The number and distribution of neurons in the retinal ganglion cell layer were studied from the metamorphic climax to adulthood in the toad Bufo marinus. Retinal wholemounts stained with cresyl violet showed that total neuron numbers increased from 55,000 at metamorphic climax to about 950,000 in adult animals. During the same time the entire retinal area increased 46-fold from an average 3.4 mm2 to 157 mm2. The morphological character of the neurons and their density across the retina changed during development. In metamorphosing animals, the neurons of the ganglion cell layer had a uniform appearance and their density increased slightly from the centre to the dorsal ciliary margin. After metamorphosis a high neuron density area, the visual streak, evolved in the retinal centre, resulting in the formation of a 6 to 1 density gradient from the visual streak out to the dorsal and ventral retinal poles in adult animals. Optic fibre numbers in juvenile and adult optic nerves were estimated to be 330,000 and 745,000, respectively, corresponding to similar ganglion cell numbers. One optic nerve was sectioned in a few animals and 4 weeks later the number of intact neurons--assumed to be displaced amacrine cells (DA)--was estimated. They amounted to 80,000 in juvenile and 189,000 in adult animals or about 20% of the total neuron population of the retinal ganglion cell layer, the remaining 80% being GC. A 1.7 to 1 density gradient of DA from the visual streak out to the dorsal and ventral retinal periphery was established.(ABSTRACT TRUNCATED AT 250 WORDS)

Arabinoxylans (AX) are prebiotics found naturally in wheat (Triticum aestivum L.) flour with well known beneficial effects on human health. Arabinoxylan concentration was measured in wheat grain of the Berkut × Krichauff doubled haploid (DH) population grown at two contrasting environments in South Australia; one at an adequate‐rainfall site in Roseworthy in 2009 and one at a low‐rainfall site in Minnipa in 2007. A linkage map of 528 genetic markers was used for quantitative trait loci (QTL) mapping. There was wide variation in the grain AX concentrations within the DH population in both environments, ranging from 5.4 to 8.5% (of dry weight), and there was a significant phenotypic correlation between two environments. Heritability was estimated as 0.51. Quantitative trait loci associated with grain AX concentrations were located on chromosomes 1A, 2A, 3D, 4D, 6B, and 7A. Quantitative trait loci on 2A (QGax.aww‐2A.1) and 4D (QGax.aww‐4D.1) had major effects. At QGax.aww‐2A.1, the favorable allele came from Berkut, while at QGax.aww‐4D.1, the favorable allele was derived from Krichauff. Effects of markers at these two QTLs were further validated using grain from more environments (Roseworthy, Minnipa, and Booleroo, South Australia, in 2006). In all cases, lines carrying both favorable alleles at those loci contributed a significant increase in wheat grain AX concentration compared to lines without the favorable alleles. These genome regions could therefore be useful targets for wheat breeding or mapping of candidate genes controlling grain AX accumulation.

The retrograde transport of horseradish peroxidase (HRP) and cobaltic-lysine complex (CLC) was used to morphologically characterize large ganglion cells (GCs) and to determine their distribution in retinal wholemounts and in sectioned material in the retina of Bufo marinus. Large GCs, amounting to about 0.5% of total GC population, were defined to be those with very large dendritic field sizes varying between 0.1 mm2 to 0.6 mm2 and cell soma sizes of between 100 microns 2 to 400 microns 2. These cells were subdivided into 3 major groups, Types I, II and III, on the basis of their dendritic field sizes, aborization patterns and the strata of dendritic branching within the inner plexiform layer (IPL). The majority of large neurons (about 90%) were classified as Type I GCs with symmetrical dendritic arbor. These cells had either bistratified branching in the scleral and vitreal sublamina of the IPL (65% of Type I Cells) or unistratified branching in the scleral (26%) or in the vitreal (9%) sublamina. Their dendritic field sizes increased linearly from the retinal centre from 0.13 mm +/- 0.02 mm2 (mean and S.D.) to 0.58 +/- 0.11 mm2 in the retinal periphery. Type II GCs (about 9% of large GC population) were characterized by an asymmetrical dendritic aborization directed towards the ciliary margin with unistratified branching in the scleral sublamina of the IPL. The mean dendritic field sizes of these cells were 0.26 +/- 0.09 mm2. Type III GCs, the least frequent (about 1%) category of large GCs had sparsely branching, elongated dendritic branching aligned approximately parallel with the nasotemporal axis of the retina. The unistratified dendritic branches of these neurons were located in the vitreal sublamina of the IPL with a mean dendritic field size of 0.42 +/- 0.11 mm2. The dendritic field sizes of Types II and III GCs did not increase with retinal eccentricity. Type I GCs were distributed unevenly across the retina, the density being greatest in the visual streak, along the nasotemporal meridian of the retina. The dendritic field sizes of these cells increased towards the retinal periphery, resulting in a constant dendritic field coverage factor across the retina. Each retinal point was covered by the dendritic fields of 4-5 adjacent GCs. In contrast, Types II and III GCs had only discontinuous dendritic coverage. The identification of morphological types of large GCs with previously described functional classes of GCs in the anuran retina is discussed.

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