Carbon Dioxide Effects on Carbohydrate Status and Partitioning in Rice

The atmospheric carbon dioxide (CO₂) concentration has beenrising and is predicted to reach double the present concentrationsometime during the next century. The objective of this investigationwas to determine the long-term effects of different CO₂ concentrationson carbohydrate status and partitioning in rice (Oryza sativaL cv. IR-30). Rice plants were grown season-long in outdoor,naturally sunlit, environmentally controlled growth chamberswith CO₂ concentrations of 160, 250, 330, 500, 660, and 900µmolCO₂ mol¹ air. In leaf blades, the priority between the partitioningof carbon into storage carbohydrates or into export changedwith developmental stage and CO₂ concentration. During vegetativegrowth, leaf sucrose and starch concentrations increased withincreasing CO₂ concentration but tended to level off above 500µmolmol^–1 CO₂. Similarly, photosynthesis also increased withCO2 concentrations up to 500µmol mol^–1 and thenreached a plateau at higher concentrations. The ratio of starchto sucrose concentration was positively correlated with theCO₂ concentration. At maturity, increasing CO₂ concentrationresulted in an increase in total non-structural carbohydrate(TNC) concentration in leaf blades, leaf sheaths and culms.Carbohydrates that were stored in vegetative plant parts beforeheading made a smaller contribution to grain dry weight at CO₂concentrations below 330µmol mol^–1 than for treatmentsat concentrations above ambient Increasing CO₂ concentrationhad no effect on the carbohydrate concentration in the grainat maturity Key words: CO₂ enrichment, starch, sucrose     

Identification of Immunogenic Epitopes of the 170-kDa Subunit Adhesin of Entamoeba histolytica in Patients with Invasive Amebiasis

ABSTRACT. Entamoeba histolytica causes amebic dysentery (AD) and liver abscess (ALA). Little is known about protective immunity to amebiasis, and studies in this area have been complicated by the paucity of defined ameba antigens. We examined the proliferative responses of peripheral blood mononuclear cells (PBMC) from patients with AD and ALA to a recombinant protein containing a portion of the 170 kDa adhesin of E. histolytica (170CR), and to two synthetic peptides (1 and 2) derived from the 170 kDa sequence that were predicted to contain T cell epitopes. A significant number of patients with AD and ALA had PBMC that proliferated to 170CR molecule, and several individuals with ALA and AD had T cells that recognized one or both peptides. Contrarily, individuals from a non-endemic region for amebiasis did not respond to 170CR protein, or to both peptides. In regard to antibody response, nine of fifteen patients with ALA showed antibodies to 170CR protein. These same patients had antibodies to peptide 2. We identified peptides from 170-kDa adhesin that may contain both T and B cell epitopes recognized by some patients with invasive amebiasis. These peptides may be valuable reagents in studies of the immune response to amebiasis.     

Reproductive interactions of the Shiny Cowbird Molothrus bonariensis and the Yellow-hooded Blackbird Agelaius icterocephalus in Trinidad

The reproductive interactions of the Shiny Cowbird Molothrus bonariensis , a brood parasite, and the Yellow-hooded Blackbird Agelaius icterocephalus , a host of the cowbird, were studied In Trinidad, West Indies. We gathered information on the breeding biology of the Shiny Cowbird and the Yellow-hooded Blackbird, the frequency of use of the host species, and the effects of brood parasitism on host breeding success. Yellow-hooded Blackbirds are polygynous for the most part; males build nests and attempt to attract females to lay in them by means of song and visual displays directed towards the nests. This behaviour probably makes it easy for cowbirds to locate breeding birds and their nests. Cowbird eggs were found in 153 of 377 (40–3 %) blackbird nests located before the nestling stage. Shiny Cowbird parasitism of the Yellow-hooded Blackbird had little negative impact on host reproductive success, whereas predation accounted for the majority of nest failures. Vigilant nest defense by male blackbirds combined with colonial breeding apparently also minimized the extent of host egg damage and removal by cowbirds, and the parasitized and unparasitized nests were equally successful at producing blackbirds. Cowbirds most frequently parasitized the first or only nesting attempts in blackbird territories, and first or only nests were also successful more frequently than subsequent nests.     

Epicuticular Wax and Cuticular Resistance in Rice

High leaf cuticular resistance has been reported as a component adaptation of plants to drought prone regions, Experiments were conducted to evaluate and characterize the role of epicuticular wax as a component of cuticular resistance to water vapor loss from rice (Oryza sativa L.) leaves. This information is necessary to determine the applicability of including higher cuticular resistance in an upland rice breeding program and to evaluate potential selection methods. Diffusion porometry, electron microscopy, and gas liquid chromatography were employed. Measurement of cuticular resistance by leaf diffusive resistance porometry after stomatal closure by exposure of rice leaves to pure CO₂ for 15 min was found sufficient to induce complete stomatal closure regardless of light level, and was superior to dark acclimation for this purpose. Removal of epicuticular wax from rice leaves by chloroform dip significantly reduced the cuticular resistance. Stressed plants were observed to increase cuticular resistance, illustrating the responsive nature of this characteristic. Gas liquid chromatography (GLC) of the chloroform leaf dip proved to be an expedient method of characterizing both quantitative and qualitative differences in the epicuticular wax of rice cullivars. The porometry and GLC techniques may be useful in selecting parents, spot checking in a pedigree program, or checking lines reaching the yield testing stage, but ate not well suited lor mass screening early generation progeny. Significant differences were found in the two rice cultivurs, ‘63–83′, an upland adapted rice from West Africa, and “IR20′, bred and selected in submerged paddy culture in ihc Philippines, by tlie above methods of characterizing cuticular resistance and epicuticular wax. These results are of ecological significance to plant breeders.     

Texas Latino College Student Attitudes Toward Natural Resources and the Environment

Abstract: Latinos in the United States are an increasing segment of the population and are becoming important stakeholders in the management of natural resources. Although Latinos have been included in attitudinal research on environmental concerns, few studies have focused exclusively on Latino attitudes toward natural resources and the environment. We surveyed Texas college and university students of Mexican descent (n = 635) to determine their environmental concerns. Using the New Ecological Paradigm (NEP), we determined an environmental concern score for each respondent and compared this index to several demographic variables. We found that gender, a political candidate's environmental position, mother's education, combined parental income, and, to a lesser degree, the number of grandparents born in the United States and religiosity (church attendance), were important model variables. We hypothesized that acculturation would be an important factor in predicting NEP scores; however, acculturation level was not an important predictor in our study, which we attribute to both the nature of our sample (i.e., highly acculturated college students) and small sample sizes of less-acculturated college students. We recommend that future research consider determining the importance of acculturation in Latino attitudes toward natural resources and the environment.