Phloem
/ˈfloʊ.əm/
Definition
Phloem is the plant vascular tissue that transports sugars and other organic nutrients made during photosynthesis from leaves to growing, storage, or repair tissues. Unlike xylem, which mainly moves water and minerals upward, phloem can move dissolved food in different directions as needed. It occurs in vascular bundles, stems, roots, and leaf veins, and consists mainly of living conducting cells with supporting cells around them.
Function in Plants
- Sugar distribution: phloem moves sugars made in the leaves to growing shoots, roots, flowers, fruits, and storage organs. This supply supports growth, flowering, seed development, and the buildup of reserves such as starch.
- Two-way transport potential: Movement in phloem can occur from one part of the plant to another depending on where sugars are being produced and where they are needed. Botanists describe these areas as sources and sinks.
- Link to plant health: When phloem is damaged by girdling, stem injury, or some pests and diseases, tissues below or beyond the injury may be starved of food. Decline can appear even when water transport in xylem is still partly working.
- Role in grafting success: In grafted plants, phloem must reconnect across the graft union along with xylem. Good alignment of the vascular cambium, the growth layer that produces transport tissue, helps that reconnection happen.
Related Terms
Xylem
Xylem is the plant vascular tissue that carries water and dissolved minerals from the roots to stems and leaves. It…
Vascular tissue
Vascular tissue is the plant transport system, made of xylem and phloem. Xylem carries water and dissolved minerals…
Translocation
Translocation describes the movement of organic nutrients and other dissolved substances from one part of a plant to…
Stem
Stem refers to the main aboveground plant structure that supports leaves, buds, flowers, and fruits, and connects them…
Root
Root refers to the plant organ, usually below ground, that anchors the plant and absorbs water and dissolved minerals…
Leaf
Leaf refers to a plant organ, usually flat and green, that grows from the stem or a branch and is specialized for…