Effect Of Elevated Carbon Dioxide On Root Hair Development And Nutrient Uptake And The Response Mechanisms Of Root Growth To Nutrient Supply In Arabidopsis Thaliana

1. Development of root hairs in Arabidopsis thaliana (L.) Heynh. under elevated CO2Root hairs may play a critical role in nutrient acquisition of plants grown under elevated CO2. This study investigated how elevated CO2enhanced the development of root hairs in Arabidopsis thaliana (L.) Heynh. The plants under elevated CO2(800μL L-1) had denser and longer root hairs, and more H-positioned cells in root epidermis than those under ambient CO2(350μL L-1). The elevated CO2increased auxin production in roots. Under elevated CO2, application of either1-naphthoxyacetic acid (1-NOA) or N-1-naphthylphthalamic acid (NPA) blocked the enhanced development of root hairs. The opposite was true when the plants under ambient CO2were treated with1-naphthylacetic acid (NAA), an auxin analogue. Furthermore, the elevated CO2did not enhance the development of root hairs in auxin-response mutants, axrl-3, and auxin-transporter mutants, axr4-1, auxl-7and pinl-1. Both elevated CO2and NAA application increased expressions of caprice, triptychon and rho-related protein from plants2, and decreased expressions of werewolf, GLABRA2, GLABRA3and the transparent testa glabra1, genes related to root-hair development, while1-NOA and NPA application had an opposite effect. Our study suggests that elevated CO2enhanced the development of root hairs in Arabidopsis via the well-characterized auxin signalling and transport that modulate the initiation of root hairs and the expression of its specific genes.2. Effect of elevated CO2on phosphorus nutrition of phosphate-deficient Arabidopsis thaliana (L.) Heynh. under different nitrogen formsPhosphorus (P) nutrition is always a key issue regarding plants responses to elevated CO2. Yet it is unclear of how elevated CO2affect P uptake under different nitrogen (N) forms. This study investigated the influence of elevated CO2(800μL L-1) on P uptake and utilization by Arabidopsis grown in pH-buffered phosphate (Pi)-deficient (0.5μM) hydroponic culture supplying with2mM nitrate (NO3-) or ammonium (NH4+). After7-d treatment, elevated CO2enhanced biomass production of both NO3-and NH4+-fed plants but decreased Pi amount absorbed by per weight of roots and Pi concentration in shoots of plants supplied with NH4+. In comparison, elevated CO2increased amount of Pi absorbed by per weight of roots as well as Pi concentration in plants and alleviated P-deficiency-induced symptoms of plants supplied with NO3-. Elevated CO2also increased root/shoot ratio, total root surface area and acid phosphatase activity, and enhanced expressions of genes or transcriptional factors involving in P uptake, allocation and remobilization in Pi-deficient plants. Furthermore, elevated CO2increased the NO level in roots of NO3--fed plants but decreased it in NH4+-fed plants. NO scavenger cPTIO inhibited plant P acquisition by roots under elevated CO2. Considering all of these findings, this study concludes that a combination of elevated CO2and NO3-nutrition can induce a set of plant adaptive strategies to improve P status from Pi-deficient soluble sources and NO may be a signaling molecule that controls these processes.3. Regulation of root hair development in Arabidopsis thaliana (L.) Heynh. by magnesiumRoot hairs are frequently reported to be plastic in response to nutrient supply in most plants, but relatively little is known about their development along with magnesium (Mg) availability, and evidence is also scarce about the signals involved in this process. Here, we characterized the response of root hair development to Mg availability in Arabidopsis thaliana grown in hydroponic culture with varied Mg concentrations, ranging from0.5to10000μM. Both density and length of root hairs decreased logarithmically in response to increasing Mg concentrations within that range, which correlated with the initiation of new trichoblast files and likelihood of trichoblasts to form hairs. Low-Mg availability resulted in greater concentrations of reactive oxygen species (ROS) and Ca2+in the roots and displayed a stronger tip-focused gradient of ROS and cytosolic Ca2+during initiation and elongation of root hairs, and this gradient could be eliminated by DPI or BAPTA drugs. Application of either BAPTA or DPI to low Mg treatment blocked the enhanced development of root hairs. The opposite was true when the plants under high Mg were supplied with Ca2+or PMS. Furthermore, root hair development of atrbohC/root hair defective2-1(rhd2-1) mutant was not affected by Mg availability. Whole-genome transcriptome data indentified a total of557differentially expressed genes, and the maximum differential expressed genes involved in’stress response’,’oxidation reduction’,’ion transport’ and ’cell wall organization’. A greater fraction of genes expressed at later developmental stages as well as hair cell genes involving cell wall organization were up-regulated by L7(0.5μM Mg for7d) and down-regulated by H7(10000μM Mg for7d). No change in expression of genes encoding Ca2+and Mg uptake. Taking all of these findings together, a distinct and previously poorly characterized response of Arabidopsis root hair development to Mg availability is presented where ROS and Ca2+were the signaling molecules that control this process.