1.5 NO and Gene Regulation in Plants
The involvement of NO in plant signaling pathways is well recognized, but it is necessary to decipher the NO signaling routes, its targets, and its inductive or repressive effects on gene expression levels. Polverari et al. (2003) investigated the NO-induced changes in expression profiles of 2500 A. thaliana transcripts and discovered NO-induced alterations in 120 transcripts. The comparison of 71 differentially expressed complementary DNAs with microarray data revealed that the majority of NO-regulated genes are also impacted by other biotic and abiotic stress situations. In addition, Polverari et al. (2003) discovered that NO generated several plant defense response modifying transcription factors such as WRKYs, EREBPs (ethylene responsive element binding proteins), numerous zinc finger proteins, and dehydration responsive element binding proteins (DREB1 and DREB 2). NO donors were administered to tobacco plants or cell suspension cultures, which promoted the expression of defense-related genes PAL and PR1. These are indicators for phenyl propanoid synthesis and SA-mediated signaling, respectively, and are encoded by cryptography. Each of these genes plays a significant role in disease resistance (Delledonne et al. 1998; Durner et al. 1998).
1.6 Conclusions and Future Prospects
Nitric oxide is a dynamic molecule that performs a variety of physiological functions in both plants and animals. NO signaling plays a part in an array of plant biological functions, growth and developmental patterns, and abiotic and biotic stress tolerance. NO biosynthesis involves a number of complex mechanisms, including both enzymatic and nonenzymatic processes. It is necessary to conduct research on the substrates and inhibitors of the NO synthase enzyme, as well as its possible action on plants, in order to identify NO-generating enzymes. The association of NO with secondary signaling molecules as well as various phytohormones, and their possible mechanisms and pathways, need to be investigated further.
Future research should focus on the spatial and temporal distribution of NO in plants, as well as its intercellular and intracellular effects. In the future, the role of S-nitrosylation in the plant system and in ABA during the NO signaling mechanism must be recognized. Although the journey of NO research has been pushed back over the past few decades, a path forward must still be explored. Agriculture’s future requires effective research on the role of NO in increasing crop productivity and balancing ecological sustainability. The role of the NO and RNS-derived family in plant biology is being studied extensively. Elucidation of the role of NO in plant growth, seed germination, antioxidant defense mechanisms, postharvest harvest management, and the ripening phenomenon will open the door for future NO signaling research. As a result, much more research activity in NO studies is required to explore nitric oxide-mediated responses in the plant kingdom, as NO research opportunities are limitless and endless.
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