Cytokinin Signaling in Plants Under Salt Stress

Abstract

AbstractSalt stress negatively affects plant growth by impairing biochemical and physiological processes. Appropriate modulation of cytokinin (CK) metabolism and signaling can improve salt tolerance in plants. Protection of the photosynthetic apparatus, promotion of antioxidant systems, improvement of plant growth and differentiation, and crosstalk with stress-related phytohormones are important mechanisms that may contribute to cytokinin-mediated enhancement of salt tolerance. CKs mainly trigger plant environmental stress responses through the regulation of gene expression. A two-component system is employed to transduce the cytokinin signal to the target genes. CKs are perceived by membrane-localized histidine kinase receptors. The signal is transduced through a His-Asp phosphorelay (Histidine-aspartate phosphorelays) to activate a family of transcription factors in the nucleus. CKs cause organ specific responses in plants. This hormone is a negative regulator of root growth. Root-specific overexpression of CKX (cytokinin oxidase/dehydrogenase) gene can enhance root growth, nutrient uptake and salt tolerance. In contrast, increasing cytokinin level (by overexpression of IPT genes) promotes shoot growth of salt stressed plants, by inducing the expression of genes that are involved in photosynthesis, chlorophyll levels, photochemical quenching, photochemical efficiency, electron transport rates and CO2 assimilation. This chapter focuses on the cytokinin metabolism, transport and signaling, and discusses the role of this phytohormone in regulating changes in gene expression and physiological processes to mediate salt tolerance in plants. KeywordsCytokinin signalingGene expressionPhysiological processesSalinity