The Root

Lab 8 The root Slides: Prepared 1) Allium root tip L.S. 2) Ranunculus root C.s 3) Vicia root C.S. 4) Tilia root C.S. 5) Pinus root C.S. 6) Smilax root C.S 7) Orchid root C.S 8) Lupinus root C.S nodules nitrogen fixing Fresh Specimens 1) Germinated seed (bean) 2) Carrot 3) Monocot root (fibrous root) 4) Dicot root (tap root) 5) Legume root with nodules 1 Lab. No.8 The Root -Roots are the first organ to emerge from seeds - Function: absorption of water and minerals, anchorage, storage and conduction. -Roots vary in structure but in general are less complex than the stems. - Roots may be divided into types, differ in presence or absence of secondary growth and in the amount of secondary growth. Root tips & Apical Meristem of Roots - The basic structure of root tips (starting from the root tip to its base) is rootcap, meristematic region, elongation region, root hair formation region and maturation region. -There are different organization of apical meristems of root, this difference in organization is due difference in development. - Primitive vascular plants have single tetrahedral apical cell 2 -The angiosperms have group of initials (three or four –tiered initials or non-stratified) Exercise 1 Examine a prepared slide of Allium cepa root tip L.S 1- rootcap, examine living parenchyma cells or and the sloughed off dead cells 2- apical meristematic region which is made of group of cells (initials) oriented in a horizontal plate. Those cells are capable of forming all regions. Examine those initials (meristems) draw shape of them. 3- try to notice (if your slide is obvious), in the region of elongation the derivatives of meristems (protoderm, ground meristems and procambium) then in maturation region notice the dense column of central cylinder (vascular tissue), cortex with intercellular spaces arranged like canals, epidermis , root hairs. Exercise 2 Prepare a slide of whole mount Allium root; try to notice the root cap and apical meristems. Be careful with this slide, the mounts are very thick and can be broken easily if use high magnification objective. - make a L.S in Allium root and prepare a wet mount slide using methylene blue stain, examine using your microscope The Primary Structure of Roots: Exercise 3 : Examine a prepared slide for Ranunculus old root c.s . Observe the following: -poorly preserved epidermis -Wide cortex, usually of parenchyma cells functioning in storage, the outermost layers form suberized exodermis, the amount of air spaces is much more than in young root - endodermis with thick secondary walls and passage cells (casparian strips in young roots) [notice the location of passage cells opposite to xylem] -unisriate pericyle of thin walled cells 3 - primary xylem (depending on pattern of maturation xylem is exarch : centripetally: matures from peripheral toward center)outer protoxylem and inner metaxylem. Notice how many ridges is xylem (triarch or tetrarch) - primary phloem alternate with archs or ridges of xylem (outer phloem protophloem and inner one the metaphloem. -no pith Types of Roots: A) Roots of herbaceous dicots without secondary growth Example Rununculus root B) Roots of herbaceous dicots with a considerable amount of secondary growth Exercise 4 Examine prepared slide for Vicia faba (bean) root c.s -Try to identify the vascular cambium cells between primary xylem and primary phloem. -pericycle cells which become active as a cambium. -notice size of cortex, if exodermis and endodermis still present. -notice if there is epidermis or periderm. - Lateral root is present (will be mentioned later) C) Roots of woody plants Exercise 5 Examine prepared slide of Tilia root c.s (dicot angiosperm) and notice the following: -the periderm replaces the epidermis -reduced cortex -secondary phloem of continues cylinder in a form of widges - secondary xylem with late and early wood forming growth layers or rings -narrow rays in xylem and phloem -Dilated ray parenchyma in phloem -vascular cambium between xylem and phloem -sclerified parenchyma in the center Exercise 6 Examine prepared slide of Pinus root c.s (gymnosperm) Notice: the periderm, secondary phloem and secondary xylem, vascular cambium, observe if pith is present or absent. 4 Compare between this section in the gymnosperm root and the previous section in the angiosperm root. E) Roots of monocots without secondary growth Exercise 7 Examine prepared slide of Smilax root c.s. as a monocot root with no secondary growth notice: - epidermis with relatively thick –walled cells -thick walled exodermis - cortex of parenchyma with intercellular spaces. -thick walled endodermis with u-shaped thickening, passage cells opposite to protoxylem tissue. - partly sclerified pericycle 5-6 cells in depth. -polyarch primary xylem alternating with primary phloem strands (in both xylem and phloem proto elements outside near pericycle and meta elements towards the inside) - parenchyma (sclerified) occupying the center (pith) F) Storage roots Storage is of the functions of root but some roots are specialized as storage organs. Those roots are characterized by abundance of parenchyma (for storage) and the vascular tissues are associated with parenchyma but with limitation in sclerified elements (no fibers) Some storage roots have secondary growth. Exercise 8 Try to make a free hand transverse section in carrot root . Examine the section using the compound microscope, observe the modification in this storage root,(carrot root has secondary growth) stain using toluidine blue. G) Lateral roots (branches for tap root) Derived from the pericyle. Exercise 9. you have already examined Vicia root, so notice the lateral root and examine its origin. There are two main types of root systems (taproot of dicots and gymnosperms and fibrous root of monocots) 5 Exercise 10 Examine two fresh specimens one for dicot plant and the other for a monocot plant. Notice the root system in both plants then differentiate between the fibrous root and tap root Exercise 11 make free hand transverse section of a dicot root, stain using Toluidine blue, notice primary structure of the root. Root Symbioses Exercise 12 Examine root system of legume plant, notice the presence of root nodules which represent a symbiotic relationship between the root and Rhizobium (species of Nitrogen –fixing bacteria). - Also examine a prepared slide for Lupinus root c.s with root nodules, notice in this section, the growth of bacteria, the outgrowth of cortical cells of the root Aerial root of epiphytic plant Exercise 13 Examine a prepared slide for Orchid root c.s Notice the velamen (multiple epidermis) in this aerial root. 6