Role of melatonin in the regulation of IAA-dependent plant reaction in different lighting conditions

Currently, expansion of melatonin (Mel) in the plant kingdom has been established. Mel has an impact on many processes in a plant. The existence of contradictory data about the Mel hormonal function in a plant is the basis for further research. Moreover, in the regulation of plant growth processes an interrelation of Mel and indole-3-acetic acid (plant hormone IAA) (as metabolic products of tryptophan) has not been found. In this regard, the aim of this research was to determine the role of Mel in auxin-dependent growth reactions and possible interaction of Mel and IAA in the regulation of plant processes in the dark and in the light. Our studied objects were 7-day-long seedlings of Arabidopsis thaliana (L.) Heynh. Columbia ecotype Col wild type and its mutant line axr1-3 with impaired transduction of auxin signal. They were grown in hormone-free Murashige and Skoog medium in the dark, under blue, red and white light (control) and with an addition of Mel (an experience) under long-day conditions (16 h light: 8 h dark) at PAR photon flux density about 120 ^mol / (m s), at a temperature 22-25C. The light source was white TL-D 36W / 54-765, blue TL-D 36W / 18 and red TL-D 36W / 15 fluorescent lamps (Fig. 1). Also, we studied wheat coleoptile segments Triticum aestivum L. of Irgina variety. These segments were cultured in the darkness using 2% sucrose (control) with an addition of IAA or Mel, or Mel + IAA (experience). The range of the studied concentrations of Mel and IAA varied from 0.1pM to 1 ^M. In the experiment, we measured growth parameters and determined the content of photosynthetic pigments. The optical density of the extract of pigments in 96%-ethanol was registered using the spectrophotometer at a wavelength of 470, 648 and 664 nm. Our experiments showed that direction and magnitude of 1 ^M Mel influence depended on the lighting conditions and IAA signal transduction (Fig. 4). In the darkness Mel inhibited the elongation of mutant axial organs, whereas it increased the size of the cotyledon wild type under the white light. Mel reduced the size of the root and the cotyledons under the white light in both lines, but increased the size of the root under the red light. Furthermore, the efficiency of Mel during axr1-3 growth regulation was higher than Col. The experience has shown that the exogenous Mel under the white light has a stimulating effect on the growth of seedlings of A. thaliana in lower concentrations (0.1 pM) than IAA (1 nM). Mel was restoring axr1-3 mutant axial organs growth and the content of photosynthetic pigments to the wild-type levels, probably by compensating violations of IAA signal transduction (Fig. 2, 3). In the absence of the IAA Mel did not affect the coleoptile segments of T. aestivum elongation, but during their coeffect Mel intensified its effectiveness in the regulation of the growth processes (Fig. 5). It appears from this that the action of Mel was not associated with the activation of plasma membrane H+-ATPase, but changed the efficiency of IAA action. The article contains 5 Figures, 31 References. Currently, expansion of melatonin (Mel) in the plant kingdom has been established. Mel has an impact on many processes in a plant. The existence of contradictory data about the Mel hormonal function in a plant is the basis for further research. Moreover, in the regulation of plant growth processes an interrelation of Mel and indole-3-acetic acid (plant hormone IAA) (as metabolic products of tryptophan) has not been found. In this regard, the aim of this research was to determine the role of Mel in auxin-dependent growth reactions and possible interaction of Mel and IAA in the regulation of plant processes in the dark and in the light. Our studied objects were 7-day-long seedlings of Arabidopsis thaliana (L.) Heynh. Columbia ecotype Col wild type and its mutant line axr1-3 with impaired transduction of auxin signal. They were grown in hormone-free Murashige and Skoog medium in the dark, under blue, red and white light (control) and with an addition of Mel (an experience) under long-day conditions (16 h light: 8 h dark) at PAR photon flux density about 120 ^mol / (m s), at a temperature 22-25C. The light source was white TL-D 36W / 54-765, blue TL-D 36W / 18 and red TL-D 36W / 15 fluorescent lamps (Fig. 1). Also, we studied wheat coleoptile segments Triticum aestivum L. of Irgina variety. These segments were cultured in the darkness using 2% sucrose (control) with an addition of IAA or Mel, or Mel + IAA (experience). The range of the studied concentrations of Mel and IAA varied from 0.1pM to 1 ^M. In the experiment, we measured growth parameters and determined the content of photosynthetic pigments. The optical density of the extract of pigments in 96%-ethanol was registered using the spectrophotometer at a wavelength of 470, 648 and 664 nm. Our experiments showed that direction and magnitude of 1 ^M Mel influence depended on the lighting conditions and IAA signal transduction (Fig. 4). In the darkness Mel inhibited the elongation of mutant axial organs, whereas it increased the size of the cotyledon wild type under the white light. Mel reduced the size of the root and the cotyledons under the white light in both lines, but increased the size of the root under the red light. Furthermore, the efficiency of Mel during axr1-3 growth regulation was higher than Col. The experience has shown that the exogenous Mel under the white light has a stimulating effect on the growth of seedlings of A. thaliana in lower concentrations (0.1 pM) than IAA (1 nM). Mel was restoring axr1-3 mutant axial organs growth and the content of photosynthetic pigments to the wild-type levels, probably by compensating violations of IAA signal transduction (Fig. 2, 3). In the absence of the IAA Mel did not affect the coleoptile segments of T. aestivum elongation, but during their coeffect Mel intensified its effectiveness in the regulation of the growth processes (Fig. 5). It appears from this that the action of Mel was not associated with the activation of plasma membrane H+-ATPase, but changed the efficiency of IAA action. The article contains 5 Figures, 31 References.

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