**6.2 Role in plant reproductive development**

Various transcription factors of R2R3-MYB family like MYB21, MYB24, and MYB57 are direct targets of JAZ proteins (**Figure 6**). These TFs have significant role in mediating JA-regulated stamen development [33]. Formation of MYB-MYC complexes due to the association of MYB21 and MYB24 with the IIIe bHLH factors MYC2, MYC3, MYC4, and MYC5 controls stamen development in Arabidopsis [34]. Besides the role of JA on stamen development, JA plays a major role in seed and embryo development in tomato The *jasmonic acid-insensitive1* (*jai1*) mutant, which exhibits a loss of function of the tomato homolog of COI1, cannot set viable seeds. Moreover, production of OPDA and a residual amount of JA, in tomato mutant *acx1a*, set viable seeds. Gene silencing (*OPR3* silenced gene*)* in *SiOPR3* a transgenic line of tomato produces comparable amount of OPDA to wild type and sets only a few viable seeds; methyl-JA treatment can restore the seed setting of *SiOPR3.*This further suggests the role of methyl jasmonate in maternal control of seed development [35].

### **6.3 Role in abiotic stress tolerance**

Numerous morphological, physiological, biochemical and molecular changes take place due to abiotic stresses like drought stress, salinity stress, high- and low-temperature stress, heavy metal toxicity, etc.; these stresses adversely affect plant growth and productivity. JA is believed to play a role in plant responses to abiotic stresses including drought, salt, and heat stress. Salinity is one of the perilous stresses that causes physiological drought and is responsible for delayed seed germination, seedling establishment and reduced growth and yield of any crop. Under salt stress, jasmonates proved to be an imperative phytohormone in mitigation. Jasmonates recovered salt inhibition on dry mass production in rice [36] and diminished the inhibitory effect of NaCl on the rate of 14CO2 fixation, protein content in *Pisum sativum* [37]. The pleiotropic effects of MeJA in protecting plants have been reported for several plants [38], reported in his studies JA is responsible for the amelioration of chilling injury, water stress, and salinity stress in *Oryza sativa* L., *Lycopersicon esculentum* L. [39], *Fragaria vesca* [40], and *Hordeum vulgare.* High-temperature stress destructively influences plant processes and disturbs the cell homeostasis [41]. Heat shock proteins (HSPs) are synthesized in plants in response to high temperature that prevent denaturation and assist refolding of

**Figure 6.**

*JA signaling and crosstalk in stamen development (Source: Huang et al, [42]).*

damaged proteins. Electrolyte leakage assays in heat-stressed plants after application of low-concentration MeJA demonstrates the cell viability responses. Heating WT Arabidopsis led to the accumulation of several jasmonates including OPDA, MeJA, JA, and JA-Ile, and the expression of jasmonate inducible gene PDF1.2 was found to be high upon heat stress exposure. Suppressor of G2 allele of SKP1 (SGT1) protein operates as a cofactor of heat shock protein 90 (HSP90) in both plants and mammals forming functional complexes and providing thermotolerance. JA also showed essential role in heavy metal and nutrient toxicity. In a study by [43], they reported that the excess amounts of boron present in soil decrease the net photosynthetic rate, closing of stomata, internal CO2 concentration, and total chlorophyll content in leaves. Foliar application of boron-stressed plants of Artemisia with MeJA started to stimulate the synthesis of antioxidant enzymes, reduce the amount of lipid peroxidation, and enhance artemisinin content. [44] found that the first report on jasmonate-induced anticancer activities exhibited their capacity to cause both cell death and suppression of cell proliferation. MJ was studied in topical application for precancerous and cancerous skin lesions [45].

#### **6.4 Role in biotic stress tolerance**

Two types of responses are shown by plants due to tissue injury, and jasmonates plays a significant role in these responses by signaling in plants. Two types of responses are local response and systemic response (**Figure 7**).

In local response during tissue damage, various attacker-derived signals or damaged-associated plant-derived signals are produced; these signals are either chemical or physical in nature and are recognized by PRRs pattern recognition receptors present on cell surface. This recognition event activates *de novo* synthesis of JA and JA-Ile by an unknown pathway. SCFCOI1/26 proteasome activation by JA-Ile results in degradation of JAZ proteins. These proteins are responsible for the repression of transcription factors (TFs) involved in the expression of defense-related traits.

**55**

**Figure 7.**

*Jasmonates: An Emerging Approach in Biotic and Abiotic Stress Tolerance*

Systemic responses are mediated by two distinct pathways involving JA. Cellnonautonomous pathway is a slow pathway and cell autonomous pathway is a fast pathway in defense responses. In cell-nonautonomous pathway upon leaf damage, JA is produced and translocated to undamaged leaf where it triggers JA responses in target cells whereas, in cell autonomous pathway, wound-induced production of a mobile signal (other than JA) activates JA/JA-Ile synthesis and subsequent responses in distal tissues. To optimize the spatial and temporal expression of responses the

Exogenous application of low concentration of methyl jasmonate below 1 micro molar do not promote premature leaf senescence, but if the concentration increases beyond 30 micro molar, symptoms of premature leaf senescence were seen in the early stages of plant growth by upregulating the expression of senescence-associated genes and by downregulating photosynthesis-related genes. JA promotes leaf senescence in a COI1-dependent manner; TFs MYC2, MYC3, and MYC4 mediate JA/ dark-induced leaf senescence by upregulating the expression of senescence-associated genes (e.g. *senescence-associated gene 29* [*SAG29*]) and chlorophyll catabolic enzyme genes (CCGs) (e.g. *pheophorbide A oxygenase*), as well as by down-regulating photosynthesis-related genes (e.g., *chlorophyll A/B binding protein 1*), whereas in germination process, JA delays the ABA-mediated inhibition of seed germination in Arabidopsis. During the cold-stimulated germination of wheat (*Triticum aestivum*) seeds, JA biosynthesis-related gene expression and JA biosynthesis increase rapidly in the dormant embryos after transfer to room temperature, and JA suppresses ABA

**6.5 Role in the promotion of leaf senescence and seed germination**

biosynthesis to promote cold-stimulated germination [47].

*DOI: http://dx.doi.org/10.5772/intechopen.84608*

two pathways may work synergistically.

*Role of JA in tissue damage (source: Abraham et al. [46]).*

*Jasmonates: An Emerging Approach in Biotic and Abiotic Stress Tolerance DOI: http://dx.doi.org/10.5772/intechopen.84608*

*Plant Science - Structure, Anatomy and Physiology in Plants Cultured in Vivo and in Vitro*

damaged proteins. Electrolyte leakage assays in heat-stressed plants after application of low-concentration MeJA demonstrates the cell viability responses. Heating WT Arabidopsis led to the accumulation of several jasmonates including OPDA, MeJA, JA, and JA-Ile, and the expression of jasmonate inducible gene PDF1.2 was found to be high upon heat stress exposure. Suppressor of G2 allele of SKP1 (SGT1) protein operates as a cofactor of heat shock protein 90 (HSP90) in both plants and mammals forming functional complexes and providing thermotolerance. JA also showed essential role in heavy metal and nutrient toxicity. In a study by [43], they reported that the excess amounts of boron present in soil decrease the net photosynthetic rate, closing of stomata, internal CO2 concentration, and total chlorophyll content in leaves. Foliar application of boron-stressed plants of Artemisia with MeJA started to stimulate the synthesis of antioxidant enzymes, reduce the amount of lipid peroxidation, and enhance artemisinin content. [44] found that the first report on jasmonate-induced anticancer activities exhibited their capacity to cause both cell death and suppression of cell proliferation. MJ was studied in topical application for precancerous and cancerous skin lesions [45].

*JA signaling and crosstalk in stamen development (Source: Huang et al, [42]).*

Two types of responses are shown by plants due to tissue injury, and jasmonates

plays a significant role in these responses by signaling in plants. Two types of

In local response during tissue damage, various attacker-derived signals or damaged-associated plant-derived signals are produced; these signals are either chemical or physical in nature and are recognized by PRRs pattern recognition receptors present on cell surface. This recognition event activates *de novo* synthesis of JA and JA-Ile by an unknown pathway. SCFCOI1/26 proteasome activation by JA-Ile results in degradation of JAZ proteins. These proteins are responsible for the repression of transcription factors (TFs) involved in the expression of defense-related traits.

responses are local response and systemic response (**Figure 7**).

**54**

**Figure 6.**

**6.4 Role in biotic stress tolerance**

**Figure 7.** *Role of JA in tissue damage (source: Abraham et al. [46]).*

Systemic responses are mediated by two distinct pathways involving JA. Cellnonautonomous pathway is a slow pathway and cell autonomous pathway is a fast pathway in defense responses. In cell-nonautonomous pathway upon leaf damage, JA is produced and translocated to undamaged leaf where it triggers JA responses in target cells whereas, in cell autonomous pathway, wound-induced production of a mobile signal (other than JA) activates JA/JA-Ile synthesis and subsequent responses in distal tissues. To optimize the spatial and temporal expression of responses the two pathways may work synergistically.

### **6.5 Role in the promotion of leaf senescence and seed germination**

Exogenous application of low concentration of methyl jasmonate below 1 micro molar do not promote premature leaf senescence, but if the concentration increases beyond 30 micro molar, symptoms of premature leaf senescence were seen in the early stages of plant growth by upregulating the expression of senescence-associated genes and by downregulating photosynthesis-related genes. JA promotes leaf senescence in a COI1-dependent manner; TFs MYC2, MYC3, and MYC4 mediate JA/ dark-induced leaf senescence by upregulating the expression of senescence-associated genes (e.g. *senescence-associated gene 29* [*SAG29*]) and chlorophyll catabolic enzyme genes (CCGs) (e.g. *pheophorbide A oxygenase*), as well as by down-regulating photosynthesis-related genes (e.g., *chlorophyll A/B binding protein 1*), whereas in germination process, JA delays the ABA-mediated inhibition of seed germination in Arabidopsis. During the cold-stimulated germination of wheat (*Triticum aestivum*) seeds, JA biosynthesis-related gene expression and JA biosynthesis increase rapidly in the dormant embryos after transfer to room temperature, and JA suppresses ABA biosynthesis to promote cold-stimulated germination [47].

Other key roles of jasmonates are:

As most of the work of jasmonates did in model plant Arabidopsis, so numerous roles of JA could be found in Arabidopsis, but some positive roles are also found in other plants.

