The Effects of Grain Nitrogen and Applied Nitrate on Growth, Photosynthesis and Protein Content of the First Leaf of Barley Cultivars

Five cultivars of barley with widely differing grain nitrogencontents were compared. In the absence of exogenous nitratesupply plants grown from high nitrogen grain showed a more rapidleaf emergence, greater leaf size, especially of the first leaf,higher photosynthetic rate and greater total souble proteinand Fraction 1 protein content of the first leaf, than plantsgrown from low nitrogen grain. However, early supply of nitrateto plants grown from low nitrogen grain enabled these to performas well as those from grain with a high nitrogen content. Regressionanalysis showed that Fraction 1 content of the first leaf isclosely correlated with grain nitrogen which exerts a progressivelygreater effect on content of this protein as application ofexogenous nitrate is delayed. The more rapid photosyntheticrate of plants grown with high nitrogen, and the consequentgreater rate of dry matter accumulation, is attributable mainlyto effects of nitrogen availability on leaf area and much lessto effects on leaf protein.     

A Comparative Study of Early Seed Development in Genotypes of Barley and Rye

Early seed development was studied in 17 genotypes of barley,Hordeum vulgare L., and 11 genotypes of rye, Secale cerealeL. The numbers of cells and nuclei in the embryos and endospermsof developing seeds were scored daily for 5 days after selfpollination. For embryos, the mean cell doubling times variedfrom 9.2–12.9 h for barley and 15.7–22.7 h for rye.Endosperm mitotic cycle times of both species were shortestover the first 24 h after pollination but then became longer.A non-linear correlation was found between the number of embryocells and the number of endosperm nuclei in barely and rye andis similar to that for other members of the Triticeae. Hordeum vulgare L., Secale cereale L., barley, rye, embryo, endosperm, mean cell doubling time     

Vegetation and nesting preferences of black noddies at Masthead Island,Great Barrier Reef. II Patterns at the micro-scale

Distribution and abundance of black noddy Anous minutus nests in relation to vegetation were studied at Masthead Island, Great Barrier Reef. Methods used included mapping, correlation and regression analyses. Number of nests varied significantly with height and species of tree. Taller trees contained more nests per tree than did smatter trees. Most nests occurred in Pisonia but the highest nesting densities occurred in Ficus and Celtis. There were significant positive correlations between treephxsiognomy (d.b.h. etc.) and number of nests in Pisonia, Ficus and Celtis but noddies may avoid nesting in senile trees. Noddies preferred to nest in some species of tree rather than others, e.g. Ficus and Celtis were apparently preferred to Pisonia. The sparse fotiage of Ficus and Celtis may facilitate access of noddies to their nests and therefore be preferred to the more densely foliaged Pisonia.     

COOPERATIVE BREEDING IN A POPULATION OF WHITEBROWED SPARROW WEAVERS PLOCEPASSER MAHALI

This paper reports on a three year study describing cooperative breeding and demography of a sampled population of approximately 108 colour-marked White-browed Sparrow Weavers in Zambia. Twenty-seven communal groups with two to 11 individuals in a group made up this population and occupied a l km² area of mopane woodland. Each group had only a single reproductive pair and the pair-bond appeared strong. Non-reproductives were generally siblings or half-siblings and they contributed a major share of nestling feeding, nest building, intruder chasing and guarding. Groups cooperatively built nests in certain preferred trees and they maintained their nests year round. Feeding range encircled the nesting site and was used almost exclusively by the communal group. Overall population density was relatively stable, and between-year variation in group size was significantly greater than within-year variation. Variation in annual reproductive success among groups was high and correlated positively with size. Mortality rates for nestlings, six-month-olds and juveniles were not correlated significantly with group size. Frequency of disappearance for reproductives of both sexes was correlated negatively with group size.     

Scale problem in classification: an application of a stochastic method to evaluate the relative homogeneity of sample units

A basic problem in experimental design is to select a sample unit at a scale appropriate to the variables being observed and to the nature of the topic. Where hierarchical classification procedures are used it is important that the scale of the basic units is such that any variation found within the sample is small relative to that between the groups formed. In this paper a method is applied to evaluate the relative homogeneity of sample units. Replicates from each sample are classified hierarchically. The method of Sandland & Young (1979a, b) is used to determine the probability at division of the number of replicates assigned at a division to the same group occurring by chance. A high probability indicates relative heterogeneity of the samples from which replicates are drawn; a low probability suggests relative homogeneity. An example from the area of urban ecology illustrates an application of the method. It is used to evaluate the relative homogeneity of spatial units (Census Collectors Districts) with respect to dwelling characteristics in inner city Brisbane. Possible applications in other areas of ecology are briefly considered.     

Reversal of Electrogenic Cl- Pump in Acetabularia Increases Level and 32P Labelling of ATP

In order to test the prediction that the Cl^– ATPase inthe plasmalemma of Acetabularia is reversible, the content and³²P labelling of ATP in centrifuged, cytoplasm-depleted stalksegments has been measured upon incubation in ³²P containingmedia with normal (c. 500 mM) and zero Cl^–concentration.Increases in content and labelling of ATP could be demonstratedwhen the preparations were exposed to zero external Cl^–(1.1 M sorbitol, isotonic with the control medium–emdashErdschreiber solution). These effects are reduced in 1: 1 mixturesof 1.1 M sorbitol with 0.55 M Nal or Na-benzenesulphonate, thelatter two of which are known to diminish the number of activeCl^– pumps. Increased ATP content upon exposure to sorbitolis not observed at 5 °C, when the Cl- pump is known to bestrongly inhibited. These results provide strong evidence forthe hypothesis that the electrogenic Cl^– pump is a reversible,primary Cl^– transporting ATPase. The relationship of theseresults to the transmembrane potential difference measured underthe same conditions is not yet clear. Key words: Acetabularia, Electrogenic Cl^– pump, Cl^– ATPase, Cl^– gradient driven ATP synthesis, Reversible ATPase     

Digestion of Added Homologous Algae by Chlorella-Bearing Paramecium bursaria

SYNOPSIS. Endosymbiotic algae from Paramecium bursaria when added to the culture medium are ingested by Chlorella -bearing P. bursaria at a rate of 2,000 algae/organism/day. That the ingested algae are digested and assimilated by the ciliates is suggested by the more rapid growth of Paramecium when algae are added to the medium ( G = 40 hr with algae compared to 190 hr without). The digestion by the ciliates of exogenous algae contrasts with the survival of these algae under normal growth conditions. It is suggested that the protection of the endogenous algae is related to their location in peripheral perialgal vacuoles.