Sugar Uptake by Maize Endosperm Suspension Cultures

Abstract

Maize (Zea mays L.) endosperm suspension cultures are a useful model system for studying biochemical and physiological events in developing maize endosperm. In this report, sugar uptake by the cultures is characterized. Uptake of '4C-labeled fructose and L-glucose was linear with time, while the rate of uptake of radioactivity from sucrose increased over a 120 min period. Both saturable and linear components of uptake were observed for fructose, glucose, sucrose, 1'-deoxy-1'-fluorosucrose, and maltose. Uptake of mannitol, sorbitol, and L-glucose took place at lower rates and was linear with concentration. Rates of incorporation of radioactivity from fructose and glucose exceeded that of sucrose at all concentrations tested. Kinetics of 1'-deoxy-1'-fluorosucrose uptake indicated that '4C from sucrose can be taken up by a saturable carrier of intact sucrose as well as by invertase hydrolysis and subsequent uptake of hexoses. Cell wall invertase was demonstrated histochemically. Further study of fructose uptake at a concentration at which the saturable component predominated revealed sensitivity to metabolic inhibitors, respiratory uncouplers, the nonpermeant sulfhydryl reagent p-chloromercuribenzenesulfonic acid, and nigericin. Uptake was not affected by valinomycin plus K' and was stimulated by fusicoccin. Fructose and glucose uptake was not pH-sensitive below pH 7.0, whereas uptake of radioactivity from sucrose and 1 '-deoxy-1 '-fluorosucrose declined as the pH was increased above 5.0. Fructose uptake was not completely inhibited by glucose and vice versa, suggesting the presence of specific carriers. These results indicate that maize endosperm suspension cultures (a) absorb fructose via a typical, energy-requiring, carrier-mediated proton cotransport system; (b) possess saturable carriers for glucose and sucrose; and (c) also absorb sucrose via hexose uptake after sucrose hydrolysis by extracellular invertase.

Coupling of Solute Transport and Cell Expansion in Pea Stems

“…6) as reported by others (10,21). L-Glucose concentration in the cell sap and apoplast samples increased with time and were statistically equal when supplied via the phloem (Fig.…”

“…SA). This pattern was similar to uptake characteristics in other plant tissues (21) and cells (10 (14). Additional evidence for uptake without extracellular hydrolysis is that 1 '-fluorosucrose, a synthetic analog which is hydrolyzed by invertase at a rate 4200 times slower than sucrose (20), was taken up with a magnitude only slightly lower than sucrose (Fig.…”

Sugar Uptake and Starch Biosynthesis by Slices of Developing Maize Endosperm

“…The metabolism of sugars also suggests that cytoplasmic uptake, rather than vacuolar uptake, was being observed. A similar experiment with endosperm suspension cultures was not possible due to the large activity of cell wall invertase in the cultures (3 In most cases, potentially competing sugars did not affect the distribution of '4C among the soluble sugars extracted from endosperm tissue slices incubated in "'C-sugars (Table III). An exception was that when [ also be expected to reduce the accumulation of 14C in starch, which was observed (Table III).…”

Stably transformed cell lines from protoplasts of maize endosperm suspension cultures

“…Protoplasts from cells of developing maize endosperms could be used for this type of work, but they are difficult to obtain (Schwall & Feix 1988). An alternative system can be provided by suspension cultures of maize endosperm cells, which accumulate reserve starch and proteins (Felker & Goodwin 1988;Lyznik & Tsai 1989;Manzocchi 1991;Quayle et al 1991), although at reduced levels with respect to in vivo cells.…”