Sucrose synthase and sucrose-phosphate synthase expression during sink-source transition in maize leaves

CURATTI LEONARDO; SALERNO GRACIELA

Vancouver, Canada

Congreso; Annual Meeting of the American Society of Plant Physiologysts; 1997

American Society of Plant Physiologysts

Biochemical and molecular evidence support the idea that carbon allocation rate depends on sink tissue strength. The object of our investigation was to characterize the expression of sucrose-phosphate synthase (SPS) and sucrose synthase (SS) in non-photosynthetic tissues in comparison with photosynthetic ones in maize. We reported bimodal accumulation of sucrose during leaf development, independently of the leaf chlorophyll content. This pattern was accompanied by an activation of SPS measured in the selective assay only in young non-photosynthetic leaves. A decrease in SPS activity correlates with the depletion of tissue sucrose levels during sink-source transition. SS activity (expressed as a ratio synthesis/cleavage direction activity) rose with maturity, even though the total activity decreased. In order to have a better insight of the physiological implications of our data, we performed immuno- and mRNA “in situ” localization of both proteins on tissue slices using specific polyclonal antibodies or RNA probes, respectively. We detected SPS expression in the elongation zone of young; non-photosynthetic leaves at both protein and mRNA levels. Signals were stronger in non-differentiated mesophyll cells, but in different vascular bundles. Expression in other organs or tissues was in accordance with previous reports. These data suggest that SPS may have a specific role in sucrose level regulation even in non-photosynthetic tissues. Regulation of SPS activity and/or modification of the expression patterns during sink-source transition could provide a sugar developmental signal.