Hachi's posts

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Symplastic domains - groups of cells and tissues connected by plasmodesmata. Proteins and RNAs coordinate their development

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Plant cells regulate pore size of plasmodesmata. Viruses make viral movement proteins that can manipulate these regulators to allow viral RNA to pass between plant cells

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Close or are eliminated during differentiation (eg. when leaf matures from sink to source)

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Plasmodesmata are dynamic - open/close in response to turgor pressure, cytosolic Ca2+ levels, or cytosolic pH

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Symplast is living and governs changes in plant transport processes

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Self-thinning - when sinks > sources, plant aborts some flowers, seeds, or fruits

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Pressure is relieved at the sink as sugar unloads and water is lost

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Sugar concentration is higher at source than at sink, water moves in by osmosis and builds positive pressure at source

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In angiosperms, translocation is driven by positive pressure (pressure flow)

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Concentration of free sugar is always lower in sink than in sieve tube → unloads by diffusion, water follows by osmosis

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Sugar movement into phloem requires active transport (H+/sucrose cotransporter) b/c sucrose is more concentrated in sieve-tube elements and companion cells than in mesophyll

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Walls of companion cells have ingrowths to enhance transfer between apoplast and symplast

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Sugar is loaded from mesophyll cells into sieve-tube elements, then exported to sinks

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Sinks receive sugar from nearby sources. Direction of transport in a sieve tube depends on location of source and sink connected by that tube