Department: Plant Physiology and Crop Production

College of Plant Science

A basic Biological Axiom

Homeostasis Control Regulation Growth Nasty Tropism Photomorphogenesis Thigmotropism Osmoregulation, Autopoiesis

Understanding the concept of homeostasis, regulation and control

Life as organisational homeostasis and its biological implications

biological stability

Basis for biological stability could be ascribed to circularity observed in living systems. For example interconnectedness and interrelatedness of biochemical pathways forming a coherent unit.

Organisational invariance Autonomy Self-referentiality

Physiological Ecological

Level of physiological activities is within certain limit for it to operate;

All physiological processes operate within certain concentration of solutes, temperature and pH.

Presupposes that there is a certain correspondence; functional and structural between the biological system and its environment. This is evident in the cycle of certain elements in nature, such as water, nitrogen, carbon, phosphorus cycles and the formation of different adaptive mechanisms to various ecological conditions. One vivid example is the formation of different ecotypes of plant depending on their adaptability to available water.

Mesophytes Hydrophytes Xerophytes Halophytes

Biological stability = Coordination or control

Perturbation: Any environmental factor, capable of disrupting system’s stability. These factors are Abiotic and biotic in nature

Sensor: element for detecting difference in status from the system goal. Within the context of a plant, there are different sensors; such as phytochrome, cryptochrome, phototropin and zeaxianthin.

Perceptor: plant organs Model: The genetic composition of the plant Goal: homeostasis Information processing: signalling elements and signal

transduction Decision making: System survivability and senescence Effector: Plant organ Action: System’s response, in plant they could take the

following forms; growth, nasty, morphogenesis, tropism and thigmotropism

Scope of balance

Process nomenclature

Organ/regulatory mechanism

Animal Plant

Water Osmoregulation Kidney 1. Active accumulation of osmolyte independent of cellular volume

2. Uptake of compatible ions

3. Ion extrusion and sequestration

Nitrate Kidney Nitrogen cycle

Glucose Glycolysis and Glycogenesis

Temperature Thermoregulation

Skin Transpiration

Basic concepts: Osmoregulation, transport, transporters, active and passive transport, primary and secondary transport, symport, antiport

Water balance in plants and strategies for acclimation and adaptation

Osmoregulation as a mechanism for maintaining water balance in plant

Methods of eliminating waste product in plants

Transport mechanism in plant

Synthesis and accumulation of osmolytes and osmoprotectants◦ Organic nitrogen-containing◦ Organic non-nitrogen containing

Uptake of compatible ions Extrusion, sequestration and

compartmentalisation of incompatible ions

Amino acids e.g. proline, glycine betaine Amino acids derivatives Quaternary amino acids

1.Sugars2.Cyclic and acyclic polyols; mannitol, sorbitol3.Fructans4.Sulphonium compounds

Accumulation of these substances in the cell will not lead to the disruption of normal metabolic activities

1.Water balance in cell2.Osmoprotective functions such as the

protection of the protein stability, scavenging reactive oxygen radical

3.Adjustment of cellular redox state and membrane stabilisation.

Organs: Vacuole, Golgi bodies and Endoplasmic reticulum, leaf

1.Channels◦ Selective (Potassium Inward Regulated Channel,

KIRC; Potassium Outward Regulated Channel, KORC, Aquaporin)

◦ Non-Selective

2.Carriers; High and low affinity carriers3.Pumps

◦ Electrogenic (H+/ ATP-ase, H+/PP)◦ Electroneutral

Definition of growth:◦ A process of irreversible increase by cell division

and enlargement, including synthesis of new cellular material and organization of sub cellular organelles

◦ Process involving conversion of reserve materials into structural materials

Increase in fresh weight Increase in dry weight Volume Length Height Surface area

◦ Determinate – flower buds initiate terminally;shoot elongation stops; e.g. bush snap beans

◦ Indeterminate – flower buds born laterally;shoot terminals remain vegetative; e.g. pole beans

Annuals

◦ Herbaceous (nonwoody) plants◦ Complete life cycle in one growing season◦ See life cycle of angiosperm annual

Biennials

◦ Herbaceous plants◦ Require two growing seasons to complete their

life cycle (not necessarily two full years)◦ Stem growth limited during first growing season;

Note vegetative growth vs. floweringe.g. celery, beets, cabbage, Brussels sprouts

Perennials

◦ Either herbaceous or woody◦ Herbaceous roots live indefinitely (shoots can)

Shoot growth resumes in spring from adventitious buds in crown

Many grown as annuals◦ Woody roots and shoots live indefinitely

Growth varies with annual environment and zone Pronounced diurnal variation in shoot growth; night

greater

Variation in pattern with species and season Growth peaks in spring, late summer/early

fall◦ Spring growth from previous year’s foods ◦ Fall growth from summer’s accumulated foods

Some species roots grow during winter Some species have some roots ‘resting’

while, in the same plant, others are growing

Definition:◦ Process of qualitative change in a living system

over time

Development is phasic in nature, i.e. progression from one physiological system state of the meristerm to another

Identified are two phases; vegetative and reproductive phases

Plant system possesses the capability of development to progress autonomously

The identifies phases of development are irreversible Development process is controlled by various

environmental and genetic factors, mainly; temperature and photoperiod (G X PX T)

Photoperiod gene and vernalisation genes possesses delaying impact on the process of development

Temperature effect is through Q10 effect on the activities of the enzymes and ultimately on the biochemical reaction

Phasic development◦ embryonic growth◦ juvenility◦ transition stage◦ maturity◦ senescence◦ death

During maturation, seedlings of many woody perennials differ strikingly in appearance at various stages of development

Juvenility ◦ terminated by flowering and fruiting◦ may be extensive in certain forest species

Maturity◦ loss or reduction in ability of cuttings to form

adventitious roots Physiologically related

◦ lower part of plant may be oldest chronologically, yet be youngest physiologically (e.g. some woody plants)

◦ top part of plant may be youngest in days, yet develop into the part that matures and bears flowers and fruit

Life spans among plants differ greatly◦ range from few months to thousands of years◦ clones should be able to exist indefinately

Senescence◦ a physiological aging process in which tissues in an

organism deteriorate and finally die◦ considered to be terminal, irreversible◦ can be postponed by removing flowers before seeds

start to form

Parameters for comparison

Energy dimensi

on

Scope of changes

Implication of

changes

Induction factor

Scope of

induction

Cumulative effect

Aging Passive Accumulative Increase in entropy

Time UnprogrammedUncontrolled

Loss of system identity

Senescence

Active Deteriorative/ degradative

Loss of homeostasis (dynamic equilibrium)

TimeHormoneEnvironmental factorsnutrient

Programmedcontrolled

System death (Loss of system functionality)

Phases◦ Flower induction and initiation◦ Flower differentiation and development◦ Pollination◦ Fertilization◦ Fruit set and seed formation◦ Growth and maturation of fruit and seed◦ Fruit senescence

DNA directs growth and differentiation◦ Enzymes catalyze biochemical reactions

Structural genes◦ Genes involved in protein synthesis

Operator genes◦ Regulate structural genes

Regulatory genes◦ Regulate operator genes

◦ Believed to include: Growth regulators Inorganic ions Coenzymes Environmental factors; e.g. temperature, light

Therefore . . . Genetics directs the final form and size of the plant as

altered by the environment

Flower induction and initiation

◦ What causes a plant to flower?

Daylength (photoperiod)

Low temperatures (vernalization)

Neither

Photoperiodism: Phenomenon of plant response to relative length of day to night◦ Short-day plants (long-night; need darkness)◦ Long-day plants (need sufficient light)◦ Day-neutral plants (flowering unaffected by

period) Change from vegetative to reproductive

Low temperature induction Vernalization

◦ “making ready for spring”◦ Any temperature treatment that induces or

promotes flowering◦ First observed in winter wheat; many biennials◦ Temperature and exposure varies among species◦ Note difference/relationship to dormancy

Many plants do not respond to changed daylength or low temperature; agricultural

Flower development◦ Stimulus from leaves to apical meristem changes

vegetative to flowering◦ Some SDPs require only limited stimulus to induce

flowering; e.g. cocklebur – one day (night)◦ Once changed the process is not reversible◦ Environmental conditions must be favorable for

full flower development

Pollination◦ Transfer of pollen from anther to stigma◦ May be:

Same flower (self-pollination) Different flowers, but same plant (self-pollination) Different flowers/plants, same cultivar (self-

pollination) Different flowers, different cultivars (cross-pollination

Self-fertile plant produces fruit and seed with its own pollen

Self-sterile plant requires pollen from another cultivar to set fruit and seed◦ Often due to incompatibility; pollen will not grow

through style to embryo sac◦ Sometimes cross-pollination incompatibility

Pollen transferred by:◦ Insects; chiefly honeybees

Bright flowers Attractive nectar

◦ Wind Important for plants with inconspicuous flowers e.g. grasses, cereal grain crops, forest tree species,

some fruit and nut crops◦ Other minor agents – water, snails, slugs, birds,

bats

What if pollination and fertilization fail to occur?

Fruit and seed don’t develop Exception: Parthenocarpy

◦ Formation of fruit without pollination/fertilization◦ Parthenocarpic fruit are seedless

Fertilization◦ Angiosperms (flowering plants)

Termed double fertilization◦ Gymnosperms (cone-bearing plants)

Staminate, pollen-producing cones Ovulate cones produce “naked” seed on cone scales

Fruit setting◦ Accessory tissues often involved

e.g. enlarged, fleshy receptacle of apple and pear True fruit is enlarged ovary

◦ Not all flowers develop into fruit◦ Certain plant hormones involved◦ Optimum level of fruit setting

Remove excess by hand, machine, or chemical Some species self-thinning; Washington Navel

Orange◦ Temperature strongly influences fruit set

Fruit growth and development◦ After set, true fruit and associated tissues begin

to grow◦ Food moves from other plant parts into fruit tissue◦ Hormones from seeds and fruit affect growth◦ Auxin relation in strawberry fruits◦ Gibberellins in grape◦ Patterns of growth vary with fruits

Change of Appearance Scope: Pigmentation Green→ yellow or other characteristic colours Dimensions: Increase in the activity of chlorophyllase Sequestration of pigment Development of carotenoid and anthocyanin

in the presence of light and phytochrome Unmasking of certain pigments

Changes in Texture Scope: Softening Hard→ Soft Dimensions: Hydrolysis of Cell wall (solubilisation of pectic substances

in middle lamellae via methylation of galaturonic acid, reduction in size of polygalacturonide or both

Cell content

Changes in Flavour Scope: Development of characteristic Aroma Taste Polymers→ monomers Loss of astringency Dimensions:o Production of the secondary metaboliteso Hydrolytic changes of biopolymers

Changes in condition Scope: Increasing degree of perishability Climacteric respiratory pattern Non-climacteric respiratory pattern Dimension: Catabolic process>Anabolic process Increasing activity of growth inhibitors e.g.

C2H2 and ABA

Light Temperature Water Gases

Quality- Photosynthetic Active Radiation (400nm-700nm), photomorphogenesis, phytochrome absorbs red (660nm) and far-red (730nm)but not at same time

◦ Quantity- Phototropism◦ Duration- Photoperiodism

Temperature◦ correlates with seasonal variation of light intensity◦ tropical-region growth between 25° C and 35° C◦ high light intensity creates heat; sunburned, heat

stress◦ low temp injury associated with frosts; not

common in the tropics

Water◦ most growing plants contain about 90% water◦ amount needed for growth varies with plant and

light intensity◦ transpiration drives water uptake from soil

water pulled through xylem exits via stomates

◦ evapotranspiration - total loss of water from soil loss from soil evaporation and plant transpiration

Gases◦ Nitrogen is most abundant◦ Oxygen and carbon dioxide are most important

plants use CO2 for photosynthesis; give off O2

plants use O2 for respiration; give off CO2

stomatal opening and closing related to CO2 levels? oxygen for respiration limited in waterlogged soils increased CO2 levels in atmosphere associated with

global warming additional pollutants harm plants

Learning objectives: Understanding the concept phytohormones

and their roles in growth of plant Classification of phytohormones and their

roles in cell division, elongation and differentiation

Phytohormones are physiologically active substances that affect plant growth and development in conjunction with other environmental factors.

o They are required in small quantity,o Transported from the site of synthesis to

mediate physiological response in other parts of the plant.

o The have organic origino They are naturally occurring or synthetic Non-nutrient chemicals:

◦ Brassinosteroids◦ Jasmonic Acid◦ Salicylic Acid◦ Polyamines

Growth promoters:1. Auxins2. Gibberellins3. Cytokinins

Growth Inhibitors1.Ethylene2.Abscisic acid

See table 3 of the lecture note

Learning Objectives: Understanding of the basic principle of

respiration Understanding of the mechanism of

respiration Comparative analysis of aerobic and

anaerobic (Fermentation) respiration Factors affecting respiration Importance of respiration in agricultural

process

bio- oxidative process; involving loss of electron, proton and the addition of oxygen.

The process of converting sugars and starches into energy through a series of biochemical steps.

Biochemical process of degradation of biological polymers into monomers, with energy and other metabolites

Redox reaction

Energy is released which is consumed in various metabolic processes essential for plant and activates cell division

It brings about the formation of other necessary compounds participating as important cell constituents

It converts insoluble food into soluble form It liberates carbon dioxide and plays a part

actively in maintaining the balance of carbon cycle in nature

It converts stored energy (potential energy) into usable form (Kinetic energy)

1. Cytosol 2. Mitochodria

Throughout the life of the plant

1. Initial degradation (hydrolysis)2. Partial degradation

(glycolysis/EMP/oxidative pentose phosphate pathway/Enter-Doudoroff pathway)

3. Total degradation (Krebs cycle and electronic transport system)

1. It is common to all plants2. It goes on throughout the life 3. Energy is liberated in larger quantity. In total,

38 ATP molecules are formed4. The process is not toxic to plants5. Oxygen is utilised during the process6. The carbohydrates are oxidised completely

and are broken down into CO2 and H2O 7. The end-products are CO2 and H2O8. The process takes place partly in cytosol

(glycolysis) and partly inside mitochondria (Krebs cycle)

1. It is a rare occurrence2. It occurs for a temporary phase of life3. Energy is liberated in lesser quantity. Only 2

ATP molecules are formed4. It is toxic to plants5. It occurs in the absence of oxygen6. The carbohydrates are oxidised incompletely

and ethyl alcohol and carbon dioxide are formed

7. The end-products are ethyl alcohol and carbon dioxide

8. The process occurs only in the cytosol

1. Growth Respiration2. Maintenance Respiration

R = grG + mrW

Where: R: Respiration gr: Coefficient of Growth Respiration G: Growth Respiration Mr: Coefficient of Maintenance Respiration W: Maintenance Respiration

1. Structural maintenance of the cellular structures

2. Gradient of ions and metabolites across the membrane

3. Phenotypic plasticity4. Turnover of macromolecules

Active uptake of ions Assimilation and reduction of NO3 and SO4

Synthesis of biological monomers Polymerisation of biological monomers Translocation of assimilates Tools maintenance

Relationship between photosynthesis, respiration and growth on crop performance