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Phloem Structure Phloem is composed of several cell types including sclerenchyma, parenchyma, sieve elements and companion cells. The sieve element and companion cell are found closely associated with each other in what is referred to as the sieve element/companion cell complex.
(1) From the phloem sieve tubes (Pc), carbohydrates can move by diffusion via plasmodesmata into the symplastic storage compartment (S) (e.g. ray cells or phloem parenchyma). Carbohydrates can diffuse through the cell membrane (2) into the apoplast (A) or (3) into the storage compartment.irst, the phloem protects the plant by its high turgor pressure and concomitant high sugar concentration in the SECCCs (Turgeon, 2010a). When a sieve tube is wounded, pressure release causes surging and forces cellular debris into the sieve pores, sealing the phloem (e.g. Ehlers et al., 2000).