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periderm, new 2023.pptx

This document discusses the periderm, a protective tissue that replaces the epidermis in plant stems and roots. It develops from the phellogen, or cork cambium, which is a lateral meristem that divides to produce cork cells outward and secondary cortex cells inward. The cork cells mature into dead waterproof cork, while the secondary cortex cells remain living. Together these three tissues - cork, cork cambium, and secondary cortex - make up the periderm, which develops to protect stems and roots from rupturing during secondary growth.

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 Periderm  Occurrence.  Development  Structure. • By Zahra bijjar • Sara murad • Rubina “from bs 3rd botany” 1
 Periderm:  Periderm is a protective secondary tissue that replaces the epidermis.  Periderm is a component of secondary growth that is formed towards the surface of stems and roots,  Having phellem, phellogen and phelloderm. Occurrence of periderm:  The first periderm most commonly originates immediately below the epidermis , but in some species, it arises deeper in the stem. 2
 Usually in the primary phloem.  some of hypodermal cell or the outer cortical cells becomes meristematic and this layer aknown as phellogen.  the cells which cut off on the outer side are phellem or cork cell, and the sections that cut off on inner side are phelloderm or secondary cortex.  Phellem, phellogen,and phelloderm collectively constitute periderm. 3
 Development of periderm:  continued secondary growth of vascular cylinder in many older roots and stems exert or pressure which results in the stretching and rupturing of epidermis, cortex and other tissues outside the secondary phloem.  To avoid such breaking of external tissues, the plant organs develop a secondary protective covering,(which replace the epidermis into periderm). 4
 develop in roots and stems of dicots, gymnosperm.  It does not develop in leaves and monocot.  The periderm also develop when a plant part injured, wounded due to leaf or branch abscission and is called wound periderm.  The formation or growth of periderm start in different time in different plants.  E.g., acacia “A plant which its formation of periderm take place beginning of secondary growth.  And in case of magnefera, formation of periderm take place 20 month old,”mean its developed late”. 5
Structure of periderm:  1.phellogen (cork cambium).  2.phellem (cork).  3.phelloderm (secondary cortex).  Three different secondary protective outer layer tissue which protect the plant. 1.Phellogen:  Secondary lateral meristem (living permanent cells) the place of origin varies in different cells.  E.g. (A) the phellogen originate in the epidermal cell (e.g.pyrus,Nerium). 6
 (B) sometimes it originate , just below the epidermis(e.g.prunus).  (C) and somehow it developed second or third layer of cortex ,(e.g. boerhaavia).  (D) and other option it developed from inner layer of cortex or phloem (e.g. vistis vinifera).  (E) and in dicot roots it arises in the pericycle.  Function:  The cells of cork cambium are thin walled ,vacuolated , rectangular and living cell ,they divide by phericlynal division and sometimes divide by anticlinal division.  They divide to form the cork cell toward the outer side and also developed secondary cortex (phelloderm) toward the inner side.  Thus the cork cambium or phellogen is a single layer. 7
2.Phellem (cork):  The cells cut off toward the outer side from phellogen, may divide once or twice time and then differentiate into phellem(cork).  As they mature, then they elongate and developed secondary wall due to deposition of subrin (subrin is a type of fatty substance ) due to which secondary wall developed, over the primary wall of cellulose and becomes dead due to loss of living protoplasm. 8
 The secondary wall is impermeable to water.  In many cases the lamina of cork cells usually contain resinous or tanniferous material which give brown or yellow color to the cell wall of cork.  The cell of cork are compactly arranged and act as a water-tight compartment. 3. Pelloderm(secondary cortex):  The cut off toward the inner side from the phellogen and differentiate into phelloderm,  The cell of phelloderm are thin walled, which contain living protoplasm. 9
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 Resemble the parenchymata cells of primary cortex ,these cells are loosely arranged with distinct intercellular spaces in some plants, the cells develop chloroplasts and perform photosynthesis.  Reference: YouTube channel by rabika saini 11
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