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The following points highlight the top six factors influencing differentiation of sclereids cells in plants. The factors are: 1. Ageing 2. Wounding 3. Position 4. Osmotic Pressure 5. Enzyme 6. Hormone.
Factor # 1. Ageing:
In the barks many parenchyma cells change to brachysclereids. It is regarded that the sclereid differentiation is due to ageing of the tissues.
Factor # 2. Wounding:
In Monstera deliciosa leaves and aerial roots stone cells appear close to wound tissues. Bloch (1944) opines that the appearance of stone cells is in response to physiological disturbances.
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Later observations reveal that wounds have inhibitory influence on the leaves of Fagraea fragrans in the differentiation of brachysclereids. In this species brachysclereids did not appear in the tissues present around the injury. These tissues normally produced sclereids.
Factor # 3. Position:
Sclereids differentiate along the margins of the developing leaves of Trochodendron aralioides. In an experiment the buds of the above species were excised and grown in sterile culture media. It was observed that astrosclereids appeared along the margin of leaf.
Brachysclereids in the air roots of Monstera deliciosa and astrosclereids in the leaf of Camellia japonica differentiate in close proximity to the surface. In the leaf of Camellia additional sclereids could be induced to differentiate by experimental incisions on the leaf surface. Sclereids appeared along new surfaces in incised leaf.
Factor # 4. Osmotic Pressure:
Osmotic pressure influences sclereid development. In an experiment the leaves of Camellia japonica were detached and cultured in a medium where sucrose concentration was high. It was noticed that fewer sclereids were developed in the leaf. A similar result was observed when the detached leaves were cultured in a medium with control level of sucrose and mannitol was added to it.
Factor # 5. Enzyme:
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The initials that are destined to differentiate into sclereids show more activity of enzyme than their neighbours. So it is regarded that enzyme influences sclerenchyma differentiation. In Rauwolfia the initials showed intensified activity of the enzyme cytochrome oxidase (Mia et al, 1965). The initials have higher degree of metabolic activity than the other cells and as a result more enzyme activity is observed in them.
Factor # 6. Hormone:
The following experiments indicate that hormone influences sclereid differentiation. In Fagraea fragrans sclereids developed in the leaves when they were treated with low concentration of auxin. But the cell walls of sclereids were non-lignified and so thin-walled. In another experiment the buds of Pseudotsuga taxifolia were grown in culture medium.
Few sclereids were differentiated in the leaves. In the culture medium various auxins with higher concentration were added. It was noticed that the number of sclereids was further reduced than the previous experiment.
It indicates that auxin at certain concentration inhibits sclereid formation. In the other experiment with Pseudotsuga the branches were defoliated and treated with indoleacetic acid in lanolin paste. It was observed that in the developing leaves sclereid differentiation was inhibited.
