Plant Structure: Roots and Leaves - Prof. Scott K. Gleeson, Study notes of Biology

Download Plant Structure: Roots and Leaves - Prof. Scott K. Gleeson and more Study notes Biology in PDF only on Docsity! PLANT STRUCTURE: PARTS (ORGANS) Roots Leaves Stems ROOTS Design problems: 1. soil resources (water, nutrients) are dispersed throughout soil volume 2. resources must be transported to the shoot 3. sugar must be transported to growing root 4. uptake system must be functional throughout plant development Solution: A growing systems of pipes connected to absorptive surfaces A branching system is the most efficient way to fill space (volume) Two basic branching structures 1. Taproot – gymnosperms and dicots, primary root grows downward, lateral roots grow out from tap root. 2. fibrous root system – monocots (eg grasses) primary root short lived, multiple “adventitious” roots arise from stem base. 30.13 Both types of roots can go very deep and produce large absorptive surfaces - a mesquite (desert shrub) had roots > 50m deep - a rye grass plant (4 months) in 6 liters of soil had root surface of 640 sq m (400 sq m were root hairs) (130 times shoot) Fig. 44.--Top view of surface roots of Comanche cactus (Opuntia camanchica). Scale in square feet Fig. 43.--Wire grass (Aristida purpurea) from the short-grass plains From J.E. Weaver 1926. Root Development of Field Crops Mature Tissues: Epidermis, Cortex, Vascular cylinder Bt PRIMARY TISSUES: Epidermis (dermal) Stele (vascular) (a) Cross section of a dicot root 500 pm (b) Cross section of a monocot root ‘Copyright & Pearson Education, Inc., publishing as Benjamin Cummings. 35.14/35.13 — 100 pm Epidermis absorbs water and nutrients aided by root hairs (trichomes) increased surface secrete root exudate promotes activity of soil microbes near root trade carbohydrate for nutrients helps create rhizosphere Initiate contact with root symbionts in soil Mycorrhizae (fungi) N-fixers (bacteria) 37.3/37.6 37.10 35.3 Cortex water & nutrients move through and between these cells many air spaces some starch storage 35.14/35.13 Vascular Cylinder 1. Pericycle layer of parenchyma cells around conducting tissues origin of lateral roots (new meristems) 2. Xylem – water and nutrients “up” to shoots 3. Phloem – carbohydrates “down” from shoots 35.15./35.14 Root Modifications Storage Roots (and also stems) often used to store carbohydrates usually in parenchyma cells of vascular cylinder e.g. – carrots, sweet potatoes, beets, radishes “cultivars” selected for food, from ancestors that store for their own benefit may be important in human evolution Functions of storage 1. Sustain plant during stress 2. Recover from damage (herbivory) 3. Allow rapid burst of growth or reproduction spring growth (competition) rosette species (reproduction) skip life stages (longleaf pine) floridata.com  ~ Ww cn LEAVES Leaves Roots – site of water and nutrient uptake Leaves – site of CO2 uptake and light absorption Together, this is the complete recipe of essential resources 36.2/37.2 Function of size variation? Larger continuous blades have thicker boundary layer more resistance to diffusion higher temperatures Monocots (grasses, palms) Blade Sheath (leaf base around stem) Meristem at base of blade creates “parallel” structure enhances recovery from grazing damage Also much variation in size and structure Leaf internal structure — tissues epidermis, mesophyll, vasculature Guard cells Dermal I Ground Stomatal pore @) vascular Epidermal cell 1 50 pm Stoma (b) Surface view of a spiderwort (Tradescantia) leat (LM) Sclerenchyma epidermis \- Lower epidermis Cuticle Vein Airspaces Guard cells 100 pm (a) Cutaway drawing of leaf tissues (c) Transverse section of a lilac (Syringa) leaf (LM) 35.18/35.17 Epidermis compact array of epidermal cells surrounds leaf covered with cuticle to reduce H2O loss Mesophyll ground tissue of leaf – parenchyma contains chloroplasts air spaces – for gas exchange 1. Palisade parenchyma elongated cells below epidermis high chloroplast concentration 2. Spongy parenchyma - large air spaces, enhance diffusion Leaf Vasculature Veins – vascular bundles throughout mesophyll both xylem and phloem Major veins – conspicuous ribs with support tissue mainly for rapid transport Minor veins – small veins in contact with mesophyll important for exchange supply water and collect photosynthate (sugars) surrounded by bundle sheath cells – exchange layer Dicots – netted venation – central midrib branches into smaller veins Monocots – parallel venation – large major veins connected by smaller veins End