Physiological and Biochemical Mechanisms Involved in the Response to Abscisic Acid in Maize Coleoptiles

The role of abscisic acid (ABA) in controlling growth and developmenthas been studied in maize (Zea mays L.) coleoptile segments.Application of ABA reduces the elongation rate by about 50%and affects ion fluxes. In particular, proton extrusion is decreasedwhile potassium efflux is greatly enhanced. Apparently, ABAdoes not: seem to influence calcium influx from the apoplastinto the cytosol, but more likely it influences its efflux.Alteration of cytosolic calcium concentration may also be obtainedby increasing its release from internal stores. This possibilitymight be sustained by the increased hydrolysis of phosphatidylinositolupon ABA application. Change in the balance of ion fluxes shouldresult from regulation of transport mechanisms at the membranelevel and should produce changes in the transmembrane electricalpotential. The H⁺- ATPase and the ATP-dependent calcium transportactivities are both influenced by the treatment with ABA, –55%and –40%, respectively. Under these conditions [Ca²⁺]_cytand pH_cyt can be modified and, as a consequence of their regulation,they may play an important role in mediating the physiologicaland biochemical effects of ABA, acting as second intracellularmessengers. ¹Research supported by National Research Council of Italy, SpecialProject RAISA, Sub-Project N. 2, Paper n. 2782.     

A Mathematical Framework for Combining Decisions of Multiple Experts toward Accurate and Remote Diagnosis of Malaria Using Tele-Microscopy

We propose a methodology for digitally fusing diagnostic decisions made by multiple medical experts in order to improve accuracy of diagnosis. Toward this goal, we report an experimental study involving nine experts, where each one was given more than 8,000 digital microscopic images of individual human red blood cells and asked to identify malaria infected cells. The results of this experiment reveal that even highly trained medical experts are not always self-consistent in their diagnostic decisions and that there exists a fair level of disagreement among experts, even for binary decisions (i.e., infected vs. uninfected). To tackle this general medical diagnosis problem, we propose a probabilistic algorithm to fuse the decisions made by trained medical experts to robustly achieve higher levels of accuracy when compared to individual experts making such decisions. By modelling the decisions of experts as a three component mixture model and solving for the underlying parameters using the Expectation Maximisation algorithm, we demonstrate the efficacy of our approach which significantly improves the overall diagnostic accuracy of malaria infected cells. Additionally, we present a mathematical framework for performing ‘slide-level’ diagnosis by using individual ‘cell-level’ diagnosis data, shedding more light on the statistical rules that should govern the routine practice in examination of e.g., thin blood smear samples. This framework could be generalized for various other tele-pathology needs, and can be used by trained experts within an efficient tele-medicine platform.     

In vitro propagation of <Emphasis Type="Italic">Helleborus</Emphasis> species

A general in vitro cloning system was established for four Helleborus species: H. argutifolius, H. foetidus, H. niger and H. orientalis. The plant material was introduced in vitro from axillary buds. A Murashige and Skoog (MS)—based medium (Murashige and Skoog 1962) was used supplemented with 2% (w/v) sucrose, 2-isopentenyladenine (2-iP) and 6-benzylaminopurine (BA). Multiplication rates depended on the genotype and varied from 1.3 for H. foetidus till 3.8 for H. niger. The first results showed that the rooting phase could be done ex vitro. Rooting was induced by a drench for one week in a solution of indole-3-butyric acid (IBA -3 mg l⁻¹) and 1-naphthaleneacetic acid (NAA-1 mg l⁻¹) at 5°C.     

Unbalanced ribosome assembly in Saccharomyces cerevisiae expressing mutant 5 S rRNAs.

Mutant 5 S rRNA genes were expressed in Saccharomyces cerevisiae to further define the function of the ribosomal 5 S RNA. RNA synthesis and utilization were assayed using previously constructed markers which have been shown to be functionally neutral and easily detected by gel electrophoresis. Most mutations were found not to affect the growth rate because they were poorly expressed or could be accommodated effectively in the ribosomal structure. Two of the mutants, Y5A99U56U57 and Y5U90i5 adversely affected cell growth as well as protein synthesis in vitro. Polyribosome profiles in both of these mutants were substantially shorter, and an analysis of the ribosomal subunit composition revealed a significant imbalance with a 25-35% excess in 40 S subunits. Kinetic analyses of RNA labeling indicated very low cellular levels of mutant RNA either because it was poorly expressed (Y5U90i5) or rapidly degraded before being incorporated into mature 60 subunits (Y5A99U56U57). The results suggest that the 5 S RNA is required for the assembly of stable ribosomal 60 S subunits and raise the possibility that this RNA or, more likely, its corresponding ribonucleoprotein complex is critical for subunit assembly or even RNA processing.