Photosynthesis of Ivy Leaves (Hedera helix) after Heat Stress I. CO2-Gas Exchange and Diffusion Resistances

For an analysis of the inhibition of the photosynthetic CO₂-uptake after heat stress attached leaves of Hedera helix L. were heat-stressed for 30 min at various temperatures. Subsequently their photosynthetic CO₂-uptake, transpiration, respiration in light and darkness, and CO₂-compensation concentration were measured under optimal conditions. After heat stress the stomatal resistance increased only corresponding to the raised CO₂-concentration inside the leaves (due to the reduced CO₂-uptake). The physical resistance between the mesophyll cell walls and the chloroplasts remained unchanged after heat stress. A non-stomatal inhibition of the CO₂-uptake is indicated by a strong increase of the CO₂-compensation concentration after heat stress. This is hardly due to a stimulation of the respiration in light, as the CO₂-evolution into CO₂-free air in light was even reduced. Therefore, it must be concluded that the photosynthetic process itself is impaired after heat stress.     

Diving behaviour and respiration in Blethisa multipunctata in comparison with two other ground beetles

ABSTRACT. The diving behaviour of Blethisa multipunctata (L.), a carabid species living on shores, is compared with that of two other hygrophilous carabid species. B. multipunctata enters the water spontaneously and is able to stay more than 1 h beneath the surface without renewing its respiratory air, In flooding experiments, c . 50% of submerged beetles do not leave the water after 2h. These animals emerge from time to time for a few seconds and then descend beneath the water again. Measurements of oxygen consumption and the volume of the respiratory air show that the underwater air-supply is sufficient for only a few minutes. B. multipunctata achieves maximum diving times of up to 97 min by using its air storage as a physical gill. In comparison with other Carabidae it shows neither morphological nor physiological adaptations, but only behavioural adaptations for its amphibious mode of life.     

Tissue-Specific Expression of Onco-Fetal Antigens During Embryogenesis

It has become evident from recent literature that especially in tumor virus systems, cell transformation leads to an arrest of differentation or to a retrodifferentiation. This may be reflected by the expression of embryonic antigens and it is therefore particularly important to characterize such antigens according to their specificity as well as to their Specificity during embryogenesis. We have demonstrated the expression of embryonic antigens which are cross-reactive in avian fibroblasts transformed either by Rous sarcoma virus or by methylcholanthrene. This paper is intended to demonstrate that these embryonic antigens are detected only at a certain period of embryogenesis and particularly in muscle cells. They are detected only occasionally or not at all in cells of other tissues such as brain, liver, lung, and the digestive organs. These antigens are absent from the target cells before transformation and are consequently induced by the transforming agent, either viral or chemical. Therefore, these results suggest that by transformation mechanism, cells become specifically reverted to an earlier stage of differentiation (retrodifferentiation).