Intriguing information is accumulating on the role of
photoreceptor-mediated light signalling, circadian rhythms,
and daylength in determining or toning the outcome of
defence responses. Such effects are clearly of potential
relevance to horticulture and agriculture, as they could
contribute to seasonal variations in plant susceptibility to
disease and other stresses. Photoreceptor pathways could be
important, for example, in determining the daylength
dependence of responses to intracellular H2O2. However,
light modulation of oxidative stress responses could be
dependent on chloroplast pathways such as those discussed
in the first part of this review. Future studies should
continue to throw further light on the complexity of the
integrated circuitry that governs how plants cope with the
attempts of microorganisms and herbivores to gain access
to their resources.
Acknowledgements