The uptake of
d-galactose was studied in detached fenugreek (Trigonella foenum-graecum L.) cotyledons. Uptake kinetics and treatment with p-chloromercury-
benzenesulfonic acid indicated that at low concentrations
d-galactose was taken up by a carrier. At higher concentrations a diffusion-like component existed.
Proton flux and pH studies, treatment with
alpha-naphthaleneacetic acid, and uptake experiments under
water stress conditions suggested that
d-galactose was not taken up via H(+) contransport. However,
d-galactose uptake was under metabolic control. Uptake kinetics under
water stress conditions suggested that moderate
water stress either increased the K(m) of the carrier or decreased the V(max). However, prolonged stress transformed the carrier-mediated uptake into a diffusion uptake transport. The uptake of
d-galactose by fenugreek cotyledons was very low before and just after germination, was maximum after 35 hours imbibition, and started decreasing thereafter. The different uptake rates of
d-galactose with imbibition times were attributed to the operation of the carrier. At low uptake rates the carrier did not operate. Treatment with
cycloheximide suggested that the carrier was synthesized de novo just after germination and stopped operating when all
galactomannan hydrolysis was over. Results were discussed in the context of control of endosperm
galactomannan hydrolysis by the cotyledons of fenugreek embryo.