Root cap- covers the apical meristem and is formed by divisions of cells at the tip in a forward direction. It’s made up of living parenchyma cells, produced in the underground meristem and which are continuously sloughed off as the root pushes through the soil during elongation.

Root apical meristem-lengthening occurs immediately behind root tip.

region of cell division- behind root cap and apical meristem

Region of cell elongation- behind region of cell division

region of maturation-absorption of water and minerals, has root hairs and functional vascular cylinder.

Primary development- Apical meristem/region of cell division extends into and overlaps with region of cell elongation. At various distances from the apical meristems, cells enlarge and develop into specific cell types according to their position in the root.

Three primary meristems-protoderm, ground meristem, and procambium, all occur close to apical meristem.

Region of elongation is located- directly behind the root tip

Function of the Region of Elongation- where most of the growth or extension root length occurs.

Region of maturation function- where root hairs occur. has a working vascular cylinder. Root hairs burn out from the pressure of metabolic processes and so don’t persist past the zone of maturation.

Sieve tube function- Extends furthest into the tip to provide sugars and energy for mitosis;the apical meristem is where cell division occurs.

Sieve tube cont.-Mature portion of the sieve tube is closer to the apical meristem than are mature portions of xylem elements, indicating that the protophloem sieve tubes reach maturity earlier. Maturation of the endodermis (with casparian strips) occurs prior to maturation of the xylem elements and development of root hairs. the sites of the first prmary xylem elements an primary phloem elements are referred to as the protoxylem and protophloem poles, respectively.

Endodermis, then the functional xylem

Water is absorbed through the root hairs, passes through the cortex, and then into the xylem where it can be transported to other tissues and organs

Primary root tissue systems- dermal tissue system (epidermis), Ground tissue system (cortex), vascular tissue system (vascular tissues, solid center in dicot, pith-like center of monocot)

Root~epidermis-Primarily for absorption of water and minerals Root hairs GREATLY increase absorptive surface area Cuticle usually not present Root hairs are short-lived Continuously produced Mycorrhizae also increase surface area

A 4 month old rye plant had estimated 14 billion root hairs, with absorptive surface area of 401 square meters, laid end to end would measure over 10,000 kilometers (over 6000 miles—roughly from here to California and back). Cuticle is on the stem and on the leaves in primary growth, but not on the root. Makes sense right, since cuticle is made of long chain hydrocarbons that “waterproofs” the epidermis.

Mycorrhizae-

Two major types: Endomycorrhizae Penetrate the root cells Most common—80% of vascular plants Not highly specific The fungal hyphae penetrate cortical cells of root form highly branched arbuscules (arbuscular mycorrhizae) Ectomycorrhizae Surrounds but does not penetrate living cells in the roots Hyphae grow between the cells of the root epidermis and cortex, forming a characteristic highly branched network

Root covered with mycorrhizae microfilaments called hyphae, which exude enzymes into the soil and help solubilize nutrients—specially phosphorus in the soil. Endomiycorrhizae Are arbuscular inside the cells and in between the cells Progressivily stronger mutualistic symbioses between the fungi and the plant, depending on species and location. Also fungal endophytes, where the entire plant is colonized by fungus, only recently discovered with the advance of PCR technology, where DNA was analyzed on non-cultivated plants. Fungi are heterotrophs, so plants are providing fungi with sugars and with suitable habitat

Endomycorrhizae- Fungal hyphae pemetrate cortical root cells and form highly branched arbuscules (arbusuclar mycorrhizae) Most common (80% of vascular plants) not highly specific.

Ectomycorrhizae- Surrounds but does not penetrate living cells in the roots Hyphae grow between the cells of the root epidermis and cortex, forming a characteristic highly branched network

Root ~cortex- Cortex occurs between epidermis and vascular cylinder. It’s composed of parenchyma cells generated by the ground meristem and functions to store food and conduct water. The inner most layer of the cortex is the endodermis. Endodermis is ground tissue. Two ways water is conducted. Symplastic, where water moves through the protoderm and between cells through membranes and plasmodesmata. Apoplastic is where the water moves through the spaces around cells by adhsion and capillary action of cellulose in the cell walls.

Symplastic- moving through the plasma membrane from one membrane to another

Root~endodermis- Innermost layer of cortex -Casparian strip Composed of hydrophobic suberin and sometimes lignin Lines the anticlinal surfaces of endodermis cell walls Prohibits apoplastic movement of water and solutes Solutes move through membrane into vascular cylinder controlled by living protoplast. Water moves by osmosis From high concentration (soil) to low concentration (protoplasm of vascular cylinder) Active transport increases solute concentration in protoplast of roots Drives osmosis

Endodermis is the inner most layer of ground tissue, produced by the ground meristem. Anticlinal is perpindicular to the surface of the root. Periclinal is parallel to the surface of the root.

Endodermis~casparian strip-Casparian strip prohibits apoplastic movement of water and solutes and insures movement of water and solutes is controlled by living protoplast. Suberin is a long chain lipid polymer, like cutin in the cuticle of leaves, both are hydrophobic and prevent movement of liquid into or out of cells. Suberin is also found in periderm of stems (secondary growth).

Pericycle- Originates from procambium Composed of parenchyma cells Redifferentiates into lateral roots Lies immediately inside endodermis Helps form root vascular cambium in secondary growth. Phloem cells occupy sinuses between protoxylem poles. Protoxylem occurs on outer projections of star-shaped core of xylem Metaxylem occurs in the middle.

Lateral roots originate by dedifferentiation and redifferentiation of the pericycle parenchyma cells. Layer of parenchyma cells inside the endodermis, sometimes hard to distinguish from phloem cells. So parenchyma-single cell walls, isodiametric in shape. Capable of dedifferentiation and redifferentiation. So pericycle is responsible for the formation of lateral roots. The pericycle parenchyma cells become meristematic cells, and a new root can be created. Pericycle is also responsible for secondary growth. Secondary growth must originiate inside the endodermis to enjoy the protection of the casparian strips –the continuous cylender--to ensure uniform symplastic movement across the cells. Must grow out through the cortex, which causes rupture and disintigration of cortex, but the continuous core is maintained for intact and integral flow into the vascular cylinder.

Roots~secondary growth Root Secondary growth in large plants Additional anchorage Additional vascular tissue -Greater flow of nutrients Secondary growth involves: Creation of secondary xylem and phloem from a vascular cambium. Periderm or bark Replaces epidermis as protective covering Originates from the lateral meristem called cork cambium.

Secondary root growth- Vascular cambium originates between primary phloem and metaxylem in sinuses of protoxylem poles from pericycle opposite protoxylem poles. Rays brick-shaped parenchyma cells in files along radii. move nutrients and storage products laterally between xylem and phloem Cork cambium originates from pericycle phelloderm toward the inside and cork toward the outer surface. Cortex and epidermis sloughed Periderm consists of cork, cork cambium, and phelloderm.

Woody plants require larger roots that are also woody. Secondary xylem and phloem from a vascular cambium and also need periderm to replace the epidermis which has ruptured and been sloughed off. The cortex will also rupture and be sloughed off. The periderm will increase in size, along with the increase in girth of the root. Not just pericycle cells, but Phloem parenchyma cells also rediff and dediff into meristematic tissue to form the vascular cambium.

Ray cells are parenchyma cells formed by vascular cambium and occur radial to vascular tissue for lateral conductance of substances (from out to in, from xylem to phloem). Apoptosis forms the conducting cells of xylem—the tracheary elements and we need living cells to transport materials (nucleic acids, mineral nutrients, etc) laterally in the plant. Non-functioning tracheary elements occur in roots, and the ray cells sequester and transport nutrients from the dying vessel and tracheid elements inside to phloem outside for distribution throughout the plant. Also mobilize secondary chemicals to help preserve the dead heartwood (resin in pines, tannins in oaks, etc).

Pericycle makes the cork cambium, mature periderm has cork, cork cambium, and phelloderm