Pyruvate Uptake by Mesophyll and Bundle Sheath Chloroplasts of a C4 Plant, Panicum miliaceum L. |
| |
Authors: | Ohnishi Jun-ichi; Kanai Ryuzi |
| |
Institution: | Department of Biochemistry, Faculty of Science, Saitama University Urawa 338, Japan |
| |
Abstract: | Intact chloroplasts were isolated from mesophyll and bundlesheath protoplasts of a C4 plant, Panicum miliaceum L., to measurethe uptake of 1-14C]pyruvate into their sorbitol-impermeablespaces at 4?C by the silicone oil filtering centrifugation method.When incubated in the dark, both chloroplasts showed similarslow kinetics of pyruvate uptake, and the equilibrium internalconcentrations were almost equal to the external levels. Whenincubated in the light, only mesophyll chloroplasts showed remarkableenhancement of the uptake, the internal concentration reaching1030 times of the external level after 5 min incubation.The initial uptake rate of the mesophyll chloroplasts was enhancedabout ten fold by light and was saturated with increasing pyruvateconcentration; Km and Vmax were 0.20.4 mM and 2040µmol(mg Chl)1 h1, respectively. The lightenhancement was abolished by DCMU and uncoupling reagents suchas carbonylcyanide-m-chlorophenylhydrazone and nigericin. Theseresults indicate the existence of a light-dependent pyruvatetransport system in the envelope of mesophyll chloroplasts ofP. miliaceum. The uptake activity of mesophyll chloroplastsboth in the light and the dark was inhibited by sulfhydryl reagentssuch as mersalyl and p-chloromercuriphenylsulfonate, but thebundle sheath activity was insensitive to the reagents. Thesefindings are further evidence for the differentiation of mesophylland bundle sheath chloroplasts of a C4 plant with respect tometabolite transport. (Received July 3, 1986; Accepted October 8, 1986) |
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|