a damage signal that dramatically increases de novo nicotine synthesis in the roots. The increased synthesis leads to increases in whole-plant nicotine pools, which in tum make plants mor e resistant to further herbivore attack. Because signal production and the response to the signal occur in widely separated tissues, the spe ed with which different damage signals exit a damaged leaf can be stud ied. We propose that electrical damage signals should exit a leaf fast er (less than 60 min) than chemical damage signals. Excision of a leaf induces a smaller increase in nicotine production than does puncture damage, so we examined our proposition by excising previously puncture d leaves at 1, 60, and 960 min after leaf puncture and quantifying the induced whole-plant nicotine pools six days later when the induced ni cotine production had reached a maximum. Significant induced nicotine production occurred only if punctured leaves were excised more than 1 hr after puncture, which is consistent with the characteristics of a s low-moving chemical signal rather than a fast-moving electrical signal . We explore the nature of the chemical signal and demonstrate that ad ditions of 90 mug or more of methyl jasmonate (MJ) in an aqueous solut ion to the roots of hydroponically grown plants induce de novo nicotin e synthesis from (NO3)-N-15 in a manner similar to that induced by lea f damage. We examine the hypothesis that jasmonic acid (JA) functions in the transfer of the damage signal from shoot to root. Using GC-MS t echniques to quantify whole-plant JA pools, we demonstrate that leaf d amage rapidly (<0.5 hr) increases shoot JA pools and, more slowly (<2 hr), root JA pools. JA levels subsequently decay to levels found in un damaged plants within 24 hr and 10 hr for shoots and roots, respective ly. The addition of sufficient quantities (186 mug) of MJ in a lanolin paste to leaves from hydroponically grown plants significantly increa sed endogenous root JA pools and increased de novo nicotine synthesis in these plants. However, the addition of 93 mug or less of MJ did not significantly increase endogenous root JA pools and did not significa ntly affect de novo nicotine synthesis. We propose that wounding incre ases shoot JA pools, which either directly through transport or indire ctly through a systemin-like signal increase root JA pools, which, in tum, stimulate root nicotine synthesis and increase whole-plant nicoti ne pools.