Tomato: a crop species amenable to improvement by cellular and molecular methods

Tomato is a crop plant with a relatively small DNA content per haploid genome and a well developed genetics. Plant regeneration from explants and protoplasts is feasable which led to the development of efficient transformation procedures. In view of the current data, the isolation of useful mutants at the cellular level probably will be of limited value in the genetic improvement of tomato. Protoplast fusion may lead to novel combinations of organelle and nuclear DNA (cybrids), whereas this technique also provides a means of introducing genetic information from alien species into tomato. Important developments have come from molecular approaches. Following the construction of an RFLP map, these RFLP markers can be used in tomato to tag quantitative traits bred in from related species. Both RFLP's and transposons are in the process of being used to clone desired genes for which no gene products are known. Cloned genes can be introduced and potentially improve specific properties of tomato especially those controlled by single genes. Recent results suggest that, in principle, phenotypic mutants can be created for cloned and characterized genes and will prove their value in further improving the cultivated tomato.

Increased plasma catecholamine levels in patients with symptomatic mitral valve prolapse

Total plasma catecholamine levels, plasma norepinephrine levels, heart rate, and systolic and diastolic pressures were measured in 15 symptomatic patients with mitral valve prolapse and in 19 normal subjects in supine baseline conditions and in a standing position. In the 15 symptomatic patients, total plasma catecholamine levels and plasma norepinephrine levels were significantly elevated in both positions, and heart rate was lower than in normal subjects in the supine position but returned to normal in the upright position. Thus, symptomatic patients with mitral valve prolapse demonstrate increased resting sympathetic tone. In addition, the associated supine bradycardia suggested that increased vagal tone might also be present at rest. These observations support the hypothesis of a dual autonomic dysfunction in these patients and could account for some of the clinical manifestations of the mitral valve prolapse syndrome. © 1982

Unraveling the diurnal atmospheric ammonia budget of a prototypical convective boundary layer.

We investigate diurnal variability of the atmospheric ammonia (NH3) budget over unfertilized grassland by combining observations with a conceptual atmospheric boundary layer model. Our combined approach of diurnal observations and modeling enables us to identify the contribution of the four governing processes to the NH3 diurnal cycle: surface-atmosphere exchange, entrainment, advection and chemical gas-aerosol transformations. The observations contain new NH3 flux and molar fraction measurements obtained using the Differential Optical Absorption Spectroscopy (DOAS) remote sensing technique, eliminating problems related to inlet tubing. Using strict filter criteria, 22 days with clear-sky summer conditions are selected. From this selection, we analyze a single representative day characterized by prototypical convective boundary layer conditions, using the boundary layer model constrained by meteorological observations. We design two numerical experiments to study the NH3 diurnal variability and the individual contributions of the processes governing the ammonia budget. These experiments only differ in their representation of the NH3 surface exchange. First, a fitted function through the observed NH3 flux is prescribed to the model. In the second numerical experiment, the surface flux is solved following the DEPosition of Acidifying Compounds (DEPAC) parameterization. With a prescribed surface flux, the modeled NH3 molar fraction closely fits the observations. Two regimes are identified in the NH3 diurnal cycle: the morning, where boundary layer dynamics dominate the budget through entrainment, and the afternoon, where multiple processes are of importance. A similarly close fit to the observed molar fraction is achieved in the second experiment, but we identify a mismatch between the observed and parameterized NH3 surface flux. As a result, the model requires an unrealistic budget representation to achieve this close fit, e.g. high free tropospheric NH3. Our findings on the NH3 budget, based on integrating modeling and observations, paves the way for future research on the NH3 surface-atmosphere exchange at the subdaily scales.</p