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University of Waterloo
BIOL 120
Simon Cheung

Lecture 8 Functions of roots:  Anchors the plant  Conducts and absorbs water and minerals  Produces hormones and secondary metabolites  Regulate plant development and structure, reproduction  Storage Two types of root systems:  Taproot :  Typical of Dicots and Gymnosperms (develops directly from embryonic root)  Taproots penetrate deeply although conifers generally do not  Small plants can have significant taproot systems  Taproots can enhance survival in harsh environments (drought tolerance)  Fibrous root:  Typical of monocots and SVPs (embryonic root dies)  Root system arises from lower part of stem: therefore adventitious  After the radicle/embryonic root dies, numerous roots form from the lower part of the stem called adventitious roots  Each adventitious root forms lateral roots  Root system is typically shallower  Better at water acquisition  Often found in annuals (plants that have only a one year growing season)  Stabilize soil - less erosion Root systems can vary in depth and length:  Typically 50-90% occurs in the top 30 cm of soil  Potato root systems: 0.9 meters  Wheat, oats, barley: 0.9-1.8 meters Lecture 8  Can have significant radius around plant  Length of root system can be far greater than shoot system (corn: 457 meters root to 2.5 meters) Root structure:  Grows from tip (downwards) and matures in a retrograde manner (upwards)  A supply of dividing cells are found at the tip of the root  This region is known as the root apical meristem (“fountain of youth”)  The root apical meristem consists of a group of ‘initials’ or dividing cells  These cells reside within the ‘quiescent centre’  The ‘quiescent centre’ (Latin meaning ‘to rest’) is made up of cells or initials that divide relatively slowly  When each initial cell divides, one daughter cell remains in the quiescent centre while the other becomes a ‘derivative’  A derivative is primed to undergo further differentiation and growth  Derivatives give rise to the primary tissues (going from outside to inside) a)  Protoderm (Greek, proto meaning “before”, derma meaning “skin”) b)  Ground meristem: produces ground tissue c)  Procambium: source of primary vascular tissue  Derivatives divide much more quickly than initials Three Overlapping Zones:  Division, growth and differentiation can be traced linearly through 3 overlapping regions or zone  Zone of Cell division  Consists of RAM and three primary tissues  Zone of Elongation Lecture 8  Division stops and cells elongate  Region where most of root growth occurs  Zone of Maturation  Where cells begin to specialize  See root hair formation and maturation of conducting tissues  Lateral roots form immediately behind this region Root Cap:  Consists of cells produced at leading edge of growth  Cells contain amyloplasts (starch grains) that likely function as gravity sensors  Sacrificed to protect growing tip (meristem)  Produce a polysaccharide known as mucigel (biological grease!) that facilitates movement through the soil Root Hairs:  Function of water and mineral absorption is mainly served by root hairs  Root hairs produced in the zone of maturation  New root hairs are continuously produced with older hairs die as the root continues to grow  The region of the root containing root hairs may be well below ground Ground and Vascul
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