Molecular and biochemical aspects underlying polyamine modulation of fruit development and ripening

Purpose of review: Improved knowledge of the physiology of polyamines (PAs) during fruit development and ripening can be achieved not only by analysing endogenous PA levels and biosynthesis, but also through experimental protocols aimed at manipulating fruit PA levels. These include: exogenous PA supply under field and postharvest conditions, isolation of mutants, and, when possible, genetic engineering of PA biosynthetic genes. This article reviews the main molecular and biochemical results obtained in this field in relation to fruit development and ripening and functional properties. Findings: PA biosynthesis is developmentally regulated, and gene expression is sensitive to exogenous and endogenous stimuli including PAs themselves. Manipulating PA titres leads to developmental changes, and almost invariably to ripening delay and prolong shelflife. This is associated with inhibition of ethylene-related gene expression, retention of flesh firmness, inhibition of activities of cell wall degrading enzymes, and, in some cases, improved nutritional and antioxidant attributes of the fruit. The only transcriptome and metabolome profiling analyses available confirm that fruits engineered for high PA content exhibit a high metabolic status compatible with a high nutritional quality. Directions for future research: This survey shows that the molecular and biochemical bases of PA function are in their infancy. Thus, further transcriptomic and metabolic profiling of PA-treated or PA over-accumulating fruits is required to shed light on this very promising scenario. For practical purposes, besides optimising application strategies, commercial products containing PAs would be highly desirable.