Polyamines and their roles in the alleviation of ion toxicities in plants

Abstract

Polyamines are ubiquitous polycationic aliphatic compounds known to be essential in physiological responses to different abiotic constraints in plants. Among others, they are involved in ion stress response. It is well known that physiological damages differ as a function of the ion type and the intensity of the stressor. Salinity, heavy metals, iron excess or aluminium are toxicities that were reported to induce modifications in polyamine metabolism. Polyamine metabolism flexibility can be directly linked with ion toxicities or with secondary stresses resulting from tissue injuries. Advances on polyamines research in relation to environmental constraints considerably benefit from the identification of genes involved in polyamine metabolism and controlling the conversion between free, conjugated and bound forms. Recent transgenic strategies performed with numerous plant species not only allowed gaining better detailed information about the molecular components of signalling pathways leading to modifications in polyamine metabolism but also about the cellular targets interacting with polyamine in ion overloaded tissues. The state of the art in the modification of polyamines metabolism and putative functions of these molecules in ion- stressed plant tissues will be presented in this review, considering the specificity of each type of mineral toxicity. A special attention will be paid to the interaction between polyamine and ethylene biosynthesis as well as to the interaction between those polycations and other plant growth regulators involved in stress response such as abscisic acid. Interactions between polyamines and ion channels and other transporters influencing mineral status of the stressed plants will be described on the basis of electrophysiological and pharmacological studies. The putative involvement of polyamines in plant water status regulation will be detailed through the analysis of higher plants overexpressing genes involved in putrescine and/or spermidine synthesis. Recent evidence gathered in plants also supports their roles in a wide range of regulatory functions of many basic cellular processes in stressed tissues including DNA replication, transcription, translation, cell division and modulation of enzyme activities. Several evidences demonstrated that polyamines can act as mitigating oxidative damages. The putative interest of polyamine synthesis as convenient and reliable criteria for selection of cultivated plants exhibiting a higher tolerance to mineral toxicities will be considered.