**Author details**

involvement MeJA and mechanical wounding in expression of the *Ipomoelin* gene (*IPO*) in sweet potato. Later, Jih et al. [150] demonstrated that SNP-derived NO delayed wounding-induced *IPO* expression, providing evidence for antagonistic association between NO and JA. In *Arabidopsis*, NO treatments led to elevated expression of key enzymes of the octadecanoid pathway, like *LOX2, AOS, or OPR3,* in wounded leaf epidermis [151]. However, this induction did not influence JA responsible genes, like PDF*1.2*, hence supporting the earlier evidences about NO and JA association. NO-induced wound-responses could act as a modulator of cell death initiation

128 Phytohormones - Signaling Mechanisms and Crosstalk in Plant Development and Stress Responses

*Lycopersicon esculentum* demonstrated neither wound-induced NO burst, nor NO-induced elevation of endogenous SA levels [153]. Moreover, SNP-derived NO inhibited the expression of the proteinase inhibitors *Inh1, Inh2*, cathepsin D inhibitor (*CDI*), and metallocarboxypeptidase inhibitor (*CPI*) and increased *AOS* or *LOX* activity. Nevertheless, these studies demonstrate clearly that induction of a wound-response in plants involve cross talk among various stress

Initiation of senescence in plants is controlled by various factors such as nutrient supply, light conditions, leaf age, and environmental stress [154]. Plant hormones such as ET and CK influence senescence by either promoting or delaying the process, respectively [155, 156]. Evidence supports the interaction of NO with other plant hormones to floral senescence and fruit maturation [157]. Recently, Ji et al. [158] demonstrated that SA treatment at low concentrations induced NOA1-dependent NO signaling and activated antioxidant defense to counteract MeJA-induced leaf senescence. NO plays a conceivable role to counteract the ABA- and

tion [159]. Mishina et al. [160] found that delayed leaf senescence in *Arabidopsis* involves NO-induced reduction in SA levels. During fruit ripening, NO cross talk with SA and ET involves the regulation of levels of secondary metabolites such as anthocyanins [161]. NO-induced suppression of cell wall softening related enzymes such as polygalacturonase (PG), pectin methylesterase (PME), and pectate lyase (PL) was found to delay softening and ripening of stored *Carica papaya* by reducing ABA, IAA and zeatin ribose (ZR) levels [123].

Although our understanding of NO interactions with plant hormones has increased dramatically in past few years, many pieces of the puzzle are still missing. It is well established that NO coordinates with plant hormones to regulate gene expression and activities of anti-oxidative enzymes under adverse environmental conditions. However, our current knowledge about NO-phytohormone interactions is derived chiefly from NO-induced posttranslational modifications of transcription factors and biosynthetic enzymes. Future work is needed to explore the interplay among NO, plant hormones, ROS, protein kinases, and cytoskeletal proteins in order to understand the complicated network of NO signaling under abiotic stress conditions. Interestingly, most of the studies related to NO-phytohormonal interactions involve experiments in controlled laboratory environments, very little is known about the

accumulation, and delay of IPO-expression [152]. Contrasting reports in

O2

accumulation and lipid peroxida-

together with H2

signaling molecules.

O2

jasmonate-induced senescence in rice by inhibiting H2

**7. Conclusion and future perspectives**

Fahim Nawaz1 \*, Rana Nauman Shabbir2 , Muhammad Shahbaz3 , Sadia Majeed4 , Muhammad Raheel5 , Waseem Hassan6 and Muhammad Amir Sohail1

\*Address all correspondence to: fahim5382@gmail.com

1 Department of Agronomy, MNS University of Agriculture, Multan, Pakistan

2 Department of Agronomy, Agriculture College, Bahauddin Zakariya University, Multan, Pakistan

3 Department of Food Science and Technology, MNS University of Agriculture, Multan, Pakistan

4 Department of Agronomy, UCA & ES, The Islamia University of Bahawalpur, Pakistan

5 Department of Plant Pathology, UCA & ES, The Islamia University of Bahawalpur, Pakistan

6 Department of Soil Science, MNS University of Agriculture, Multan, Pakistan
