ISHS Acta Horticulturae 343: Physiological Basis of Postharvest Technologies
PHYSIOLOGICAL BASIS OF LOW O2-INDUCED RESIDUAL RESPIRATORY EFFECT IN BELL PEPPER FRUIT |
| Authors: | A.-S.A. Rahman, D.J. Huber, J.K. Brecht |
| Abstract:
Our previous studies have shown that bell pepper fruit (var. Jupiter) exposed to 1.5% O2 (balance N2) for 1 day exhibit reduced rates of CO2 production and O2 consumption which persist for at least 24 hours following return to normal atmospheres (J. Amer. Soc. Hort. Sci. 1992 (in press)). Storage of bell pepper in 1.5% O2 at 20C was extended to 5 days, followed by transfer to air at the same temperature. Total respiratory activity (VT) of mitochondria from fruit stored for 5 days in 1.5% O2 was suppressed, but mitochondria prepared after transfer of fruit to air for 24 hr attained values similar to air-stored samples. The alternative (V-alt) and cytochrome-mediated (V-cyt) respiratory pathways were suppressed during storage, but recovered to normal levels when fruit were transferred to air. The magnitude of suppression was greater for the alternative pathway (62%) than for the cytochrome pathway (35%). Storage of bell pepper in 1.5% O2 for 5 days caused no alterations in the ultrastructural features of isolated mitochondria. Although whole fruit CO2 production and O2 consumption rates exhibit residual inhibition following low O2 exposure, the inhibition does not persist in isolated mitochondria. These data suggest that the residual respiratory responses may be due to the suppression of extramitochondrial, low-affinity oxidases. It is well documented that reduced O2 and/or elevated CO2 in CA environments cause significant reductions in respiration and other associated metabolic processes (Kader, 1986). In some commodities, the respiration rate continues to be attenuated even after transfer from the low O2 environment to air. The occurrence of post-store residual effect can impart practical significance in maintaining the quality of fresh produce during subsequent handling in air. Our previous studies have shown that the residual effect of short-term low O2 exposure on the respiratory activity of intact fruit stored initially in 1.5% O2 for 1 day at 20C is not manifested in isolated mitochondria. These data indicated that mitochondrial oxidative reactions were either not responsible for the residual, post low O2 storage respiratory effect or perhaps that limitations in mitochondrial oxidative capacity were not preserved under in vitro conditions. To further evaluate these possibilities, bell pepper fruit were subjected to more extended storage periods in low O2 and subsequently examined for mitochondrial oxidative capacity and ultrastructure. | |
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