Identification and functional characterization of the sugarcane (Saccharum spp.) AMT2-type ammonium transporter ScAMT3;3 revealed a presumed role in shoot ammonium remobilization.

Sugarcane (Saccharum spp.) is an important crop for sugar and bioethanol production worldwide. To maintain and increase sugarcane yields in marginal areas, the use of nitrogen (N) fertilizers is essential, but N overuse may result in the leaching of reactive N to the natural environment. Despite the importance of N in sugarcane production, little is known about the molecular mechanisms involved in N homeostasis in this crop, particularly regarding ammonium (NH4 +), the sugarcane's preferred source of N. Here, using a sugarcane bacterial artificial chromosome (BAC) library and a series of in silico analyses, we identified an AMMONIUM TRANSPORTER (AMT) from the AMT2 subfamily, sugarcane AMMONIUM TRANSPORTER 3;3 (ScAMT3;3), which is constitutively and highly expressed in young and mature leaves. To characterize its biochemical function, we ectopically expressed ScAMT3;3 in heterologous systems (Saccharomyces cerevisiae and Arabidopsis thaliana). The complementation of triple mep mutant yeast demonstrated that ScAMT3;3 is functional for NH3/H+ cotransport at high availability of NH4 + and under physiological pH conditions. The ectopic expression of ScAMT3;3 in the Arabidopsis quadruple AMT knockout mutant restored the transport capacity of 15N-NH4 + in roots and plant growth under specific N availability conditions, confirming the role of ScAMT3;3 in NH4 + transport in planta. Our results indicate that ScAMT3;3 belongs to the low-affinity transport system (Km 270.9 µM; Vmax 209.3 µmol g-1 root DW h-1). We were able to infer that ScAMT3;3 plays a presumed role in NH4 + source-sink remobilization in the shoots via phloem loading. These findings help to shed light on the functionality of a novel AMT2-type protein and provide bases for future research focusing on the improvement of sugarcane yield and N use efficiency.

Role of sphingomyelin on the interaction of the anticancer drug gemcitabine hydrochloride with cell membrane models.

The fight against drug resistance in chemotherapy requires a molecular-level understanding of the drug interaction with cell membranes, which today is feasible with membrane models. In this study, we report on the interaction of gemcitabine (GEM), a pyrimidine nucleoside antimetabolite used to treat pancreatic cancer, with Langmuir films that mimic healthy and cancerous cell membranes. The cell membrane models were made with eight compositions of a quaternary mixture containing 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS), sphingomyelin (SM), and cholesterol (CHOL). The relative concentration of SM was increased so that four of these compositions represented cancerous cells. GEM was found to increase the mean molecular area, also increasing their surface elasticity, with stronger interactions being observed for membranes corresponding to cancerous cells. More specifically, GEM penetrated deepest in the membrane with the highest SM concentration (40 mol%), as inferred from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). This finding was confirmed with molecular dynamics simulations that also indicated how GEM approaches the membrane, which could be useful for guiding the design of drug delivery systems. The experimental and simulation results are consistent with the preferential attachment of GEM onto cancerous cells and highlight the role of SM on drug-cell interactions.