Protophloem vs Metaphloem
Similarities and Difference between Protophloem and Metaphloem
Vascular bundles (fascicles) are the component of the stelar system in higher plants and their main function is the conduction of water, minerals and food materials. Typically, a vascular bundle composed of xylem and phloem arranged together as bundles. In a young stem, both in dicots and monocots, Phloem, the food conducting tissue of vascular bundles, are differentiated into PROTOPHLOEM and METAPHLOEM based on the structural and functional modifications of their elements.
The present post describes the similarities and difference between Protophloem and Metaphloem in a primary vascular bundle of a young stem.
Similarities between Protophloem and Metaphloem
Ø Both protophloem and metaphloem can conduct food materials.
Ø Both are complex tissues, composed of many types of cells.
Ø Both components contain living and dead cells.
Ø Both are developed from the primary meristem, the pro-cambium.
Ø Protophloem and metaphloem develop only in primary vascular bundles.
Difference between Protophloem and Metaphloem
Sl. No. Protophloem Metaphloem
1 Frist formed part of the phloem of vascular bundles Formed after protophloem
2 Mature before the plant organs have completed their elongation Mature after the plant organs have completed their elongation
3 Composed of sieve elements, phloem parenchyma and fibres. Composed of sieve elements, companion cells, phloem parenchyma and phloem fibres
4 Companion cells usually absent Companion cells are present
5 In stem protophloem is arranged towards the periphery In stem metaphloem is arranged towards the inner side
6 Protophloem is usually thinner and inconspicuous Metaphloem is usually with large and conspicuous sieve elements
7 Sieve areas are indistinct in sieve tubes, Sieve areas absent in the phloem of Gymnosperms Sieve areas are well developed
8 Protophloem is short lived, become non-functional when the plant matures Remain functional for longer periods, in plants without secondary growth, the metaphloem survive till the end of the plant
9 Specilized phloem fibres are sometimes present Phloem fibres will be of normal type
10 Subjected to stress during elongation and maturation Not subjected to stress during elongation and maturation, but with secondary growth
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