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  • Author or Editor: Jeff Hoyle x
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Ambiol, a derivative of 5-hydroxybenzimidazole, has been well documented to function as a growth promoter, an antistress compound, and an antioxidant when applied as a seed preconditioning agent. However, evidence suggests that Ambiol decreases transpiration and promotes root growth similar to the phytohormone abscisic acid (ABA), leading to the development of the hypothesis that Ambiol promotes drought resistance through an ABA-dependent pathway. The effect of 0 mg·L−1 and 10 mg·L−1 was tested on wild-type tomato seedlings (Lycopersicon esculentum Mill. var. Scotia), ABA-deficient flacca tomato seedlings, and ABA-inhibited (with fluridone) tomato seedlings. In both fluridone-treated and flacca seedlings, Ambiol preconditioning resulted in significant increases in shoot growth, root growth, leaf area, and plant height consistent with gains experienced by wild-type tomatoes. In addition, flacca tomatoes experienced increases in photosynthesis and water use efficiency consistent with wild-type tomatoes. Ambiol was able to confer benefits to drought-stressed tomatoes in ABA-deficient and ABA-inhibited conditions, suggesting that Ambiol functions through an ABA-independent pathway.

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There is strong evidence that Ambiol® (a derivative of 5-hydroxybenzimazole) promotes drought tolerance in many plants; it is often suggested that this is the result of its antioxidant properties. Recent evidence has also shown that several natural antioxidants promote carrot germination under drought stress. Thus, it was hypothesized that seed preconditioning using natural antioxidants might confer drought tolerance. Ambiol®, ascorbic acid, β-carotene, lutein, and lycopene were chosen as antioxidants at concentrations of 0.1 mg·L−1, 1.0 mg·L−1, and 10 mg·L−1. A preconditioning treatment was applied by soaking tomato (Solanum lycopersicum L.) seeds in an antioxidant solution for 24 h. Of the antioxidants tested, 10 mg·L−1 Ambiol®, 1.0 mg·L−1 β-carotene, 1.0 mg·L−1 ascorbic acid, and 0.1 mg·L−1 lycopene were shown to increase shoot dry mass by 114%, 94%, 56%, and 83%, respectively, in droughted seedlings when compared with a droughted control. Similar benefits were observed in root dry mass, leaf area, photosynthesis, and water use efficiency. Proteins were extracted from the seeds of certain treatments, before and after germination, and separated using isoelectric focusing. Specific proteins were found to be induced through all preconditioning treatments, whereas Ambiol® and β-carotene were found to induce specific proteins, independent of those induced through imbibition, both before and after germination. This result suggests that Ambiol® and β-carotene evoke specific proteins that may confer drought tolerance to the key physiological processes studied. In addition, protein profiles of ascorbic acid, β-carotene, and Ambiol® after germination had fewer visible bands than the controls, suggesting an accelerated mobilization or conversion of proteins within the seed.

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