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The pressure flow hypothesis, also known as the mass flow hypothesis, is the best-supported theory to explain the movement of sap through the phloem of plants.[1][2] It was proposed in 1930 by Ernst Münch, a German plant physiologist.[3] Organic molecules such as sugars, amino acids, certain hormones, and messenger RNAs are known to be transported in the phloem through the cells called sieve tube elements. According to the hypothesis, the high concentration of organic substances, particularly sugar, inside the phloem at a source such as a leaf creates a diffusion gradient (osmotic gradient) that draws water into the cells from the adjacent xylem. This creates turgor pressure, also called hydrostatic pressure, in the phloem. The hypothesis states that this is why sap in plants flows from the sugar producers (sources) to sugar absorbers (sinks).
- ^ Translocation of Food
- ^ Michael Kent (2000). Advanced Biology: A new mainstream text for the new specifications (illustrated ed.). OUP Oxford. p. 286. ISBN 9780199141951.
- ^ Münch, Ernst (1930). "Die Stoffbewegungen in der Pflanze". Verlag von Gustav Fischer, Jena: 234.