Osmotic stress stimulates shoot organogenesis in callus of rice (Oryza sativa L.) via auxin signaling and carbohydrate metabolism regulation

Abstract

This study aimed to clarify the possible mechanism of endogenous phytohormone signaling and carbohydrate metabolism during shoot organogenesis induced by osmotic stress in rice (Oryza sativa L. cv. Tainung 71) callus. Non-regenerable calli derived from Tainung 71 immature embryos were inoculated on Murashige and Skoog medium containing 10 μM 2,4-D. They turned to highly regenerable calli (HRC) (regeneration frequency more than 75 %) with lower calli fresh weight and water content when 0.6 M sorbitol was supplemented into the medium. The regeneration frequency was prominently decreased to 25 % while an auxin transport inhibitor, 2,3,5-triiodobenzoic acid (TIBA), was added into the sorbitol-treated medium. It suggested that endogenous auxin signal may be involved in the induction of HRC under osmotic stress treatment. As well, HRC showed high levels of glucose, sucrose, and starch and high expression of cell wall-bound invertase 1, sucrose transporter 1 (OsSUT1), OsSUT2, PIN-formed 1, and late embryogenesis abundant 1 (OsLEA1) genes. Their expressions are all dramatic inhibited except OsLEA1 under TIBA treatment. It suggests a key role of auxin may be linked to the effect of shoot regeneration under osmotic stress treatment. Therefore, we present a putative hypothesis for regenerable calli induction by osmotic stress treatment in rice. Osmotic stress may regulate endogenous levels of auxin interacting with abscisic acid, then affect carbohydrate metabolism to trigger callus initiation and further shoot regeneration in rice. © 2013 The Author(s).