Sap

"sap" redirects here. For other uses, see sap (disambiguation).

Leafhoppers and many other insects feed off plant sap

Sap is a fluid transported in xylem cells (tracheids or vessel elements) or phloem sieve tube elements of a plant. Fluid found in the vacuoles of other cells is sometimes referred to as "cell sap". Other liquid compounds found in plants or exuded by plants, such as latex, resins or mucilage, are sometimes incorrectly referred to as sap.

Xylem sap consists primarily of water, with hormones, mineral elements and other nutrients dissolved in it. Transport of sap in xylem is generally "acropetal", or upward from the roots toward the leaves. Over the past century, there has been some controversy regarding the mechanism of xylem sap transport; today, most plant scientists agree that the cohesion-tension theory best explains this process.

Phloem sap consists primarily of water, with sugars, hormones, and mineral elements dissolved in it. Phloem sap transport occurs from sources (locations where carbohydrates are produced or stored) toward sinks (locations where carbohydrates are utilized). The pressure flow hypothesis proposes a mechanism for phloem sap transport.

Maple syrup is made from reduced sugar maple xylem sap. In some countries (e.g., Russia, Latvia, Estonia or Finland) it is common to collect the early spring sap of birch trees (so called "birch juice") for human consumption; the sap can be used fresh or fermented and contains xylitol.

References

• Angeles, G., B.J. Bond, J.S. Boyer, T.J. Brodribb, J.R. Brooks, M.J. Burns, J.M. Cavender-Bares, M.J. Clearwater, H. Cochard, J.P. Comstock, S.D. Davis, J.-C. Domec, L.A. Donovan, F.W. Ewers, B.L. Gartner, U.G. Hacke, T.M. Hinckley, N.M. Holbrook, H.G. Jones, K.L. Kavanagh, B.E. Law, J. Lopez-Portillo, C. Lovisolo, T.A. Martin, J. Martinez-Vilalta, S. Mayr, F.C. Meinzer, P.J. Melcher, M. Mencuccini, S.S. Mulkey, A. Nardini, H. Neufeld, J.B. Passioura, W.T. Pockman, R.B. Pratt, S. Rambal, H. Richter, L. Sack, S. Salleo, A. Schubert, P.J. Schulte, J.P. Sparks, J.S. Sperry, R.O. Teskey, and M.T. Tyree. 2004. Letter: The cohesion-tension theory. New Phytologist 163: 451-452.