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  • Author or Editor: Steven E. Lasley x
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Abstract

The effect of age on CO2 exchange rates of cucumber (Cucumis sativus L.) cotyledons was measured. A biphasic process was noted, with a period of relatively high exchange rates up to 17-18 days from planting, when the first true leaf was nearly fully expanded, followed by a decline in exchange rates thereafter. The relative contribution of cotyledons versus leaves to photosynthesis as a function of age was measured. At 16 days from planting, the cotyledons accounted for 80% of the total net CO2 exchange and slightly more than 50% of the total foliage area. Twenty-four days after planting, the cotyledons still accounted for about one-fourth of the total net CO2 exchange and 20% of the total foliage area. The use of cotyledons in chilling injury studies of cucumber is justified by both the large photosynthetic contribution of cotyledons to growth and development, and the presence of cotyledons during early growth when chilling is most likely to occur.

Open Access

Abstract

Photosynthesis was measured in excised cucumber (Cucumis sativus L. cv. Marketer) cotyledons subjected to chilling temperatures in the presence or absence of photo synthetically active radiation (PAR), under conditions that precluded water stress. Cotyledon CO2 exchange rates (CER) were reduced after chilling in the light, but not after chilling in the dark. In the light, reduction occurred more rapidly at lower than at higher chilling temperatures. The level of PAR had little or no effect on CER reductions at lower temperatures within the chilling range, but at higher chilling temperatures, reduction occurred more rapidly at higher PAR levels. Recovery of photosynthesis following chilling in the light occurred more rapidly in the dark than in the light, and this difference in recovery rate was greater with longer exposure to light and chilling conditions. The removal of light during the recovery phase accelerated the rate of recovery to a level comparable to the dark control.

Open Access