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.…”

Cytokinin inhibition of Arabidopsis root growth: An examination of genotype, cytokinin activity, and N6-benzyladenine metabolism

“…Evidence for a role for cytokinins in root growth comes from many sources, but transgenic plants that overproduce cytokinins provide some of the strongest evidence that increased endogenous cytokinins reduce root growth (Groot et al 1995, Binns 1994, Li et al 1992. Cytokinin metabolism is also important to root growth because these biochemical pathways regulate active compounds, cytokinin transport, temporary storage, and irreversible inactivation (Binns 1994, Jameson 1994, Letham and Palni 1983.…”