Leaf photosynthetic rate is correlated with biomass and grain production in grain sorghum lines

Significant genetic variation in leaf photosynthetic rate has been reported in grain sorghum [Sorghum biocolor (L.) Moench]. The relationships between leaf photosynthetic rates and total biomass production and grain yield remain to be established and formed the purpose of this experiment. Twenty two grain sorghum parent lines were tested in the field during the 1988 growing season under well-watered and water-limited conditions. Net carbon assimilation rates were measured at mid-day during the 30 day period from panicle initiation to head exertion on upper-most fully expanded leaves using a portable photosynthesis system (LI-6200). Total biomass and grain production were determined at physiological maturity. The lines exhibited significant genetic variation in leaf photosynthetic rate, total biomass production and grain yield. Significant positive correlations existed between leaf photosynthesis and total biomass and grain production under both well-watered and water-limited conditions. The results suggest that leaf photosynthetic rate measured prior to flowering is a good indicator of productivity in grain sorghum.     

Characteristics of dispersal in sexually mature dragonflies

Abstract.

• 1 The population dynamics of a natural population of Sympetrum danae (Sulzer) were studied, by means of a mark—release—recapture method, to find indications of dispersal by mature adults. Additional information on orientation and the influence of phenotype (including age), density and weather was obtained by observations under natural conditions and in a large outdoor field cage.
• 2 80% of all mature adults caught around the natural pond were estimated to be immigrants. Considerable immigration was confirmed by the abdomen length of unmarked matures which did not accord with that expected from the locally emerged population. Total numbers captured and the minimum number known to be alive fell sharply at the time when most individuals were mature. At the same time, new matures continued to enter and disappear from the study area at an increasing rate.
• 3 Dispersive behaviour (escape flights) in the field enclosure was primarily age dependent in both sexes: it occurred from an age of 25–30 days onwards. This coincides with the time-lag between the emergence peak and increased dispersal in the field. Secondary effects on escape flights suggested that males tended to abandon low density areas.
• 4 Males flew relatively more southward than females.

     

Root turnover and production by14C dilution: implications of carbon partitioning in plants

Summary Estimates of belowground net primary production (BNP) obtained by using traditional soil core harvest data are subject to a variety of potentially serious errors. In a controlled growth chamber experiment, we examined the aboveground-belowground, labile to structural tissue, and plant to soil dynamics of carbon to formulate a¹⁴C dilution technique for potential successful application in the field and to quantify sources of error in production estimates.Despite the fact that the majority of net¹⁴C movement between above- and belowground plant parts occurred between the initial labeling and day 5, significant quantities of¹⁴C were incorporated into cell-wall tissue throughout the growing period. The rate of this increase at late sampling dates was greater for roots than for shoots. Total loss of assimilated¹⁴C was 47% in wheat and 28% in blue grama. Exudation and sloughing in wheat and blue grama, respectively, was 15 and 6% of total uptake and 22 and 8% of total plant production.When root production estimates by¹⁴C dilution were corrected for the quantities of labile¹⁴C incorporated into structural carbon between two sampling dates, good agreement with actual production was found. The error associated with these estimates was ±2% compared with a range of –119 to –57% for the uncorrected estimates. Our results suggest that this technique has potential field application if sampling is performed the year after labelling.Sources of errors in harvest versus¹⁴C dilution estimates of BNP are discussed.     

Characterisation of the magnesium status of soils by means of the EUF-Mg fractions

Summary On the basis of pot experiments carried out on soils with different Mg contents using ryegrass, it could be established that Mg uptake by ryegrass is closely related to Mg in the EUF extracts. The Mg contents in the EUF extracts are therefore suitable indices of actually and potentially available Mg in soils.The ratio between Mg in the EUF extracts and Mg deposited on the electrode + filter varies. The absolute amount of Mg in the EUF extracts increases with increasing Mg content of the soils. The higher, however, the total desorbable Mg the lower are the Mg contents in the EUF extracts in comparison with the Mg contents deposited on electrode + filter. Besides total desorbable Mg the EUF-Mg fractions are influenced as well by the organic and inorganic CEC and by soil pH. The amount of EUF filtrate flowing through filter and electrode also has an influence on the amount of Mg in the EUF filtrate.Consequently for a proper evaluation of available soil Mg total EUF-Mg (Mg in the EUF filtrate + Mg deposited on electrode + filter) should be used.     

The influence of oxygen concentrations on denitrification in soil

Summary The influence of different O₂ concentrations on denitrification was studied in an agricultural soil. In both nitrate and nitrite amended soil, denitrification was not observed until the O₂ concentration decreased to 0.20 and 0.21 mol/ml, respectively. Denitrification was not observed in soil samples with O₂ concentrations above 0.28 mol/ml in the gas phase. These findings suggest that a completely anoxic environment is not required for denitrification to occur in soil.     

Diffusion of inorganic carbon across an unstirred layer: a simplified quantitative approach

Abstract The quantitative approach used here is based on a model comprising a well-stirred medium, an unstirred layer, and a CO₂ absorbing leaf. The unstirred layer is divided up by planes into a number of sub-layers. Within each plane the concentration of each solute is everywhere the same as is the electric potential. These variables constitute the basic data. Thus the planes were characterized by their pH value. An equation is derived which enables the calculation of the basic data of a plane from the known data of another plane. In this way it is possible to calculate the basic data for all planes. From these data the rate of assimilation, the thickness of the unstirred layer and its sub-layers, the fluxes across the sub-layers and the conversions among the carbon components can be estimated. The CO₂ flux decreases, and the HCO^?₃ flux increases towards the leaf. There are negative fluxes of OH^& and CO^2–₃. H⁺ fluxes are of minor importance and can be ignored if the pH of the medium is higher than 8.0, provided no non-inorganic C buffers with appropriate pK_a are present. The significance of the carbon diffusion facilitating effect of an inorganic carbon system is expressed in various ways. The values obtained represent maxima, as the assumption is made that the equilibrium reactions are very fast. It is argued that even better effects are possible if the back-diffusion of CO^2–₃ could be prevented by lowering the pH of the unstirred layer.     

Enzymes metabolizing dimethylamine, trimethylamine and trimethylamine N-oxide in the yeast Sporopachydermia cereana grown on amines as sole nitrogen source

Abstract Sporopachydermia cereana , an ascosporogenous yeast, grew on dimethylamine, trimethylamine or trimethylamine N -oxide as sole nitrogen sources and produced mono-oxygenases for dimethylamine and trimethylamine that were significantly more stable than the corresponding enzymes found in Candida utilis . No trimethylamine mono-oxygenase activity was found in S. cereana grown on dimethylamine. In cells grown on trimethylamine N -oxide (but not on the other nitrogen sources), evidence for an enzyme metabolizing the N -oxide, possibly an aldolase, but more probably a reductase was obtained. All these activities showed a similar requirement for the presence of FAD or FMN in the extract buffer during isolation to retain activity. Amine mono-oxygenase activities showed a similar sensitivity to inhibitors, including proadifen hydrochloride and carbon monoxide as the corresponding enzymes in C. utilis . The trimethylamine N -oxide-dependent oxidation of NADH was more sensitive to inhibition by EDTA, N -ethylmaleimide and β-phenylethylamine than the mono-oxygenases, and less sensitive to KCN, and activity was significantly higher with NADPH than was observed with the 2 mono-oxygenases.     

The effect of soil water status on critical phosphorus concentrations inStylosanthes hamata cv. Verano

Summary The effect of soil water status on the critical phosphorus concentration (CPC) determined in apices and whole tops ofStylosanthes hamata cv. Verano was investigated in a glasshouse trial. The species was grown with six rates of P and three ranges of soil water potential and was harvested at 10 and 14 weeks after germination. The CPC of both whole tops and apices decliced between the two harvests. At the first harvest the CPC of both whole tops and apices increased as the soil water potential decreased but at the second harvest there was no effect of soil water potential on CPC. It is suggested that at the earlier harvest water stress was delaying physiological development, resulting in a CPC characteristic of chronologically younger tissue, but that by the second harvest the decline in CPC with age had ceased for all water treatments.     

Functions and social consequences of infant–adult male interaction in a captive group of lowland gorillas (Gorilla gorilla gorilla)

The functions and social consequences of infant-adult male interaction in a captive group of lowland gorillas were evaluated. The two males repeatedly attempted to interact with the infant, the infant sometimes attempted to interact with the males, and the mother usually interrupted interactions between male and infant. Infant-directed actions by the two males frequently showed their interest in the infant and infrequently showed care giving toward her; their other infant-directed actions occurred near the time of excitement or of playful actions between adults. Male-directed actions by the infant frequently showed its interest in one male and infrequently showed care seeking from him. All infant-adult male interactions but one occurred in the less stimulating of the gorillas' two enclosures. Boredom and the mother's frequent thwarting of contact between a male and infant are suggested as influences on the males' interest in the infant. The data suggest that availability of interesting objects alleviated the boredom of captivity for males and thus dissuaded them from seeking stimulation which sometimes resulted in harmful behaviors toward the infant.     

A note on sequence-dependence of DNA structure

A circular dichroism study was conducted on the solution structure of several different oligonucleotides, whose X-ray structures have been solved. It is suggested that in aqueous solution the oligonucleotides can form structures that maintain geometrical elements which are typical of B-DNA, A-DNA, and their intermediate forms. It is shown that 5'GGATGGGAG:5'CTCCCATCC, which forms an A-DNA helix in the crystal state (McCall et al. 1986), in aqueous solution maintains an A-DNA like structure at temperatures below 10 degrees C. At temperatures between 10 degrees C and 25 degrees C it shows a tendency to form an intermediate structure between A-DNA and B-DNA. Also, it is shown that TFE does not cause a transition from B-DNA to A-DNA helix in short DNA fragments, but instead disrupts the helix.