Abstract
Sugars produced from photosynthesis in leaves are transported through the phloem tissues within veins and delivered to non-photosynthetic organs, such as roots, stems, flowers, and seeds, to support their growth and/or storage of carbohydrates. However, because the phloem is located internally within the veins, it is difficult to access and to study the dynamics of sugar transport. Radioactive tracers have been extensively used to study vascular transport in plants and have provided great insights into transport dynamics. To better study sucrose partitioning in vivo, a novel radioactive analog of sucrose was synthesized through a completely chemical synthesis route by substituting fluorine-18 (half-life 110 min) at the 6’ position to generate 6’-deoxy-6’[18F]fluorosucrose (18FS). This radiotracer was then used to compare sucrose transport between wild-type maize plants and mutant plants lacking the Sucrose transporter1 (Sut1) gene, which has been shown to function in sucrose phloem loading. Our results demonstrate that 18FS is transported in vivo, with the wild-type plants showing a greater rate of transport down the leaf blade than the sut1 mutant plants. A similar transport pattern was also observed for universally labeled [U-14C]sucrose ([U-14C]suc). Our findings support the proposed sucrose phloem loading function of the Sut1 gene in maize, and additionally demonstrate that the 18FS analog is a valuable, new tool that offers imaging advantages over [U-14C]suc for studying phloem transport in plants.
Highlights
Carbon assimilated via photosynthesis in source leaves is transported to non-photosynthetic sink tissues through the phloem tissues of veins [1,2,3,4]
Our objective was to develop a 18F-fluorinated analog of sucrose, and to determine whether 18FS can be used as a tracer in plant imaging studies to monitor sugar dynamics by comparing its transport in maize sut1 mutants to wild-type plants
We report a fully automated, two-pot, two-step synthesis of 18FS that has been achieved with reasonable yields and high purity
Summary
Carbon assimilated via photosynthesis in source leaves is transported to non-photosynthetic sink tissues through the phloem tissues of veins [1,2,3,4] This process, known as carbohydrate partitioning, is highly dynamic and is fundamental to plant growth and development. Because low energy beta particles from 14C-decay escape from thin plant tissues and will likely be absorbed by thicker tissues, its use for in vivo imaging work is not ideal This is the reason why 14C-radiolabeled plants are often destructively sampled and processed for quantitation, such as by liquid scintillation counting, which makes this isotopic analysis technique informative to study carbon allocation, but not appropriate to look at short-term transport dynamics in an intact plant [22,25,26]. The latter, with its extended half-life, makes it more feasible than the other short-lived isotopes for dynamic imaging studies
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