The incidence of gangrene of potatoes caused by Photna exigua in relation to handling and storage

Damage to potatoes during harvesting and grading increases the incidence of gangrene. Among the factors involved, the condition of the soil and the type of damage caused by the implements may be of importance. Gangrene is most evident in tubers which have been stored cold or moved when cold; warmer storage at some stage usually reduces its incidence and severity. Seasonal incidence is not directly related to rainfall but is determined by factors affecting ripening and destruction of haulm, moisture status of soils at harvest, susceptibility to damage, and exposure during storage and in transit.     

Influence de la 6-benzylaminopurine sur la différenciation plastidiale dans les cotylédons de concombre

Treatment with 6-benzylaminopurine (6-BAP; 10⁻⁵ g/ml) accelerates the growth of detached cucumber cotyledons (Cucumis sativas L.), primarily through an increased water uptake by the tissues. A comparative study of pigment composition and ultrastructure in 6-BAP treated and untreated cotyledons shows that cytokinin, in the presence of light, accelerates the transformation of etioplasts into chloroplasts. 6-BAP also enhances the synthesis of membrane precursors as indicated by the formation of a dense prolamellar body and by the persistence of a pseudo-cristalline structure in 6-BAP treated material. Stimulation of biosynthetic activity by cytokinin leads simultaneously to an increase in the rate of the pigment synthesis and to an acceleration in the building of the lamellar system. Furthermore, chloroplasts of 6-BAP treated cotyledons show abnormal features such as a striking increase in the number of thylacoids per granum and a poor development of the intergranal system.     

Allosteric Properties of Chorismate Mutase from Quercus pedunculata

Chorismate mutase from Quercus pedunculata Ehrh. leaves has been purified by ammonium sulfate precipitation, molecular sieving and hydroxyapatite chromatography. Some results obtained during the purification suggest the presence, in oak, of two isofunctional forms of the enzyme, the one sensitive, the other insensitive to the action of aromatic amino acids. The regulable form exhibits a molecular weight of about 45,000. It is inhibited by tyrosine and by phenylalanine and is activated by tryptophan. In addition to its activating properties, this latter compound, endowed with a great affinity for the enzyme, reverses the inhibition due to the two other amino acids. The H⁺ concentration of the medium plays an important role in the sensitivity of the enzyme with regard to its effectors. Inhibition by tyrosine and by phenylalanine is maximal at pH 6.5, at which value the two ligands present an identical effect. At alkaline pH values, the rate of inhibition decreases regularly, tyrosine becoming the most effective inhibitor. Activation by tryptophan is particularly acute in a mildly acid medium; at pH 6.5, this effector increases the enzymatic activity threefold. Its action is weak (20% activation) in the optimum pH zone (pH 7.8) and increases towards the more basic pH values. As a result, tryptophan maintains a constant level of enzymatic activity throughout a large pH zone (between 6.5 and pH 9.0). The physiological significance of these results is discussed.     

Taxonomy of Fasciosminthurus (Collembola, Symphypleona, Bourletiellidae), with descriptions of two new European species

The taxonomy of Fasciosminthurus (Collembola, Symphypleona, Bourletiellidae) is reviewed. Two Fasciosminthurus species are redescribed, F. sauteri (Nayrolles & Lienhard, 1990) and F. virgulatus (Skorikow, 1899), and two new species, F. saportae sp. n. and F. pseudovirgulatus sp. n., are described. Fasciosminthurus virgulatus and F. pseudovirgulatus display similar colour patterns. They can be distinguished by presence vs absence of a pair of flecks on the head and chaetotaxy of the third antennal segment. A key to species and comments on taxonomic characters and biogeography are provided. It is proposed that F. virgulatus and F. pseudovirgulatus sp. n. are allopatric sister species.