EFFECT OF LOW SOIL-TEMPERATURE ON WEIGHT INCREASE, GAS-EXCHANGE AND DISTRIBUTION OF C-14 ASSIMILATES IN SEEDLINGS OF A MAIZE HYBRID

Seedlings of a maize hybrid sensitive to chilling initially grew in th e growth chamber of the phytotron at 20/17-degrees-C (day/night) and a fter the formation of the fourth leaf, the soil temperature was lowere d to 5-degrees-C. Under such growth conditions the dynamics of dry wei ght change, gas exchange and the distribution of C-14-assimilates in s eedlings were examined. The low soil temperature inhibited daily growt h of dry weight of whole seedlings more than their photosynthesis. Sim ultaneously, it was also responsible for a greater increase in dissimi lative losses. During 37 hours (day-night-day), following exposure to (CO2)-C-14, dissimilation in seedlings in cool soil (5-degrees-C) and in non-chilling conditions amounted to 35.1 % and 23.4 % of assimilate d C-14 (AC), respectively. At lower soil temperature relatively high d issimilative losses were observed on the first day after exposure (23. 5 %), lower at night (9.9 %) and the lowest on the following day - mer ely 1.7 % AC. Higher losses of C-14 under chilling conditions occurrin g on the first day were a result of limited photosynthetic refixation of (CO2)-C-14. At night, however, they were associated with a prolonge d period of intensive translocation of assimilates to the stem. It was assumed that an excessive accumulation of assimilates in leaf blades might be an additional factor responsible for increased dissimilative losses at low temperature during the first twenty-four hours. In the t hird period of measurements, as a result of a limited transport of C-1 4, dissimilative losses were lower than in previous ones and were not dependent upon soil temperature.