Plant Anatomy 2006-2007

Basic plant anatomy root shoot (stem) leaves root tip root hairs nodes internodes buds terminal or apical buds axillary buds flower buds & flowers leaves mesophyll tissue veins (vascular bundles)

Meristem Regions of growth stem cells: perpetually embryonic tissue regenerate new cells apical shoot meristem growth in length primary growth apical root meristem lateral meristem growth in girth secondary growth

Apical meristems shoot root

Leaves Function of leaves photosynthesis gas exchange transpiration energy production CHO production gas exchange transpiration

colored leaves (poinsetta) Modified leaves tendrils (peas) spines (cacti) succulent leaves colored leaves (poinsetta)

Interdependent systems Both systems depend on the other roots depend on sugars produced by photosynthetic leaves shoots depend on water & minerals absorbed from the soil by roots sugars water & minerals

Plant TISSUES Dermal Ground Vascular epidermis (“skin” of plant) single layer of tightly packed cells that covers & protects plant Ground bulk of plant tissue photosynthetic mesophyll, storage Vascular transport system in shoots & roots xylem & phloem

Structure–Function again! Vascular tissue vessel elements Xylem move water & minerals up from roots dead cells at functional maturity only cell walls remain need empty pipes to efficiently move H2O transpirational pull vessel element dead cells Aaaah… Structure–Function again! tracheids

Phloem: food-conducting cells carry sugars & nutrients throughout plant sieve tube companion cell sieve plate plasmodesmata living cells

Putting it all together Obtaining raw materials sunlight leaves = solar collectors CO2 stomates = gas exchange H2O uptake from roots nutrients

Transport in Plants 2006-2007

Why does over-watering kill a plant? Transport in plants H2O & minerals transport in xylem transpiration evaporation, adhesion & cohesion negative pressure Sugars transport in phloem bulk flow Calvin cycle in leaves loads sucrose into phloem positive pressure Gas exchange photosynthesis CO2 in; O2 out stomates respiration O2 in; CO2 out roots exchange gases within air spaces in soil Why does over-watering kill a plant?

Ascent of xylem fluid Transpiration pull generated by leaf

Water & mineral absorption Water absorption from soil osmosis aquaporins Mineral absorption active transport proton pumps active transport of H+ aquaporin root hair proton pumps H2O

Mineral absorption Proton pumps active transport of H+ ions out of cell chemiosmosis H+ gradient creates membrane potential difference in charge drives cation uptake creates gradient cotransport of other solutes against their gradient The most important active transport protein in the plasma membranes of plant cells is the proton pump , which uses energy from ATP to pump hydrogen ions (H+) out of the cell. This results in a proton gradient with a higher H+ concentration outside the cell than inside. Proton pumps provide energy for solute transport. By pumping H+ out of the cell, proton pumps produce an H+ gradient and a charge separation called a membrane potential. These two forms of potential energy can be used to drive the transport of solutes. Plant cells use energy stored in the proton gradient and membrane potential to drive the transport of many different solutes. For example, the membrane potential generated by proton pumps contributes to the uptake of K+ by root cells. In the mechanism called cotransport, a transport protein couples the downhill passage of one solute (H+) to the uphill passage of another (ex. NO3−). The “coattail” effect of cotransport is also responsible for the uptake of the sugar sucrose by plant cells. A membrane protein cotransports sucrose with the H+ that is moving down its gradient through the protein. The role of proton pumps in transport is an application of chemiosmosis.

Transport of sugars in phloem Loading of sucrose into phloem flow through cells via plasmodesmata proton pumps cotransport of sucrose into cells down proton gradient

Pressure flow in phloem Mass flow hypothesis “source to sink” flow direction of transport in phloem is dependent on plant’s needs phloem loading active transport of sucrose into phloem increased sucrose concentration decreases H2O potential water flows in from xylem cells increase in pressure due to increase in H2O causes flow can flow 1m/hr In contrast to the unidirectional transport of xylem sap from roots to leaves, the direction that phloem sap travels is variable. However, sieve tubes always carry sugars from a sugar source to a sugar sink. A sugar source is a plant organ that is a net producer of sugar, by photosynthesis or by breakdown of starch. Mature leaves are the primary sugar sources. A sugar sink is an organ that is a net consumer or storer of sugar. Growing roots, buds, stems, and fruits are sugar sinks. A storage organ, such as a tuber or a bulb, may be a source or a sink, depending on the season. When stockpiling carbohydrates in the summer, it is a sugar sink. After breaking dormancy in the spring, it is a source as its starch is broken down to sugar, which is carried to the growing tips of the plant. A sugar sink usually receives sugar from the nearest sources. Upper leaves on a branch may send sugar to the growing shoot tip, whereas lower leaves export sugar to roots. A growing fruit may monopolize sugar sources around it. For each sieve tube, the direction of transport depends on the locations of the source and sink connected by that tube. Therefore, neighboring tubes may carry sap in opposite directions. Direction of flow may also vary by season or developmental stage of the plant. On a plant… What’s a source…What’s a sink?

water moves into guard cells water moves out of guard cells Control of Stomates Epidermal cell Guard cell Chloroplasts Nucleus Uptake of K+ ions by guard cells proton pumps water enters by osmosis guard cells become turgid Loss of K+ ions by guard cells water leaves by osmosis guard cells become flaccid K+ K+ H2O H2O H2O H2O K+ K+ K+ K+ H2O H2O H2O H2O K+ K+ Thickened inner cell wall (rigid) H2O H2O H2O H2O K+ K+ K+ K+ Stoma open Stoma closed water moves into guard cells water moves out of guard cells

Plant Reproduction In a nutshell 2007-2008

Plant Diversity Bryophytes non-vascular land plants mosses ferns conifers flowering plants Bryophytes non-vascular land plants Pteridophytes seedless vascular plants Gymnosperm pollen & “naked” seeds Angiosperm flowers & fruit flowers & fruits pollen & seeds vascular system xylem cells tracheids common ancestor

Animal vs. Plant life cycle diploid multicellular individual 2n diploid multicellular sporophyte 2n mitosis mitosis meiosis fertilization meiosis gametes 1n spores 1n fertilization mitosis mitosis haploid unicellular gametes 1n haploid multicellular gametophyte 1n alternation of generations

diploid multicellular haploid multicellular Bryophytes Mosses & liverworts non-vascular swimming sperm dominant haploid gametophyte dependent sporophyte spores for reproduction diploid multicellular sporophyte 2n mitosis fertilization meiosis gametes 1n spores 1n mitosis mitosis haploid multicellular gametophyte 1n alternation of generations

diploid multicellular haploid multicellular Pteridophytes Ferns vascular swimming sperm dominant sporophyte independent gametophyte fragile spores for reproduction diploid multicellular sporophyte 2n mitosis fertilization meiosis gametes 1n spores 1n haploid archegonia mitosis mitosis haploid multicellular gametophyte 1n antheridia alternation of generations

diploid multicellular haploid multicellular Gymnosperm Conifers vascular pollen (sperm) dominant sporophyte dependent reduced gametophyte cones, seeds for reproduction diploid multicellular sporophyte 2n mitosis fertilization meiosis gametes 1n spores 1n mitosis mitosis haploid multicellular gametophyte 1n female male

diploid multicellular Angiosperm Flowering plants vascular pollen (sperm) dominant sporophyte dependent reduced gametophyte flowers, fruits, seeds for reproduction diploid multicellular sporophyte 2n mitosis fertilization meiosis gametes 1n spores 1n male gametophyte in pollen (haploid) mitosis mitosis haploid multicellular gametophyte 1n female gametophyte in ovary (haploid)

Angiosperm: flowering plants

Angiosperm life cycle male gametophyte in pollen (haploid) polar nuclei Angiosperm life cycle pollen grains male gametophyte in pollen (haploid) egg cell fertilization female gametophyte in ovary (haploid) sporophyte in seed (diploid)

Seed dispersal r-strategy K-strategy Plants produce enormous numbers of seeds to compensate for low survival rate vast amount of genetic variation for natural selection to screen Seed Aviation r-strategy K-strategy

Plant Responses to Stimuli

Plant hormones auxin gibberellins abscisic acid ethylene and more…

Auxin (IAA) Effects controls cell division & differentiation phototropism growth towards light asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side apical dominance

Gibberellins Family of hormones Effects over 100 different gibberellins identified Effects stem elongation fruit growth seed germination plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

Abscisic acid (ABA) Effects slows growth seed dormancy high concentrations of abscisic acid germination only after ABA is inactivated or leeched out survival value: seed will germinate only under optimal conditions light, temperature, moisture

One bad apple spoils the whole bunch… Ethylene Hormone gas released by plant cells Effects fruit ripening leaf drop like in Autumn apoptosis One bad apple spoils the whole bunch…

Fruit ripening Adaptation Mechanism hard, tart fruit protects developing seed from herbivores ripe, sweet, soft fruit attracts animals to disperse seed Mechanism triggers ripening process breakdown of cell wall softening conversion of starch to sugar sweetening positive feedback system ethylene triggers ripening ripening stimulates more ethylene production

Other Responses Gravitropism Occurs as soon as seed germinates, ensures root grows into soil and shoot grows toward sunlight. (Auxin)

Other Responses Thigmotropism Response to touch, allows the plant to use mechanical supports as it grows, also can result in rapid leaf movements (similar to action potentials in nerves)

Other Responses Photoperiodism A physical response, such as flowering to the photoperiod Actually controlled by night length not day length Long-day plants flower in late spring or early summer Short-day plants flower in late summer fall or winter

Other Responses Photoperiodism