Characterization of an Ethylene Overproducing Mutant of Tomato (Lycopersicon esculentum Mill. Cultivar VFN8)

Abstract

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.

Ethylene Plays Multiple Nonprimary Roles in Modulating the Gravitropic Response in Tomato1

“…This finding is in agreement with observations that hypocotyls are the tissue least affected by the epi lesion and the only organ tested that does not overproduce ethylene (Fujino et al, 1988). The morphology of epi seedlings is strikingly similar to a constitutive ethylene response in many respects, including thicker and shorter hypocotyls ( Fig.…”

“…The epi mutant was reported to overproduce ethylene in all tissues except hypocotyls (Fujino et al, 1988). Our results confirm this finding for the most part.…”

“…2). The epi mutant was previously shown to overproduce ethylene (Fujino et al, 1988), whereas nr is an ethylene-insensitive mutant (Wilkinson et al, 1995). Curvature of both mutants in response to gravistimulation is delayed in comparison with wild-type seedlings, with the epi phenotype being much more severe than that of nr (Fig.…”

“…To this end, we used two tomato mutants with altered gravitropic responses: the auxin-resistant dgt mutant (Kelly and Bradford, 1986;Hicks et al, 1989), which exhibits a reduced gravitropic response , and the lz-2 (lazy-2) mutant in which the direction of shoot gravitropism is reversed in a phytochromedependent manner . We also investigated whether two tomato mutants altered in their ethylene physiology, the ethylene-overproducing epi (epinastic) mutant of tomato (Fujino et al, 1988) and the ethylene-insensitive nr (never-ripe) mutant (Wilkinson et al, 1995;Yen et al, 1995) exhibit alterations in their gravitropic response mechanism. Taken together, the results from these experiments lead us to propose that ethylene plays multiple, but not primary, roles in modulating the gravitropic response in tomato.…”

Ethylene Inhibitors Restore Nodulation to sym 5 Mutants of Pisum sativum L. cv Sparkle

“…Plant developmental mutants altered in their response to ethylene have been reported (16). Some mutants overproduce ethylene and show the classic triple response syndrome (7,18), whereas other mutants appear insensitive to exogenous ethylene (2,10).…”