Anatomy & Growth of Angiosperms

Two plant groups: monocots & eudicots

I. Introduction A. Uniqueness of Plants http://www.fugu-sg.org/~elia/cambodia/templesfacesweb/pages/A3_Embracing_Roots.htm

B. Forces for Change 1. Genetics 2. Environment – two time scales: a. Long-term: accumulation of adaptations that enhanced survival & reproduction (evolution by natural selection) b. Short-term: plasticity = wide range of phenotypes for each genotype. Allows plants to adjust to changing environment (ex. Shorter plant in dry year so that it can still reproduce)

Muscle cell Muscle tissue Heart Circulatory system Parenchyma cell Dermal tissue Leaves Shoot system Cells Tissues Organs Systems

II. Plant Organs: Roots, Stems, Leaves A. Roots 1. Functions a. Collect water & minerals from soil b. Anchor plant c. Store food (carb’s from photosynthesis) to be used for flowering & fruiting d. Covered with root hairs – increases surface area for absorption

Fig. 35.2

2. Types a. Prop root c. Aerial strangler root b. Storage root Fig. 35.4 a. Prop root c. Aerial strangler root b. Storage root d. Buttress root e. Pneumatophore

B. Stems/shoots 1. Functions a. Support, transport b. Some photosynthesis 2. Two types of shoots a. Vegetative – leaves only b. Reproductive – produces flowers

3. Two parts of the stem: a. Node – point of leaf attachment b. Inter-node – stem segments between nodes

4. Buds Apical dominance = the presence of an apical bud inhibits the growth of axillary buds. - remove or depress apical bud, axillary buds begin to grow. a. Terminal bud – contains a shoot apical meristem; shoot growth is concentrated here b. Axillary buds – in angle (axil) between leaf & branch, contain meristem with potential to become a vegetative shoot. Mostly dormant.

Fig. 35.2

5. Modified Shoots (stems): a. Stolons – above-ground runners b. Rhizomes – below-ground runners Asexual, vegetative propagation c. Bulbs – swollen underground shoots d. Tubers – swollen rhizomes Stores food for later growth

Fig. 35.5

C. Leaves – main photosynthetic organs 1. Parts a. Petiole b. Blade http://www.knotweed.co.uk/japknot_Info.htm

2. Types Compound, doubly compound – why??

a. Tendrils Fig. 35.7 3. Modified leaves b. Spines c. Succulents

III. Plant Tissue Fig. 35.8

A. Dermal or Epidermis 1. Characteristics a. single layer of tightly packed cells covering the young parts of the plant. b. Functions in protection c. Root hairs are specialized epidermal extensions d. Secretes waxy cuticle of the leaf

a. Fills the space between dermal and vascular tissue systems. B. Ground 1. Characteristics a. Fills the space between dermal and vascular tissue systems. b . Diverse functions: Photosynthesis, storage, & support pith In eudicots stems: cortex

C. Vascular 1. Characteristics a. function in transport between roots & shoots, and structural support of plant 2. Types a. Xylem: H2O & minerals transported up to shoot system b. Phloem: Food transported to roots & non- photosynthetic parts such as the flowers

IV. The Plant Cell Fig. 7.8

A. Generalized Same as animals, except: 1. No lysozomes (digestive organelle) 2. Cell walls: maintains shape, structural support, protects from damage. Made of cellulose, protein, & sometimes lignin 3. Chloroplasts 4. Vacuole – storage, waste breakdown, growth! 5. Plasmodesmata – holes in cell wall, creates channels to connect cytoplasm of adjacent cells

B. Plant Cell Categories 1. Parenchyma 4. Water-conducting cells of the xylem 3. Sclerenchyma 5. Sugar-conducting cells of the phloem 2. Collenchyma

1. Parenchyma a. Characteristics i. Least specialized cell. Can differentiate into other cell types ii. Primary cell walls only - thin and flexible iii. Lack secondary plant cell walls iv. Most metabolically active – lots of chloroplasts for PSN (PhotoSyNthesis) v. Starch, carbohydrate production & storage in stems

2. Collenchyma a. Characteristics i. Primary walls are unevenly thickened ii. Usually lack secondary walls. iii. Usually grouped in strands to support young parts of plants without restraining growth iv. Flexible, elongate with growing shoots

3. Sclerenchyma a. Characteristics i. Function in mechanical support ii. Have rigid and thick secondary walls strengthened with lignin. iii. May be dead at functional maturity iv. Cell walls left behind as skeleton

Lignin:

3. Sclerenchyma b. Two types, both function in support: i. Fibers - long, slender, tapered cells occurring in bundles. ii. Sclereids - short, irregularly-shaped. Ex. hard seed coats

Fig.35.9

4. Water/Mineral conducting cells of the xylem: a. 2 types: tracheids & vessel elements

i. Tracheids are long, thin tapered cells having lignin-hardened secondary walls with pits. Dead at maturity Water flows from cell to cell (laterally) through pits in cell wall (1o wall only) Support function ii. Vessel Elements are wider, shorter Arranged end-to-end to form tubes End walls are perforated for free flow of water More efficient as water conductors than tracheids

Fig. 35.9

5. Sugar-conducting cells of the phloem a. 2 types i. Sieve-tube members: Chains of cells arranged end-to-end, Alive at functional maturity, Lack a nucleus, ribosomes, & vacuole, and Cells separated by perforated sieve plates – allow sugar movement. ii. Companion cells: Load sugars into the sieve tube member, Nucleus and ribosomes also serve the sieve-tube member.

Fig. 35.9

V. Growth & Development http://www.cneccc.edu.hk/subjects/bio/album/Chapter20/PLANT_GROWTH.html

A. Definitions 1. Development is the sum of all the changes 2. Cell Division 3. Morphogenesis

B. Processes of plant cellular development: 1. Cell Growth a. Cell division (Mitosis) in itself does not mean an increase in growth. b. Cell division yields no expansion of size. c. Cell elongation increases growth.

Fig. 35.22

2. Cell elongation a. due to water uptake b. Direction of expansion = perpendicular to alignment of cellulose microfibrils in cell wall c. Enzymes weaken cross-link between microfibrils, allowing cell to expand.

Fig. 35.24

Fig. 39.8

3. Morphogenesis a. The coordinated arrangement of cells into tissues & organs b. Pattern formation – development of specific structures in specific places (e.g. Flowers born on the terminus of branches as opposed to leaf axils. c. Depends on: i. Positional information – chemical signals from surrounding cells indicate the cell’s position on plant ii. Polarity of the plant, asymmetrical cell divisions iii. Both affect the transcription of homeotic genes

4. Cellular Differentiation a. Transformation of genetically identical cells into cells with diverse biochemical and structural features. How? i. Selective transcription of appropriate genes ii. How? Chapters 18 & 39 iii. Flow of Info

The Flow of Information Transcription Replication Translation Modification RNA Polypeptide Functional Protein DNA Energy Amino Acids Additional Materials

b. Regulation i. at transcriptional level ii. Regulation at translational level iii. Regulation at post translational level iv. Hormonal controls v. Regulation at substrate level vi. Regulation by environmental signals: light, gravity,…..

c. Processes i. Meristem identity genes – cause a vegetative shoot to become a floral shoot ii. Positional information (derived from chemical messengers) selectively turn on or off organ–identity genes. iii. Organ – identity genes - code for transcriptions factors that regulate expression of genes controlling the development of specific organs.

By “turning off” organ identity genes, we can give a rose more petals Fig. 35.31 By “turning off” organ identity genes, we can give a rose more petals

C. Plant growth vs. Animal growth 1. Comparison: a. Embryonic, developing, and mature organs exist together at the same time on one plant. b. Grow until they die, called indeterminate growth. Some determinate parts: leaves, flowers.

D. Plant life cycles: 1. Annual – complete life cycle (germination through fruiting) in one year or less. Examples: grasses, crops, wildflowers 2. Biennial – complete life cycle in two years (first year = vegetative, second year = reproductive). Some need a cold winter period to initiate flowering from vegetative state. Ex. carrots 3. Perennial – live year after year, do not die after reproduction. Examples: trees, shrubs, some grasses. Causes of death = fire, disease

E. Plant Growth Sites Meristems Meristems are regions of the plant with continuous cell division (i.e. perpetually embryonic tissue) 1. Types of meristems: a. Apical meristem – located at the root and shoot tips, responsible for growth in length (called primary growth) b. Lateral meristems – extend lengthwise along the axis of the stem & roots. Responsible for growth in girth in older parts of the plant (called secondary growth). Exist only in perennials How is indeterminate growth possible?????

Fig. 35.10

2. Primary Growth of Roots a. Description i. Occurs at root tip (Root Apical Meristem) ii. Root cap – layer of cells that protect the RAM as it pushes through the soil

b. Zones i. Zone of cell division – contains the RAM ii. Zone of cell elongation – cells elongate, thereby pushing the root tip through the soil iii. Zone of maturation – cells differentiate and become functionally mature (i.e. become part of one of the 3 tissue systems)

Fig. 35.12

3. Shoots a. Leaves arise on sides of the Shoot Apical Meristem (SAM) b. Axillary buds arise from areas of meristematic cells left behind at the bases of the leaf primordia. c. Bud = cluster of leaf primordia created by meristem. No internodes d. Lateral branches arise from axillary buds

Fig. 35.15

F. Secondary Growth in Shoots 1. Description a. Shoots of perennials only, not in leaves b. Occurs in oldest parts of plant 2. Layers (two lateral meristems): a. Vascular cambium – produces secondary xylem (= wood) & phloem

i. Vascular cambium – layer of cells between primary xylem & primary phloem. Puts on successive layers of secondary phloem to outside & secondary xylem to inside =====> stem widens ii. Dormant in winter, leaves scar when activity resumes ==> annual ring iii. Wood = accumulation of secondary xylem. Dead at maturity, contains lignin

b. Cork cambium – replaces the epidermis with cork: tough, thick cover for stems, roots. i. Located in the cortex ii. Produces cork cells to replace epidermis iii. Periderm = cork + cork cambium iv. Lenticels = cracks in the periderm that allow gas exchange for living cells in the interior v. “bark” = all cells external to the vascular cambium (secondary phloem & periderm) vi. Cork continually sloughs off vii. Growing secondary phloem becomes new cork cambium (thus no build up of secondary phloem)

Fig. 35.19

Fig.35.18

Fig. 35.20

G. Secondary growth in roots 1. Description a. Vascular cambium forms within stele, produces secondary xylem & phloem b. Cortex & epidermis shed c. Cork cambium arises from pericycle & produces the periderm d. Periderm – impermeable to water! Thus only young roots absorb from soil, old roots function = anchor & transport

VI. Tissue Arrangement in Plant Parts A. Roots 1. Epidermis – water, minerals absorbed through root hairs 2. Stele – central cylinder of vascular tissue (monocots have slightly different arrangement). 3. Pericycle = outermost layer of stele. Lateral roots arise from this in order to remain continuous with vascular system.

4. Ground tissue – mostly parenchyma cells of the cortex – area between the stele & epidermis; stores food & takes up minerals. 5. Endodermis – single cell layer between cortex & stele. Selective barrier for uptake of soil solution contents into vascular system.

Eudicot/Gymnosperm root cross section Endodermis Epidermis Cortex xylem phloem Stele Fig. 35.13

epidermis pith endodermis xylem phloem cortex pericycle Fig. 35.13 Cross section of a monocot root

B. Stems 1. Eudicots: a. Epidermis b. Vascular bundles arranged in ring i. Ground tissue = pith & cortex ii. xylem faces pith, phloem faces cortex 2. Monocots: vascular bundles scattered throughout ground tissue

Eudicot/Gymnosperm stem cross section pith cortex epidermis phloem xylem Sclerenchyma cells Fig. 35.16

Monocot stem cross-section Ground Tissue Epidermis Vascular bundle Monocot stem cross-section Fig. 35.16

C. Leaves Ex. of how structure reflects function – designed for maximum photosynthetic efficiency 1. Layers: a. Upper & lower epidermis – tightly interlocked cells, secrete waxy cuticle. Contains stomata flanked by guard cells b. Vascular tissue – leaf veins, branch throughout mesophyll

c. Mesophyll – ground tissue between upper & lower epidermis i. 2 kinds of parenchyma cells: Palisade – columnar, at top of leaf Spongy – smaller, below palisade, gas-filled spaces between cells

Fig. 35.17

The fleeting moments captured in engrams of the mind.