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Sieve cells are long, conducting cells in the phloem that do not form sieve tubes. The major difference between sieve cells and sieve tube members is the lack of sieve plates in sieve cells. [1] They have a very narrow diameter and tend to be longer in length than sieve tube elements as they are generally associated with albuminous cells. [4]
The presence of sieve plates greatly increases the resistance along the pathway, thereby generating and maintaining substantial pressure gradients in the sieve elements between source and sink. The movement in phloem is multi-directional, unlike in xylem cells, where the flow is upwards only.
Additionally, the expression of NAC45/86 genes during phloem differentiation functions to enucleate specific cells in the plants to produce the sieve elements. [19] In the embryo, root phloem develops independently in the upper hypocotyl, which lies between the embryonic root, and the cotyledon. [20]
Phloem is a complex tissue, consisting of two main cell types, the sieve tubes and the intimately associated companion cells, together with parenchyma cells, phloem fibres and sclereids. [ 19 ] : 171 Sieve tubes are joined end-to-end with perforated end-plates between known as sieve plates , which allow transport of photosynthate between the ...
The phloem, on the other hand, consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive. [citation ...
Sieve tube; Companion cell; Phloem fiber; Phloem parenchyma. Phloem is an equally important plant tissue as it also is part of the 'plumbing system' of a plant. Primarily, phloem carries dissolved food substances throughout the plant. This conduction system is composed of sieve-tube member and companion cells, that are without secondary walls.
The phloem tissue arises from the cell facing outside and consists of sieve tubes and their companion cells. The function of phloem tissue is to distribute food from photosynthetic tissue to other tissues. The two tissues are separated by cambium, a tissue that divides to form xylem or phloem cells.
Callose gets synthesized after the sieve tube elements undergo damage and/or stress. The use of wound callose occurs when callose gets deposited following sieve element damage. [2] Wound callose is proven to first be deposited at the sieve plate pores, or the intracellular connections, where it then spreads to different regions. [2]