GROWTH AND MAINTENANCE RESPIRATORY COSTS OF CUCUMBER FRUITS AS AFFECTED BY TEMPERATURE, AND ONTOGENY AND SIZE OF THE FRUITS

The rates of dry weight increase and respiration of fruits were measur ed throughout Fruit ontogeny at 20, 25 and 30 degrees C in cucumber (C ucumis sativus L. cv. Corona). By maintaining one or five fruits per p lant, which strongly affected fruit dry weight but not ontogeny, the e ffects of fruit size and ontogeny on respiration could be studied sepa rately. The respiration rate per fruit followed a sigmoid curve during fruit ontogeny, while the specific respiration rate (respiration rate per unit dry weight) declined with time after anthesis. The specific respiration rate was almost linearly related to the relative growth ra te. The specific respiratory costs for both growth and maintenance wer e highest in young fruits, but were not affected by fruit size. The av erage specific respiratory costs for growth and maintenance at 25 degr ees C were 3.3-3.9 mmol CO2 g(-1) and 4.0 nmol CO2 g(-1) s(-1), respec tively. An increase in temperature had no effect on the specific respi ratory costs for growth, while the costs for maintenance increased wit h a Q(10) of about 2. The costs for growth agreed reasonably well with theoretical estimates based on the chemical composition of the fruits but not with estimates based on only the carbon and ash content. The respiratory losses as a fraction of the total carbon requirement of a fruit changed during fruit ontogeny, but were independent of temperatu re and were similar for slow- and fast-growing fruits. The cumulative respiratory losses accounted for 13-15% of the total carbon requiremen t.