Abstract
The intercellular distribution of the enzymes and metabolites of
assimilatory sulfate reduction and glutathione synthesis was analyzed
in maize (Zea mays L. cv LG 9) leaves. Mesophyll cells and
strands of bundle-sheath cells from second leaves of 11-d-old maize
seedlings were obtained by two different mechanical-isolation
methods. Cross-contamination of cell preparations was determined
using ribulose bisphosphate carboxylase (EC 4.1.1.39) and nitrate
reductase (EC 1.6.6.1) as marker enzymes for bundle-sheath and
mesophyll cells, respectively. ATP sulfurylase (EC 2.7.7.4) and adenosine
5*-phosphosulfate sulfotransferase activities were detected
almost exclusively in the bundle-sheath cells, whereas GSH synthetase
(EC 6.3.2.3) and cyst(e)ine, g-glutamylcysteine, and glutathione
were located predominantly in the mesophyll cells. Feeding experiments using [35S]sulfate with intact leaves indicated that cyst(e)ine was the transport metabolite of reduced sulfur from bundle-sheath to mesophyll cells. This result was corroborated by tracer experiments, which showed that isolated bundle-sheath strands fed with [35S]sulfate secreted radioactive cyst(e)ine as the sole thiol into the resuspending medium. The results presented in this paper show that assimilatory sulfate reduction is restricted to the bundle-sheath cells, whereas the formation of glutathione takes place predominantly in the mesophyll cells, with cyst(e)ine functioning as a transport metabolite between the two cell types.
assimilatory sulfate reduction and glutathione synthesis was analyzed
in maize (Zea mays L. cv LG 9) leaves. Mesophyll cells and
strands of bundle-sheath cells from second leaves of 11-d-old maize
seedlings were obtained by two different mechanical-isolation
methods. Cross-contamination of cell preparations was determined
using ribulose bisphosphate carboxylase (EC 4.1.1.39) and nitrate
reductase (EC 1.6.6.1) as marker enzymes for bundle-sheath and
mesophyll cells, respectively. ATP sulfurylase (EC 2.7.7.4) and adenosine
5*-phosphosulfate sulfotransferase activities were detected
almost exclusively in the bundle-sheath cells, whereas GSH synthetase
(EC 6.3.2.3) and cyst(e)ine, g-glutamylcysteine, and glutathione
were located predominantly in the mesophyll cells. Feeding experiments using [35S]sulfate with intact leaves indicated that cyst(e)ine was the transport metabolite of reduced sulfur from bundle-sheath to mesophyll cells. This result was corroborated by tracer experiments, which showed that isolated bundle-sheath strands fed with [35S]sulfate secreted radioactive cyst(e)ine as the sole thiol into the resuspending medium. The results presented in this paper show that assimilatory sulfate reduction is restricted to the bundle-sheath cells, whereas the formation of glutathione takes place predominantly in the mesophyll cells, with cyst(e)ine functioning as a transport metabolite between the two cell types.
| Original language | English |
|---|---|
| Pages (from-to) | 1315–1322 |
| Journal | Plant Physiology |
| Volume | 116 |
| DOIs | |
| Publication status | Print publication - Apr 1998 |
| Externally published | Yes |