Mechanical wounding

The emission of volatiles from wounded plants is rapid and they follow interesting time evolutions. It is therefore of considerable interest to track these time dependences. PTR-MS is particularly well suited to this area of plant science because of its fast response capabilities. This was nicely demonstrated in the early work of Fall et al. [224], mentioned above, where they were able to quantify the emission of (Z)-3-hexenal (based on the ion signal at m/z 81) within just 1 or 2 s after the wounding of aspen leaves. The disappearance 

---

Mechanical, physical, or chemical external irritants act not only at the place of occurrence, but the excitation can be also transferred along the whole plant [3,6-21]. The speed of transfer depends on many factors, such as the intensity of the irritation, temperature, chemical treatment, or mechanical wounding it is also influenced by previous excitations. The excitation reaction travels in both directions, from the top of a stem to roots and conversely, but not always at identical rates. The transfer of excitation has a complicated character accompanied by an internal change in cells and tissues. 

Wounding and herbivore attack Different situations such as mechanical wounding or insect feeding produced the induction of LOX transcripts in wounded and systemic leaves in the same plant. The function of LOX in wounding seems to be related to the synthesis of a number of different compounds with signaling activity. 

Fig. 4 VOCs emitted by young seedlings of Tanacetum cinerariaefolium in response to mechanical wounding. VOCs from undamaged and wounded seedlings were recorded by GS-MS. Reproduced from [35] with permission of Oxford University Press...

Mithofer A, Wanner G, Boland W (2005) Effects of feeding Spodoptera Uttoralis on lima bean leaves. II. Continuous mechanical wounding resembling insect feeding is sufficient to elicit herbivory-related volatile emission. Plant Physiol 137 1160-1168... 

We were also able to show that lupin leaves can increase their alkaloid content by a factor of 2-4 within a few hours after mechanical wounding (which could imitate a herbivoral attack) (29). This means that the defense system is able to respond to environmental stress. 

We have examined the time course of changes induced in isozymes of chorismate mutase and DAHP synthase in potato tubers following mechanical wounding (Table III). In each case both isozymes responded—the plastidic isozyme responding sooner and to a greater extent than the cytosolic isozyme. All five of the other pathway enzymes so far examined were induced by mechanical wounding. 

Table III. Response of aromatic-pathway enzymes to mechanical wounding...

Two proteinase inhibitors, Inhibitors I and II, accumulate in leaves of tomato plants when attacked by chewing Insects or mechanically wounded. The accumulation of these two antinutrient proteins is apparently a defense response and is initiated by the release of a putative wound hormone called the proteinase Inhibitor inducing factor (PIIF). The direction of flow of PIIF out of wounded leaves is primarily towards the apex and transport occurs maximally about 120 min following wounding. After a single severe wound, the vitro translatable tomato leaf mRNA specific for Inhibitors I and II Increases to a maximum within four hours and remains constant for about five hours when it decreases rapidly to about 50% of the maximum. 

A severe mechanical wound on a single leaf of tomato plants initiates a complex series of extracellular and intracellular reactions which result in the synthesis and accumulation of two proteinase Inhibitors, Inhibitors I and II, in leaf cells (J, 2. A second wounding, within a few hours, results in a 2-3 fold Increase in the rates of accumulation initiated by the... 

EFFECT OF THE HOT AIR-DESTRUCTION OF PETIOLE PHLOEM ON THE MOVEMENT OF PIIF OUT OF MECHANICALLY WOUNDED LEAVES... 

Fig. 1. Ethylene biosynthesis. The numbered enzymes are (1) methionine adenosyltransferase, (2) ACC (l-aminocyclopropane-l-carboxylic acid) synthase, (3) ethylene forming enzyme (EFE), (4) 5 -methylthio-adenosine nucleosidase, (5) 5 -methylthioribose kinase. Regulation of the synthesis of ACC synthase and EFE are important steps in the control of ethylene production. ACC synthase requires pyridoxal phosphate and is inhibited by aminoethoxy vinyl glycine EFE requires 02 and is inhibited under anaerobic conditions. Synthesis of both ACC synthase and EFE is stimulated during ripening, senescence, abscission, following mechanical wounding, and treatment with auxins.

Centuries ago, time was measured by the gnomon, the clepshydra, weights and gears (eventually controlled by an escapement), incense sticks, hourglasses, and then finally mechanical clocks, pendula, and self-winding watches (mechanically wound, self-winding, or by now controlled by a quartz crystal oscillator tank circuit). 

Although elicitors from insect oral secretions have received special attention, the quality and quantity of HIPVs may also be affected by insect feeding behavior such as continuous or interrupted leaf chewing, phloem sucking, and even egg deposition.193,194 Recently, it was shown that continuous mechanical wounding was sufficient to induce local as well as systemic emission of volatiles that are emitted as HIPVs.195 Thus, the role of insect elicitors in HIPV production still remains largely an open question. 

Another pathway is the fatty acid hydroperoxidase lyase (HPL) pathway. This pathway produces C6-aldehydes and C12-oxo acids. 2 C6-volatiles, including ( )-2-hexenal, (Z)-3-hexenal, hexanal, as well as their corresponding alcohols or esters, are produced from mechanically wounded plant tissue.197,203 C6-aldehydes are also formed during hypersensitive response to infection by bacterial pathogens, after insect feeding, and after exogenous application ofJA.204,205 As already shown in this chapter, some of C6-volatiles are known to be attractants of parasitoids and predators. 

The inisK was sbwing growing even more discordant as the mechanism wound dowa As it died there was the scratch and flare of a match. For a moment the shadows jerked away from its yelbw flame, and then darkness flooded back. But not before Jenty cau a glimpse of the face above it... 

Putrescine A-methyltransferase (PMT, EC 2.1.1.53) catalyses the first specific step in the biosynthesis of tropane alkaloids, cocaine and nicotine [123]. Putrescine is methylated by PMT via SAM (S-adenosylmethionine) transferring the methyl group from SAM to an amino group of putrescine. Fig. (1). This enzyme has been isolated from roots of both Nicotiana tabacum and D. stramonium [124], and the activity of this enzyme is restricted to the roots of Solanaceous species corroborated by results describing a root pericycle-specific activity in A. belladonna [125]. Nevertheless, more recently, a low mRNA pmt transcript level in leaves of N. tabacum, with a rise in transcript level after mechanical wounding has been detected [126]. 

This chapter follows the pattern of previous Reports with the various sesquiterpenoids considered in structural groups based on their postulated or established biosynthesis. Interest in sesquiterpenoid structure, synthesis, and biosynthesis has continued at a high level during the period covered by the present Report. Two excellent reviews have been published one provides an up-to-date account of sesquiterpenoid biosynthesis while the other provides an authoritative description of studies on sesquiterpenoid stress compounds. Stress metabolites are produced by plants after infection with fungi, bacteria, and viruses or after mechanical wounding, irradiation with u.v. light, dehydration, cold, or treatment with phytotoxic agents. 

P.L. McNeil, L. Muthukrishnan, E. Warder, and P.A. D Amore, Growth factors are released by mechanically wounded endothelial cells, J Cell Biol 109,811 822 (1989). 

---