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General Biology

Course No: BNG2003"

Credits: 3.00 "

""13.1. Plants

Prof. Dr. Klaus Heese

The Greening of Earth

•  Looking at a lush landscape it is difficult to imagine the land without any plants or other organisms

Plants – BioMedical Engineering: Source for: - Energy (Biofuel Cell, Biomass) - Nutrition - Medicine - ‘IKEA’ … Effect on the environment / ecosystems: -  CO2 / O2 -  Humidity -  Temperature -  …

•  Whatever the age of the first land plants, those ancestral species gave rise to a vast diversity of modern plants

•  Land plants can be informally grouped based on the presence or absence of vascular tissue

•  An overview of land plant evolution Bryophytes

(nonvascular plants) Seedless vascular plants Seed plants

Vascular plants

Land plants

Origin of seed plants

Origin of vascular plants

Origin of land plants

Ancestral green alga

Cha

roph

ycea

ns

Live

rwor

ts

Hor

nwor

ts

Mos

ses

Lyco

phyt

es

(clu

b m

osse

s, s

pike

mos

ses,

qui

llwor

ts)

Pter

ophy

te

(fern

s, h

orse

tails

, whi

sk fe

rn)

Gym

nosp

erm

s

Ang

iosp

erm

s

Classification of Seedless Vascular Plants

•  Seedless vascular plants form two phyla

–  Lycophyta/(e), including club mosses, spike mosses, and quillworts

–  Pterophyta/(e), including ferns, horsetails, and whisk ferns and their relatives

LYCOPHYTES (PHYLUM LYCOPHYTA)

PTEROPHYTES (PHYLUM PTEROPHYTA)

WHISK FERNS AND RELATIVES HORSETAILS FERNS

Isoetes gunnii, a quillwort

Selaginella apoda, a spike moss

Diphasiastrum tristachyum, a club moss

Strobili (clusters of sporophylls)

Psilotum nudum, a whisk fern

Equisetum arvense, field horsetail

Vegetative stem

Strobilus on fertile stem

Athyrium filix-femina, lady fern

•  The general groups of seedless vascular plants

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Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts

•  Modern species of lycophytes are relics from a far more eminent past; they are small herbaceous plants

Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives •  Ferns are the most diverse seedless vascular plants The Significance of Seedless Vascular Plants

•  The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Carboniferous, forming the first forests

The growth of these early forests: may have helped to produce the major global cooling that characterized the end of the Carboniferous period; decayed and eventually became coal

Seeds changed the course of plant evolution

–  enabling their bearers to become the dominant producers in most terrestrial ecosystems

•  The reduced gametophytes of seed plants are protected in ovules and pollen grains

•  In addition to seeds, the following are common to all seed plants

–  Reduced gametophytes

–  Heterospory

–  Ovules

–  Pollen

•  Living seed plants can be divided into two groups: gymnosperms and angiosperms

Douglas fir

Pacific yew

Common juniper

Wollemia pine

Bristlecone pine Sequoia

PHYLUM CYCADOPHYTA

•  Gymnosperms bear “naked” seeds, typically on cones •  Among the gymnosperms are many well-known conifers or

cone-bearing trees, including pine, fir, and redwood •  The gymnosperms include four plant phyla: - Cycadophyta, - Gingkophyta, -

Gnetophyta, - Coniferophyta

Gnetum

Ephedra

Ovulate cones

Welwitschia

PHYLUM GNETOPHYTA

PHYLUM CYCADOPHYTA PHYLUM GINKGOPHYTA

Cycas revoluta

•  Exploring Gymnosperm Diversity

•  The key reproductive adaptations in the evolution of angiosperms include flowers and fruits

•  Angiosperms –  are commonly known as flowering plants –  are seed plants that produce the reproductive

structures called flowers and fruits –  are the most widespread and diverse of all plants

Flowers

•  The flower is an angiosperm structure specialized for sexual reproduction

Angiosperms

Anther

Filament

Stigma Style

Ovary

Carpel

Petal

Receptacle Ovule

Sepal

Stamen

•  A flower is a specialized shoot with modified leaves –  Sepals, which enclose

the flower –  Petals, which are

brightly colored and attract pollinators

–  Stamens, which produce pollen

–  Carpels, which produce ovules

•  Fruits typically consist of a mature ovary

(b) Ruby grapefruit, a fleshy fruit with a hard outer layer and soft inner layer of pericarp

(a) Tomato, a fleshy fruit with soft outer and inner layers

of pericarp

(c) Nectarine, a fleshy fruit with a soft outer layer and hard inner

layer (pit) of pericarp

(e) Walnut, a dry fruit that remains closed at maturity

(d) Milkweed, a dry fruit that splits open at maturity

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•  Fruits can be carried by wind, water, or animals to new locations, enhancing seed dispersal

Wings enable maple fruits to be easily carried by the wind.

(a)

Seeds within berries and other edible fruits are often dispersed

in animal feces.

(b)

The barbs of cockleburs facilitate seed dispersal by

allowing the fruits to “hitchhike” on animals.

(c)

Angiosperm Diversity

•  The two main groups of angiosperms are monocots and eudicots

•  Basal angiosperms are less derived and include the flowering plants belonging to the oldest lineages

•  Magnoliids share some traits with basal angiosperms but are more closely related to monocots and eudicots

Amborella trichopoda Water lily (Nymphaea “Rene Gerard”)

Star anise (Illicium floridanum)

BASAL ANGIOSPERMS

HYPOTHETICAL TREE OF FLOWERING PLANTS

MAGNOLIIDS

Am

bore

lla

Wat

er li

lies

Star

ani

se

and

rela

tives

Mag

nolii

ds

Mon

ocot

s

Eudi

cots

Southern magnolia (Magnolia grandiflora)

•  Exploring Angiosperm Diversity Orchid (Lemboglossum fossii)

Monocot Characteristics

Embryos

Leaf venation

Stems

Roots

Pollen

Flowers

Pollen grain with one opening

Root system Usually fibrous (no main root)

Vascular tissue scattered

Veins usually parallel

One cotyledon Two cotyledons

Veins usually netlike

Vascular tissue usually arranged in ring

Taproot (main root) usually present

Pollen grain with three openings

Zucchini (Cucurbita Pepo), female (left) and male flowers

Pea (Lathyrus nervosus, Lord Anson’s blue pea), a legume

Dog rose (Rosa canina), a wild rose

Pygmy date palm (Phoenix roebelenii)

Lily (Lilium “Enchant- ment”)

Barley (Hordeum vulgare), a grass

Anther

Stigma

California poppy (Eschscholzia californica)

Pyrenean oak (Quercus pyrenaica)

Floral organs usually in multiples of three

Floral organs usually in multiples of four or five Filament Ovary

Eudicot Characteristics

MONOCOTS EUDICOTS

Evolutionary Links Between Angiosperms and Animals •  Pollination of flowers by animals and transport of seeds by

animals

–  are two important relationships in terrestrial ecosystems (ecology / diversity)

(a) A flower pollinated by honeybees. This honeybee is harvesting pollen and nectar (a sugary solution secreted by flower glands) from a Scottish broom flower. The flower has a tripping mechanism that arches the stamens over the bee and dusts it with pollen, some of which will rub off onto the stigma of the next flower the bee visits.

(c) A flower pollinated by nocturnal animals. Some angiosperms, such as this cactus, depend mainly on nocturnal pollinators, including bats. Common adaptations of such plants include large, light-colored, highly fragrant flowers that nighttime pollinators can locate.

(b) A flower pollinated by hummingbirds. The long, thin beak and tongue of this rufous hummingbird enable the animal to probe flowers that secrete nectar deep within floral tubes. Before the hummer leaves, anthers will dust its beak and head feathers with pollen. Many flowers that are pollinated by birds are red or pink, colors to which bird eyes are especially sensitive.

Products from Seed Plants •  Humans depend on seed

plants for

–  Food

–  Wood

–  Many medicines

•  Human welfare depends greatly on seed plants

•  No group is more important to human survival than seed plants

•  Threats to Plant Diversity: Destruction of habitat is causing extinction of many plant species and the animal species they support

•  No two Plants Are Alike

•  To some people the fanwort is an intrusive weed, but to others it is an attractive aquarium plant

•  This plant exhibits plasticity - the ability to alter itself in response to its environment

•  In addition to plasticity, entire plant species have by natural selection accumulated characteristics of morphology that vary little among plants within the species

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•  The plant body has a hierarchy of organs, tissues, and cells

•  Plants, like multicellular animals, have organs composed of different tissues, which are in turn composed of cells

The Three Basic Plant Organs: Roots, Stems, and Leaves •  The basic morphology of vascular

plants reflects their evolutionary history as terrestrial organisms that draw nutrients from two very different environments: below-ground and above-ground

•  Three basic organs evolved: roots, stems, and leaves

•  They are organized into a root system and a shoot system

Reproductive shoot (flower)

Terminal bud

Node Internode

Terminal bud

Vegetative shoot

Blade Petiole

Stem

Leaf

Taproot

Lateral roots Root system

Shoot system

Axillary bud

Roots

•  Roots are organs that anchor vascular plants; the roots enable vascular plants to absorb water and nutrients from the soil; the roots may have evolved from subterranean stems

•  Many plants have modified roots

(a) Prop roots (b) Storage roots (c) “Strangling” aerial roots

(d) Buttress roots (e) Pneumatophores

Roots •  A root is an organ that anchors the vascular plant; it absorbs

minerals and water and it often stores organic nutrients

•  In most plants the absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs increase the surface area of the root

•  Stems: A stem is an organ consisting of an alternating system of nodes, the points at which leaves are attached, and of internodes, the stem segments between nodes

•  An axillary bud is a structure that has the potential to form a lateral shoot, or branch

•  A terminal bud is located near the shoot tip and causes elongation of a young shoot

Rhizomes. The edible base of this ginger plant is an example of a rhizome, a horizontal stem that grows just below the surface or emerges and grows along the surface.

(d)

Tubers. Tubers, such as these red potatoes, are enlarged ends of rhizomes specialized for storing food. The “eyes” arranged in a spiral pattern around a potato are clusters of axillary buds that mark the nodes.

(c) Bulbs. Bulbs are vertical, underground shoots consisting mostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise.

(b)

Stolons. Shown here on a strawberry plant, stolons are horizontal stems that grow along the surface. These “runners” enable a plant to reproduce asexually, as plantlets form at nodes along each runner.

(a)

Storage leaves

Stem

Root Node

Rhizome

Root

•  many plants have modified stems See also TCM/oriental medicine: e.g. tubers from Tian Ma

Tissue Organization of Stems •  In gymnosperms and most

eudicots the vascular tissue consists of vascular bundles arranged in a ring Xylem Phloem

Sclerenchyma (fiber cells)

Ground tissue connecting pith to cortex

Pith

Epidermis

Vascular bundle

Cortex

Key

Dermal

Ground

Vascular 1 mm

(a) A eudicot stem. A eudicot stem (sunflower), with vascular bundles forming a ring. Ground tissue toward the inside is called pith, and ground tissue toward the outside is called cortex. (LM of transverse section)

Ground tissue

Epidermis

Vascular bundles

1 mm

(b) A monocot stem. A monocot stem (maize) with vascular bundles scattered throughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith and cortex. (LM of transverse section)

•  In most monocot stems the vascular bundles are scattered throughout the ground tissue, rather than forming a ring

Leaves

•  Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis

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Vascular tissue

Microphylls, such as those of lycophytes, may have originated as small stem outgrowths supported by single, unbranched strands of vascular tissue.

(a) Megaphylls, which have branched vascular systems, may have evolved by the fusion of branched stems.

(b)

•  Leaves are categorized by two types

–  Microphylls, leaves with a single vein

–  Megaphylls, leaves with a highly branched vascular system

•  The leaf is the main photosynthetic organ of most vascular plants

•  Leaves generally consist of a flattened blade and a stalk as well as the petiole, which joins the leaf to a node of the stem

•  Monocots and dicots differ in the arrangement of veins, the vascular tissue of leaves •  Most monocots have parallel veins •  Most dicots have branching veins

•  In classifying angiosperms, taxonomists may use leaf morphology as a criterion

Petiole

(a) Simple leaf. A simple leaf is a single, undivided blade. Some simple leaves are deeply lobed, as in an oak leaf.

(b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base.

(c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets.

Axillary bud

Leaflet

Petiole Axillary bud

Axillary bud

Leaflet Petiole

•  Some plant species have evolved modified leaves that serve various functions

(a) Tendrils. The tendrils by which this pea plant clings to a support are modified leaves. After it has “lassoed” a support, a tendril forms a coil that brings the plant closer to the support. Tendrils are typically modified leaves, but some tendrils are modified stems, as in grapevines.

(b) Spines. The spines of cacti, such as this prickly pear, are actually leaves, and photosynthesis is carried out mainly by the fleshy green stems.

(c) Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water.

(d) Bracts. Red parts of the poinsettia are often mistaken for petals but are actually modified leaves called bracts that surround a group of flowers. Such brightly colored leaves attract pollinators.

(e) Reproductive leaves. The leaves of some succulents, such as Kalanchoe daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil.

•  Each plant organ has dermal, vascular, and ground tissues

Dermal tissue

Ground tissue Vascular

tissue

Key to labels

Dermal Ground Vascular

Guard cells

Stomatal pore Epidermal cell

50 µm Surface view of a spiderwort (Tradescantia) leaf (LM)

(b) Cuticle

Sclerenchyma fibers

Stoma

Upper epidermis

Palisade mesophyll

Spongy mesophyll Lower epidermis

Cuticle Vein

Guard cells

Xylem Phloem

Guard cells

Bundle- sheath cell

Cutaway drawing of leaf tissues (a)

Vein Air spaces Guard cells

100 µm Transverse section of a lilac (Syringa) leaf (LM)

(c)

•  Leaf anatomy

•  Tissue Organization of Leaves: The epidermal barrier in leaves is interrupted by stomata, which allow CO2 exchange between the surrounding air and the photosynthetic cells within a leaf •  The ground tissue in a leaf is sandwiched between the upper and lower epidermis •  The vascular tissue of each leaf is continuous with the vascular tissue of the stem

(chloroplasts)

Parenchyma cells 60 µm

PARENCHYMA CELLS

80 µm Cortical parenchyma cells

COLLENCHYMA CELLS

Collenchyma cells

SCLERENCHYMA CELLS

Cell wall

Sclereid cells in pear

25 µm

Fiber cells

5 µm

Common Types of Plant Cells

•  Like any multicellular organism a plant is characterized by cellular differentiation, the specialization of cells in structure and function

•  Some of the major types of plant cells include: Parenchyma, Collenchyma, Sclerenchyma, Water-conducting cells of the xylem, sugar-conducting cells of the phloem

•  The dermal tissue system consists of the epidermis and periderm •  Vascular plants have two types of vascular tissue; the vascular tissue system carries out long-distance transport of materials between roots and shoots; it consists of two tissues, xylem and phloem •  Xylem (includes dead cells called tracheids) conveys/conducts water and dissolved minerals upward from roots into the shoots •  Phloem (consists of living cells) transports organic nutrients (sugars, amino acids, and other organic products) from where they are made to where they are needed •  Ground tissue includes various cells specialized for functions such as storage, photosynthesis, and support

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•  Water-conducting cells of the xylem and sugar-conducting cells of the phloem WATER-CONDUCTING CELLS OF THE XYLEM

Vessel Tracheids 100 µm

Tracheids and vessels

Vessel element

Vessel elements with partially perforated end walls

Pits

Tracheids

SUGAR-CONDUCTING CELLS OF THE PHLOEM

Companion cell

Sieve-tube member

Sieve-tube members: longitudinal view

Sieve plate

Nucleus

Cytoplasm Companion cell

30 µm

15 µm

•  Meristems generate cells for new organs •  Apical meristems are located at the tips of roots and in the

buds of shoots; they elongate shoots and roots through primary growth

•  Lateral meristems add thickness to woody plants through secondary growth

An overview of primary and secondary growth

In woody plants, there are lateral meristems that add secondary growth, increasing the girth of roots and stems.

Apical meristems add primary growth, or growth in length.

Vascular cambium

Cork cambium

Lateral meristems

Root apical meristems

Primary growth in stems

Epidermis

Cortex Primary phloem

Primary xylem

Pith

Secondary growth in stems Periderm

Cork cambium

Cortex Primary phloem

Secondary phloem

Vascular cambium

Secondary xylem

Primary xylem

Pith

Shoot apical meristems (in buds)

The cork cambium adds secondary dermal tissue.

The vascular cambium adds secondary xylem and phloem.

•  In woody plants primary and secondary growth occur simultaneously but in different locations

This year’s growth (one year old)

Last year’s growth (two years old)

Growth of two years ago (three years old)

One-year-old side branch formed from axillary bud near shoot apex

Scars left by terminal bud scales of previous winters

Leaf scar

Leaf scar

Stem

Leaf scar

Bud scale

Axillary buds

Internode

Node

Terminal bud

•  Primary growth lengthens roots and shoots •  Primary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristems

Primary Growth of Roots •  The root tip is covered by a root cap, which protects the

delicate apical meristem as the root pushes through soil during primary growth

Dermal Ground Vascular

Key

Cortex Vascular cylinder

Epidermis

Root hair Zone of maturation

Zone of elongation

Zone of cell division

Apical meristem

Root cap

100 µm

•  The primary growth of roots produces the epidermis, ground tissue, and vascular tissue

•  Organization of primary tissues in young roots

Cortex

Vascular cylinder

Endodermis

Pericycle

Core of parenchyma cells

Xylem

50 µm

Endodermis

Pericycle

Xylem

Phloem

Key

100 µm

Vascular Ground Dermal

Phloem

Transverse section of a root with parenchyma in the center. The stele of many monocot roots is a vascular cylinder with a core of parenchyma surrounded by a ring of alternating xylem and phloem.

(b) Transverse section of a typical root. In the roots of typical gymnosperms and eudicots, as well as some monocots, the stele is a vascular cylinder consisting of a lobed core of xylem with phloem between the lobes.

(a) 100 µm

Epidermis

Primary Growth of Shoots •  A shoot apical meristem is a dome-shaped mass of

dividing cells at the tip of the terminal bud; it gives rise to a repetition of internodes and leaf-bearing nodes

Apical meristem Leaf primordia

Developing vascular strand

Axillary bud meristems

0.25 mm

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•  Secondary growth adds girth to stems and roots in woody plants

•  Secondary growth occurs in stems and roots of woody plants but rarely in leaves

•  The secondary plant body consists of the tissues produced by the vascular cambium and cork cambium

•  The vascular cambium is a cylinder of meristematic cells one cell thick; it develops from parenchyma cells

Vascular cambium

Pith

Primary xylem

Secondary xylem

Vascular cambium

Secondary phloem

Primary phloem

Periderm (mainly cork

cambia and cork)

Pith

Primary xylem

Vascular cambium

Primary phloem

Cortex

Epidermis

Vascular cambium

4 First cork cambium

Secondary xylem (two

years of production)

Pith Primary xylem Vascular cambium

Primary phloem

2

1

6

Growth

Primary xylem

Secondary xylem

Secondary phloem

Primary phloem Cork

Phloem ray 3 Xylem

ray

Growth

Bark

8 Layers of periderm

7 Cork 5 Most recent cork cambium

Cortex Epidermis

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In the youngest part of the stem, you can see the primary plant body, as formed by the apical meristem during primary

growth. The vascular cambium is beginning to develop.

As primary growth continues to elongate the stem, the portion of the stem formed earlier the same year has already started

its secondary growth. This portion increases in girth as fusiform initials of the vascular cambium form secondary xylem to the

inside and secondary phloem to the outside.

The ray initials of the vascular cambium give rise to the xylem and phloem rays.

As the diameter of the vascular cambium increases, the secondary phloem and other tissues external to the cambium

cannot keep pace with the expansion because the cells no longer divide. As a result, these tissues, including the

epidermis, rupture. A second lateral meristem, the cork cambium, develops from parenchyma cells in the cortex. The

cork cambium produces cork cells, which replace the epidermis.

In year 2 of secondary growth, the vascular cambium adds to the secondary xylem and phloem, and the cork cambium

produces cork.

As the diameter of the stem continues to increase, the outermost tissues exterior to the cork cambium rupture and

slough off from the stem.

Cork cambium re-forms in progressively deeper layers of the cortex. When none of the original cortex is left, the cork

cambium develops from parenchyma cells in the secondary phloem.

Each cork cambium and the tissues it produces form a layer of periderm.

Bark consists of all tissues exterior to the vascular cambium.

1

2

3

4

5

6

7

8

9

Secondary phloem

(a) Primary and secondary growth in a two-year-old stem

•  Primary and secondary growth of a stem

Secondary phloem Vascular cambium Late wood

Early wood Secondary xylem

Cork cambium Cork

Periderm

(b) Transverse section of a three-year- old stem (LM)

Xylem ray

Bark

0.5 mm 0.5 mm

•  Viewed in transverse section, the vascular cambium appears as a ring, with interspersed regions of dividing cells called fusiform initials and ray initials

Vascular cambium

C X C P

C X C

X C

P P P C X X P C X X

C C

Types of cell division. An initial can divide transversely to form two cambial initials (C) or radially to form an initial and either a xylem (X) or phloem (P) cell.

(a)

Accumulation of secondary growth. Although shown here as alternately adding xylem and phloem, a cambial initial usually produces much more xylem.

(b)

•  As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals

•  The outer layers, known as sapwood still transport materials through the xylem

Growth ring

Vascular ray

Heartwood

Sapwood

Vascular cambium

Secondary phloem

Layers of periderm

Secondary xylem

Bark

Cork Cambia and the Production of Periderm

- The cork cambium gives rise to the secondary plant body’s protective covering, or periderm - Periderm consists of the cork cambium plus the layers of cork cells it produces - Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm

Molecular Biology: Revolutionizing the Study of Plants

•  New techniques and model systems are catalyzing explosive progress in our understanding of plants

•  Arabidopsis is the first plant to have its entire genome sequenced Cell organization and biogenesis (1.7%)

DNA metabolism (1.8%) Carbohydrate metabolism (2.4%)

Signal transduction (2.6%) Protein biosynthesis (2.7%)

Electron transport (3%)

Protein modification (3.7%)

Protein metabolism (5.7%)

Transcription (6.1%)

Other metabolism (6.6%)

Transport (8.5%)

Other biological processes (18.6%)

Unknown (36.6%)

Growth: Cell Division and Cell Expansion •  By increasing cell number cell division in meristems

increases the potential for growth

•  Cell expansion accounts for the actual increase in plant size

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Microtubules and Plant Growth •  Studies of fass mutants of Arabidopsis have confirmed the

importance of cytoplasmic microtubules in cell division and expansion

Wild-type seedling

fass seedling

Mature fass mutant (a)

(b)

(c)

Morphogenesis and Pattern Formation

•  Pattern formation is the development of specific structures in specific locations; it is determined by positional information in the form of signals that indicate to each cell its location

•  Morphogenesis in plants, as in other multicellular organisms, is often under the control of homeotic genes

Gene Expression and Control of Cellular Differentiation •  In cellular differentiation cells of a developing organism

synthesize different proteins and diverge in structure and function even though they have a common genome

•  Cellular differentiation to a large extent depends on positional information; is affected by homeotic genes

When epidermal cells border a single cortical cell, the homeotic gene GLABRA-2 is selectively expressed, and these cells will remain hairless. (The blue color in this light micrograph indi- cates cells in which GLABRA-2 is expressed.)

Here an epidermal cell borders two cortical cells. GLABRA-2 is not expressed, and the cell will develop a root hair.

The ring of cells external to the epi- dermal layer is composed of root cap cells that will be sloughed off as the root hairs start to differentiate.

Cortical cells

20 µm

Location and a Cell’s Developmental Fate •  A cell’s position in a developing organ determines its

pathway of differentiation

Shifts in Development: Phase Changes

•  Plants pass through developmental phases, called phase changes, developing from a juvenile phase to an adult vegetative phase to an adult reproductive phase

•  The most obvious morphological changes typically occur in leaf size and shape

Leaves produced by adult phase of apical meristem

Leaves produced by juvenile phase of apical meristem

Genetic Control of Flowering •  Flower formation involves a

phase change from vegetative growth to reproductive growth; it is triggered by a combination of environmental cues and internal signals

•  The transition from vegetative growth to flowering is associated with the switching-on of floral meristem identity genes

•  Plant biologists have identified several organ identity genes that regulate the development of floral pattern

(a) Normal Arabidopsis flower. Arabidopsis normally has four whorls of flower parts: sepals (Se), petals (Pe), stamens (St), and carpels (Ca).

(b) Abnormal Arabidopsis flower. Reseachers have identified several mutations of organ identity genes that cause abnormal flowers to develop. This flower has an extra set of petals in place of stamens and an internal flower where normal plants have carpels.

Ca

St

Pe

Se

Pe

Pe

Se

Pe

Se

Lignin biotechnology: Antisense (gene ko) CAD and COMT genes in poplars

Red color shows different type of lignin has been

produced.

Kraft pulping of tree trunks showed that the reduced-CAD lines had improved characteristics, allowing easier de-lignification, using smaller amounts of chemicals, while yielding more high-quality pulp. This work highlights the potential of engineering wood quality for more environmentally benign papermaking without interfering with tree growth or fitness. Nature Biotechnology 20, 607 - 612 (2002)

More infos about this application and problem also in CHM4006 Biochem. course

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Lignin and biofuel production

•  Lignin has negative impacts on biofuel prodution

–  lignin impedes access of hydrolytic enzymes to wall polysaccharides

–  lignin adsorbs hydrolytic enzymes

–  lignin interferes with pretreatment processes

–  lignin degradation products inhibit fermentation

–  lignin is not fermentable (but its energy can be utilized)

•  Lignin, part of the plant cell wall, is essential for plant viability; all the genes are known. Lignin (20%) provides stiffness, rigidity and prevents water absorption so that water can be transported; and protects against insects and fungi.

•  Can reducing lignin content, composition, and tissue specificity improve biomass quality? Plants seem to tolerate substantial lignin modification.

Biomass to Bioenergy

³ Biomass: renewable energy sources coming from biological material such as plants, animals, microorganisms and municipal wastes

Cellulose is an organic compound with the formula (C6H10O5)n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Some species of bacteria secrete it to form biofilms.

Cellulose The crystalline regions of cellulose have intramolecular and

intermolecular hydrogen bonds, allowing the linear glucan chains to form crystalline structures that exclude water and enzymes.

Intramolecular: The H of the OH on C3 to the O that makes the glycosidic bonds. Intermolecular: The H of the OH on C6 to the O of the OH on C3. These are the bonds that make the very tight structure of cellulose microfibrils. Microfibrils have 30-40 chains each with 2000 to 10,000 glucose units.

Lignin modification may decrease the need for pretreatment

Lignin biosynthetic pathway in woody angiosperms ���(e.g. aspen or poplar)

10

Lignin biosynthetic pathway in woody angiosperms (the flowering plants) (e.g. aspen or poplar)

Secretion is followed by oxidative polymerization catalyzed by peroxidase

<--- Phenylalanine