1 - Overview of nitric oxide homeostasis: strategies for altering the levels of this signaling molecule in plants

Abstract

In the last 20years, nitric oxide (NO) has emerged as an important signaling molecule in plant growth and development and in the response to abiotic and biotic stresses. The control of NO homeostasis in plant cells is thereby essential to modulate the signaling functions of this radical. Endogenous NO levels are determined by the balance between routes of synthesis and degradation of this molecule. Nitrite and l-arginine are considered the main substrates for NO production in plants, although the involved molecular mechanisms are still under debate. NO degradation may occur through nonenzymatic reactions or mechanisms mediated by enzymes such as nonsymbiotic hemoglobins and S-nitrosoglutathione reductase. The manipulation of the expression of genes related to NO homeostasis is a biotechnological tool to obtain genotypes with altered NO content. In addition, NO levels in plant cells can be manipulated through the exogenous administration of molecules that alter NO homeostasis. The recent progresses in the design and applications of NO donors to increase NO content of plants under different abiotic and biotic stress conditions are reviewed. The application of other molecules that affect NO homeostasis, such as NO precursors, scavengers and inhibitors, is also summarized. Moreover, the recent use of polymeric nanoparticles for controlled NO supply in plants is discussed.