Increase of endogenous zeatin riboside by introduction of the ipt gene in wild type and the lateral suppressor mutant of tomato

Abstract

We studied axillary meristem formation of the lateral suppressor ( Is) mutant of tomato after elevating the endogenous cytokinin levels through introduction of the isopentenyltransferase (ipt) gene from Agrobacterium tumefaciens. Growth and development of several transformants were examined during in vitro culture. Transformants exhibited phenotypes varying in severity and were divided into four classes. A number of the ipt transformants had a normal phenotype, as non-transformed plants. Others showed a mild to severe 'cytokinin-like' phenotype. Transformants with a mild phenotype exhibited reduced internode length and reduced root development. Transformants with a severe phenotype showed even shorter internodes, loss of apical dominance, reduction of leaf size, production of callus at the basis of the shoots and absence of root development or development of green non-branching roots. The severity of the phenotype correlated well with the level of ipt gene expression, as measured by northern analysis. Transformants with a severe phenotype also exhibited increased levels of zeatin riboside, but zeatin levels were not elevated. The increase in endogenous zeatin riboside levels in the IS mutant did not restore axillary meristem formation, but sometimes bulbous structures were formed in the initially 'empty' leaf axils. Several adventitious meristems and shoots developed from below the surface of these structures. It is concluded that a reduced level of cytokinins in the Is mutant shoots is not responsible for the absence of axillary meristem formation.

Root-synthesized cytokinins improve shoot growth and fruit yield in salinized tomato (Solanum lycopersicum L.) plants

“…The stimulation of CK synthesis of HSP70::IPT plants by elevated RZT resulted in concentrations similar to those reported in WT tomato xylem sap (Kudorayova et al , 2007) and IPT -transformed tomato shoots ( Groot et al , 1995 ), but higher (∼10-fold) than reported in WT tomato leaves ( Walker and Dumbroff, 1981 ; Rahayu et al , 2005 ; Kudorayova et al , 2007). Absolute CK concentrations vary according to plant developmental stage, tissue sampled, and plant nutrition.…”

Strigolactones Suppress Adventitious Rooting in Arabidopsis and Pea

“…Consistent with these results, the cytokinin receptor mutant arabidopsis histidine kinase4 (ahk4) and plants overexpressing either CYTOKININ OXIDASE1 (CKX1) or CKX2, resulting in higher breakdown of cytokinin, display enhanced adventitious root production (Werner et al, 2003;Lohar et al, 2004;Kuroha et al, 2006, Riefler et al, 2006. Similarly, fewer adventitious roots are formed on cuttings of petunia (Petunia hybrida) or tomato (Solanum lycopersicum) that have enhanced cytokinin synthesis due to the overexpression of an ISOPENTENYLTRANSFER-ASE gene (Groot et al, 1995;Clark et al, 2004). Collectively, these results demonstrate a role for cytokinin in negatively regulating adventitious root formation.…”

Comparative Analysis of Seven Endogenous Hormones in a Novel Dual-axillary Bud Mutant Genotype of Sugarcane

“…While these findings support the concept that elevated ZR levels lead to dual-axillary bud formation in YZ 07-86, they also present conflicting evidence. For example, CKs inhibit flower bud formation in tobacco (Tanimoto and Harada 1981), and despite increased endogenous ZR levels, the ls mutant of tomato fails to restore axillary meristem formation (Groot et al 1995). These contradictions challenge our suggestion regarding the role of ZR.…”

“…They proposed that this might occur due to CKs stimulating shoot formation from vegetative bud primordia. Groot et al (1995) observed an increase in endogenous zeatin riboside (ZR) levels in the ls mutant of tomato, known for its inability to produce axillary buds in most leaf axils. This led to the formation of bulbous structures in initially empty leaf axils, from which adventitious shoots could arise, suggesting a role for cytokinins in inducing tissue proliferation in these regions.…”