Evidence for an active transport of methyl-α-D-glucopyranoside in pea stem segments

Michelis, Maria Ida De; Radice, Marco; Colombo, Roberta; Lado, P.

doi:10.1016/0304-4211(78)90141-4

Cited by 2 publications

(1 citation statement)

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“…The literature has been reviewed (2). In recent studies, proton co-transport has been implicated in pea-stem segments (4,5), maize coleoptiles and roots (4), intact duckweed (18,20), tomato internode segments and discs (21,22), sugar-beet leaves (9), and isolated protoplasts and vacuoles from pea-leaf mesophyll cells (10,11). Use of highly differentiated tissue, such as Ricinus cotyledons (12,13), creates certain difficulties in comparing the relationship between proton motive force and sugar uptake.…”

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confidence: 99%

Sugar Uptake in Lily Pollen

Deshusses¹,

Gumber²,

Loewus³

1981

Plant Physiol.

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The data presented here are consistent with a proton-sugar co-transport in germinated pollen of Lilium longiflorum Thunb. Optimal uptake occurs at pH 5.0. A Km of 1.7 to 1.8 millimolar is obtained from the initial rate of pH change induced by sucrose uptake as well as from uptake of IU-`4C1-sucrose. The energy of activation is -11 kilocalories mole-'. The effect of several inhibitors and sugar competitors on IU-'4Clsucrose and D-IU-`4C1 glucose uptake is given. The possibility of hydrolysis of sucrose prior to its transport into the poUlen tube has been considered and reasons for choosing a sucrose-type uptake are presented. The possible in vivo significance of this co-transport process during pollen germination is discussed. Germinated pollen has features to recommend it as an experimental system of choice for studies of sugar uptake.Proton co-transport of sugar as first-described in Chlorella (15) is now known to occur in higher plants and is probably a process found in all species. The literature has been reviewed (2). In recent studies, proton co-transport has been implicated in pea-stem segments (4, 5), maize coleoptiles and roots (4), intact duckweed (18,20), tomato internode segments and discs (21,22), sugar-beet leaves (9), and isolated protoplasts and vacuoles from pea-leaf mesophyll cells (10,11 with test medium, and gently resuspended in test medium. Large quantities of germinated pollen were allowed to settle for 5 min in a tall glass cylinder in order to decant about 0.5 volume prior to filtering. In some studies, resuspended pollen was held for periods up to 2 h at 20 C without impairment of cytoplasmic streaming and with little additional tube elongation (see "Results" and Table II).Measurements. In pH studies, germinated pollen (usually 50 mg) was resuspended in 3.5 ml test medium at 28 C in a thermostated titration vessel (Metrohm, Herisau, Switzerland). A fine stream of air bubbles kept the pollen in suspension. pH changes were measured with a combination glass electrode (Radiometer GK2321-C) and were recorded with a 1-mv Varian A-5 recorder.The initial rate ofproton uptake was calculated from the difference in slope of the pH curve before and after addition of sugar to the medium.In uptake studies involving labeled sucrose, 1 ml pollen suspension was added to 1 ml 100 mm Mes/Ca buffer at pH 5.0 [Mes buffer was adjusted to the indicated pH with Ca(OH)2] and held for 2 min to attain 28 C. One-half ml sugar analog, inhibitor, or test medium was added and, 0.5 min later, 0.5 ml 6 mm [U-'4C]sucrose was added. The final concentration of sucrose was 1 mM. Addition of label was taken as zero time. After incubation, uptake was terminated by filtering l-ml aliquots on 0.8-,am membranes and washing the pollen with 3 ml test medium. The washed pollen and its membrane support were transferred to 5 ml "tritosol" (8) and counted in a Packard model 3320 liquid scintillation spectrometer at a 14C efficiency of 70%.To characterize the nature of labeled products of [U-_4C]sucrose uptake after transport...

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