Stress-induced Ethylene Production in the Ethylene-requiring Tomato Mutant Diageotropica

Abstract

Ethylene synthesis in vegetative tisues is thought to be controlled by indoleacetic acid (IAA). However, ethylene The diageotropica (dgt) mutant of tomato is characterized by its diageotropic habit in both shoots and roots, dark green hyponastic leaves, and lack of lateral roots. These phenotypic characters are pleiotropic effects of a single gene mutation in the parent variety VFN8 (13). Zobel (14) reported that ethylene concentrations as low as 5 nl 1-1 would completely normalize the mutant. IAA would also restore the normal morphology, but dgt was 10 times less sensitive to the auxin than was VFN8. Zobel (14) suggested that the aberrant phenotype of dgt might be due to this reduction in auxin-induced ethylene synthesis. When wounded by excision, tissues of both dgt and VFN8 produced a burst of "stress ethylene." These observations suggest that IAA is not involved in the production of wound ethylene.Waterlogging is also known to increase ethylene synthesis in tomato (2,6). It has recently been demonstrated that the stimulation of ethylene synthesis in waterlogged plants is due to export of an ethylene precursor, ACC2, from anaerobic roots (3). Anaerobic stress accelerates synthesis and accumulation of ACC in the roots, and ACC is transported in the xylem to the shoot where it is rapidly converted to ethylene. It has been proposed that IAA induces the synthesis of the enzyme which converts SAM to ACC in mung bean hypocotyls (11,12). Little is known, however, about the regulation of stress ethylene synthesis (10).In this paper, ethylene production rates in response to waterlog-

Insensitivity of the Diageotropica Tomato Mutant to Auxin

“…1). The stimulation of ethylene synthesis by FC in both dgt and VFN8 tissues (Table III) is consistent with the conclusion that the mutant's ethylene-synthesizing capacity is normal except for reduced response to auxin (3,5). As dgt tissues readily convert ACC to ethylene (3), it is apparently the induction of ACC synthase which is insensitive to IAA (24).…”

“…The stimulation of ethylene synthesis rates by FC in both VFN8 and dgt hypocotyls was completely inhibited by AVG (Table III). (3,5,27) that the dgt mutant has reduced sensitivity to IAA as an inducer of ethylene synthesis compared to its parent line, VFN8 (Fig. 1).…”

“…plants (3,5). In addition, the induction of ethylene synthesis in dgt by wounding or anaerobiosis was apparently normal (3,5).…”

“…In addition, the induction of ethylene synthesis in dgt by wounding or anaerobiosis was apparently normal (3,5). Thus, the fundamental genetic lesion of dgt does not simply result in an inability to synthesize ethylene.…”

“…The failure of auxin to induce ethylene synthesis in dgt tissues could be due to altered regulation ofthe expression ofthe gene(s) encoding the rate-limiting enzyme, ACC synthase (3,24). Alternatively, the ineffectiveness ofIAA in inducing ethylene synthesis may be only one manifestation of a more general insensitivity of dgt plants to IAA.…”