Leaf anatomy Leaf anatomy Leaves start as outgrowths from apical meristem leaf primordia 3 primary meristems Leaf anatomy protoderm becomes procambium becomes ground meristem becomes Epidermis note cuticle stomata Veins with vascular tissues Supply water nutrients remove sugars for transport elsewhere Leaf anatomy Mesophyll Leaf anatomy Parenchyma tissue layers palisade and spongy do Monocot vs dicot anatomy Stem Dicot with bundles Pith and cortex present Monocot scattered vascular bundles No Monocot vs dicot anatomy Root Dicot 6 phloem patches no pith Monocot vs dicot anatomy Root Monocot many pith present Monocot vs dicot summary Note root system type dicot often with single major root axis taproot system monocot lacking this fibrous root system Plant Growth Phenomena Hormones molecules produced in small amounts that change Can inhibit or stimulate processes to occur 5 major types auxins cytokinins gibberellins ethylene abscisic acid Auxins Promote stem elongation and growth Example Bending of stem toward light Auxins Also involved in suppression of lateral meristems by apical meristem Auxins Can stimulate production of roots roots produced on stem or leaf Useful in rooting cuttings asexual plant reproduction Cytokinins Stimulate cell division where auxin is also present Acts as hormone keeps detached leaves green Gibberellins Promote stem elongation Mutant plants with low amounts are internode lengths short Ethylene Promotes fruit ripening Stimulates dropping of leaves flowers Abscisic acid Induces formation of winter buds bud scales dormant meristem Involved in opening and closing of Can cause seed dormancy Other plant growth phenomena Gravitropism response of stem root to gravity Stems bend away from gravity gravitropism Roots bend toward gravity gravitropism Other plant growth phenomena Mechanism unclear May involve called statoliths in root cap of root in parenchyma cells of stem Other plant growth phenomena Thigmotropism response of plant to Examples Many tendrils grow toward stimulus and wrap around object Turgor movement Not growth involves loss of water pressure turgor pressure in some cells Can be reversed May involve rapid movement electrical QuickTime and aCinepak decompressorare needed to s signal Ex sensitive plant Flowering Some plants use daylength as flowering cue Can measure length of night photoperiod by pigment called Long day plants flower when night is than some critical time Short day plants flower when night is than some critical time Day neutral plants don t use photoperiod as flowering cue Flowering Flowering Use Can make some plants bloom when we want them Ex poinsettia A short day plant that growers make flower for Christmas holidays Plant transport Phloem sugars and water often from leaf to root Xylem water and minerals from root to shoot Movement driven by measure of tendency of water to move from one place to another Plant transport Water potential is affected by solutes high solutes tendency to move pressure high pressure tendency to move tension pull high tension tendency to move Water transport Xylem water and minerals from root to shoot How much of water remains in plant Water transport Transpiration evaporation of water from leaves Driven by from leaves Water under tension Water potential high in soil and low in air Water transport Driven by pull from leaves Water under tension Water potential high in soil and low in air Water transport Transpiration greatly controlled by stomata Stomata open in but can close if plant lacks sufficient water Stomata Sugar transport Phloem sugars and water Flow from to Pressure flow mechanism Sugar transport Source lots of sugar dissolved in water Generates pressure as water flows in to sugar Sink little sugar dissolved in water Low pressure as water flows out Creates gradient that moves fluid thru sieve tubes Sugar transport Result sugar flows to wherever demand is high Secondary Growth Secondary Growth Two types of growth Primary growth up and down Generated by apical meristems Form tissues Secondary growth growth in girth Generated by lateral secondary meristems Form tissues All plants do primary growth Woody plants do growth Secondary Growth Lateral meristems 1 makes new phloem and xylem Called phloem and xylem tissues vs primary phloem and xylem made directly from procambium Function xylem takes water minerals to leaves phloem takes sugars to roots Secondary Growth Lateral meristems 2 makes new cell type cork cell Cork cells with primary wall impregnated with waxy material Dead at maturity Forms waterproof layer on outside of body to replace epidermis Tissue composed of cork cells and made by cork cambium Also is a secondary tissue Secondary Growth Stem cross section Secondary Growth Vascular bundles contain Located between primary xylem and phloem Meristematic can still do Secondary Growth Residual procambium cells start to divide Produce new cells Secondary Growth Parenchyma cells between bundles also start to divide Together form solid ring of cells all dividing laterally This is Secondary Growth Vascular cambium makes secondary xylem on secondary phloem on Note how cambium moves outward over time Secondary Growth Note arrangement of primary phloem and secondary phloem primary xylem and secondary xylem Secondary Growth Secondary xylem may contain 1 Vessel elements 2 Tracheids 3 4 Fibers Secondary phloem may contain 1 Sieve tube elements 2 Companion cells 3 Parenchyma 4 Secondary Growth Two Secondary Growth Later secondary growth Secondary Growth First cork cambium Forms under Secondary Growth Cork cambium Makes files of cork cells to outside Forms first Epidermis cut off from rest of stem and dies Secondary Growth Problem cork cells are dead at maturity Cork layer cannot as vascular cambium continues to grow Solution form new in cortex under old one After time several build up yellow lines Newest inner one cuts off water to layers beyond it and they Secondary Growth Periderm replaces epidermis How get into stem Secondary Growth Lenticels Loosely packed Allow oxygen to diffuse into stem to support living cells there Secondary Growth Note made by vascular cambium Form transport system often parenchyma cells In phloem phloem ray In xylem xylem ray wood ray Secondary Growth In temperate zone cambium activity varies between and in growing season Spring big cells wood Summer small cells wood Form growth ring tree ring one season s growth Ex pine mostly tracheids Secondary Growth Ex oak note vessels thick