Phosphorylation of histone H1 during the cell cycle of artichoke

Abstract. Histones have been extracted from tuber and cultured tuber explant material and separated by gel electrophoresis. Histone H1 is heterogenous with 3–4 components in addition to the widely recognized histone H1a and H1b. Using labelling procedures and alkaline phosphatase treatment, histone H1 has been shown to be phosphorylated on both serine and threonine residues and possibly other acid-labile linkages. Variations in histone H1 phosphorylation have been measured through the cell cycle and the evidence indicates enhanced phosphorylation occurring during the G2/M phase as in animal systems.     

Trichoderma harzianum antagonistic activity and competition for seed colonization against seedborne pathogenic fungi of sunflower

This study investigated the antagonistic effects of Trichoderma harzianum isolate (TRIC8) on mycelial growth, hyphal alteration, conidial germination, germ tube length and seed colonization by the seedborne fungal pathogens Alternaria alternata, Bipolaris cynodontis, Fusarium culmorum and F. oxysporum, the causes of seedling rot in over 30% of sunflowers. The antagonistic effect of TRIC8 on mycelial growth of pathogens was evaluated on dual culture that included two inoculation assays: inoculation of antagonist at 48 h before pathogen (deferred inoculation) and inoculation at the same time with pathogen (simultaneous inoculation). TRIC8 inhibited mycelial growth of the fungal pathogens between 70·67 and 76·87% with the strongest inhibition seen with deferred inoculation. Alterations in hyphae were observed in all pathogens. Conidial germination of F. culmorum was inhibited by most of the fungal pathogens (38·28%) by TRIC8. Inhibition of germ tube length by the antagonist varied from 31·83 to 37·67%. In seed colonization experiments, TRIC8 was applied in combination with each pathogen to seeds of a sunflower genotype that is highly tolerant to downy mildew. Seed death was inhibited by TRIC8 and the antagonist did not allow growth of A. alternata, B. cynodontis and F. culmorum on seeds and inhibited the growth of F. oxysporum at the rate of 58·32%.     

Influence of the g-force on the circumnutations of sunflower hypocotyls

Circumnutations of hypocotyls of sunflower ( Helianthus annuus L. cv. Californicus) were studied under 1 g and 3 g conditions. Root mean square values of the hypocotyl deviation from the plumbline and period of the movements were determined from Calculations of the autocorrelation functions of the movements. The amplitude and the period of the circumnutations increased under 3 g as compared to 1 g . A transition from 3 to 1 g or vice versa also caused changes in period and amplitude of the movoments. The results are interpreted as a support for the idea that gravity influences the circumnutation parameters in this sunflower variety. A comparison is made with published results on the dwarf sunflower ev. Teddy Bear where the force influence is very small or negligible. Simulations of a model for circumnutations show movements which are in qualitative agreement with the experimental results, provided adaptation to g -levels is included in the model. Finally, the results are discussed with the recent Spacelab-experiment (SLI) as a background.     

Toxicity of nitrapyrin to sunflower under different N nutrition regimes

Summary The purpose of this study was to investigate the phytotoxicity of nitrapyrin 2-chloro-6-(trichloromethyl)pyridine to sunflower (Helianthus annuus L.) under different N regimes and to see if N forms affect the phytotoxicity of nitrapyrin. Sunflower was grown in pot culture for 21 days and was fertilized with (NH₄)₂SO₄, NH₄NO₃ and NaNO₃ to provide 0, 100 and 200 ppm N and with nitrapyrin application of 0 and 20 ppm. All N-treated sunflower plants in all N regimes and regardless of titrapyrin treatment produced more root and shoot dry weights and contained a significantly higher N than untreated check. Nitrapyrin toxicity appeared as a curling of leaf margin and a tendril type of stem growth, the visible toxicity symptoms decreased in the order: (NH₄)₂SO₄>NH₄NO₃>NaNO₃. Furthermore nitrapyrin addition suppressed sunflower growth in each N regime, the suppressing effect being greater with (NH₄)₂SO₄ and NH₄NO₃ than as with NaNO₃. Although, shoot growth from plants receiving nitrapyrin was not significantly affected by any N regime, root growth of nitrapyrin-treated plants was somewhat restricted by NH₄ ⁺−N nutrition relative to NO₃ ⁻−N nutrition.     

A functional analysis of large‐scale temporal shifts from 1970 to 2000 in weed assemblages of sunflower crops in France

Questions: What are the relationships between weed species traits and their change in distribution over a 30‐year period? What does it tell us about factors that have driven shifts in the composition of weed communities? Location: France. Methods: We analysed the links between change in the status of weed species in sunflower crops (decreasing or increasing) and a set of 17 traits using data sets collected in the 1970s and the 2000s, respectively. We analysed the contribution of traits to explain changes in the status of species both individually and in a multivariate way by mean of a clustering of species into functional groups. Results: 69% of the most widespread species had significantly changed their frequency rank status over the last 30 years. Nearly two thirds of the increasing species belonged to a single functional group, out of the five groups identified in this analysis. Overall, the weed flora occurring in sunflower crops has specialised since the 1970s in favour of ‘sunflower mimicking’ functional groups: increasing species were more nitrophilous, more heliophilous, less sensitive to sunflower herbicides and shared a rapid summer life cycle. Conclusions: The individual trait approach gave some indication as to the environmental factors likely to have caused the shift in sunflower weed communities. The functional group approach seemed to outperform direct trait comparisons as it accounted for major traits combinations i.e. cases where a species has a number of favourable traits, but is severely disadvantaged by the possession of one or a few deleterious traits.     

Intra-individual heterogeneity of rDNA allows the distinction between two closely related species in the Genus Helianthus

The Ribosomal DNAs of Helianthus annuus and H. argophyllus were analysed. Total DNA from single individuals of six cultivated lines, one wild ecotype ofH. annuus, and three ecotypes of H. argophyllus, were digested with various restriction enzymes. Hybridisation of Southern blots with sunflower ribosomal probes containing most of the interspacer regions (R3) or the 25 s coding region (R2) reveals different patterns from those expected: while no difference between H. annuus and H. argophyllus had been observed in previous rDNA RFLP analysis, our study clearly distinguished the two species on the basis of two different patterns when using R3 and BamHI, BstYI, or EcoRI/BamHI. Furthermore, the sum of the fragment weights of the BamHI restriction patterns was much greater than that of the rDNA entire unit-weight space. The co-existence of different rDNA units within single individuals is proposed as a model to explain these results. Four rDNA units were distinguished, which differed in their state of methylation and by the presence of mutations at two BamRI restriction sites. H. annuus individuals displayed two types of rDNA units while H. argophyllus individuals displayed four types.     

The kinetics of rehydration of detached sunflower leaves from different initial water deficits

Abstract. The tempo of rehydration of sunflower ( Helianthus animus L.) leaves was measured after dehydration in a pressure bomb down to water potentials of −0.5 to −1.6 MPa. When rehydrated from small water deficits (−0.5 to −0.8 MPa) the plot of log rehydration rate versus time is concave. When rehydration starts from large deficits (−1.2 to −1.6 MPa) the semilog plot has a characteristic shoulder, i.e. a rehydration phase of long half-time is followed by a phase of short half-time. The experimental curves were fitted with parallel and series models of rehydration. In the parallel model two compartments are connected by resistances in parallel with the water source and rehydrate independently. In the series model one compartment is connected with the water source via a resistance and the second compartment is connected in series with the first by another resistance so that water entering the second compartment must pass through the first. Amongst nineteen experiments, ten could be fitted very closely by both the parallel and series models and nine could not be fitted by either model.     

Stressed Jerusalem artichoke tubers (Helianthus tuberosus L.) excrete a protein fraction with specific cytotoxicity on plant and animal tumour cell

Wounds from Jerusalem artichoke (Helianthus tuberosus L.) tubers excrete bioactive metabolites from a variety of structural classes, including proteins. Here we describe a protein specifically active against tumour cells arising either from human, animal or plant tissues. The non-tumour animal cells or the plant callus cells are not sensitive to these excreta. The active product was only obtained after a wound-drought stress of plant tubers. The cytotoxicity varies according to the tumour cell type. For instance, some human tumour cell lines and especially the human mammary tumour cells MDA-MB-231 were shown to be very susceptible to the active product. The active agent is shown to contain an 18-kDa polypeptide with homology to a superoxide dismutase (SOD). A 28-kDa polypeptide, related to an alkaline phosphatase (AP), was shown to be tightly linked to this 18-kDa polypeptide. The excreted 28-kDa polypeptide also displayed a consensus sequence similar to the group of DING proteins, but with a smaller molecular weight. The superoxide dismutase polypeptide was shown to be involved in the antitumour activity, but the presence of smaller factors (MW < 10 kDa), such as salicylic acid, can enhance this activity.     

Relationship of the cell cycle to xylem cell differentiation: A new model

Abstract. Conflicting data have appeared in the literature concerning the necessity for DNA synthesis prior to xylem cell differentiation. In some systems DNA synthesis is not required before differentiation, while in other systems DNA synthesis appears to be an absolute necessity. The construction of a model for the cell cycle in which the G1 phase is subdivided into a separate 'early' and 'late' phase can resolve this apparent conflict.