摘要
In most higher plants, sucrose is the primary organic carbon that is translocated through phloem from photosynthetic leaves （source） into non-photosynthetic tissues （sink） such as seed, fruit, and root. After phloem unloading in sinks, sucrose needs to be degraded into hexoses for diverse use by either invertase （Inv） that hydrolyses sucrose into glucose and fructose or sucrose synthase （Sus） that degrades sucrose into UDPglucose and fructose. By generating hexoses and their derivates, Inv- or Sus-mediated sucrose metabolism and re- lated transport process provide （1） energy source to power cel- lular processes; （2） starting molecules convertible to numerous metabolites and building blocks for synthesizing essential pol- ymers including starch, cellulose, callose, and proteins; and （3） a mechanism to reduce sucrose concentration at the unloading sites to facilitate its source-to-sink translocation, thereby pre- venting feedback inhibition on photosynthesis and sustaining carbon flow at the whole-plant level.
In most higher plants, sucrose is the primary organic carbon that is translocated through phloem from photosynthetic leaves （source） into non-photosynthetic tissues （sink） such as seed, fruit, and root. After phloem unloading in sinks, sucrose needs to be degraded into hexoses for diverse use by either invertase （Inv） that hydrolyses sucrose into glucose and fructose or sucrose synthase （Sus） that degrades sucrose into UDPglucose and fructose. By generating hexoses and their derivates, Inv- or Sus-mediated sucrose metabolism and re- lated transport process provide （1） energy source to power cel- lular processes; （2） starting molecules convertible to numerous metabolites and building blocks for synthesizing essential pol- ymers including starch, cellulose, callose, and proteins; and （3） a mechanism to reduce sucrose concentration at the unloading sites to facilitate its source-to-sink translocation, thereby pre- venting feedback inhibition on photosynthesis and sustaining carbon flow at the whole-plant level.
