Vessel differentiation along different tissue polarities

Organized vessel differentiation in an isolated system was studied on a quantitative basis. An auxin source was oriented on isolated pieces of turnip storage root ( Brassica campestris cv. Rapifera) to allow diffusion a) in the direction of, b) at right angle to, and c) opposite to the original polarity. New vessel members differentiated within 44 h, and a minimum average auxin (IAA) concentration of 3.10⁻⁶ M was required to induce initial vessel differentiation. The differentiation rates in three experimental orientations were 167, 60 and 43 cells h⁻¹ at 10⁻³ M IAA, and 1445, 1346 and 838 cells (log IAA concentration)⁻¹ after 96 h, respectively. The difference between the differentiation rates in the original polarity orientation (a) and in the orientation at right angle (b) is interpreted as reflecting reorientation itself, which requires a minimum time.     

Rhizoctonia solani injuries in oilseed crops in Finland and impacts of different crop management practices on disease incidence and severity

A disease survey in Finnish oilseed Brassica (OSR) fields in 2007–09 revealed the widespread occurrence and several fold increase of necrotic stem base lesions and severely injured blackened roots in comparison to a corresponding survey carried out in 1984–89. Rhizoctonia solani was the predominant fungi detected in the isolations and was followed by several species of Fusarium and Thielaviopsis basicola. In 60% of the samples all three species were detected together. Only the R. solani AG 2–1 strains isolated from OSR and other cruciferous hosts caused damping off or stem base symptoms on turnip rape in a greenhouse experiment. Therefore R. solani AG 2–1 was considered the main pathogen associated with the observed symptoms in OSR crops. Cultural practices changed significantly between the 1980s and 2000s. In the 2007–09 survey there was an increase in the cultivation of oilseed rape instead of turnip rape, increase in the use of no soil or reduced soil tillage and of chemical control of weeds, but a reduction in macronutrient fertilization, especially P and K, when compared to the 1980s survey. The risk for high incidence of stem base lesions and blackened roots was affected by different cultural practices. No tillage and maintaining sufficient soil pH and NPK fertilisation decreased the risk for both types of R. solani induced symptoms. Late sowing date increased the risk for high incidence of stem base lesions, while application of fungicides against Sclerotinia reduced it. The incidence of R. solani damages in many fields was very high in spite of relatively long crop rotations and therefore the average effect of crop rotation in the disease was insignificant. Current turnip rape cultivars are vulnerable to root rot while oilseed rape is vulnerable to stem base symptoms. The higher incidence of R. solani induced diseases could be associated with the decline in productivity of OSR crops in Finland. This study showed that cultural practices such as reduced or no soil tillage, adequate levels of pH and of NPK fertilization could reduce the severity of the symptoms in OSR fields.     

Mating Behavior and Reproductive Potential in the Turnip Moth Agrotis segetum (Lepidoptera: Noctuidae)

We investigated the lifetime mating potential and the reproductive behavior of male and female turnip moths Agrotis segetum (Schiff.) under field and laboratory conditions. The sex ratio was 1 : 1 in a lab-reared population as well as in two wild populations. Males were capable of mating repetitively a relatively large number of times (mean of 6.7 ± 2.7 matings) when given access to new virgin females throughout their lifetimes. Females seldom mated more than once (mean ± 1.3 ± 0.6 matings), indicating a male-biased operational sex ratio. The mean potential lifetime mating was five times higher in males, while the coefficient of variance was lower in males. There was no differences in longevity between animals that were allowed to mate and animals not allowed to mate, indicating no direct costs or benefits of mating in physiological terms. In males, the number of matings was positively correlated with longevity, but this was not the case in females. Nor was there a correlation between the number of female matings and the number of fertilized eggs. There was a negative correlation between the number of eggs fertilized and the number of times males had previously mated, indicating that male ejaculates were limited. Male spermatophore size also decreased with number of achieved matings. Laboratory-reared females attracted males in the field throughout their lifetimes, with a peak at 3–7 days of age. Wild males, allowed to choose between pairs of caged females in the field, were attracted in equal numbers to females of different ages. Females did not show any mate-rejection behavior in the field. They mated with the first male that courted them. No incidence of mate replacement by males arriving later to already courted females were recorded.     

Relationships between turnip root fly (Delia floralis) larval development and the sugar content of swede (Brassica napus ssp. rapifera) roots

Eight genotypes of swede (Brassica napus L. ssp. rapifera [Metz.] Sinsk.) at the 8–10 true leaf stage were inoculated with five, 10 or 20 eggs of the turnip root fly Delia floralis (Fall). The roots were sampled, with control roots, after 6 weeks of larval development. D. floralis root damage, as measured by reduction in root weight, was found to be linked to inoculation level. Neither D. floralis egg numbers nor swede genotype had a significant effect on the percentage of larvae developing to pupation. Mean pupal weight varied by a factor of ×1.4 and consistently decreased with increasing egg inoculation level. Changes in the root concentrations of glucose, sucrose and fructose were measured. All swede genotypes showed a similar response in their sugar concentrations after root damage. Glucose and fructose concentrations were reduced whilst sucrose concentration remained unaffected. The concentrations of glucose and fructose were highly correlated. Pupal weight, used as a measure of larval development, was significantly correlated with the concentrations of individual and total sugars in the roots. The implications of sugar responses to damage in brassicas, and the correlation between sugar concentrations in the roots and D. floralis pupal weights are discussed.     

Structure of satellite tobacco necrosis virus after crystallographic refinement at 2.5 Å resolution

The structure of the protein subunit of satellite tobacco necrosis virus has been solved at 3.7 Å resolution. We have now crystallographically refined the original model and extended the resolution to 2.5 Å in order to get a model accurate enough to explain the details of the subunit interactions. The refinement was done with a novel method utilizing the icosahedral symmetry of the virus particle.The final model shows a complicated network of interactions, involving salt linkages, hydrogen bonds and hydrophobic contacts. In addition, we have located three different metal ion sites in the protein shell, linking the protein subunits together. These sites are probably occupied by calcium ions. One site is found in a general position near the icosahedral 3-fold axis of the virus. The ligands form an octahedral arrangement, with two main chain carbonyl oxygens (O-61 and O-64), one carboxylate oxygen (OD1 from Asp194) of the same subunit and a second carboxylate oxygen (OE1 of Glu25) from a 3-fold related subunit. Two water molecules complete the octahedral arrangement. A second site is on the icosahedral 3-fold axis and is liganded by the carboxylate oxygens of the 3-fold related Asp55 residues. The third metal ion site is found on the 5-fold axis, liganded by the five carbonyl oxygens of Thr138 and two water molecules.We are unable to locate the first 11 N-terminal amino acid residues, which point into the virus interior. No interpretable density for RNA has been found, indicating that the nucleic acid of the virus does not have a unique orientation in the crystal.     

Clones of cauliflower mosaic virus identified by molecular hybridization in turnip leaves

Mechanical inoculation of turnip leaves with cauliflower mosaic virus (CaMV) results after one to two weeks in the appearance on these leaves of local lesions. Local lesions were detected by hybridization of radioactive CaMV DNA with nucleic acid immobilized in leaf skeletons by solvent extraction, proteinase digestion, and alkali treatment. The pattern of lesions detected as dark circles on autoradiographs of the washed leaf skeletons was the same as that detected by staining of solvent-extracted leaves for starch. Starch lesions appeared as white areas against a dark purple back-ground. These lesions were first detected between 5 and 8 days after inoculation and grew in size until 10 days after inoculation. Lesions were also detected by staining solvent-extracted and proteinase digested leaves with ethidium bromide. The lesions appeared as dark areas in a bright fluorescent background, and were found in the same positions as the starch lesions.     

Faithful and efficient translation of viral and cellular eukaryotic mRNAs in a cell-free S-27 extract of Saccharomycescerevisiae

The preparation of yeast spheroplast 27,000 × g supernatant /S-27/ which initiates translation of endogenous and exogenous mRNAs is described. The activity of this protein synthesis system is comparable to that of the most efficient cell-free extracts currently in use. The yeast S-27 system is able to carry out faithful translation of distinct eukaryotic mRNAs into proteins as large as 180,000 daltons.     

Translationally controlled tumour protein: A protein necessary for potyvirus intracellular multiplication that supports plant infection by unrelated viruses

The multifunctional protein translationally controlled tumour protein (TCTP) was previously identified as necessary for infection by the potyvirus pepper yellow mosaic virus. Using turnip mosaic virus (TuMV) as a model to study potyvirus biology, we confirmed that TCTP has a positive effect on virus infection. Living cell confocal microscopy demonstrated that TCTP colocalises with 6K2-tagged replication vesicles and with a perinuclear globular structure typically observed during potyvirus infection. Also, TCTP silenced protoplasts showed reduced virus accumulation, quantified by qRT-PCR, which suggests an effect on virus replication, translation or other intracellular process. Finally, TCTP silencing in plants reduced the accumulation of two species belonging to Orthotospovirus and a Begomovirus genus, which are not closely related to potyviruses. The results suggest that TCTP is a general susceptibility factor to several unrelated viruses.