A handbook of environmental toxicology: human disorders and ecotoxicology.

Chapter 4 (Page no: 49)

Amino acids and peptides as mediators of abiotic stress tolerance in higher plants.

This chapter discusses the role of amino acids and peptides in mediating abiotic stress tolerance in higher plants. The pathways involved in plant responses to abiotic stress (such as salinity, ambient temperature, drought, acid rain, anoxia and heavy metal contamination) are highly complex, entailing initial perception, signal transduction and defence gene expression, culminating in the establishment of tolerance or programmed cell death. The potential significance of crosstalk between biotic and abiotic defence pathways is only just unfolding but needs to be incorporated into future models. In addition, signal transduction, whether effected directly or via associated metabolites of amino acids, represents another significant example transcending traditional concepts of plant biochemistry. Amino acid accumulation and the phytochelatin-induced transport and sequestration of potentially toxic metals will depend on the relative activities of signalling compounds such as ethylene, salicyclic acid, auxins, jasmonate and abscisic acid, but research is still at a preliminary stage and any conclusions would be premature. It is readily admitted that other aspects of abiotic stress responses need to be addressed to obtain a more comprehensive perspective of metabolism in higher plants. For example, the contribution of proteomics in the understanding of stress responses should be considered and incorporated within a general model of plant toxicology. The complexities and significance of additive, synergistic and antagonistic interactions of signal transduction in plant immunity require elucidation in the context of environmental pressures. On the basis of current evidence, it is concluded that abiotic stress in plants is profoundly associated with aspects of cellular toxicology. Manifestations are reflected in alterations in the metabolism of amino acids and certain peptides. The mechanisms underlying these changes remain largely speculative, but may involve amino acid-derived and other signalling compounds in complex crosstalk between abiotic and biotic pathways.

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