Spatio-temporal dynamics of the metabolome of climacteric fruit during ripening and post-harvest storage

Fruit quality traits are determined to a large extent by their metabolome. The metabolite content of climacteric fruit changes drastically during ripening and post-harvest 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 hydrolyzed during ripening, has been used for a long time 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 probably affected by diffusive transport of gaseous molecules that act as substrate (O2), inhibitor (CO2), or regulator (ethylene and 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 techniques available to measure the metabolite distribution repeatedly by non-destructive 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 post-harvest storage of climacteric fruit that is detached from the plant, and discuss future research needs.

Skin Permeance and Internal Gas Composition in `Hass' Avocado (Persea americana Mill.) Fruits

The gas skin permeance and the internal atmosphere composition of `Hass' avocado (Persea americana Mill.) fruits were evaluated during the ripening period by using surface chambers. Plant material was harvested at physiological maturity at Uruapan, Michoacan, Mexico, in November of 2001. Storage was conducted under natural atmosphere at 20°C and 81% RH; the physiological stages were expressed in terms of ethylene internal partial pressures and pulp firmness. The climacteric onset occurred at 18.2 N and the peak was reached at 5.0 N. The interñal partial pressure decreased consistently for O2 while for CO2 increased. This result suggested that the resistance to gas exchange imposed by skin caused that O2 taken up was not enough to supply fruit requirements and also that CO2 was produced faster than the rate at which it was given off to ambient. It was found that skin permeance to O2 and CO2 could vary during ripening period and that avocado skin was more permeable to O2 than to CO2 with a 1.7:1 ratio. Surface chambers were useful to determine internal concentrations and gas skin permeance, but care must be taken to select the best sampling procedure to allow getting accurate values of these parameters.