Physiological differences between cttokinins are well documented. An explanation for these differences is that cytokinins differentially regulate genes. Gene response has been analyzed in cell culture and organized tissue of Phaseolus vulgaris L. cv. Great Northern. Two novel cDNAs, L-221 and L-22, have been identified that are cytokinin responsive. In leaf tissue L-221 was repressed by zeatin, benzyladenine and thidiazuron at 50 μM. In suspension cell culture mRNA abundance of L-221 remained constant regardless of cytokinin treatment. By contrast, the abundance of L-22 mRNA was increased differentially by treatment with each of the 3 cytokinins in leaf tissue. Suspension cells analyzed for expression of L-22 after cytokinin treatment also showed differential gene expression. S-1 Nuclease Protection Assays revealed that gene expression is a transient phenomenon dependent upon the time of cytokinin application and cytokinin concentration. Callus bioassays showed that dihydrozeatin and O-glucosylzeatin gave greater responses than the co-application of zeatin and dihydrozeatin or zeatin and O-glucosylzeatin. The conjugate and the reduction derivative also gave greater responses than zeatin alone. Effects of dihydrozeatin and O-glucosylzeatin on gene expression will be reported.
Several cytokinins at various concentrations were tested to determine which would stimulate the most synchronous shoot initiation. Kinetin was effective only at concentrations of 50 mg/L, while 2iP and zeatin where effective from 5 to 50 mg/L. BA at 10 mg/L produced the most synchronous and the greatest number of shoots. This treatment was used to determine at what point in development cytokinins stimulate shoots. Tissue was grown in the presence and absence of BA for various lengths of time. Application of BA for at least 10 days was required to initiate shoots. Explants were not effected by BA during the first 5 days of culture. Starving tissue for various periods caused a proportional lag in shoot production. Short pulses of BA at different developmental stages did not alter the cytokinin response. Vacuum infiltration of cytokinins prior to culture did not increase the BA response.
Several cytokinins at various concentrations were tested to determine which would stimulate the most synchronous shoot initiation. Kinetin was effective only at concentrations of 50 mg/L, while 2iP and zeatin where effective from 5 to 50 mg/L. BA at 10 mg/L produced the most synchronous and the greatest number of shoots. This treatment was used to determine at what point in development cytokinins stimulate shoots. Tissue was grown in the presence and absence of BA for various lengths of time. Application of BA for at least 10 days was required to initiate shoots. Explants were not effected by BA during the first 5 days of culture. Starving tissue for various periods caused a proportional lag in shoot production. Short pulses of BA at different developmental stages did not alter the cytokinin response. Vacuum infiltration of cytokinins prior to culture did not increase the BA response.
been considered as signaling molecules for inducing plant antioxidant defense systems against abiotic stresses ( Xiong et al., 2002 ). Cytokinins exhibit antisenescence and antioxidant function. Heino et al. (1990) reported that ABA deficiency
responses of plants to environmental stresses. Abscisic acid (ABA) and cytokinins are two major groups of plant hormones that play important roles in regulating plant responses to decreases in soil water availability ( PospÃÅ¡ilová et al., 2000 ; Wilkinson
been implicated in both breaking dormancy and initiating growth after dormancy, but the role of these hormones has not been clearly defined ( Coleman, 1998 ). Cytokinins have been implicated in the maintenance of dormancy in potato tubers ( Coleman
the distal half to two-third of the axillary bud should remove the differentiated meristem. Cytokinin application to buds favors shoot formation and inhibits root initiation in stem cuttings, but in decapitated pea ( Pisum sativum ) cuttings
salt concentrations and cytokinin concentrations should result in improved in vitro shoot growth. Nitrogen (N) is taken up in the form of nitrate (NO 3 − ) or ammonium (NH 4 + ) and is an important component of amino acids, amides, nucleic acids
( Kamenicka and Lanakova, 2000 ). Although several cytokinins have been used to induce shoot proliferation, BAP has been used most often for magnolia. For Magnolia × soulangeana, 1.2 μM BAP was shown to produce greater shoot proliferation than 2iP, kinetin
of leaves as chlorophyll and other cellular components (e.g., proteins and nucleic acids) are degraded during natural or stress-induced leaf aging. Cytokinins (CK) have been well known for delaying leaf senescence, and in some cases, reversing this