Lignin composition in leaf, fruit, and fruit outer epidermis of transgenic tomato (Lycopersicon esculentum Mill.) plants that overproduce the enzyme tobacco anionic peroxidase (TobAnPOD) was analyzed. This enzyme may catalyze the polymerization of cinnamyl alcohols into lignin in tobacco (Nicotiana tabacum L.); therefore, we predicted that its presence in the transformed tissue would increase lignin levels in healthy and wounded tissue. Lignin levels in healthy plants increased by 20% in leaf, 49% in fruit, and 106% in fruit outer epidermal tissue. Mature-green fruit were aseptically wounded and incubated in darkness for up to 7 days. Soluble phenols in wounded transgenic fruit increased by more than 300% hut changed little in control fruit. As with soluble phenols, lignin content in wounded transformed fruit increased by more than 20-fold hut increased less than two-fold in control fruit. Transgenic seedlings overproducing TobAnPOD were screened for susceptibility to several pathogens, but resistance did not increase. Possible TobAnPOD roles in lignin biosynthesis, phenol metabolism, stress response, and disease resistance are discussed.
L. Mark Lagrimini, Jill Vaughn, W. Alan Erb, and Sally A. Miller
L. Mark Lagrimini, Jill Vaughn, John Finer, Karen Klotz, and Patrick Rubaihayo
Tomato plants (Lycopersicon esculentum cv. OH 7814) were transformed via Agrobacterium tumefaciens with a chimeric tobacco anionic peroxidase (EC 126.96.36.199) gene joined to the cauliflower mosaic virus (CaMV) 35S promoter. Transgenic plants obtained by selection on kanamycin were found to have more than five times the total leaf peroxidase activity of control plants. Transformed tomato plants chronically wilted upon reaching sexual maturity. Two independently selected transformants were self-fertilized, and progeny were obtained that were homozygous for the foreign gene. Isoelectric focusing gels stained for peroxidase activity revealed a new tomato leaf peroxidase isoenzyme with a pI of 3.75, which is similar to that seen in Nicotiana sylvestris L. Mature tomato fruit were found to have up to 1600-fold higher peroxidase activity in transformants expressing the tobacco anionic peroxidase (TobAnPOD) than control plants. Tissue blots showed the tobacco enzyme evenly distributed throughout the tomato fruit tissue. Progeny plants possessing the tobacco peroxidase gene (now homozygous) showed stunting, and fruit size was reduced by >80%. However, fruit set was normal and the rate of ripening was not altered from control plants. Fruit from transformed plants were found to have normal pigmentation, but the soluble solids concentration was 400% higher than in control tomato fruit. This result was predicted from the peroxidase-induced water stress. Possible roles for the tobacco anionic peroxidase in growth, development, and stress resistance are discussed.