Nh

Volicitine

Jasmonic acid

Coronatine

Indanone-isoleucine methyl ester

Volicitine

Fig. 1.10.6. Structure of jasmonic acid and jasmonic acid like compounds or derivatives. In certain plants, these induce the same effects as jasmonate. (After Mitchell-Olds et al. 1998)

Wounding

Elicitation

Wounding

Elicitation

MAP-kinase

12-oxo-phytodienoic acid and jasmonic acid

MAP-kinase

Induction of enzymes of secondary metabolism

Volatiles:

monoterpenes sesquiterpenes

. Alkaloids Flavonoids

■ Anthocyanins Cell wall constituents

Fig. 1.10.7. Induction of secondary plant metabolites by jasmonic acid. Wounding and elicitation lead to an increase in the external pH, to a transient rise in 12-OPDA and jasmonate within the cells, and to the expression of genes encoding enzymes involved in secondary metabolism. Volatile compounds act as signals (e.g. for insects), alkaloids and phyto-alexins are defence compounds and the flavonoids protect against light and UV radiation. Re-enforcement of the cell wall by cross-linking also prevents pathogen attack. (After Wasternack and Parthier 1997)

In addition to the induction of Pin genes, jasmonate induces particularly the expression of genes whose products serve in some way or the other in defence against stress: PR proteins (pathogenesis-related proteins), phytoalexin-synthesising enzymes, dehydrins and osmotin, as well as genes which are also induced by ABA or ethylene. A possible signal transduction chain leading to these products is shown in Fig. 1.10.7. As can be seen, the concentration of jasmonate (and 12-OPDA) rises only transiently; defence, however, is permanent as a result of the induced synthesis of biologically active proteins. Since these proteins (enzymes) are now also synthe-

sised in plant parts which are not wounded or even not existent at the time of wounding, the systemic reaction (with respect to pathogen attack) is also called immunisation of plants.

The biochemistry of activation of a jasmo-nate-responsive promoter of JIPs is still relatively unknown. Promoters of Pin 2 and LOX 1 are best analysed. A palindromic element (TGACG) was found in the promoter of LOX 1 which is essential for inducibility by jasmonate. This sequence is known as the cis element of transcription factors possessing a bZIP element (see Chap. 1.5.2.2; Rouster et al. 1997).

Table 1.10.2. Influence of the type of leaf damage on the pattern of enzymes involved in protection against damage (after Stout et al. 1994)

Type of damage

Protein pattern

0 0

Post a comment