It is now clear that hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) function as signalling molecules in plants. A wide range of abiotic and biotic stresses results in H(2)O(2) generation, from a variety of sources. H(2)O(2) is removed from cells via a number of antioxidant mechanisms, both enzymatic and non-enzymatic. Both biotic and abiotic stresses can induce NO synthesis, but the biosynthetic origins of NO in plants have not yet been resolved. Cellular responses to H(2)O(2) and NO are complex, with considerable cross-talk between responses to several stimuli. In this review the potential roles of H(2)O(2) and NO during various stresses and the signalling pathways they activate are discussed. Key signalling components that might provide targets for enhancing crop production are also identified.

It is now clear that hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) function as signalling molecules in plants. A wide range of abiotic and biotic stresses results in H(2)O(2) generation, from a variety of sources. H(2)O(2) is removed from cells via a number of antioxidant mechanisms, both enzymatic and non-enzymatic. Both biotic and abiotic stresses can induce NO synthesis, but the biosynthetic origins of NO in plants have not yet been resolved. Cellular responses to H(2)O(2) and NO are complex, with considerable cross-talk between responses to several stimuli. In this review the potential roles of H(2)O(2) and NO during various stresses and the signalling pathways they activate are discussed. Key signalling components that might provide targets for enhancing crop production are also identified.

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Polyphenolic phytochemicals are ubiquitous in plants, in which they function in various protective roles. A 'recommended' human diet contains significant quantities of polyphenolics, as they have long been assumed to be 'antioxidants' that scavenge excessive, damaging, free radicals arising from normal metabolic processes. There is recent evidence that polyphenolics also have 'indirect' antioxidant effects through induction of endogenous protective enzymes. There is also increasing evidence for many potential benefits through polyphenolic-mediated regulation of cellular processes such as inflammation. Inductive or signalling effects may occur at concentrations much lower than required for effective radical scavenging. Over the last 2-3 years, there have been many exciting new developments in the elucidation of the in vivo mechanisms of the health benefits of polyphenolics. We summarise the current knowledge of the intake, bio-availability and metabolism of polyphenolics, their antioxidant effects, regulatory effects on signalling pathways, neuro-protective effects and regulatory effects on energy metabolism and gut health.

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