A principal feature of plant growth is the maximisation of surface area. This arises from the need of a sedentary organism to obtain the full spectrum of nutrients from the environment. One consequence of this survival strategy is increased vulnerability to pathogens and adverse conditions, since the subterranean and aerial boundaries of the organism with the external world will be immense.

Given this immensity and the lack of any specialised surveillance cells equivalent to the mammalian immune system, cells throughout the organism have evolved an ability to recognise foreign from self. The results of these molecular recognition events are reflected at the local site of stimulus perception but, importantly, are also transmitted to distant regions of the plant. There is now good evidence that defence gene expression and changes in the levels of defence-related products such as phytoalexins, callose and lignin are modulated by these local and systemic signalling events.

This chapter reviews research carried out on these topics at the University of Leeds, with particular reference to (1) plant defence responses to parasitic nematodes and (2) the molecular effectors of the wound-response. General literature to 1990, on defence-related proteins in higher plants has been reviewed by Bowles (1990a).

Plant–nematode interactions

One of the plant–nematode systems under study in my laboratory at Leeds University involves the response of potato (Solanum tuberosum) plants to potato cyst nematodes (Globodera spp.). The potato cultivar Maris Piper carries a single dominant gene for resistance (H1) that is effective against certain pathotypes of Globodera rostochiensis (for example, Ro1), but is ineffective against others (for example, Ro2) and against the closely related Globodera pallida (Sidhu & Webster, 1981).