Induction of Terminal Oxidases of Electron Transport Chain in Broccoli Heads under Controlled Atmosphere Storage

Controlled atmosphere (CA) storage, that is, at low O2 and high CO2 concentrations, effectively extends the shelf life of horticultural products. The influence of CA storage (O2/CO2: 2.5%/6.0% or 2.5%/0.0%) and in normal air (both at 1 °C for 21 d) on the physicochemical (O2 uptake, mass loss and L-ascorbate) and biological properties of broccoli (Brassica oleracea var. italica, Plenck, 1794) via amounts and activities of terminal oxidases of the electron transport chain was investigated. Mass loss, a sensitive index of freshness for broccoli heads under CA, was significantly lower under CA than under normoxia (p < 0.05). Mass loss was depressed 7 d earlier under CA, including 6.0% CO2 than under CA without CO2. High CO2 effectively depressed the degradation of L-ascorbate. During storage, the activity of the alternative oxidase (AOX) was lower under CA than in normal air (p < 0.05), while the amount of cytochrome c oxidase (COX), and the AOX/COX activity ratio (based on oxygen isotope discrimination), were not affected during storage. Our results indicate that CA storage effectively retained the freshness of broccoli heads by depressing the induction of AOX. However, depression of AOX amount was not associated with CO2 around broccoli heads.

Induction and Activity of Terminal Oxidases of Electron Transport Chain in Broccoli Heads under Controlled Atmosphere Storage

Controlled atmosphere (CA) storage, under atmospheres with low O2 and high CO2 concentrations, is effective for extending the shelflife of horticultural products. We investigated the influence of CA storage (O2/CO2: 2.5%/6.0% or 2.5%/0.0%) at 1C for 21 d versus normoxia (normal air) on the physicochemical and biological properties of broccoli (Brassica oleracea var. italica, Plenck, 1794) via amounts and activities of terminal oxidases of electron transport chain. Mass loss, a sensitive index of freshness for broccoli heads under CA, was significantly lower under CA than under normoxia. The effect for depressing mass loss was observed 7 d earlier under CA including 6.0% CO2 than under CA without CO2. Environmental CO2 was also effective for depressing loss of L-ascorbate. The alternative oxidase (AOX) level under CA was lower than under normoxia during storage, while the level of cytochrome c oxidase (COX), and the AOX/COX activity ratio (based on oxygen isotope discrimination), were stable during storage. Our results indicate that CA storage is effective for retaining freshness of broccoli heads during storage by depressing the induction of AOX. However, depression of AOX level was found to be independent of environmental CO2.

Calculation of the oxygen isotope discrimination factor for studying plant respiration

Measurement of discrimination against 18O during dark respiration in plants is currently accepted as the only reliable method of estimating the partitioning of electrons between the cytochrome and alternative pathways. In this paper, we review the theory of the technique and its application to a gas-phase system. We extend it to include sampling effects and show that the isotope discrimination factor, D, is calculated as –dln(1 + δ)/dlnO*, where δ is isotopic composition of the substrate oxygen and O*=[O2]/[N2] in a closed chamber containing tissue respiring in the dark. It is not necessary to integrate the expression but, if the integrated form is used, the resultant regression should not be constrained through the origin. This is important since any error in D will have significant effects on the estimation of the flux of electrons through the two pathways.

Beyond Sham and Cyanide: Opportunities for Studying the Alternative Oxidase in Plant Respiration Using Oxygen Isotope Discrimination.

Discrimination against 18O during dark respiration forms the basis of a new technique for measuring- flux through the alternative pathway during plant respiration. This technique, first reported by Guy and coworkers, is the first to allow measurements of the alternative oxidase in vivo under steady-state conditions. Improvements to the technique have produced a gas-phase system which allows measurements of alternative pathway flux in intact tissues in less than an hour. The development and application of these techniques and the potential for future experiments are discussed in this review.