03 Respiration Practical - Copy - PLS 172 Lecture 3 1 of 8...

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PLS 172 Lecture 3 1 of 8 RESPIRATION: THE PHYSIOLOGIST'S YARDSTICK Mikal E. Saltveit and Michael S. Reid, University of California, Davis 95616 TABLE OF CONTENTS Topic page Introduction 1 Internal factors 1 Environmental factors 3 Physical stress 7 References 7 INTRODUCTION In the previous lecture we discussed the various com- ponents of the complex biochemical process called res- piration and briefly reviewed the means by which it is measured in intact tissues. In this lecture we will con- sider the various factors affecting respiration, and how they relate to the overall respiratory scheme and post- harvest physiology. INTERNAL FACTORS Because respiration is tightly controlled so that no more ATP is produced than is needed for metabolism, and because ATP production is tightly coupled to respira- tion, the rate of respiration is normally a very accurate indicator of the metabolic activity of the tissue. We do not measure respiration to only find out the rate of CO 2 production or O 2 consumption, but to measure the un- derlying rate of metabolism in the tissue. A number of commodity parameters are directly related to respiration rate and respiratory pattern. a. Genotype - among and within species Some fruits are more perishable than others. You would not, for example, expect a strawberry to last as long as an apple in your fruit bowl. This relative per- ishability is usually reflected in the respiration of the different commodities (Table I). The respiration of strawberries is much higher than that of apples. Some short-lived apple and melon fruit are from cultivars with higher rates of respiration than long-lived cultivars. b. Type of plant part Previously we discussed the enormous range of plant organs that are harvested as edible commodities. The metabolism of these different organs relates to their physiological role, and varies greatly (Table I). Storage tissues such as nuts and tubers have low respiration rates. Tissues with vegetative or floral meristems such as asparagus and broccoli have very high respiration rates. c. Stage of development at harvest As plant organs mature, their rate of respiration typi- cally declines. This means that commodities harvested during active growth, such as many vegetables and im- mature fruits, have high respiration rates. Mature fruits, dormant buds and storage organs have relatively low respiration rates (Table I). After harvest, the respiration rate typically declines; slowly in non-climacteric fruits and storage organs, rapidly in vegetative tissues and immature fruits (Fig. 1). The rapid decline presumably reflects depletion of respirable substrates that are typically low in such tis- sues. Fig. 1. The postharvest, non-climacteric pattern of res- piration for slowly and rapidly senescing tissue.
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