Intercellular Localization of Assimilatory Sulfate Reduction in Leaves of Zea mays and Triticum aestivum

Abstract

The intercellular distribution ofassimilatory sulfate reduction enzymes between mesophyll and bundle sheath cells was analyzed in maize (Zea mays L.) and wheat (Triticum aestivum L.) leaves. In maize, a C4 plant, 96 to 100% of adenosine 5'-phosphosulfate sulfotransferase and 92 to 100% of ATP sulfurylase activity (EC 2.7.7A) was detected in the bundle sheath cells. Sulfite reductase (EC 1.8.7.1) and O-acetyl-L-serine sulfhydrylase (EC 4.2.99.8) were found in both bundle sheath and mesophyll cell types. In wheat, a C3 species, ATP sulfurylase and adenosine 5'-phosphosulfate sulfotransferase were found at equivalent activities in both mesophyll and bundle sheath cells. Leaves of etiolated maize plants contained appreciable ATP sulfurylase activity but only trace adenosine 5'-phosphosulfate sulfotransferase activity. Both enzyme activities increased in the bundle sheath cells during greening but remained at negligible levels in mesophyll cells. In leaves of maize grown without addition of a sulfur source for 12 d, the specific activity of adenosine 5'-phosphosulfate sulfotransferase and ATP sulfurylase in the bundle sheath cells was higher than in the controls. In the mesophyll cells, however, both enzyme activities remained undetectable. The intercellular distribution of enzymes would indicate that the first two steps of sulfur assimilation are restricted to the bundle sheath cells of C4 plants, and this restriction is independent of ontogeny and the sulfur nutritional status of the plants.C4 plants are characterized by an intercellular compartmentation of CO2 and NO3-assimilation between mesophyll and bundle sheath cells (2,3,6,16). Recently, a predominant localization ofenzymes ofassimilatory sulfate reduction in the bundle sheath cells was proposed (7,8,14). This pathway begins with the formation ofAPS2 from ATP and S042-via ATP sulfurylase (EC 2.7.7.4) (1,18 Kolibri) were imbibed for 24 h in aerated tap water at room temperature and then transferred to moist filter paper. After 3 d in the dark, the seedlings were cultivated on quartz sand watered regularly with nutrient solution (23). Nutrient solution deficient in S was composed by replacing the SO42-salts by equimolar amounts of the corresponding Cl-salts. The plants were grown at 26°C, with a RH of 40% and a light intensity of 46 ,uE m-2 s-' provided by incandescent lamps (Philips TL 40 w).Cell Isolation. Mesophyll cells and bundle sheath strands were obtained either by a mechanical or by an enzymic isolation procedure. For both procedures, leaves were cut diagonally in approximately 1-mm-wide strips with a razor blade and then transferred to a medium for protoplast isolation according to Mills and Joy (12), containing 2% cellulase and 2% pectinase. Ten ml of medium were used per g leafstrips. The plant material was infiltrated by applying a vacuum. The incubation time was 15 min in the light for the mechanical procedure. The plant material was then homogenized using a Servall Omni Mixer (Ivan Sorvall, Norwalk, CT) for 10 s at 100 v (6,700 rpm) an...

Assimilatory Sulfate Reduction in C3, C3-C4, and C4 Species of Flaveria

“…However, both APR mRNA and protein were clearly detected in both types of cells in the C 4 species F. trinervia. These results are surprising because in several reports the activity of ATPS and APR were localized exclusively or almost exclusively to bundle sheath cells of various C 4 species (Gerwick et al, 1980;Schmutz and Brunold, 1984;Burgener et al, 1998). However, F. trinervia is a dicot and in all previous reports only monocot species were analyzed.…”

“…The aim of this study was to determine whether the well-documented bundle sheath-specific localization of sulfate assimilation in C 4 plants (Gerwick et al, 1980;Schmutz and Brunold, 1984;Burgener et al, 1998) was a prerequisite or a consequence of C 4 photosynthesis. Analogously to the results achieved with maize (Kopriva et al, 2001), we expected that the APR and ATPS mRNA and protein would be localized exclusively in bundle sheath cells in the C 4 Flaveria spp.…”

“…Also, sulfate assimilation was proposed to be restricted to the bundle sheath cells of C 4 plants (Gerwick et al, 1980;Schmutz and Brunold, 1984). Several groups reported that 75% to 100% of total leaf ATPS activity in maize (Zea mays) is confined to bundle sheath cells (Gerwick et al, 1980;Passera and Ghisi, 1982;Schmutz and Brunold, 1984).…”

“…These findings were extended to 17 other C 4 species where 95% to 100% of total leaf ATPS activity was found in chloroplasts of bundle sheath cells. Also, the next enzyme in the sulfate reduction pathway, APR, was found exclusively or almost exclusively in bundle sheath cells of maize (Schmutz and Brunold, 1984;Burgener et al, 1998), whereas the activities of the subsequent enzymes of the pathway, sulfite reductase and O-acetyl-Ser-(thiol) lyase, were found in both cell types at comparable levels (Passera and Ghisi, 1982;Burnell, 1984;Schmutz and Brunold, 1985). In accordance, in maize the mRNAs for APR, ATPS, and sulfite reductase accumulated in bundle sheath only, whereas the mRNA for O-acetyl-Ser-(thiol) lyase was also detected in mesophyll cells (Kopriva et al, 2001).…”

Alliinase [S‐alk(en)yl‐ L‐cysteine sulfoxide lyase] from Allium tuberosum (Chinese chive)

“…In the cloves of A. sativum, alliinase is localized in the bundle sheath cells around the vascular bundle [51]. The formation of cysteine also takes place in the bundle sheath cells of maize [52] and also of Allium plants (Yamazaki, M., Sugiyama, M. and Saito, K., unpublished results). These results suggest that bundle sheath cells are important for the metabolism of sulfur-containing compounds, at least, in monocotyledonous plants.…”