No abstract

Nitrogen is the main limiting nutrient after carbon, hydrogen and oxygen for photosynthetic process, phyto-hormonal, proteomic changes and growth-development of plants to complete its lifecycle. Excessive and inefficient use of N fertilizer results in enhanced crop production costs and atmospheric pollution. Atmospheric nitrogen (71%) in the molecular form is not available for the plants. For world’s sustainable food production and atmospheric benefits, there is an urgent need to up-grade nitrogen use efficiency in agricultural farming system. The nitrogen use efficiency is the product of nitrogen uptake efficiency and nitrogen utilization efficiency, it varies from 30.2 to 53.2%. Nitrogen losses are too high, due to excess amount, low plant population, poor application methods etc., which can go up to 70% of total available nitrogen. These losses can be minimized up to 15–30% by adopting improved agronomic approaches such as optimal dosage of nitrogen, application of N by using canopy sensors, maintaining plant population, drip fertigation and legume based intercropping. A few transgenic studies have shown improvement in nitrogen uptake and even increase in biomass. Nitrate reductase, nitrite reductase, glutamine synthetase, glutamine oxoglutarate aminotransferase and asparagine synthetase enzyme have a great role in nitrogen metabolism. However, further studies on carbon–nitrogen metabolism and molecular changes at omic levels are required by using “whole genome sequencing technology” to improve nitrogen use efficiency. This review focus on nitrogen use efficiency that is the major concern of modern days to save economic resources without sacrificing farm yield as well as safety of global environment, i.e. greenhouse gas emissions, ammonium volatilization and nitrate leaching.

No abstract

The taccalonolides are a class of microtubule stabilizing agents isolated from plants of the genus Tacca. In efforts to define their structure activity relationships, we isolated 5 new taccalonolides, AC-AF, and H2, from one fraction of an ethanol extract of Tacca plantaginea. The structures were elucidated using a combination of spectroscopic methods, including 1D and 2D NMR and HRESIMS. Taccalonolide AJ, an epoxidation product of taccalonolide B, was generated by semi-synthesis. Five of these taccalonolides demonstrated cellular microtubule stabilizing activities and antiproliferative actions against cancer cells, with taccalonolide AJ exhibiting the highest potency with an IC50 value of 4.2 nM. The range of potencies of these compounds, from 4.2 nM to greater than 50 µM, for the first time provides the opportunity to identify specific structural moieties crucial for potent biological activities as well as those that impede optimal cellular effects. In mechanistic assays taccalonolide AF and AJ stimulated the polymerization of purified tubulin, an activity that had not previously been observed for the taccalonolides A and B, providing the first evidence that this class of microtubule stabilizers can interact directly with tubulin/microtubules. Taccalonolides AF and AJ were able to enhance tubulin polymerization to the same extent as paclitaxel, but with a distinct kinetic profile, suggesting a distinct binding mode or the possibility of a new binding site. The potencies of taccalonolides AF and AJ, their direct interaction with tubulin, together with the previous excellent in vivo antitumor activity of this class reveal the potential of the taccalonolides as new anticancer agents.