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Ethylene production rates and tissue ethylene concentrations were determined for the single-gene, Epinastic (Epi) tomato (Lycopersicon esculentum Mill.) mutant, and its parent, cv VFN8. The Epi phenotype was characterized by severe leaf epinasty, thickened stems and petioles, and a compact growth habit. In 4-day-old seedlings, ethylene production was significantly higher in Epi than in VFN8. Ethylene production rates also were higher for excised root, hypocotyl, cotyledon, and shoot tissue of 14-day-old Epi seedlings as compared with VFN8. The greatest difference in the ethylene production rate was observed in excised Epi shoot tissue, which was more than 2.5 times higher than in VFN8. Tissue ethylene concentrations of 19-, 25-, and 31-day-old Epi plants were 8, 172, and 307% higher than for VFN8, corresponding to increasing expression of the Epi phenotypic characteristics with age. The highest ethylene concentrations occurred in the shoot apex of both genotypes. Higher ethylene concentrations in Epi resulted from greater 1-aminocyclopropane-l-carboxylic acid content rather than increased ethyleneforming enzyme activity. The elevated ethylene levels in Epi did not result from increased auxin sensitivity. The sensitivity of root growth to inhibition by ethylene did not differ between VFN8 and Epi. Although elevated levels of ethylene in Epi plants apparently exacerbate its epinastic growth characteristics, other evidence indicates that this may not be the fundamental lesion. This mutant may provide a unique system for investigating the regulation of ethylene biosynthesis and the role of target cell types in plant development.

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ABSTRACIEndogenous indoleacetic acid (IAA) levels were examined in 7-dayold, dark-grown tomato seedlings (Lycopersicon esculentum Mill. cv VFN8), and in two single-gene mutants, Epinastic and diageotropica. Gas chromatography-mass spectrometry was employed to quantify IAA using '3C6-Ibenzene ringlindoleacetic acid as internal standard. IAA concentrations ranged from 89 to 134 nanograms per gram dry weight and were not significantly different for the three genotypes. Ethylene overproduction by dark-grown Epi seedlings is not likely to result from increased IAA. Assuming similar recovery percentages for each genotype, indole-3-ethanol, a purported storage form of IAA, was identified by GC-MS and found to be more prevalent in the parent tomato, VFN8, with only trace amounts observed in Epi. No IEt was detected by high performance liquid chromatography/fluorescence in dgt (detection limit >100 picograms).The Epi2 tomato mutant is characterized by extreme leaf epinasty, thickened stems and petioles, a shortened and highly branched root system, and a very compact and erect growth habit (7,22 In contrast, the dgt mutant, which is derived from the same parent line as Epi, has reduced auxin sensitivity with respect to hypocotyl elongation (9) and ethylene production (3,8, 30). This suggests that like Epi, dgt also possesses altered target cell responses.We believe these mutants represent a useful genetic system for investigating the mechanisms of auxin perception and action. However, in order to fully interpret the responses to exogenous auxin application, it is imperative to determine the endogenous IAA levels ofthe three genotypes. Therefore, we have investigated the levels of LAA in shoot apices of 7-d-old, dark-grown seedlings of VFN8, and its two mutants, dgt and Epi. Free IAA levels were found to be similar among the three genotypes suggesting that the epinastic phenotype was not the result of IAA induced ethylene production. A second fluorescent compound which eluted just after IAA during HPLC purification did appear to differ in relative amounts between the three genotypes. This compound was identified by GC-MS as indole-3-ethanol.MATERIALS AND METHODS Plant Material. Tomato (Lycopersicon esculentum Mill.) seeds of cultivar VFN8 and the two mutants Epi and dgt were surfacesterilized for 45 min in 40% commercial bleach and rinsed with 3 L of distilled water. Seeds were sown onto moist filter paper in 11 x 11 x 3 cm plastic germination boxes, covered, and placed in the dark at 24C. On d 7, SAs were harvested under a greensafe light and immediately frozen in liquid nitrogen. The tissue was then transferred to a 300 mL freeze-drying flask which was placed in the dark into a modified, refrigerated, recirculating bath (Lauda K-4/R) at -9°C. The flask was then connected to a 780 www.plantphysiol.org on May 11, 2018 -Published by Downloaded from