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Chapter 35 � Roots and Mineral Nutrition

Chapter 35 � Roots and Mineral Nutrition - 22:55...

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Chapter 35 – Roots and Mineral Nutrition 22:55 Roots Systems o Taproot system – one main root formed from seedling’s radicle / embryonic root . – more roots grow from this main root. Ex: trees and dandelions Eudicots and gymnosperms Adapted to get water from deep underground o Fibrous Root system- several small roots. Adventitious roots – develop from stem not another root. Adapted to get rain water from the surface Structure o Root cap – covers root tips. Protective, thimble like layer many cells thick that cover delicate root apical meristem. Release lubricating polysaccharides to decrease friction while moving through soil. o Root Hairs – tubular extensions of epidermal cells located behind growing root tip. Form in area of cell maturation < 1 cm / 0.4 in in length increase absorptive capacity by increasing surface area o lack nodes and internodes. Herbaceous Eudicot Roots o Epidermis – single layer of protective tissue covering the roots. Lack of cuticle and presence of root hairs increase absorption. *cell wall contains cellulose that absorbs water quickly o Cortex – loosely packed parenchyma cells.
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Bulk of herbaceous eudicot root. Lack support collenchyma cells. As age, roots can form sclerenchyma tissue. Primary function : storage Amyloplasts – store starch (most common form of stored enery in plants) Intercellular spaces: provide a pathway for water and aeration of the root. Water transport – 2 systems : symplast and apoplast Symplast: continuum or living cytoplasm – connected from one cell to next by bridges called plasmodesmata Apoplst – interconnected porous cell walls of plants. Water moves reely. Diffuse across cortex Inner layer of cortex: Endodermis – regulates movement of water and minerals that enter the xylem in the root’s center. Endodermis cells fit next to each other with Casparian strip – bandlike region containing suberin fatty material that is waterproof. Water moves through endodermis through osmosis or aquaporins – proteins that facilitate rapid transport of water – with concentration gradient Minerals enter through carrier-mediated active transport: against concentration gradient o Stele / Vascular Cylinder – center cylinder of vascular tissues. Outermost layer: Pericycle: single layer of parenchyma cells give rise to multicellular lateral roots / forming lateral meristems that produce secondary growth in woody roots Middle layer: Xylem : “xylem arms”. Phloem : in patches between the xylem arms. Water dissolved minerals are conducted in tracheids and vessel elements of the xylem. Dissolved sugar in sieve tube elements oh phloem. TRANSPORT OF WATER UP TO THIS POINT: FROM SOIL To CENTER OF ROOT: root hair / epidermis cortex endodermis pericycle root xylem Vascular cambium – gives rise to secondary tissues sandwhiched between xylem and phloem.
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