Sucrose Phosphate Synthase Expression at the Cell and Tissue Level Is Coordinated with Sucrose Sink-to-Source Transitions in Maize Leaf

Abstract

lmmunohistological analyses for sucrose phosphate synthase (SPS) show that the protein is localized in both bundle-sheath cells (BS) and mesophyll cells (M) in maize (Zea mays) leaves. I n young leaves, SPS protein was predominantly i n the BS, whereas mature leaves showed nearly equal levels of signal i n both BS and M. A cell-type-specific response was also seen in light and dark treatments. Dark treatments led t o reduced signal in M; however, little or no change was detected in BS. We suggest that SPS in BS is engaged i n sucrose biosynthesis by both photoassimilatory and starch turnover reactions in maize leaves. In addition, we suggest that the enzyme in BS may play a major role in the early biosynthesis of sucrose i n young leaves. These cell-specific changes in expression in situ were in agreement with the estimates of extractable enzyme activity from isolated BS and M of mature leaves (R. Ohsugi, S.C. Huber [19871 Plant Physiol 84: 1096-1101). In contrast, western blot analyses did not show any significant changes i n the levels of SPS protein in either young or mature leaves subsequent to similar dark treatments. It is interesting that the northern blot analyses indicate that the steady-state levels of SPS transcripts were markedly reduced after dark treatments of >12 h. Overall, our results indicate that Sps gene expression i n maize leaf is modulated at multiple levels of controls by both developmental and environmental factors.

Structural and Metabolic Transitions of C4 Leaf Development and Differentiation Defined by Microscopy and Quantitative Proteomics in Maize

“…This is perhaps surprising since based on the distribution of SPS and labeling, it was previously concluded that most of the sucrose (in mature leaves) is synthesized in MCs (Usuda and Edwards, 1980;Lunn and Furbank, 1997). However, a later immunohistological study came to a completely different conclusion and showed that SPS is localized in both BSCs and MCs (Cheng et al, 1996). In fact, in young leaves, SPS protein was predominantly in BSCs, whereas mature leaves showed nearly equal levels of signal in both BSCs and MCs (Cheng et al, 1996).…”

The Differential Expression of Sucrose Synthase in Relation to Diverse Patterns of Carbon Partitioning in Developing Cotton Seed

“…The protein concentrations were determined using the Bio-Rad DC protein assay kit with BSA as a standard. SuSy activity was measured as the rate of Suc cleavage (Chourey, 1981). The resultant reducing sugars were estimated according to the method of Nelson (1944).…”

“…Immunolocalization was conducted according to the procedure described by Chen and Chourey (1989) and the modifications described by Cheng et al (1996). To avoid physical contamination of the seed sections by fiber due to its softness, the fiber was removed from the remaining seed and treated in parallel.…”

Tissue-Specific and Developmental Pattern of Expression of the Rice sps1 Gene

“…The level of SPS activity in source tissues appears to be mainly regulated, at the enzyme level, by allosteric (Doehlert and Huber, 1984) and covalent (Huber and Huber, 1990;Huber and Huber, 1991;Toroser and Huber, 1997) modifications. In contrast with this, the developmental and tissue-specific distribution of SPS has been suggested to be regulated at the transcriptional level (Harn et al, 1993;Klein et al, 1993;Cheng et al, 1996;Valdez-Alarcó n et al, 1996).…”