Wound-induced Proteinase Inhibitor in Tomato Leaves

Abstract

Wounding of single leaflets of young tomato (Lycopersicum esculentum var. Bonnie Best) plants causes the release of a proteinase inhibitor inducing factor. This factor is rapidly transported throughout the plant where it causes accumulation of inhibitor I, a potent inhibitor of several serine proteinases from both animals and microorganisms. The wound-induced accumulation of inhibitor I is both light-and temperature-dependent. In total darkness no accumulation results from wounding. The accumulation exhibits a linear dependence upon light up to 300 foot candles. At 600 foot candles and above, the response is maximal. In light the wound response possesses an unusual temperature dependence with an optimum rate of accumulation near 36 C. Below 20 C no accumulation occurs. The overall process contains two light-and temperature-dependent steps, one involving wounding and transport, the other involving accumulation. day and 30 C with a night time temperature of 18 C. Plants were fertilized weekly with approximately one-half gram of fertilizer (18-18-18) per peat pot. The plants under study were from 2 to 3 weeks after emergence, 6 to 10 cm in height, and had three well developing leaves and a small apical leaf. Plants were wounded by crushing single leaves between a wooden dowel 0.8 cm in diameter and a rat tail file as previously described (1). This gave a uniform size wound that resulted in the production of inhibitor I. For the experiments described herein the lowest leaf was wounded five times near or on the main vein to elicit a maximal response without completely destroying the leaves. After wounding, the plants were incubated in a growth chamber at varying light intensities and temperatures for appropriate intervals as described in the text. For each experimental point shown from six to ten plants were utilized. Light intensities were controlled by varying the distance between plants and fluorescent light fixtures and by Our search (4) for the role of proteinase inhibitors in vegeta-tive plant tissue has recently resulted in the discovery that an inhibitor of chymotrypsin and trypsin, called inhibitor I, is produced in leaves throughout the plants in large quantities in response to insect or mechanical wounding of single leaves (1). The accumulation of inhibitor is apparently an immune response, directed against insects or microbes, that is mediated by a hormone-like factor released from the wound site called PIIF.4 We here report the conditions of light and temperature that contribute to the wound response. MATERIALS AND METHODS Young tomato plants (Lycopersicum esculentum var. Bon-nie Best) were utilized 25 to 30 days after planting. The seeds were germinated in peat pots in a headhouse without regard to lighting. Upon germination they were transferred to a growth chamber and maintained at 1000 ft-c under a 14-hr I