Effect of partial rootzone drying on the concentration of zeatin-type cytokinins in tomato (Solanum lycopersicum L.) xylem sap and leaves

Abstract

Decreased cytokinin (CK) export from roots in drying soil might provide a root-to-shoot signal impacting on shoot physiology. Although several studies show that soil drying decreases the CK concentration of xylem sap collected from the roots, it is not known whether this alters xylem CK concentration ([CK(xyl)]) in the leaves and bulk leaf CK concentration. Tomato (Solanum lycopersicum L.) plants were grown with roots split between two soil columns. During experiments, water was applied to both columns (well-watered; WW) or one (partial rootzone drying; PRD) column. Irrigation of WW plants aimed to replace transpirational losses every day, while PRD plants received half this amount. Xylem sap was collected by pressurizing detached leaves using a Scholander pressure chamber, and zeatin-type CKs were immunoassayed using specific antibodies raised against zeatin riboside after separating their different forms (free zeatin, its riboside, and nucleotide) by thin-layer chromatography. PRD decreased the whole plant transpiration rate by 22% and leaf water potential by 0.08 MPa, and increased xylem abscisic acid (ABA) concentration 2.5-fold. Although PRD caused no detectable change in [CK(xyl)], it decreased the CK concentration of fully expanded leaves by 46%. That [CK(xyl)] was maintained and not increased while transpiration decreased suggests that loading of CK into the xylem was also decreased as the soil dried. That leaf CK concentration did not decline proportionally with CK delivery suggests that other mechanisms such as CK metabolism influence leaf CK status of PRD plants. The causes and consequences of decreased shoot CK status are discussed.

Characterization of New Maize Genes Putatively Involved in Cytokinin Metabolism and Their Expression during Osmotic Stress in Relation to Cytokinin Levels

“…For instance, the essential role of mitogenactivated protein and salt overly sensitive kinase cascades and the function of transcription factors containing ABA-responsive elements are undoubtedly well established. CKs are an important signal traveling from roots to the shoots in response to nutrient insufficiency ; however, conclusions concerning their role in drought, osmotic, and salinity responses or signalization are derived from inferences with no cause/effect data (Kuiper et al, 1990;Davies and Zhang, 1991;Kudoyarova et al, 2007;Tran et al, 2007). In this article, we, to our knowledge for the first time, describe complete gene families of CK biosynthetic and degradation genes in maize and regulation of their expression in a short-term response to osmotic and salinity stress as well as during the plant acclimatization to these adverse environmental stimuli.…”

Spatiotemporal aspect of cytokinin-auxin interaction in hormonal regulation of the root meristem

“…The developmental specificity of AtIPT genes' expression 27 suggests autocrine and/or paracrine type of CK signalling in addition to its role as a long-distance signal. 24,[28][29][30] This implies that CK effects and its interactions with auxin must be studied in specific plant tissues and cell types with regard to their developmental status.…”

Conditional up-regulation of cytokinin status increases growth and survival of sugarcane in water-limited conditions

“…Endogenous ABA levels in leaves increase rapidly and induce rapid stomatal closure when plants are subjected to water stress as well as other abiotic stresses (Kudoyarova et al, 2007, Ehlert et al, 2009, Wilkinson and Davies, 2010. ABA is also recognised for its role in modulating leaf and canopy expansion under water deficit conditions (Bower andBirch, 1992, Wilkinson andDavies, 2002).…”

“…CK content and transport are reduced by drought stress, either through reduced biosynthesis or by accelerated degradation (Shani et al, 2006, Kudoyarova et al, 2007, Barazesh and McSteen, 2008, Argueso et al, 2009, Nishiyama et al, 2011. It has been proposed that a reduction in CK amplifies leaf responses such as increased ABA synthesis and stomatal closure during stress (Alvarez et al, 2008, Schachtman and Goodger, 2008, Kravtsov et al, 2011, Wilkinson et al, 2012.…”

“…Zeatin represents the major CK transported in the xylem Vanstaden, 1976, Hirose et al, 2008). However, more recent studies indicate that CK metabolism itself can influence the CK status in leaf tissue under drying conditions (Neuman et al, 1990, Kudoyarova et al, 2007. It is therefore important to consider that CK concentrations in leaves depend on the balance between CK input from xylem sap delivery and putative CK synthesis in leaves, and CK loss via catabolism and phloem export.…”