Internal Structures of a Plant Leaf - All Global Updates

Internal Structures of a Plant Leaf


·         The leaf is made up of three tissue systems (Dermal, Ground and Vascular)

·         The dermal tissue system consists of lower and upper epidermis

·         The ground tissue system is found between the epidermal layers of leaf


·         Epidermis

§  In dicot leaves, the epidermis is dorsiventral

§  Generally, the epidermis is made up of a single layer of cells that are closely packed and covered with a cuticle

§  The epidermal tissue is made up of;

§  Epidermal cells

§  Guard cells

§  Subsidiary cells

§  Epidermal trichomes

§  Epidermal cells

§  Epidermal cells are the most numerous, largest, and least specialized

§  Epidermal cells are more elongated in the leaves of monocots than in dicots

§  Guard cells

§  Consist of a pair of bean- shaped cells surrounding the stoma

§  They contain chloroplasts

§  Other epidermal cells do not contain chloroplasts 

§  Subsidiary cells

§  They are 2 to 4 cells that surround the stoma

§  They do not contain chloroplasts

§  The epidermal layer consists of stomata

§  The stomata are part of a stoma complex which consists of a pore surrounded on each side by guard cells and subsidiary cells

§  The stoma complex regulates the exchange of gases and water vapour between the outside air and the interior of the leaf

§  There are more stomata over the abaxial that the adaxial epidermis t

§  Main function of the epidermis is to protect inner tissues


·         Mesophyll

§  Mesophyll is the entire tissue between the upper and lower epidermis is Mesophyll is differentiated in two regions;

§  Palisade parenchyma and

§  Spongy parenchyma

§  This differentiation gives two anatomical designations of the leaf

·         Dorsiventral leaf

Mesophyll is differentiated into palisade parenchyma (or palisade mesophyll) on the adaxial (upper) side   and spongy parenchyma (or spongy mesophyll) on the abaxial (lower) side

o   Common in dicot leaves

·         Isobilateral leaf

o   Leaf mesophyll is not differentiated this way (i.e., made of only spongy or palisade parenchyma)

o   Common in monocots

§  Palisade Parenchyma (Palisade Mesophyll)

·         Palisade parenchyma lies beneath the adaxial epidermis

o   Palisade mesophyll may be present below both surfaces or occur only below the upper epidermis

·         Consists of vertically elongated cylindrical cells in one or more layers

·         Cells are compactly arranged with the chloroplasts close to the walls of the cell

·         Main function is photosynthesis

§  Spongy Mesophyll

·         Lies below the palisade mesophyll, with irregularly shaped, loosely arranged cells
·         Contain fewer chloroplasts than palisade mesophyll

·         Spongy cells facilitate exchange of gases with the help of air spaces

·         The pores or stomata of the epidermis open into sub stomatal chambers, connecting to air spaces between the spongy layer cells


§  Vascular Tissues

·         Veins are the vascular tissue of the leaf located in the spongy layer of the mesophyll

·         Based on pattern of venation, the vascular system of leaves falls into two main classes:

§  The reticulate (or net) venation typical of dicotyledons

§  The parallel venation of the monocotyledons

·         The veins are made up of xylem and phloem tissues

·         The xylem typically lies over the phloem

·         In dicotyledonous leaves the main veins are open and usually collateral (less commonly bicollateral), closed in monocot leaves



Green Leaves

References
 Evans, W. C. (2009). Trease and Evans Pharmacognosy. India: Reed Elsevier Limited.
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