This book offers an up-to-date review of the regulatory role of nitric oxide (NO) changes in the morphological, physio-biochemical as well as molecular characteristics of plants under abiotic stress. The first of two parts comprises four chapters and focuses on the properties, chemical reactions involving NO and reactive nitrogen species in plants. The second part, consisting of eleven chapters, describes the current understanding of the role of NO in the regulation of gene expression, NO signaling pathways and its role in the up-regulation of the endogenous defense system and programmed cell death. Furthermore, its interactions with other signaling molecules and plant hemoglobins under environmental and soil related abiotic stresses, including post-harvest stress in fruits, vegetables and ornamentals and wounding are discussed in detail. Together with the companion book , this volume provides a concise overview of the field and offers a valuable reference work for teachers and researchers in the fields of plant physiology, biochemistry and agronomy.