Nitrogen sources and CO2 concentration synergistically affect the growth and metabolism of tobacco plants

The initial stimulation of photosynthesis under elevated CO2 concentrations (eCO2) is often followed by a decline in photosynthesis, known as CO2 acclimation. Changes in N levels under eCO2 can have different effects in plants fertilized with nitrate (NO3-) or ammonium (NH4+) as the N source. NO3- assimilation consumes approximately 25% of the energy produced by an expanded leaf, whereas NH4+ requires less energy to be incorporated into organic compounds. Although plant-N interactions are important for the productivity and nutritional value of food crops worldwide, most studies have not compared the performance of plants supplied with different forms of N. Therefore, this study aims to go beyond treating N as the total N in the soil or the plant because the specific N compounds formed from the available N forms become highly engaged in all aspects of plant metabolism. To this end, plant N metabolism was analyzed through an experiment with eCO2 and fertigation with NO3- and/or NH4+ as N sources for tobacco (Nicotiana tabacum) plants. The results showed that the plants that received only NO3- as a source of N grew more slowly when exposed to a CO2 concentration of 760 μmol mol-1 than when they were exposed to ambient CO2 conditions. On the other hand, in plants fertigated with only NH4+, eCO2 enhanced photosynthesis. This was essential for the maintenance of the metabolic pathways responsible for N assimilation and distribution in growing tissues. These data show that the physiological performance of tobacco plants exposed to eCO2 depends on the form of inorganic N that is absorbed and assimilated.

A proposed model for the flowering signaling pathway of sugarcane under photoperiodic control

Molecular analysis of floral induction in Arabidopsis has identified several flowering time genes related to 4 response networks defined by the autonomous, gibberellin, photoperiod, and vernalization pathways. Although grass flowering processes include ancestral functions shared by both mono- and dicots, they have developed their own mechanisms to transmit floral induction signals. Despite its high production capacity and its important role in biofuel production, almost no information is available about the flowering process in sugarcane. We searched the Sugarcane Expressed Sequence Tags database to look for elements of the flowering signaling pathway under photoperiodic control. Sequences showing significant similarity to flowering time genes of other species were clustered, annotated, and analyzed for conserved domains. Multiple alignments comparing the sequences found in the sugarcane database and those from other species were performed and their phylogenetic relationship assessed using the MEGA 4.0 software. Electronic Northerns were run with Cluster and TreeView programs, allowing us to identify putative members of the photoperiod-controlled flowering pathway of sugarcane.