AEBI 210 Lecture Notes - Raffinose, Phloem, Leaf
8 Jan 2013
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Document Summary
Water, carbon dioxide and sunlight is taken in, oxygen and sugar is produced. A source produces more photosynthate then it needs (leaves) A sink is a non-photosynthetic organ which requires photosynthate (roots, shoots) Carbohydrates are often produced in leaves and stored in roots. Carbohydrates formed by photosynthesis are moved from the chloroplast to cytosol. At night, these are converted to sucrose in the mesophyll. Sucrose is then loaded into sieve and companion cells (short distance transport) Symplastic loading in some plants (primarily tropical ones) Raffinose is synthesized and diffuses into phloem with sucrose. Following this is sucrose proton cotransport across the plasma membrane. Companion cells are attached to sieve cells and sieve tubes. Most common compound transported in phloem is sucrose (glucose + fructose) Reducing sugars like glucose, mannose and fructose are too reactive to be transported. Transportation from the source to sink is called long distance transport. Osmotic gradient (from sucrose) causes the flow of water into the phloem.
