Time‐course of uptake of dissolved inorganic carbon through willow roots in light and in darkness

Abstract

Uptake of dissolved inorganic carbon (DIC) from a nutrient solution by willow roots was measured in light and darkness and the distribution in the plant of DIC taken up by the roots was determined. It was also studied whether the transport system could be activated by preincubation with dissolved inorganic carbon. Willow plants ( Salix cv. Aquatica gigantea) grown in hydroponic culture media were preincubated for 2 days with or without 0.74 mM NaHCO 3 . After preincubation, either unlabelled or [ 14 C]‐labelled NaHCO 3 was injected into the media and after 1, 5, 10 and 24 h either in light or in darkness the plants were harvested in pieces into liquid nitrogen, lyophilized and burned in a combustion chamber. 14 C was transported through the roots to the shoots and leaves both in light and in darkness, although incorporation of 14 C in darkness was only half of that in light at the end of the 24‐h feeding period. Both in light and in darkness the amount of 14 C increased in all parts of willow plants with time. In light the rate of labelling was highest into cuttings and shoots. In darkness more than half of the total label was detected in cuttings of both the non‐activated and the activated treatments. In the shoots the middle part was most strongly labelled after 5 and 10 h, but after 24 h 14 C moved towards the base of the shoot. In the leaves at all feeding times most radioactivity was incorporated into the young, fully open leaves on the upper part of the shoots. Preincubation of plants with unlabelled NaHCO 3 in growth media had no clear effect on the rate of DIC uptake either in light or in darkness.