Why, oh why, should I bother with plants?

Indeed why?• Hunger, starvation, and malnutrition are

endemic in many parts of the world today.

• Rapid increases in the world population have intensified these problems!

• ALL of the food we eat comes either directly or indirectly from plants.

• Can’t just grow more plants, land for cultivation has geographic limits– Also, can destroy ecosystems!

Figure 9.1Indeed why?The Earth is currently experiencing the most population increase in Humanhistory.

2.5 billion in 1955 to 6 billion in 1999

At current rate, will double within 30 years!

Fastest growing nations have growth rates at or above 4% - this will double the countries population every 17 years

Indeed why?• At the latest count there are between 250,000

and 400,000 plant species on the earth.

• But three - maize, wheat and rice - and a few close runners-up, have become the crops that feed the world. All produce starch, helping to provide energy and nutrition, and all can be stored.

• Maize converts the sun’s energy into sugar faster, and potentially produces more grains, than any of the other major staples.

Plants to feed the world

• The term Green Revolution is used to describe the transformation of agriculture in many developing nations that led to significant increases in agricultural production between the 1940s and 1960s

• Scientists bred short plants that converted the sun’s energy into grain rather than stem, so preventing the mass starvation in the developing world predicted before the 1960s, at a cost of higher inputs from chemical fertilizers and irrigation.

Plants to feed the world

• Disease-resistant wheat varieties with high yield potentials are now being produced for a wide range of global, environmental and cultural conditions.

• The Green Revolution has had major social and ecological impacts, which have drawn intense praise and equally intense criticism.

Plants to feed the world

• The Green Revolution is sometimes misinterpreted to apply to present times.

• In fact, many regions of the world peaked in food production in the period 1980 to 1995, and are presently in decline, since desertification and critical water supplies have become limiting factors in a number of world regions.

What comes from plantsPopular stimulants like coffee, chocolate, tobacco, and tea.

Simple derivatives of botanical natural products; for example, aspirin is based on the pain killer salicylic acid which originally came from the bark of willow trees.

Most alcoholic beverages come from fermenting plants such as barley (beer), rice (sake) and grapes (wine).

What comes from plants• Plants also provide us with many natural materials

–  hemp, cotton, wood, paper, linen, vegetable oils, some types of rope, and rubber.

• The production of silk would not be possible without the cultivation of the mulberry plant. 

• Sugarcane, rapeseed, soy and other plants with a highly fermentable sugar or oil content have recently been put to use as sources of biofuels, which are important alternatives to fossil fuels

A few of the many medicinal plants

Environmental changes• Plants can also help us understand changes in on

our environment in many ways.

– Understanding habitat destruction and species extinction is dependent on an accurate and complete catalog of plant systematics and taxonomy.

– Plant responses to ultraviolet radiation can help us monitor problems like ozone depletion.

– Analyzing pollen deposited by plants thousands or millions of years ago can help scientists to reconstruct past climates and predict future ones, an essential part of climate change research.

– Recording and analyzing the timing of plant life cycles are important parts of phenology used in climate-change research.

– Lichens, which are sensitive to atmospheric conditions, have been extensively used as pollution indicators.

A typical Plant cell

The Chloroplast• Contain their own DNA and

protein-synthesizing machinery– Ribosomes, transfer

RNAs, nucleotides.– Thought to have evolved

from endosymbiotic bacteria.

– Divide by fusion– The DNA is in the form of

circular chromosomes, like bacteria

– DNA replication is independent from DNA replication in the nucleus

The Chloroplast• Membranes contain chlophyll

and it’s associated proteins– Site of photosynthesis

• Have inner & outer membranes

• 3rd membrane system– Thylakoids

• Stack of Thylakoids = Granum

• Surrounded by Stroma– Works like mitochondria

• During photosynthesis, ATP from stroma provide the energy for the production of sugar molecules

• Energy enters as sunlight

• Producers convert sunlight to chemical energy.

• Consumers eat the plants (and each other).

• Decomposer organisms breakdown the organic molecules of producers and consumers to be used by other living things

• Heat is lost at every step – So Sun must provide constant energy input for the process to continue!

Energy flow through an ecosystem

Photosynthesis•Very little of the Sun’s energy gets to the ground

gets absorbed by water vapor in the atmosphere

•The absorbance spectra of chlorophyll.

Absorbs strongly in the blue and red portion of the spectrumGreen light is reflected and gives plants their color.

•There are two pigments•Chlorophyll A and B

Photosynthetic pigments• Two types in plants:• Chlorophyll- a• Chlorophyll –b

• Structure almost identical,– Differ in the composition of a

sidechain – In a it is -CH3, in b it is CHO

• The different sidegroups 'tune' the absorption spectrum to slightly different wavelengths– light that is not significantly

absorbed by chlorophyll a, will instead be captured by chlorophyll b

The chemical reaction of photosynthesis is driven by

light• The initial reaction of

photosynthesis is:– CO2 +H2O (CH2O) + O2 – Under optimal conditions

(red light at 680 nm), the photochemical yield is almost 100 %

– However, the efficiency of converting light energy to chemical energy is about 27 %

• Very high for an energy conversion system

Overview of the carbon reactions

• The Calvin cycle:• The cycle runs six

times:– Each time incorporating a

new carbon . Those six carbon dioxides are reduced to glucose:

– Glucose can now serve as a building block to make:• polysaccharides • other monosaccharides • fats • amino acids • nucleotides

The Plant Golgi Network

The Plant Cell wall• Cell walls are held

together by the middle Lamella.

• Made up of:• Cellulose• Xyloglucan• Pectin• Proteins• Ca ions• Lignin• other ions• Water

The Plant Cell wall• The plant cell wall is a layer

of structural material external to the protoplast, built from polysaccharides and proteins.

• Contains components for signaling and communication

• Is the organelle that ultimately controls the shape of plant cells and consequently of organs and whole organisms.

Example of cell wall growth

Best known:Phototropism

Tropisms: Positive or negative growth responses of plants to external stimuli that mainly come from one direction.

As tropisms effect the growth patternof plants, they greatly effect the plantcell wall.

Induces cells AWAY from light toelongate. Cell wall expands in a specific direction.

From: Biochemistry and Molecular Biology of plants

The Plant cell wall•Critical to:• plant cell growth • plant growth and development• differentiation • response to biotic and abiotic

stress

• Impact human activities in many ways:• wood • paper • textile • fuel• food • livestock feed• brewing • pharmaceuticals

Genetically modified crops• All plant characteristics, such as size, texture, and

sweetness, are determined on the genetic level.

• Also:• The hardiness of crop plants.• Their drought resistance. • Rate of growth under different soil conditions. • Dependence on fertilizers.• Resistance to various pests and diseases.

• Used to do this by selective breeding

Genetically modified crops• Agrobacterium method

– Uses the natural infection mechanism of a plant pathogen

– Agrobacterium tumefaciens naturally infects the wound sites in dicotyledonous plant causing the formation of the crown gall tumors.

– Capable to transfer a particular DNA segment (T-DNA) of the tumor-inducing (Ti) plasmid into the nucleus of infected cells where it is integrated fully into the host genome and transcribed, causing the crown gall disease.

• So the pathogen inserts the new DNA with great success!!!

Genetically modified crops• The vir region on the plasmid inserts DNA between

the T-region into plant nuclear genome

• Insert gene of interest and marker in the T-region by restriction enzymes – the pathogen will then “infect” the plant material

• Works fantastically well with all dicot plant species– tomatoes, potatoes, cucumbers, etc– Does not work as well with monocot plant species - corn

• As Agrobacterium tumefaciens do not naturally infect monocots

Genetically modified crops• Issues:• Destroying ecosystems – tomatoes are

now growing in the artic tundra with fish antifreeze in them!

• Destroying ecosystems – will the toxin now being produced by pest-resistance stains kill “friendly” insects such as butterflies.

• Altering nature – should we be swapping genes between species?

Genetically modified crops• Issues:• Vegetarians – what about those tomatoes?

• Religious dietary laws – anything from a pig?

• Cross-pollination – producing a super-weed

• Human health – what of the antibiotic marker gene?

The End.Any Questions?