Isozymes of β-Glucosidase in Dictyostelium discoideum

The activity of beta-glucosidase (EC 3.2.1.21) in extracts of Dictyostelium discoideum was investigated. The specific activity increased early in development, declined during pseudoplasmodium formation, and increased again during sorocarp formation. The beta-glucosidase which was present in growing amoebae and during the first stages of multicellular development was electrophoretically distinct from the enzyme which accumulated during the final stages of morphogenesis. Ribonucleic acid synthesis and protein synthesis during development were required for the accumulation of the later isozyme. Analysis of beta-glucosidase activity in a number of morphological mutants suggests that the enzyme which accumulates late in morphogenesis is developmentally controlled.     

Apparent Reassimilation of Respiratory Carbon Dioxide by Different Plant Species

Differences among species in respiration rates in CO₂-free air, in light and dark, were studied using the standard leaf chamber technique and the infrared carbon dioxide analyzer. Photosynthesis, transpiration and respiration were measured. In all species studied, rates of respiration were considerably higher in dark than in light. This effect was assumed to be due to reassimilation of the respiratory CO₂. A resistance analogy model was derived to account for the apparent differences in internal recycling of CO₂ among species; the differences were correlated with differences in maximum photosynthetic rates in normal air and optimal conditions (P₃₁₀) and with internal resistances to CO₂ diffusion (r_k). Species with high P₃₁₀ and low r_k appear to reassimilate all the endogenous CO₂, whereas other species with lower P₃₁₀ and higher r_k appear to reassimilate only a part of their respiratory CO₂. Experiments with the photosynthetic inhibitor, 3-(3,4-dichlorophcnyl)-l,l-dimethyl urea (DCMU), indicated that species with zero respiration in CO₂-free air and light release respiratory CO₂ when photosynthesis is inhibited. It is concluded that the CO₂ released in the presence of DCMU represents respiratory CO₂ which recycles to photosynthesis under normal conditions.     

Effects of light and temperature on the monoterpenes of peppermint

Peppermint (Mentha piperita L.) was grown in a growth chamber under several combinations of temperature and illumination, and the monoterpenes of each leaf pair were analyzed by gas chromatography. Effects on the monoterpenes could be seen in the new leaves after a few days in the growth chamber. Long-day conditions enhanced growth, with a corresponding increase in the total amount of monoterpenes. Either short nights or cool nights, combined with full light intensity during the day, enhanced the formation of menthone and depressed the accumulation of menthofuran and pulegone. Experiments with interrupted night and with low light intensity indicated that photoperiod, as such, does not directly influence the terpene composition. It is suggested that the oxidation-reduction level of the monoterpenes reflects the oxidation-reduction state of the respiratory coenzymes of the terpene-producing cells, and that this, in turn, depends on the concentrations of respiratory substrates in the cells. This suggestion is based on the likelihood that warm nights cause depletion of respiratory substrates, resulting in oxidizing conditions, while cool nights preserve high levels of respiratory substrates, and thus maintain reducing conditions.     

DIFFUSION THROUGH STOMATES

Ting, Irwin P., and Walter E. Loomis. (Iowa State U., Ames.) Diffusion through stomates. Amer. Jour. Bot. 50(9): 866–872. Illus. 1963.—It is shown that the rule that diffusion through isolated, small pores is proportional to the diameter rather than the area of the pores is valid for pores of diameters as small as 20 μ, and that the curve extends to the origin at zero diameters, indicating that the law is effective throughout the range of stomatal sizes. Suggestions that an elliptical pore will be relatively more effective in diffusion than a circular one and that diffusion is concentrated at the periphery of the pore are not supported by experimental evidence and are physically improbable. Brown and Escombe's conclusion that there is no interference in the diffusion through the individual pores of a multiperforate membrane if the pores are spaced 10 diameters apart is not valid for diffusion through the stomates of a leaf. With pores of 200 μ and less spaced 10 diameters apart, interference increases rapidly with a smaller size and larger number of pores. As a result, the diffusion through a membrane with pores 19 μ in diameter and 190 μ apart was the same as that through a membrane with pores 132 μ in diameter and 1.32 mm apart, although the calculated capacity of the first membrane was 7 times that of the second. The diffusion of water vapor through multiperforate membranes with pores spaced 10 diameters apart has an apparent maximum of 65–70% of the diffusion through an open tube. Calculations of the effect of partial closing of stomates, using Verduin's equation for interference between pores, indicate that the theoretical diffusion capacity of 10 μ stomates spaced at 10 diameters would be increased several times by closing to an average diameter of 5 μ. This increase illustrates the dominant effect of interference in diffusion through small, closely spaced pores. Calculated diffusion through these stomates would not be decreased until they were more than 95% closed. It is concluded that stomatal opening will have no important effect on diffusion from or into a leaf until the stomates are essentially closed.     

Spore coat genes SP60 and SP70 of Dictyostelium discoideum.

We cloned and sequenced the genes for two of the major proteins found in spore coats of Dictyostelium discoideum. The predicted translation product of each of these genes starts with a hydrophobic signal sequence that is subsequently cleaved. Expression of these spore coat genes is coordinate in prespore cells.