Level II Horticulture CourseWeek 2 – Plant Science

Tuesday, 28th October 2014Graeme Cross, CAFRE

Tonight’s Course Content:

• Plant Structures• Plant Processes• Plant Development

Plant Structures• Scientists like to classify and name things!• What are the parts of a plant?• Leaves, stems/shoots, roots, flowers, seeds,

fruits• Why are these plant parts significant?• All have different roles / functions

Plant Structures & Functions

Leaf: photosynthesis & transpiration

Stem/shoot: support & water movement

Root: support/anchorage & water/nutrient uptake

Flower: pollination (reproduction)

Seed (fruit/nut): new generation (reproduction)

LEAVESThe home of photosynthesis: the means by

which energy is captured from sunlight for plant growth and storage

Carbon dioxide + water = sugar + oxygenCO2 + H20 = C6H12O6 +

O2

Carbon dioxide + water = sugar + oxygenCO2 + H20 = C6H12O6 + O2

LEAF COMPLEXITY

A simple leaf

Compound Leaves

LEAF AREA INDEX (L.A.I.)A calculation (measurement) of the total coverage that plant foliage creates for the

interception (capture) of available light.

Of all the energy emitted from the sun, we can only see what is called the “visible spectrum”. This is

also the range in which plants absorb energy through photosynthesis.

Different pigments in plants (e.g chlorophyll) absorb different wavelengths of light.

FACTORS INFLUENCING PHOTOSYNTHESIS• Carbon dioxide

• Light

• Temperature

• Water (opening & closing of stomata)

• Health of the leaves - nutrition

A NOTE ON LEAF HEALTH (NUTRITION)Mineral deficiencies (shortage of essential nutrients) can lead to poor colour of the leaf (pigmentation) and so reduce ‘performance’.

SHOOTSThese structural

supports are formed from strong, fibrous tissues arranged in

bundles to carry weight and resist

damage from wind and animal feeding.

They also contain the transport system for

the plant

WHAT IS RESPIRATION?This process of respiration is

the reverse to photosynthesis i.e. It is the conversion of sugars into energy for life (growth,

reproduction, etc.)

Sugar + oxygen => Carbon dioxide + water

C6H12O6 + O2

=> CO2 + H20

RESPIRATION : KEY POINTS

• Occurs all the time (and not dependent on light levels)

• Takes place in every living cell (inc. roots)• Requires oxygen, so anaerobic conditions are

bad! temperature = respiration = growth rate• High respiration in stores is not recommended

Why is this?

ROOTSA network of specialist tissues for the

anchorage of plants in the soil or medium on which they grow.

Roots also act to uptake water and dissolved nutrients.

TRANSPIRATIONThe movement of

water from soil through root

tips to the leaf and hence

through the whole body of

the plant

Mature tree may lose 70-100 l/hr in daylight

FLOWERA specialist

structure which allows the transfer of pollination

between plants and creates seed for the

next generation.

POLLINATIONThe transfer of pollination between male and

female reproductive parts of flower(s) which leads to fertilisation.

How is pollen transferred between flowers?

FERTILISATIONThe fusion of the two gametes (the pollen from male

and the ovum from female)

within the flower, to form a new

seed

SEEDS / FRUITS / NUTSThe structures which allow the germination of a

new generation of plants (= embryo plants + food reserve)

PLANT HORMONESSpecific chemical compounds which are produced naturally within the plant’s own

tissues to regulate the growth of new organs and parts.

Some Named Plant Hormones

AuxinsCytokinins

GibberrellinsEthylene (Ethene)

Abscisic acid

AUXINSIndole-acetic acid (IAA),

Napthyl acetic acid (NAA)

Used in Rooting Powder

Auxins encourage roots and discourage shoots

CYTOKININS

Work in combination

with auxins to control the extent and direction of

shoot (stem) growth

(“Apical Dominance”)

GIBERRELINSInvolved in a range of growth responses such as

flower and fruit formation, seed development

EHTHYLENE (ETHENE)A simple gas (C2H4) which controls the

maturation of fruits and the aging process in fruits and flowers

ABSCISIC ACID (ABA)A single carbon compound which triggers a

range of responses such as dormancy, maturation, leaf fall, cell division.

1. Seed (sown)2. Germination /

seedling3. Young plant /

vegetative phase

4. Established flowering plant

5. Mature / Harvest plant

CROP GROWTH STAGES IN CEREALS

1 Seedling development (leaves).2 Tillering. 3 Stem elongation.4 Booting (developing head inside sheath).5 Heading (ear emerging).6 Flowering (anthers visible).7 Milk (grains soft and milky).8 Dough (grains firm and doughy)9 Ripening (grains hard).

Zadok’s Cereal Growth Stages

Potato Growth Stages

IDENTIFY THE GROWTH STAGES

Seedling / Young Plant

Established/ Flowering

plant

Mature / harvest /

senescent plant