In higher plants, sugars are required not only to sustain heterotrophic growth but also to regulate the expression of a variety of genes. Environmental stresses, such as pathogen infection and ...wounding, activate a cascade of defense responses and may also affect carbohydrate metabolism. In this study, the relationship between sugar- and stress-activated signal transduction pathways and the underlying regulatory mechanism was analyzed. Photoautotrophically growing suspension culture cells of Chenopodium rubrum were used as a model system to study the effects of the metabolic regulator D-glucose and of different stress-related stimuli on photosynthesis, sink metabolism, and defense response by analyzing the regulation of mRNAs for representative enzymes of these pathways. Glucose as well as the fungal elicitor chitosan, the phosphatase inhibitor endothall, and benzoic acid were shown to result in a coordinated regulatory mechanism. The mRNAs for phenylalanine ammonia-lyase, a key enzyme of defense response, and for the sink-specific extracellular invertase were induced. In contrast, the mRNA for the Calvin cycle enzyme ribulose bisphosphate carboxylase was repressed. This inverse regulatory pattern was also observed in experiments with wounded leaves of C. rubrum plants. The differential effect of the protein kinase inhibitor staurosporine on mRNA regulation demonstrates that the carbohydrate signal and the stress-related stimuli independently activate different intracellular signaling pathways that ultimately are integrated to coordinately regulate source and sink metabolism and activate defense responses. The various stimuli triggered the transient and rapid activation of protein kinases that phosphorylate the myelin basic protein. The involvement of phosphorylation in signal transduction is further supported by the effect of the protein kinase inhibitor staurosporine on mRNA levels
Chenopodium rubrum L. , is a suitable model plant for studying ontogenesis in vitro as an early flowering species. Culture of intact plants in vitro and antioxidative enzymes detection were ...performed. Growth pattern to the end of ontogenesis, flowering and seed development are all determined by the photoperiod seedlings experience during induction and evocation of flowering. Different phases of vegetative and reproductive development are characterized by changes in antioxidative enzymes activities. We showed sequential expression of antioxidative enzymes during seed germination. Prior to radicule protrusion, CAT and SOD showed maximal activity, while POD activity appeared later. The highest catalase (CAT) activity was measured at the time of flowering while peroxidases (PODs) are involved in determination of growth and development in accordance with the environmental clues. The absence of some superoxide dismutase (SOD) isoforms could be the indicator of senescence. Seed ageing affect changes in antioxidative status of seeds, germination, seedling growth and flowering.
Summary
Extracellular or cell wall invertase is regarded as crucial to supply sink tissues with carbohydrates via an apoplastic pathway. A cell wall invertase from Chenopodium rubrum was purified to ...homogeneity and the corresponding cDNA encoding CIN1 was identified via peptide sequences. The CIN1 mRNA was found to be highly induced by physiological concentrations of both adenine‐ and phenylurea‐derived cytokinins in suspension culture cells. This was paralleled both by a higher steady‐state protein level and a higher enzyme activity of the extracellular invertase. The cytokinin‐inducible accumulation of CIN1 mRNA in tissues of C. rubrum plants supports the physiological significance of this regulatory mechanism. In contrast to the extracellular sucrose cleaving enzyme, the mRNA levels of the two putative intracellular invertases CIN2 and CIN3 and of sucrose synthase were not elevated. In addition, it has been found that the accumulation of mRNA for one out of three hexose transporters present in the suspension culture cells is induced co‐ordinately with the mRNA for extracellular invertase by cytokinins. It has been shown that this regulatory mechanism results in higher uptake rates both for sucrose, via the hexose monomers, and for glucose. The increased level of both extracellular invertase and hexose transporters and the resulting higher carbohydrate supply are discussed with respect to the control of carbohydrate partitioning by plant hormones and the molecular basis for known physiological cytokinin responses such as the stimulation of cell division.
The occurrence of melatonin (5-methoxy-
N-acetyltryptamine), a common animal hormone, in extracts of the above-ground parts of 15-day-old plants of
Chenopodium rubrum was confirmed by liquid ...chromatography/tandem mass spectrometry. Using both this method and radioimmunoassay, changes in melatonin content during a 12 hr light/12 hr dark cycle were demonstrated. The melatonin concentration remained low or undetectable during the light period and increased during the darkness reaching a maximum at hours 4–6 of the dark period before rapidly decreasing. Both the nocturnal increase and the range of concentration are similar to those known in animals.
A method for visualization of cytosolic Ca super(2+) distribution was applied to living plant tissue. A mixture of the fluorescent probes Fluo-3 and Fura Red was used. The emitted fluorescence was ...scanned simultaneously in two channels with a laser-scanning confocal microscope and rationing was performed. The homogeneity of the Fluo-3/Fura Red concentration ratio throughout the tissue after AM-ester loading was proven. In vitro calibration permitted conversion of Fluo-3/Fura Red fluorescence ratios to Ca super(2+) values. Apparent K sub(D) of 286 nM, R sub(min) of 0.43 and R sub(max) of 18 were calculated. The in vivo determination of extreme ratio values was performed by permeabilizing the plasmalemma for Ca super(2+) with a ionophore and manipulating the extracellular Ca super(2+). The resultant R sub(minv) of 1.33 and R sub(maxv) of 2.69 for vegetative apices, and R sub(mini) of 1.26 and R sub(maxi) of 3.45 for apices induced to flowering, suggested incomplete equalization of extra- and intracellular Ca super(2+) levels in these experiments. In Chenopodium rubrum, the cytosolic Ca super(2+) patterns of apical tissue obtained using Fluo-3 and Fura Red were significantly different between vegetative apices and apices after photoperiodic flower induction. This methodological approach may also be helpful for studying cytosolic Ca super(2+) distribution in other living plant tissues.
The cyclin-dependent kinase (CDK) inhibitors ICK1 and ICK2 have been shown to inhibit plant CDK activity in vitro, and the expression of ICK1 was able to inhibit cell division in the plant and modify ...plant growth and morphology. In order to characterize other ICK1-related inhibitor genes and understand possible differences among plant CDK inhibitors, the interactions of plant CDK inhibitors with cell cycle regulators were analysed in the yeast two-hybrid system and their functions were compared in transgenic Arabidopsis plants. Yeast two-hybrid results indicate that there are likely two groups of plant CDK inhibitors. The A-group inhibitors ICK1, ICK2, ICK6 and ICK7 interact with Cdc2a and three D-type cyclins (D1, D2 and D3), while the B-group inhibitors ICK4, ICK5 and ICKCr interact with D-type cyclins but not with Arabidopsis Cdc2a. ICK1 (A-group), and ICK4 and ICKCr (B-group) were expressed separately in transgenic Arabidopsis plants. Overexpression of the three inhibitor genes resulted in plants of a smaller size with serrated leaves and modified flowers. These plants also had reduced nuclear DNA content (polyploidy), suggesting that expression of these inhibitors affected endoreduplication. Further, there were apparent differences in the strength of effect among the inhibitors. These results provide the first evidence on the CDK inhibitory function for ICK4 and ICKCr. They also suggest that these CDK inhibitors play important roles in cell division and plant growth.
A controlled feeding study and field collections of duck feces were used to examine the potential of ducks for dispersing wetland plant species in the prairie pothole region of North America. To ...determine how long seeds of wetland species remain in their digestive system, captive mallards were fed known quantities of seed of either Atriplex patula, Chenopodium album, Chenopodium rubrum, Echinochloa crusgalli, Polygonum spp., Scirpus acutus, Scirpus validus, or Sparganium eurycarpum. Fecal samples were collected hourly from ducks for 24 to 30 hours after seeds were ingested. On average, 23% of the seeds ingested were recovered intact, and 36% of these were still viable. In other words, only 7% of the seeds ingested were still viable when they were evacuated, with a range from 1% for Echinochloa crusgalli to 16% for Scirpus validus. The mean passage time of seeds was 7.6 h, with a range of 5.1 h for Echinochloa crusgalli to 11.1 h for Chenopodium rubrum. Nearly all seeds were evacuated after 24 to 30 h. Seed size and seed coat strength (lignin content) were negatively correlated with the probability of a viable passage but not correlated with passage rates. After ingestion, mallards are estimated to be able to transport internally viable seeds up to 1,400 km but more typically 20 to 30 km. Field collections of duck feces at five locations in the prairie pothole region confirmed that ducks are dispersing intact seeds of common wetland species (Carex sp., Echinochloa sp., Panicum sp., Polygonum spp., Potamogeton spp., Salix sp., and Scirpus spp.). There were between 0.3 to 5.2 intact seeds per duck. Only 1.6% of this intact seed of four taxa (Carex sp., Potamogeton spp., Salix sp., and Scirpus spp.) germinated under greenhouse conditions. Although any given duck is carrying only a few viable seeds, the millions of ducks moving among wetlands, especially during spring and fall migrations, collectively are effective dispersal agents for many wetland plant species.
Changes in aquatic and marsh vegetation at Lake Zeribar in the Zagros Mountains, Iran, during the last 40 000 years were reconstructed on the basis of plant macrofossils. Several episodes of low ...water level and increased salinity were evidenced by peaks of Chenopodium rubrum seeds and the occurrence of obligate (Salicornia sp., Ruppia maritima and Suaeda sp.) and facultative (Zannichellia palustris) halophytic macrophytes as well as brackish water and marine diatoms. Some of these events can be correlated with an increase in diatoms indicative of higher conductivity and with changes in oxygen-isotope data. They are interpreted as the expression of general climatic dryness, although water-level changes might also have resulted from episodes of deposition on the alluvial fans that dam the lake. A few such water-level changes occurred in the Pleniglacial. The most pronounced lowering corresponds to the Younger Dryas interval of high climatic aridity. Macrofossil indicators of water-level changes appeared also in the Holocene section of the profiles at the same time as Quercus expanded on the surrounding uplands, culminating about 6000- 5000 14C yr BP, giving support to the hypothesis that the delay of forest expansion in this part of the Zagros Mountains was caused by climatic dryness.
Melatonin is an animal hormone that regulates photoperiodic reactions in many vertebrates. Its level is usually higher at night, and the duration of elevated melatonin levels is proportional to the ...length of the night, thus giving information about day length. We have previously identified melatonin in the dicotyledonous plant
Chenopodium rubrum. We compared melatonin daily profiles in
C. rubrum shoots when given three different photoperiodic regimes with 8 h, 12 h, and 16 h of darkness. As in vertebrates, melatonin levels reached its maximum at night, but the duration of elevated melatonin content did not change with the photoperiod. The maximum melatonin content occurred at later times after lights off as night length increased, but always 6 h before lights on in all light/dark cycles. These results indicate differences in the regulation of melatonin levels between vertebrates and higher plants. We suggest that the timing of melatonin maximum relative to lights off may provide photoperiodic information for
C. rubrum.
Arthropod–plant interactions are vital in agriculture and pharmacology. However, enhancement and quantification of plant cell behavioural activity is still a challenge. Therefore, the finding of ...chitosan-induced anti-fungal activity in plants suggested a promising potential. Consequently, we treated autotroph and heterotroph
Chenopodium rubrum
L. cell cultures with chitosan to test behavioural activity with
Tenebrio molitor
L. larvae. We found chitosans to enhance repelling, depending on low molecular weight, partial degree of deacetylation, plant cell type and age. These effects of chitosans were compared with abiotic stresses induced by salt, osmotic changes and heat shock, collecting data of six plant cell samples, 18 plant cell treatments, 6,912 larvae and 8,424 analyses of regression and variance. Behavioural activity was quantified by linear, multivariate and nonlinear approaches, testing an exponential model in 78 segments of 5 h time kinetics. Thereby, we introduced a sensitive, low-cost bio-assay and a preference index constant as a measure of transient behaviour. Multivariate analyses revealed the five principal factors to enhance the behavioural activity in plant cells: (1) salt-osmo-sensor, (2) high molecular weight chitosan sensor, (3) acetic acid-antagonized low molecular weight chitosan sensor, (4) heat shock sensor and (5) mannitol-sensitive chitosan sensor. Thus, we suggest the independent factors (1)–(5) for the management of insect pests by autotroph and heterotroph plant materials.
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