Abstract
Cucumber plants (Cucumis sativus L. cv. Sharp I) with 3 leaves were grown in hydroponics at root temperatures of 25°, 32°, 35° and 38°C for up to 9 days. The rates of photosynthesis and transpiration as well as leaf chlorophyll content was not affected by the root temperatures from 25° to 35°C. In plants grown at 38°C the rates of photosynthesis and transpiration were unaffected over the first 5 days, but a large decrease occurred in the two parameters as well as chlorophyll content after 9 days. When a shoot was pulse-fed with 14CO2 after 6 days growth at 25° or 38°C root temperatures, translocation of 14C-photosynthates to the roots during a 10-h chase in darkness was faster at 38°C than it was at 25°C. However, the amounts of the 14C accumulated per unit dry weight of root tissue were not different between the two treatments, becuase of an increased carbon loss by respiration of the roots at 38°C. At 38°C, more 14C was allocated to soluble C than to insoluble C; the reverse was the case at 25°C. Fractionation of soluble 14C into sugars, organic acids, and amino acids revealed that in the roots at 38°C, a very large proportion of 14C was in the sugar fraction, particularly raffinose. This was in contrast to the 25°C roots in which the soluble 14C was distributed evenly to the three fractions. Possible relationships of the changes in photosynthesis and photosynthate translocation and metabolism in the roots with root growth and functions under the high root temperature conditions are discussed
