OLIGOAGARS ELICIT A PHYSIOLOGICAL RESPONSE IN GRACILARIA CONFERTA (RHODOPHYTA)

Gracilaria conferta (Schousboe ex Montagne) J. et G. Feldmann responded with an oxidative burst and rapid increases in respiration and halogenating activity when agar, agarose, or the agarose degradation products neoagarotetraose and neoagarohexaose were added to the growth medium. In contrast, carrageenan, oligocarrageenans, neoagarobiose, l-galactose, d-galactose, and several other mono- and oligosaccharides did not have any effect. Sixfold increases in respiration were observed 3 min after addition of neoagarohexaose. The response could only be induced in species of the genera Gracilaria and Gracilariopsis. Neoagarohexaose also elicited a release of hydrogen peroxide in less than 15 min, resulting in an immediate increase in algal brominating activity. Bleached thallus tips appeared a few hours after the addition of neoagarohexaose. This effect was dependent on the release of hydrogen peroxide and exposure to light. Exposure to light and oligosaccharide elicitors increased the production of reactive oxygen species, which reached destructive concentrations when both mechanisms were simultaneously active. Concentrations of 0.1 to 3.3 μM agarose or agars were sufficient to trigger an increase in respiration, an oxidative burst response, and tip bleaching. However, higher concentrations of neoagarohexaose and neoagarotetraose were necessary to elicit the responses, indicating that the alga is more sensitive to oligoagars with degrees of biose-polymerization > 3. The extremely short reaction time and high specificity indicate that intermediates of agar degradation are recognized by Gracilaria as messengers when microbial degradation of its cell wall occurs. The physiological responses may represent the early stages of algal defense mechanisms involved in repression of pathogen ingress.     

Cellular immunity in pyelonephritis: inhibition of the spleen cell response to the mitogen concanavalin A

Spleen cells from rats given experimental pyelonephritis using Escherichia coli and Proteus mirabilis as infecting organisms were evaluated for their ability to respond to the mitogen Concanavalin A. Results indicate an 80% reduction in the response of animals with gross suppuration in the kidney, but no inhibition is observed in animals with kidney infection, but not renal abscesses. The inhibition is not, apparently, due to serum factors.     

Protein kinase C activation has dissimilar effects on sodium-coupled uptakes in renal proximal tubular cells in primary culture

Protein kinase C (Ca2+/phospholipid-dependent enzyme) was shown to be present in renal brush border membranes. To evaluate the influence of protein kinase C activation on three apical transport systems, we studied the effect of phorbol myristate acetate (PMA) and of two diacylglycerol analogs, oleoylacetylglycerol and dioctanoylglycerol, on sodium-dependent uptakes of phosphate (Pi), L-alanine, and alpha-methyl-D-glucopyranoside (MGP), as well as on specific phlorizin binding, in cultured rabbit proximal tubular cells. PMA, at 100 ng/ml, decreased the Vmax of Pi and MGP uptake by 30 and 17%, respectively, but not that of alanine uptake. None of the Km values were affected. PMA also decreased the number of phlorizin binding sites by 40%. PMA-induced inhibition of Pi and MGP uptake was time- and concentration-dependent, was mimicked by oleoylacetylglycerol, dioctanoylglycerol, and the diacylglycerol kinase inhibitor R59022, and was reversed by the protein kinase C antagonist 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7). The effects of PMA persisted in the presence of amiloride and dimethyl amiloride, and were potentiated by Ca2+ ionophore A23187. Opening of tight junctions blunted subsequent PMA-induced decrease of MGP uptake, but not of Pi uptake. It is concluded that: (i) activation of protein kinase C does not affect similarly Na-Pi, Na-hexose, and Na-alanine cotransport; and (ii) different pathways are likely to be involved in the observed effects.     

From Reef to Table: Social and Ecological Factors Affecting Coral Reef Fisheries,Artisanal Seafood Supply Chains,and Seafood Security

Ocean and coastal ecosystems provide critical fisheries, coastal protection, and cultural benefits to communities worldwide, but these services are diminishing due to local and global threats. In response, place-based strategies involve communities and resource users in management have proliferated. Here, we present a transferable community-based approach to assess the social and ecological factors affecting resource sustainability and food security in a small-scale, coral reef fishery. Our results show that this small-scale fishery provides large-scale benefits to communities, including 7,353 ± 1547 kg yr^-1 (mean ± SE) of seafood per year, equating to >30,000 meals with an economic value of $78,432. The vast majority of the catch is used for subsistence, contributing to community food security: 58% is kept, 33.5% is given away, and 8.5% is sold. Our spatial analysis assesses the geographic distribution of community beneficiaries from the fishery (the “food shed” for the fishery), and we document that 20% of seafood procured from the fishery is used for sociocultural events that are important for social cohesion. This approach provides a method for assessing social, economic, and cultural values provided by small-scale food systems, as well as important contributions to food security, with significant implications for conservation and management. This interdisciplinary effort aims to demonstrate a transferable participatory research approach useful for resource-dependent communities as they cope with socioeconomic, cultural, and environmental change.     

Identification of a Novel Function of PiT1 Critical for Cell Proliferation and Independent of Its Phosphate Transport Activity

PiT1 is a Na⁺-phosphate (P_i) cotransporter located at the plasma membrane that enables P_i entry into the cell. Its broad tissue expression pattern has led to the idea that together with the closely related family member PiT2, PiT1 is the ubiquitous supplier of P_i to the cell. Moreover, the role of P_i in phosphorylation reactions, ATP production, DNA structure, and synthesis has led to the view that P_i availability could be an important determinant of cell growth. However, these issues have not been clearly addressed to date, and the role of either P_i or PiT proteins in cell proliferation is unknown. Using RNA interference in HeLa and HepG2 cells, we show that transient or stable PiT1 depletion markedly reduces cell proliferation, delays cell cycle, and impairs mitosis and cytokinesis. In vivo, PiT1 depletion greatly reduced tumor growth when engineered HeLa cells were injected into nude mice. We provide evidence that this effect on cell proliferation is specific to PiT1 and not shared by PiT2 and is not the consequence of impaired membrane Na⁺-P_i transport. Moreover, we show that modulation of cell proliferation by PiT1 is independent from its transport function because the proliferation of PiT1-depleted cells can be rescued by non-transporting PiT1 mutants. PiT1 depletion leads to the phosphorylation of p38 mitogen-activated protein (MAP) kinase, whereas other MAP kinases and downstream targets of mammalian target of rapamycin (mTOR) remain unaffected. This study is the first to describe the effects of a P_i transporter in cell proliferation, tumor growth, and cell signaling.