Dynamics of responses in compatible potato-Potato virus Y interaction are modulated by salicylic acid.

To investigate the dynamics of the potato-Potato virus Y (PVY) compatible interaction in relation to salicylic acid-controlled pathways we performed experiments using non-transgenic potato cv. Désirée, transgenic NahG-Désirée, cv. Igor and PVY(NTN), the most aggressive strain of PVY. The importance of salicylic acid in viral multiplication and symptom development was confirmed by pronounced symptom development in NahG-Désirée, depleted in salicylic acid, and reversion of the effect after spraying with 2,6-dichloroisonicotinic acid (a salicylic acid-analogue). We have employed quantitative PCR for monitoring virus multiplication, as well as plant responses through expression of selected marker genes of photosynthetic activity, carbohydrate metabolism and the defence response. Viral multiplication was the slowest in inoculated potato of cv. Désirée, the only asymptomatic genotype in the study. The intensity of defence-related gene expression was much stronger in both sensitive genotypes (NahG-Désirée and cv. Igor) at the site of inoculation than in asymptomatic plants (cv. Désirée). Photosynthesis and carbohydrate metabolism gene expression differed between the symptomatic and asymptomatic phenotypes. The differential gene expression pattern of the two sensitive genotypes indicates that the outcome of the interaction does not rely simply on one regulatory component, but similar phenotypical features can result from distinct responses at the molecular level.

A comparative study on the role of cytokinins in caryopsis development in the maize miniature1 seed mutant and its wild type.

We report here on a comparative developmental profile of plant hormone cytokinins in relation to cell size, cell number and endoreduplication in developing maize caryopsis of a cell wall invertase-deficient miniature1 (mn1) seed mutant and its wild type, Mn1, genotype. Both genotypes showed extremely high levels of total cytokinins during the very early stages of development, followed by a marked and genotype specific reduction. While the decrease of cytokinins in Mn1 was associated with their deactivation by 9-glucosylation, the absolute and the relative part of active cytokinin forms was higher in the mutant. During the exponential growth phase of endosperm between 6 d after pollination and 9 d after pollination, the mean cell doubling time, the absolute growth rate and the level of endoreduplication were similar in the two genotypes. However, the entire duration of growth was longer in Mn1 compared with mn1, resulting in a significantly higher cell number in the Mn1 endosperm. These data correlate with the previously reported peak levels of the Mn1-encoded cell wall invertase-2 (INCW2) at 12 d after pollination in the Mn1 endosperm. A model showing possible crosstalk among cytokinins, cell cycle and cell wall invertase as causal to increased cell number and sink strength of the Mn1 developing endosperm is discussed.

PVY(NTN) elicits a diverse gene expression response in different potato genotypes in the first 12 h after inoculation.

Host gene expression changes in the early response to potato virus Y(NTN) interaction were compared in two differently sensitive potato cultivars: the resistant cultivar Santé and the sensitive cultivar Igor. Hybridization of potato TIGR cDNA microarrays allowed us to monitor the expression of approximately 10,000 genes simultaneously at 0.5 and 12 h post-inoculation (hpi). Microarray data, analysed by statistics and data mining, were complemented by subtraction library construction and sequence analysis to validate the findings. The expression profiles of the two cultivars were similar and faint at 0.5 hpi, but they differed substantially at 12 hpi. Although, at 0.5 hpi, cv. Santé responded by the differential expression of a greater number of genes, at 12 hpi the number was higher in cv. Igor. The majority of genes in this cultivar were down-regulated at 12 hpi, indicating a host gene shut-off. Suites of genes that exhibited altered transcript abundance in response to the virus were identified, and included genes involved in the processes of photosynthesis, perception, signalling and defence responses. The expression of the considerable number of genes associated with photosynthesis was surprisingly up-regulated as early as 0.5 hpi and down-regulated at 12 hpi in both cultivars. The expression of genes involved in perception and signalling was increased in the sensitive cultivar at 12 hpi. By contrast, a simultaneous strong defence response at the transcriptional level was evident in the resistant cultivar, as shown by the up-regulation of genes involved in brassinosteroid, polyamine and secondary metabolite biosynthesis, and of genes coding for pathogenesis-related proteins.

Phenolic content and antioxidative capacity of green and white tea extracts depending on extraction conditions and the solvent used.

The efficiencies of different solvents in the extraction of phenolics from bagged and loose leaves of white and green tea, after different extraction times, as well as the antioxidative capacity of the obtained extracts, were investigated. The developed HPLC method has the potential to separate and determinate 17 phenolics widely distributed in plants, but in investigated tea extracts only four catechins and traces of three flavonols and one flavone were separated and detected based on comparison with authentic standards. The extraction efficiency of phenolics depended strongly on the time of extraction and the solvents used. The extraction of catechins from green tea was significantly affected by the form (bagged or loose) of the tea, whereas this effect was shown not to be statistically significant for white tea. Green tea was a richer source of phenolics than was white tea. The extraction of phenolics from white tea by water could be accelerated by the addition of lemon juice. Aqueous ethanol (40%) was most effective in the prolonged extraction of catechins. The antioxidative capacity of the investigated tea extracts correlated with their phenolic content.

Developing fruit direct post-floral morphogenesis in Helleborus niger L.

In fertilized flowers of Helleborus niger L., the sepals (the showy elements of the perianth at anthesis) grow, spread, and turn green, and the peduncles elongate. These processes did not proceed to completion when the pistils were removed at the bud stage, but could be restored by the application of plant growth regulators. Cytokinins and gibberellins stimulated the formation of well-developed chloroplasts in, and spreading of, the sepals; the gibberellin, GA3, and the auxin, 4-chloroindole-3-acetic acid, promoted peduncle elongation. In fruit-bearing flowers, on the other hand, paclobutrazol, an inhibitor of gibberellin biosynthesis, reduced chlorophyll formation in the sepals, reversed sepal spreading, and inhibited peduncle elongation. Of the endogenous growth regulators in developing fruit, the following cytokinins were identified: zeatin, dihydrozeatin, N6-(2-isopentenyl)adenine and their ribosides and 9-glucosides. Zeatin riboside drastically increased in abundance (about 200 times), shortly after fertilization, when chlorophyll accumulation in the sepals occurred at the fastest rate, and remained the most prominent identified cytokinin until seed ripening.

Jasmonic acid stimulates taxane production in cell suspension culture of yew (Taxus x media).

Cell lines of Taxus x media Rehd. were established via embryo and callus culture and grown on B5 medium containing 10 microM 2,4-D and 1 microM kinetin. Jasmonic acid (JA) was used to elicit taxane synthesis in a selected yew cell line. 100 microM JA was added 7 days after subculture. JA strongly increased taxane content in the cells and in the medium. At the time of the highest amount in elicited cultures, the enhancement of paclitaxel production was 19-fold and 4-fold in the cells and medium, respectively, compared to controls (non-elicited cultures). The time course of taxane accumulation in the cells and in the medium and the release of taxanes into the medium were not changed after JA elicitation.