It is a gas at ambient temperature and it plays important roles as phytohormone in most plants . Lin et al.  review all aspects of ethylene metabolisms in plant biology, including production and perception (Fig. 3.6).
Regarding the ethylene role in grape defence, there has been a series of recent papers by the team of Prof. J. M. Merillon, University of Bordeaux 2, France showing that 2-chloroethylphosphonic acid, an ethylene precursor also called ethephon, led to a decrease of fungus growth when sprayed onto grapevines, through elicitation of natural defences . More details are available in the Chap. 5 in this book.
Additionally, a recent series of microarray analyses, using mRNAs extracted from berry tissues after exogenous application of ethylene on grape clusters, has been partly published by Chervin et al. : the expression of some genes involved in plant defence was shown to be modulated by such a phytohormone.
Fig. 3.6 Ethylene (MW: 28 g; gas at ambient temperature)
Fig. 3.7 Methyl jasmonate (MW: 224 g; BP: 89°C, 192°F)
3.8 Jasmonic Acid and Methyl Jasmonate
Jasmonic acid is present naturally in grape berries, particularly in seeds  up to 50 pmol/seed, and methyl jasmonate is also present to a lesser extent (about ten times less) (Fig. 3.7). Data are lacking to check the variability over various cultivars.
Methyl jasmonate has been shown to promote stilbene accumulation  and natural defenses of grape. There will be more details developed in the Chap. 5 in this book.
The salicylic acid is well-known to be part of the SAR: Systemic Acquired Resistance . Park et al.  showed that both conversions of salicylic acid to methyl salicylate and methyl salicylate to salicylic acid were essential for SAR in tobacco, and they concluded that methyl salicylate is a SAR signal in this plant (Fig. 3.8).
However, there is still some controversy about the direct involvement of salicylic acid and methyl salicylate in SAR [40, 42].
Fig. 3.8 Methyl salicylate (MW: 152 g; BP: 222°C, 432°F)
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