Diurnal rhythmicity of endogenous phytohormones and phototropic bending capacity in potato (Solanum tuberosum L.) shoot cultures

Taking advantage of advanced high performance liquid chromatography–electrospray tandem–mass spectrometry (HPLC–ESI–MS/MS), we screened daily changes in concentrations of endogenous phytohormones of in vitro grown potato ( Solanum tuberosum L. cv. Désirée) shoot cultures and checked for possible connections between the rhythmicity of endogenous phytohormones and phototropic bending capacity of the same cultures. Studies done under diurnal 16 h light and 8 h darkness (diurnal) and continuous light (CL) conditions showed prominent daily rhythmicity of endogenous phytohormone levels in both light regimes. Phototropic bending in potato is known to be rhythmic only in the diurnal, whereas in CL conditions the bending response is present but without any daily rhythmicity. For all of the studied phytohormone groups significant differences between the diurnal and CL conditions were found. Changes in the concentration of indole auxins, indole-3-acetic acid (IAA) and its catabolite 2-oxindole-3-acetic acid (OxIAA), were the most prominent. Their levels clearly alternated with level of IAA being high in diurnal and OxIAA in CL conditions. Significant concentration changes were also observed for other phytohormones such as cytokinin ribosides, salicylic acid, abscisic acid and phaseic acid. Observed changes in daily phytohormone levels indicate strong and complex involvement of diverse phytohormone groups in realization of the phototropic bending response of potato shoots.