Oxygen uptake rates have contrasting responses to temperature in the root meristem and elongation zone

Growing at either 15 or 25°C, roots of Arabidopsis thaliana, Columbia accession, produce cells at the same rate and have growth zones of the same length. To determine whether this constancy is related to energetics, we measured oxygen uptake by means of a vibrating oxygen-selective electrode. Concomitantly, the spatial distribution of elongation was measured kinematically, delineating meristem and elongation zone. All seedlings were germinated, grown, and measured at a given temperature(15 or 25°C). Columbia was compared to lines where cell production rate roughly doubles between 15 and 25°C: Landsberg and two Columbia mutants,er-105andahk3-3. For all genotypes and temperatures, oxygen uptake rate at any position was highest at the root cap, where mitochondrial density was maximal, based on the fluorescence of a reporter. Uptake rate declined through the meristem to plateau within the elongation zone. For oxygen uptake rate integrated over a zone, the meristem had steady-stateQ10values ranging from 0.7 to 2.1; by contrast, the elongation zone had values ranging from 2.6 to 3.3, implying that this zone exerts a greater respiratory demand. These results highlight a substantial energy consumption by the rootcap, perhaps helpful for maintaining hypoxia in stem cells, and suggest that rapid elongation is metabolically more costly than is cell division.Maura J. Zimmermann, Jayakumar Bose, Eric M. Kramer, Owen K. Atkin, Stephen D. Tyerman, Tobias I. Baski

Modelling Ammonium Transporters in Arbuscular Mycorrhiza Symbiosis

The Stochastic Calculus ofWrapped Compartments (SCWC) is a recently proposed variant of the Stochastic Calculus of Looping Sequences (SCLS), a language for the representation and simulation of biological systems. In this work we apply SCWC to model a newly discovered ammonium transporter. This transporter is believed to play a fundamental role for plant mineral acquisition, which takes place in the arbuscular mycorrhiza, the most wide-spread plant-fungus symbiosis on earth. Investigating this kind of symbiosis is considered one of the most promising ways to develop methods to nurture plants in more natural manners, avoiding the complex chemical productions used nowadays to produce artificial fertilizers. In our experiments the passage of NH3 / NH+4 from the fungus to the plant has been dissected in known and hypothetical mechanisms; with the model so far we have been able to simulate the behavior of the system under different conditions. Our simulations confirmed some of the latest experimental results about the LjAMT2;2 transporter. Moreover, by comparing the behaviour of LjAMT2;2 with the behaviour of another ammonium transporter which exists in plants, viz. LjAMT1;1, our simulations support an hypothesis about why LjAMT2;2 is so selectively expressed in arbusculated cells

Night-time responses to water supply in grapevines (Vitis vinifera L.) under deficit irrigation and partial root-zone drying

Night-time water uptake (S-n) mainly corresponds to stem and organ rehydration and transpiration, the latter through stomata and cuticle. Nocturnal transpiration is uncoupled from photosynthesis, therefore it contributes to reduce water use efficiency (WUE). Night-time grapevine physiology was measured on field grown grapevines (cv. Shiraz) under partial root-zone drying (PRD) and deficit irrigation (Exp. 1), on potted vines (cv. Tempranillo) (Exp. 2) and on potted vines (cv. Cabernet Sauvignon) on a progressive drought treatment in the glasshouse (Exp. 3). Sap flow probes using the compensated heat pulse method (cHP) were installed in vines (Exp. 1 and 3). Night-time gas exchange measurements were performed for Exp. 3. Other vine water status monitoring methods used were: midday stem water potential (Psi(s)) for all experiments, and abscisic acid (ABA) concentration monitored from leaf sap for Exp. 3. Results showed that Sr, was parabolically correlated to Psi(s) measured on the previous day for all treatments and cultivars. Two distinct zones where vines exhibit different night-time behaviour within the Psi(s) vs S-n parabolic relationships were identified for all experiments. The differences between the two identified areas were related to the water status conditions of the vines: (i) non-water stress conditions (0 < Psi(s) < -1.0 MPa); (ii) water stress conditions (-1.0 MPa < Psi(s) < -2.0 MPa). Furthermore, levels of water stress were negatively correlated to concentrations of leaf sap ABA, which helped to explain the parabolic curve found for cv. Cabernet Sauvignon. (C) 2014 Elsevier B.V. All rights reserved