Aphid resistance: an overlooked ecological dimension of nonstructural carbohydrates in cereals

Nonstructural carbohydrates in cereals have been widely investigated from physiological, genetic, and breeding perspectives. Nonstructural carbohydrates may contribute to grain filling, but correlations with yield are inconsistent and sometimes negative. Here we ask if there are hidden functions of nonstructural carbohydrates, advance an ecological dimension to this question, and speculate that high concentration of nonstructural carbohydrates may challenge the osmotic homeostasis of aphids, thus providing a working hypothesis that connects nonstructural carbohydrates with aphid resistance in cereals. In the light of this proposition, the amount and concentration of nonstructural carbohydrates should be regarded as functionally different traits, with amount relevant to the carbon economy of the crop and concentration playing an osmotic role. We conclude with suggestions for experiments to test our hypothesis

Wheat Oxylipins in Response to Aphids, CO2 and Nitrogen Regimes

Wheat is critical for food security, and is challenged by biotic stresses, chiefly aphids and the viruses they transmit. The objective of this study was to determine whether aphids feeding on wheat could trigger a defensive plant reaction to oxidative stress that involved plant oxylipins. Plants were grown in chambers with a factorial combination of two nitrogen rates (100% N vs. 20% N in Hoagland solution), and two concentrations of CO2 (400 vs. 700 ppm). The seedlings were challenged with Rhopalosiphum padi or Sitobion avenae for 8 h. Wheat leaves produced phytoprostanes (PhytoPs) of the F1 series, and three types of phytofurans (PhytoFs): ent-16(RS)-13-epi-ST-Δ14-9-PhytoF, ent-16(RS)-9-epi-ST-Δ14-10-PhytoF and ent-9(RS)-12-epi-ST-Δ10-13-PhytoF. The oxylipin levels varied with aphids, but not with other experimental sources of variation. Both Rhopalosiphum padi and Sitobion avenae reduced the concentrations of ent-16(RS)-13-epi-ST-Δ14-9-PhytoF and ent-16(RS)-9-epi-ST-Δ14-10-PhytoF in relation to controls, but had little or no effect on PhytoPs. Our results are consistent with aphids affecting the levels of PUFAs (oxylipin precursors), which decreased the levels of PhytoFs in wheat leaves. Therefore, PhytoFs could be postulated as an early indicator of aphid hosting for this plant species. This is the first report on the quantification of non-enzymatic PhytoFs and PhytoPs in wheat leaves in response to aphids.Agricultura y Veterinari

High temperature during the budswell phase of grapevines increases shoot water transport capacity

Knowledge about heat acclimation in perennial plants is limited. Our hypotheses were (i) that high temperature during budswell before budbreak elicits acclimation in grapevines that is mediated by greater water transport capacity, and (ii) that water deficit modulates acclimation to high temperature. We compared field grown Malbec grapevines heated before budbreak during 3 or 15 days with untreated controls. We also combined these thermal regimes with two water regimes, well-watered and water deficit. The heat treatment was applied to vines enclosed in individual chambers. Under well-watered conditions, 3 days of heating during budswell were enough to increase number and diameter of primary xylem vessels in the emerging shoots, leaf stomatal density, transpiration, CO2 assimilation, shoot hydraulic conductance, specific shoot hydraulic conductivity, rates of shoot growth, leaf and lateral shoot appearance. Water deficit, while influencing xylem architecture, before budbreak did not alter the temperature effects on the water transport capacity. In vines with water deficit before budbreak, shoot hydraulic conductance was correlated with primary vessel number and total area of vessels, while in well-watered vines, with vessel size and total area of vessels. Irrigation practices need to manage this tradeoff between adaptation to elevated temperature and increased risk of hydraulic failure in plants with more and larger xylem vessels.Fil: Galat Giorgi, Eugenia. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Mendoza-San Juan. Estación Experimental Agropecuaria Mendoza; ArgentinaFil: Keller, Markus. Washington State University; Estados UnidosFil: Sadras, Víctor. University of Adelaide; AustraliaFil: Roig Junent, Fidel Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Perez Peña, Jorge. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Mendoza-San Juan. Estación Experimental Agropecuaria Mendoza; Argentin