The cellular basis of the elongation response in submerged deep-water rice

The cellular basis of internode elongation was studied in intact deep-water rice plants (Oryza sativa L. cv. Habiganj Aman II) and in isolated stem sections. In intact plants, growth was stimulated by submergence in water and by ethylene treatment. In isolated sections, growth was enhanced by submergence, by ethylene, and by exposure of the tissue to an atmosphere of 3% O₂, 91% N₂ and 6% CO₂ or 3% O₂, 91% N₂, 6% CO₂ and 1 l l^-1 C₂H₄ (by vol.). Under all these conditions, growth was localized in the intercalary meristem at the bases of the internodes. Autoradiography of [³H]thymidine-labeled tissue showed activation of cell division and longitudinal expansion of the intercalary meristem. Increased production of new cells and their subsequent elongation thus form the basis for the growth response to submergence and ethylene treatment in deep-water rice plants.     

Lack of mutagenic effect of vinyl chloride monomer in the mammalian spot test

The kinetics of the killing effect of ethanol was studied at 6–30% concentrations. Ploidy of cells, deficiency of the excision-repair system or holding under no-growth conditions did not influence survival.Ethanol at 24% increased, in the strain, the number of respiration-deficient cells from a spontaneous level of 0.4% up to nearly half of all survivors.Genetic analysis showed the mitochondrial nature of induced respiration-deficient mutants (or rho^?).The influence of yeast resistance to some antibiotics was studied on rho^? mutagenesis, both spontaneous and induced by ethanol. Neomycin-resistant strains were characterized by a significantly lower level of these mutations than were neomycin-sensitive strains.     

Growth pattern of Carex arenaria (Cyperaceae)

The origin of the orthotropic aerial shoot from the plagiotropic, horizontal rhizome of Carex arenaria L. (Cyperaceae) was studied. A previously proposed adnation or fusion of the first internode of the orthotropic shoot and the fourth internode of the plagiotropic shoot could not be anatomically confirmed. The rhizome branches sympodially and the point of branching results from intercalary meristematic activity in the plagiotropic shoot.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 145–151.     

The Significance of the Vestibular Cell in Trap Nesting Wasps (Hymenoptera: Crabronidae): Does its Presence Reduce Mortality?

In a study carried out with the trap-nesting solitary wasp Trypoxylon attenuatum (Hymenoptera: Crabronidae) in 2000, we analysed the significance of different nest characteristics, like the vestibular cell and empty intercalary cells, and its role in the reduction of mortality. Analysis of the presence of the vestibular cell suggested that it represents a nest completion structure, whose presence reduces mortality in the initial stages (M1) but does not affect that due to chrysidid parasitoids (MP). The length of such vestibular cell was found to depend mainly on the space between the last provisioned cell and the exterior, pointing to a possible role in the reduction of the remaining space that could be used by other females to establish a nest exterior to the completed one. The empty intercalary cells were smaller than the vestibular cells, did not affect M1 or MP mortality rates in the nest, and exhibited an “aggregated” pattern of occurrence. This suggests that they could be the result of “abnormal” behaviour by the female owning the nest. The total mortality rate decreased with the increase in the number of cells in the nests, also being greater in nests established at low heights above the ground. M1 was lower in the innermost cells, while MP increased towards the interior and in the nests with more cells. The distribution in the nests of cells parasitized by Trichrysis cyanea (the main natural enemy found in the wasp population studied) reflects an “aggregated” pattern, suggesting repeated attacks against certain nests.