Melatonin may exert a protective role against drought stress in maize

Melatonin (N‐acetyl‐5methoxytryptamine) is an amphiphilic low‐molecular‐weight compound found in evolutionary distant living organisms, from bacteria to mammals. It can be synthesized by plants and acts as a potent antioxidant and/or a regulator of plant growth and development. Here, we investigated the role of melatonin in plant response to drought stress and recovery in maize (Zea mays L.) plants, with an emphasis on its possible photoprotective and antioxidant role and/or signalling function in relation to the stress‐related phytohormones, abscisic acid, salicylic acid and jasmonic acid. Results show a positive correlation between endogenous contents of melatonin and photoprotection, as indicated by the maximum efficiency of photosystem II photochemistry (F_v/F_m ratio), which was confirmed further by exogenous application of melatonin during recovery from drought stress. Melatonin applications during drought recovery improved the F_v/F_m ratio in maize plants exposed to a subsequent drought stress. Furthermore, endogenous contents of melatonin positively correlated with those of stress‐related phytohormones, particularly with those of salicylic acid, although exogenous application of melatonin did not alter the contents of these defence compounds. It is concluded that melatonin can exert a defensive role in maize plants exposed to drought stress, particularly improving the efficiency of photosystem II photochemistry.     

Foliar Nutrient Analyses in Bananas Grown in the Highlands of East Africa

Data gathered from 45 farms in the Kagera Region of Tanzania were used to estimate critical nutrient levels (CNL) of foliar tissue and norms of the Diagnosis and Recommendation Integrated System (DRIS) for bananas ( Musa spp.) grown in the highlands of East Africa.
CNL values are proposed as 3.1 % N, 1.13 % Ca, 0.48 % Mg, 18.4 ppm Zn and 10.0 ppm B. Optimum ranges for cation ratios were estimated as 0.54—0.67 for K/(K + Ca + Mg), 0.22—0.32 for Ca/(K + Ca + Mg) and 0.09—0.15 for Mg/(K + Ca + Mg). Productivity of bananas and foliar levels of P, K, S, Fe, Mn and Cu were too weakly related to estimate CNLs for these nutrients. A set of DRIS norms for East African Highland bananas is presented.     

Clinical efficacy of prophylactic administration of trimethoprim/sulfadiazine in a Streptococcus equi subsp. zooepidemicus infection model in ponies

Tissue chambers, implanted subcutaneously in the neck in six ponies, were inoculated with Streptococcus equi subsp. zooepidemicus in order to determine the clinical efficacy of prophylactic administration of trimethoprim/sulfadiazine (TMP/SDZ) against this infection. The TMP/SDZ treatment consisted of one intravenous (i.v.) injection of 5 mg/kg TMP and 25 mg/kg SDZ and the same dose of TMP/SDZ per os (p.o.), both given 3 h before inoculation. The oral dose was then repeated every 12 h for 5 days. TMP/SDZ concentrations in tissue chamber fluid (TCF) were above 10 times MIC at the moment of inoculation, and they were maintained at this level or higher throughout the duration of treatment. Trimethoprim/sulfadiazine treatment resulted in a marked reduction of viable bacteria in the tissue chamber but did not eliminate the infection, resulting in abscessation from day 19 onwards in all six ponies. This shows that, even when TCF is not yet purulent, TMP/SDZ is unable to eliminate the streptococci. Therefore, TMP/SDZ should not be the antimicrobial treatment of choice in infections in secluded sites in horses.     

Follicle Development in Mares

The mare provides a unique experimental model for studying follicle development in monovular species. Development of antral follicles in horses is characterized by the periodic growth of follicular waves which often involve the selection of a single dominant follicle. If properly stimulated, the dominant follicle will complete development and eventually ovulate a fertile oocyte. Regulation of follicular wave emergence and follicle selection involves an interplay between circulating gonadotropins and follicular factors that ensures that individual follicles are properly stimulated to grow (or to regress) at any given stage of follicular wave development. Periodic development of follicular waves continuously occurs during most of post-natal life in the mare and is influenced by factors such as stage of oestrous cycle, season, pregnancy, age, breed and individual so that different types of follicular waves (minor or major, ovulatory or anovulatory) and different levels of activity within waves may develop under different physiological conditions. Changes in gonadotropin levels and/or in the sensitivity of follicles to circulating gonadotropins seem to account largely for these physiological variations in follicle development.     

The origin and early development of wheat glutenin particles

Breadmaking quality is strongly related to the glutenin macropolymer (GMP) fraction. Don and co-workers [Don, C., Lichtendonk, W.J., Plijter, J.J., Hamer, R.J., 2003a. Glutenin macropolymer: a gel formed by particles. Journal of Cereal Science 37, 1–7] showed that GMP consists of spherical glutenin particles and suggested that these originate from the protein bodies (PBs) observed in developing grain. We have tested this hypothesis by systematically comparing SDS-soluble and SDS-insoluble protein fractions from both PBs and flour. These preparations were analysed at the molecular, oligomer, particle and microscopic levels. Comparison of PBs isolated from immature seeds with glutenin particles isolated from mature seeds revealed strong similarities in protein composition and the presence of large glutenin oligomers. However, the glutenin particles from mature wheat were significantly larger than PBs. We suggest that PBs are the building blocks for the formation of much larger glutenin particles which are formed during the desiccation phase of kernel development.     

Synchronization of flowering in maize (Zea mays L.) by the genetic system pg11 pg12

Summary The mutant genotype pg11pg11 pg12pg12-epistasis of double recessive factors-determines greater precocity of flowering. The possibility of using this mutant in the production of hybrid seed as a mean of synchronizing flowering in parent strains of different earliness is studied. The differences between mutant and green control genotypes in the characters of days to pollen shedding, pollen production, and height of plants are evaluated. Four mutant lines are considered together with their respective green near-isolines in two distinct localities and across four successive plantings.The mutant near-isolines presented lower values than those of the green near-isolines for all the characters. The maximum reductions in days to flowring were obtained in early plantings and late maturity strains. The reduction in pollen production was about 50%. The reduced height of the mutants is explained, at least in part, by the correlation of this factor with days to flowering. The mutants did not prove to be more sensitive to the environment than their green near-isolines. Seed production was not studied since the mutant is very deficient for this character and it could therefore only be utilized as the male parent. We concluded that the mutant, could be used to synchronize flowering in the industrial production of hybrid seed.     

Epidemiological importance of Solanum sisymbriifolium, S. nigrum and S. dulcamara as alternative hosts for Phytophthora infestans

Lesions of Phytophthora infestans were found on woody nightshade ( Solanum dulcamara ), black nightshade ( S. nigrum ) and S. sisymbriifolium during a nationwide late blight survey in the Netherlands in 1999 and 2000. Pathogenicity and spore production of P. infestans isolates collected from potato ( S. tuberosum ), S. nigrum , S. dulcamara and S. sisymbriifolium were determined on several host plant species, and oospore formation in naturally infected and inoculated foliage of hosts was quantified. The present population of P. infestans in the Netherlands is pathogenic on S. nigrum , S. dulcamara and S. sisymbriifolium . Oospores were produced in leaves of S. nigrum , S. dulcamara and S. sisymbriifolium following infection with A1 and A2 isolates. Therefore these plant species should be regarded as alternative hosts for the late blight pathogen. In the case of S. nigrum and S. dulcamara infection was a relatively rare event, suggesting that diseased plants do not significantly contribute to the overall late blight disease pressure present in potato-production areas. Oospore production in ageing S. nigrum and S. dulcamara plants in autumn, however, may generate a considerable source of (auto) infections in following years. Considerable numbers of sporangia and oospores were produced on S. sisymbriifolium following infection with P. infestans . Additional field infection data are needed to evaluate the epidemiological consequences of a commercial introduction of S. sisymbriifolium as a potato cyst nematode trap crop.