Insensitivity of the Diageotropica Tomato Mutant to Auxin

Abstract

The sensitivity of excised hypocotyl segments to indoleacetic acid (IAA) in two assays, ethylene production and elongation, was determined in the ethylene-requiring tomato (Lycopersicon esculentum Mill.) mutant, diageotropica (dgt), and its isogenic parent, cv VFN8. Endogenous (uninduced) ethylene synthesis rates were slightly lower in dgt hypocotyls than in VFN8 hypocotyls. Ethylene production was essentially unaffected by IAA in dgt, but was stimulated up to 10-fold by 10 micromolar IAA in VFN8. Elongation of dgt hypocotyls was also insensitive to concentrations of IAA as high as 100 micromolar, as compared to significant elongation of VFN8 hypocotyls in response to 0.1 micromolar IAA. A range of IAA analogs active in VFN8 was also ineffective in stimulating elongation of dgt hypocotyls, suggesting that the differences were not due to rapid metabolism of IAA by dgt tissues. Auxin-induced elongation of VFN8 hypocotyls was unaffected by 2,3,5-triiodobenzoic acid and naphthylphthalamic acid, indicating that polar auxin transport was not a factor in these experiments. Exogenous and auxin-induced ethylene had no effect on the elongation respone of either genotype, nor did exogenous ethylene restore the sensitivity of dgt hypocotyls to IAA. Despite their apparent insensitivity to auxin, dgt hypocotyls elongated dramatically and synthesized ethylene rapidly in response to 1.2 micromolar fusicoccin. These results suggest that the primary effect of the dgt mutation is to reduce the sensitivity of the tissue to auxin. As altered regulation of ethylene synthesis is only one symptom of this fundamental deficiency, dgt should more properly be considered to be the auxin-insensitive tomato mutant.

Assessment of the Number and Expression of P-Type H+-ATPase Genes in Tomato

“…We chose this system as a convenient one in which to examine the possibility that the transcript abundance of one or more of the LHA isoforms increases in response to IAA. We repeated the experiment of Kelly and Bradford (1986) in which hypocotyl section lengths were compared after 10 h of treatment in buffer with or without the addition of 10 ^M IAA and obtained similar results. We also extended the analysis by examining the time course of hypocotyl section extension with treatments of up to 18 h (Fig.…”

“…106,1994 frozen in liquid nitrogen. The remaining sections were incubated for 1 h in buffer containing 2.5 m~ KHJ'O4 (pH 5.2) and then transferred to buffer containing 2.5 m~ KHzP04 (pH 5.2), 2.5 m~ KCl, 1 m~ Ca(NO&, and 3% Suc with or without IAA added at a concentration of 1 X M (Kelly and Bradford, 1986). Incubations were carried out at 2OoC with gentle agitation on a rotary shaker.…”

Master and servant: Regulation of auxin transporters by FKBPs and cyclophilins

“…Interestingly, similar to plant FKBPs, plant cyclophlins have been strongly linked to regulation of development (Box 2). Mutations in tomato DGT result in auxin-related phenotypes such as lack of lateral roots, deregulation of gene expression, ROS imbalance, and defects in polar auxin transport [80][81][82][83][84][85][86][87][88] (Table 1). DGT is both nuclear and cytoplasmic localized [10] (Table 1, Fig.…”

Differential activation of the primary auxin response genes, PS‐IAA4/5 and PS‐IAA6, during early plant development

“…CycIAt expression is restricted to the lateral root primordium and, later in development, to the meristematic zone in a cell-specific pattern similar to that observed in the primary root (Ferreira et aL, 1994). Cell cycle progression is under hormonal control (Jacobs, 1995), and several lines of evidence suggest that auxin is intricately involved in lateral root initiation and development: (i), exogenous application of auxin initiates lateral roots in a wide variety of plants (Kerk, 1990;Thimann, 1936;Torrey, 1950); (ii), transgene-mediated overexpression of auxin results in plants with increased lateral root production (Kares et aL, 1990;Klee et aL, 1987); (iii) auxin-insensitive mutants of tomato, dgt (Kelly and Bradford, 1986), and Arabidopsis, auxl, axrl, axr4 (Hobble and Estelle, 1995), are defective in lateral root formation; and (iv) a mutant impaired in lateral root maturation, alf3-1, can be rescued by IAA (Celenza et aL, 1995).…”