kuliah anatomi akar

through the division and elongation of cells located in the apical portion of the root.

The growth in length of a root

The tip of the root is covered by a mass of cells called the root cap.

The cells of the root cap are parenchyma, and frequently have thick, mucilage-containing walls.

The root cap protects the root meristem and lubricates the tip to pushed through the soil.

The root cap also appears to play a role in the roots response to gravity.Starch-containing plastids may act as statoliths, or gravity-sensing bodies.

The quiescentCenter is a relatively inactive of slowly dividing cells

Surrounding the quiescent center is the apical meristem which actively divides

Fungsi ?

The epidermis arise from protoderm The cortex from the ground meristem The vascular tissue from the procambium.

The cortex between the epidermis and the vascular cylinder

The cortex is composed of parenchyma cells which frequently store starch.

The innermost layer of the cortex is called the endodermis (a cylinder of tightly packed cells without intercellular spaces).

There are air spaces between the cells.

The endodermisThe endodermis The endodermis The endodermis

separates the Cortex from separates the Cortex from the Stele the Stele

an endodermis to regulate an endodermis to regulate water uptake by the roots water uptake by the roots and maintain the water and maintain the water balance of the plant balance of the plant

The Exodermis has the The Exodermis has the same anatomy as the same anatomy as the Endodermis and probably Endodermis and probably restricts water loss to the restricts water loss to the outside in older roots.outside in older roots.

The cells of the endodermis have specialized The cells of the endodermis have specialized walls that known as the walls that known as the Casparian stripCasparian strip

The specializedspecialized walls, composed of a mixture suberin and lignin

The presence of the Casparian strip makes the walls impervious to water, so that all substances entering the vascular tissue must pass through the cytoplasm of the endodermal cells.

The walls of the epidermis and the cortical cellsform a continuous system through which water and dissolved substances candiffuse withoutentering the cytoplasm; that is, until they reach the endodermis, where the wayis blocked by the Casparian strip.Here, any substance entering the vascular tissue must pass through thecytoplasm of the endodermal cells where, presumably, the flow is regulated

STELESTELE The vascular tissue, or The vascular tissue, or

stele, at the stele, at the center of the center of the root. root.

The stele is The stele is composedcomposed of of xylem and phloemxylem and phloem, and is , and is surrounded by the surrounded by the pericycle.pericycle.

The The pericyclepericycle is the is the outermost layer of the outermost layer of the stelestele and is directly and is directly beneath the endodermis.beneath the endodermis.

In In young rootsyoung roots the the pericycle is composed of pericycle is composed of thin-walled parenchymathin-walled parenchyma cells, but in cells, but in older rootsolder roots the walls may become the walls may become thickenedthickened. .

The cells of the pericycle retain their meristematic capacity and are the site of formation of secondaryroots.

The cells of the metaxylem Differentiate, larger in diameter than the protoxylem

They are located inside protoxylem and may occur in the center of the root if pith is not present If pith is present,the metaxylem forms a ring around it

The phloem consists of protophloem and metaphloem.

The direction of differentiation and maturation of the phloem is the same as the xylem,namely from the younger portions of the root toward the mature and from the edges toward the center.

Lateral (Secondary) Roots Lateral (Secondary)

Roots originate in the Stele or the Endodermis.

They grow through the Cortex and Epidermis

Vascular Connection between it and the parent Stele

in most angiosperms The pericycle of the root is usually a single-cell-layer thick.

It retains its ability to divide long after the other cells of the root have lost this ability.

Because of this capacity, it is the site of formation of the secondary roots.

It also functions in the thickening of the root during secondary growth

The first sign of secondary root initiation is the periclinal division of a limited number of periderm cells.

These are followed by divisions in both periclinal and anticlinal planes.

These divisions result in the formation of a group of meristematic cells that soon becomes organized into an apical meristem having the same pattern as the parent root.

As this new apical meristem grows, it pushes its way As this new apical meristem grows, it pushes its way through the cortex and epidermis of the parent root. through the cortex and epidermis of the parent root.

As the tissues of the new root differentiate and As the tissues of the new root differentiate and mature, the xylem and phloem develop, so that they mature, the xylem and phloem develop, so that they become continuous with the xylem and phloem of become continuous with the xylem and phloem of the parent root.the parent root.

cells that remain undifferentiated between the primary phloem and primary xylem form the vascular cambium that gives rise to the secondary phloem and secondary xylem.

Divisions of the pericycle initiate the formation of the cambium.

The cambium differentiating from the provascular tissue between the phloem and xylem and from the pericycle over the protoxylem poles.

THE DIFFERENCE THE DIFFERENCE MONOCOTYL AND MONOCOTYL AND

DICOTYL ROOTDICOTYL ROOT

THE DIFFERENCE THE DIFFERENCE MONOCOTYL AND MONOCOTYL AND

DICOTYL ROOTDICOTYL ROOT

Number of Xylem Arms

Two = DiarchThree = TriarchFour = TetrarchFive = PentarchSix   = HexarchMore than five =

Polyarch

Monocots are usually Polyarch