Spatio-temporal dynamics of the metabolome of climacteric fruit during ripening and postharvest storage.

Fruit quality traits are determined to a large extent by their metabolome. The metabolite content of climacteric fruit changes drastically during ripening and postharvest storage and has been investigated extensively. However, the spatial distribution of metabolites and how it changes in time has received much less attention as fruit are usually considered as homogenous plant organs. Yet, spatio-temporal changes of starch, which is hydrolysed during ripening, has been used for ages as a ripening index. As vascular transport of water, and, hence, convective transport of metabolites slows down in mature fruit and even stalls after detachment, spatio-temporal changes in their concentration are likely affected by diffusive transport of gaseous molecules that act as substrate (O2), inhibitor (CO2) or regulator (ethylene, NO) of the metabolic pathways that are active during climacteric ripening. In this review we discuss such spatio-temporal changes of the metabolome and how they are affected by transport of metabolic gases and gaseous hormones. As there are currently no measurement techniques available to measure the metabolite distribution repeatedly by nondestructive means, we introduce reaction-diffusion models as an in silico tool to compute it. We show how the different components of such a model can be integrated and used to better understand the role of spatio-temporal changes of the metabolome in ripening and postharvest storage of climacteric fruit that is detached from the plant and discuss future research needs.