The ultrastructure of protophloem sieve elements in leaves of Aegilops comosa var. thessalica
1982
Eleftheriou, E.P. | Tsekos, I.
The differentiation and obliteration of protophloem sieve elements in leaves of the grass Aegilops comosa var. thessalica have been studied by electron microscopy. These elements differentiate similarly to metaphloem sieve elements of the same plant and other monocotyledons. Plasmalemma, smooth endoplasmic reticulum (ER), mitochondria, P-type plastids and sometimes nuclear remnants constitute the protoplasmic components at maturity, all are peripherally distributed. The differentiation of end walls into sieve plates and the presence of sieve areas on the lateral walls indicate that protophloem sieve elements are components of sieve-tube. They may be functional for a brief period but soon after their maturation they are compressed and finally obliterated by the stretching of actively-growing surrounding cells. The protoplasmic components of mature elements degenerate and are destroyed during obliteration of the sieve elements.
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