Search Results

You are looking at 1 - 10 of 617 items for :

Clear All
Free access

Ellen T. Paparozzi, Jazbaat K. Chahal, Petre Dobrev, Elizabeth A. Claassen, Walter W. Stroup and Radomira Vankova

of N limitation, leaves will abscise and reintroduction of N will then cause development of new leaves from terminal meristems and axillary buds. Plant responses to N deficiency are mediated by plant hormones, especially by cytokinins ( Argueso et al

Free access

Zhaolong Wang, John Pote and Bingru Huang

This study was designed to examine whether shoot injury induced by high root-zone temperature is associated with changes in shoot detoxifying metabolism and to determine the level and duration of high root-zone temperatures that would induce physiological changes in two cultivars of creeping bentgrass (Agrostis stolonifera var. palustris Huds) differing in heat tolerance. Plants of `Penn A-4' (heat tolerant) and `Putter' (heat susceptible) were grown in sand and exposed to root-zone temperatures of 20 (control), 21, 22, 23, 25, 27, 31, and 35 °C in water baths while air temperature was maintained at 20 °C in a growth chamber. Turf quality, leaf cytokinin content, and antioxidant enzyme activities declined at increased soil temperatures and the duration of treatment for both cultivars. A decline in turf quality occurred following 40 days of exposure to 35 °C for `Penn A-4' and 26 days of exposure to 31 °C for `Putter'. The root-zone temperature causing the decline of isopentenyl adenosine and zeatin cytokinins was 25 °C at 37 d for `Putter' and 27 °C at 47 days for `Penn A-4'. The temperature causing the decline of superoxide dismutase and catalase activities was 25 °C and 27 °C at 33 days for `Putter' and 27 °C and 31 °C at 43 days for Penn A-4, respectively. Malondialdehyde content increased at 27 °C for `Putter' and 31 °C for `Penn A-4' at 43 days of treatment. The decline in cytokinin content and antioxidant enzyme activity occurred at a lower soil temperature and earlier during the treatment than the decline in turf quality, possibly contributing to turf quality decline. The root-zone temperatures causing the decline in turf quality, cytokinin content, and oxidative damage were higher in the heat-tolerant cultivar than heat-susceptible cultivar.

Free access

Mahalaxmi Veerasamy, Yali He and Bingru Huang

damage by enhancing thermotolerance ( Park et al., 1996 ; Sun et al., 2002 ). Different approaches have been examined in alleviating heat stress injury, including exogenous application of plant hormones, such as cytokinins. Cytokinins regulate many

Free access

Eleanor W. Hoffman, Dirk U. Bellstedt and Gerard Jacobs

budbreak is correlated with an increased concentration of cytokinins in the xylem sap just before budbreak ( Tromp and Ovaa, 1990 ; Van Staden and Davey, 1979 ). Furthermore, exogenous application of cytokinins can promote budbreak during late dormancy

Free access

Takahiro Tezuka, Masashi Harada, Masahumi Johkan, Satoshi Yamasaki, Hideyuki Tanaka and Masayuki Oda

of PGRs in the culture medium; relatively high levels of cytokinin promote shoot formation, whereas high levels of auxin promote rooting, and intermediate levels induce callus formation ( Thorpe, 2007 ). In CDM, adventitious shoots are likely to be

Free access

Kerrie McDaniel and David Lightfoot

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.

Free access

John J. Frett and Richard McCardell

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.

Free access

John J. Frett and Richard McCardell

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.

Free access

Lixin Xu, Mili Zhang, Xunzhong Zhang and Lie-Bao Han

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

Full access

Fatemeh Haddadi, Maheran Abd Aziz, Hossein Kamaladini and Seyed Ali Ravanfar

. Thidiazuron, a substituted phenylurea with its cytokinin- and auxin-like effects, is the most recently studied of the cytokinins ( Debnath and Teixeira da Silva, 2007 ). There are many reports of improved regeneration capacity with TDZ compared with other