Biotech Updates

Scientists Discover the Functional Independence of Phloem Systems in Cucurbits

July 9, 2010

Cucurbitaceous plants (cucurbits) have been used by researchers in investigating phloem physiology. These plants are one of a kind because they have two different phloem systems-the fascicular phloem (FP) which is located within the main vascular bundles; and the extrafascicular phloem (EFP), located in the petiole and stem cortex tissues.

Donald Danforth Plant Science Center scientist Baichen Zhang and other researchers reinvestigated the assumption that "the sap released after shoot incision originates from the FP" and examined why the sugar content of the FP sap is approximately 30-fold less than the requirements of photosynthate delivery. After conducting video microscopy and phloem labeling experiments, they discovered that the FP sap is inhibited upon cutting, while the EFP bleeds for an extended time. The protein composition of the phloem systems were also found to be different, indicating a variation in function. The researchers assume that FP is responsible for sugar transport, while the EFP functions for signaling, defense, and metabolite transport.

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