Cell wall composition in juvenile and adult leaves of maize (Zea mays L.)

Many leaf characteristics vary with position along the culm in maize (Zea mays L.) due to the existence of vegetative phase change and heteroblasty. The objective of this work was to determine if differences in cell wall composition exist among developmental phases and between Cg1, a developmental mutant, and wild-type maize. In one experiment, the middle third of fully elongated leaf blades from lower and upper regions of the shoot was harvested (midribs removed) and analyzed for several cell wall components. Averaged over five inbreds (De811, Ia5125, Mo17, P39, and Wh8584), lower leaf blades had higher levels of xylose and lower levels of total uronosyls, glucose, arabinose, and galactose (P < 0.05) than did upper leaf blades. With the exception of glucose, upper and lower leaves of Cg1 plants varied in the same manner as their near-isogenic siblings, except cell walls of Cg1 plants were more "juvenile" than cell walls of wild-type siblings at the same leaf stage. These data support the hypothesis that Cg1 delays but does not eliminate the transition from juvenile-vegetative to adult-vegetative phase. In a second experiment, juvenile (leaves 3 and 5), transition (leaf 7), and adult (leaves 9 and 11) leaves from inbreds B73 and De811 were harvested and analyzed as in the first experiment. As leaf number rose, total cell wall content of sample dry matter, total neutral sugars, glucose, xylose, and ester-linked monomers of p-coumaric acid and total ferulates including ferulate dimers increased linearly while total uronosyls acids, arabinose, and galactose declined linearly (P < 0.05). Glucose and xylose are major cell wall components released from cellulose and xylans after acid hydrolysis. Pectin, a minor component of grass cell walls, is composed of galacturonosyls, arabinose, and galactose. Secondary cell wall deposition increased between leaves 3 and 11 in a heteroblastic series, due to either increased cell wall content concomitant with decreased cell lumen size, changes in proportion of cell types (i.e., sclerenchyma), or a combination of these factors.     

Extracellular enzyme activity in the mycorrhizospheres of a boreal fire chronosequence

Saprotrophic microbes are typically credited with producing extracellular enzymes that recycle organic matter, though roots and mycorrhizal fungi also can contribute and may compete with the saprotrophs. We examined extracellular enzyme activity associated with the mycorrhizospheres of arbuscular mycorrhizal, ectomycorrhizal, dual-colonized (arbuscular and ectomycorrhizal), and ericoid mycorrhizal plants in a fire chronosequence in Alaska. Bulk soil and soil from beneath host plants were gathered in July 2004 and assayed for five enzymes that target organic C, P, and N substrates. Compared to bulk soil, activities of the C-targeting enzymes β-1,4-glucosidase and peroxidase were lower in arbuscular mycorrhizospheres and ericoid mycorrhizospheres, respectively. Moreover, extracellular enzyme activity varied among mycorrhizosphere types. Specifically, N-targeting leucine aminopeptidase was highest in arbuscular mycorrhizospheres, followed by ericoid and ectomycorrhizal/dual-colonized mycorrhizospheres; β-1,4-glucosidase had the reverse pattern. In addition, enzymatic stoichiometry suggested that extracellular enzyme producers invested more in C-acquisition than in N-acquisition in recent fire scars compared to mature forests. These data extend previous findings that roots and mycorrhizal fungi compete with saprotrophs by showing that the strength of this effect varies by mycorrhizal host. As a result the community composition of mycorrhizal host plants might mediate enzymatic activity in boreal soils.     

Protecting islands from pest invasion: optimal allocation of biosecurity resources between quarantine and surveillance

Removing pests from islands, and then keeping them pest free, is a common management goal. Given that goal we face a decision: how much effort should we invest in quarantine to reduce the risk of a pest arriving vs. surveillance, looking for the pest on the island with the view of eradicating it before it gets out of control. We use models of an island under threat of invasion by a pest (animal, plant or disease) and a cost minimisation approach to optimally allocate management resources between quarantine and surveillance. In the optimal allocations joint investment in both quarantine and surveillance is uncommon. Investment in quarantine is optimal if quarantine is more effective than surveillance or if large costs associated with pest impact and eradication are incurred at low pest density. Investment in quarantine is also favoured as our ability to eradicate a pest declines. Surveillance is optimal if it is considerably more cost-effective than quarantine and we can generate significant savings through early detection of the pest population. We illustrate how theses models are useful ways to examine these trade-offs by applying the model to the prevention of black rat (Rattus rattus) invasion on Barrow Island, Western Australia. Our model predicts an optimal strategy different to the management strategy currently being used on the island. We suggest that this is due to a risk-averse tendency in managers and the difficulty of estimating costs that combine management, environmental and social factors.     

Australopithecus sediba hand demonstrates mosaic evolution of locomotor and manipulative abilities

Hand bones from a single individual with a clear taxonomic affiliation are scarce in the hominin fossil record, which has hampered understanding the evolution of manipulative abilities in hominins. Here we describe and analyze a nearly complete wrist and hand of an adult female [Malapa Hominin 2 (MH2)] Australopithecus sediba from Malapa, South Africa (1.977 million years ago). The hand presents a suite of Australopithecus-like features, such as a strong flexor apparatus associated with arboreal locomotion, and Homo-like features, such as a long thumb and short fingers associated with precision gripping and possibly stone tool production. Comparisons to other fossil hominins suggest that there were at least two distinct hand morphotypes around the Plio-Pleistocene transition. The MH2 fossils suggest that Au. sediba may represent a basal condition associated with early stone tool use and production.     

Characterization of growth hormone binding sites in the goldfish,Carassius auratus: effects of hypophysectomy and hormone injection

A recombinant carp growth hormone (rcGH) was used to develop for a GH radioreceptor binding assay in the goldfish (Carassius auratus). Specific binding of¹²⁵I-rcGH to goldfish liver membranes was a pH, time, temperature, and membrane protein dependent process. Scatchard and LIGAND analysis indicated a single class of high affinity and low capacity binding site, with an association constant (Ka) of 1.9×10¹⁰ M^–1 and a maximum binding capacity (B_max) of 9 fmol mg^–1 protein. Liver tissue displayed the highest¹²⁵I-rcGH binding of all the tissues examined. Displacement of¹²⁵I-rcGH with various unlabeled teleost and mammalian GHs and prolactins revealed that the goldfish hepatic binding site was highly specific for teleost GH. Intraperitoneal administration of 0.1, 1.0, and 10 g rcGH g^–1 body weight to hypophysectomized goldfish resulted in a 27, 52, and 68% decrease in total binding sites, respectively. Injection of a high dose of rat prolactin (rPRL) (5 g rPRL g^–1 body weight) also resulted in a 32% decrease in total binding sites. These results suggest that endogenous GH may have a role in the regulation of its own receptors in the goldfish.     

Hypothalamic peptides influencing growth hormone secretion in the goldfish,Carassius auratus

In vivo andin vitro techniques were used to examine the influence of various vertebrate peptides on growth hormone (GH) secretion in the goldfish. Tetradecapeptide somatostatin (SRIF-14) was found to inhibit GH secretionin vitro from perifused pituitary fragments, whereas similar concentrations of a salmonid SRIF peptide (sSRIF-25) did not affect GH secretion from the goldfish pituitary fragments. This indicates that SRIF receptors on the goldfish pituitary are very specific for SRIF-14-like peptides. Salmon gonadotropin (GTH)-releasing hormone (sGnRH) was found to elevate serum GH levels in male goldfish. The dopamine antagonist pimozide alone or injected in combination with sGnRH did not influence serum GH levels, although injection of pimozide alone significantly elevated serum GTH levels, in addition to potentiating the effects of sGnRH on GTH secretion. sGnRH stimulated GH secretion from goldfish pituitary fragmentsin vitro, indicating that sGnRH acts directly at the level of the pituitary to stimulate GH secretion in the goldfish. These results suggest that GnRH may also function as a GH-releasing factor in the goldfish, although the release-inhibitory factors for GH and GTH secretion do appear to be separate and distinct. Two human GH-releasing hormone (hGHRH) peptides were found to be ineffective in altering GH secretionin vitro from the perifused pituitary fragments. Consequently, a role for a mammalian GHRH-like peptide in the hypothalamic regulation of GH secretion in the goldfish remains questionable.     

In vitro comparison of feline bone marrow-derived and adipose tissue-derived mesenchymal stem cells

Mesenchymal stem cells (MSC) are increasingly being proposed as a therapeutic option for a variety of different diseases in human and veterinary medicine. At present, MSC are most often collected from bone marrow (BM) or adipose tissue (AT) and enriched and expanded in vitro before being transferred into recipients. However, little is known regarding the culture characteristics of feline BM-derived (BM-MSC) versus AT-derived MSC (AT-MSC). We compared BM-MSC and AT-MSC from healthy cats with respect to in vitro growth and cell surface phenotype. Mesenchymal stem cells isolated from AT proliferated significantly faster than BM-MSC. Phenotypic differences between BM-MSC and AT-MSC were not present in the surface markers assessed. We conclude that BM-MSC and AT-MSC are similar phenotypically but that cultures of AT-MSC are easier to generate because of their higher intrinsic proliferative rate. Thus, AT-MSC may be the preferred MSC for clinical applications where rapid and efficient generation of MSC is important.