Lecturer: Sakariyawo PhD PCP 101

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Lecturer Sakariyawo PhDPCP 101

• Department Plant Physiology and Crop Production
• College of Plant Science

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Topic Homeostasis

• A basic Biological Axiom

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Basic concepts

• Homeostasis
• Control
• Regulation
• Growth
• Nasty
• Tropism
• Photomorphogenesis
• Thigmotropism
• Osmoregulation,
• Autopoiesis

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Learning Objectives

• Understanding the concept of homeostasis,
  regulation and control
• Life as organisational homeostasis and its
  biological implications

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Homeostasis defined

• 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.

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Conceptual framework of homeostasis in a
biological system
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Implication of autopoietic model of Humberto
Maturana

• Organisational invariance
• Autonomy
• Self-referentiality

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Dimensions of Biological stability

• Physiological
• Ecological

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Physiological stability

• Level of physiological activities is within
  certain limit for it to operate
• All physiological processes operate within
  certain concentration of solutes, temperature and
  pH.

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Ecological stability

• 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

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Model of biological stability

• Biological stability Coordination or control

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Elements of biological control system
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Elements of Biological control (continue)

• Perturbation Any environmental factor, capable
  of disrupting systems 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 Systems response, in plant they could
  take the following forms growth, nasty,
  morphogenesis, tropism and thigmotropism

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Comparative plant and animal homeostasis matrix
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Topic Osmoregulation and Methods of Elimination
of Waste Materials in Plant

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

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Learning objectives

• 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

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Osmoregulatory strategies at molecular level
towards water balance

• 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

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Nitrogen containing compatible osmolytes

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

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Non-Nitrogen containing compatible osmolytes

• Sugars
• Cyclic and acyclic polyols mannitol, sorbitol
• Fructans
• Sulphonium compounds

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Defining compatibility

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

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Some biological functions of compatible osmolytes

• Water balance in cell
• Osmoprotective functions such as the protection
  of the protein stability, scavenging reactive
  oxygen radical
• Adjustment of cellular redox state and membrane
  stabilisation.

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Extrusion, sequestration and compartmentalisation

• Organs Vacuole, Golgi bodies and Endoplasmic
  reticulum, leaf

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Active mediators of Extrusion, sequestration and
compartmentalisation

• Channels
• Selective (Potassium Inward Regulated Channel,
  KIRC Potassium Outward Regulated Channel, KORC,
  Aquaporin)
• Non-Selective
• Carriers High and low affinity carriers
• Pumps
• Electrogenic (H/ ATP-ase, H/PP)
• Electroneutral

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Growth and Development

• 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

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Measuring growth

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

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Classifying shoot growth

• 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

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SHOOT GROWTH PATTERNS

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

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SHOOT GROWTH PATTERNS

• 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. flowering
• e.g. celery, beets, cabbage, Brussels sprouts

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SHOOT GROWTH PATTERNS

• 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

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ROOT GROWTH PATTERNS

• Variation in pattern with species and season
• Growth peaks in spring, late summer/early fall
• Spring growth from previous years foods
• Fall growth from summers accumulated foods
• Some species roots grow during winter
• Some species have some roots resting while, in
  the same plant, others are growing

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Development

• Definition
• Process of qualitative change in a living system
  over time

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Phasic theory of Development

• 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

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PHASE CHANGE JUVENILITY, MATURATION, SENESCENCE

• 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

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Continues

• 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

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AGING AND SENESCENCE

• 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

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Comparative evaluation of aging and senescence
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REPRODUCTIVE GROWTH AND DEVELOPMENT

• 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

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GENETIC FACTORS AFFECTING GROWTH AND DEVELOPMENT

• 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

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What signals trigger these 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

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Continues

• Flower induction and initiation
• What causes a plant to flower?
• Daylength (photoperiod)
• Low temperatures (vernalization)
• Neither

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Photoperiodim

• 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

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Effect of low temperature

• 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

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Flower developmet

• 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

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Pollination

• 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

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Continues

• 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

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Continues

• 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

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Continues

• What if pollination and fertilization fail to
  occur?
• Fruit and seed dont develop
• Exception Parthenocarpy
• Formation of fruit without pollination/fertilizati
  on
• Parthenocarpic fruit are seedless

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Continues

• Fertilization
• Angiosperms (flowering plants)
• Termed double fertilization
• Gymnosperms (cone-bearing plants)
• Staminate, pollen-producing cones
• Ovulate cones produce naked seed on cone scales

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Fruit setting

• 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

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Fruit growth and development

• 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

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Transformational changes observed during fruit
growth

• 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

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Continues

• 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

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Continues

• Changes in Flavour
• Scope
• Development of characteristic
• Aroma
• Taste
• Polymers? monomers
• Loss of astringency
• Dimensions
• Production of the secondary metabolites
• Hydrolytic changes of biopolymers

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Continues

• Changes in condition
• Scope
• Increasing degree of perishability
• Climacteric respiratory pattern
• Non-climacteric respiratory pattern
• Dimension
• Catabolic processgtAnabolic process
• Increasing activity of growth inhibitors e.g.
  C2H2 and ABA

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ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH

• Light
• Temperature
• Water
• Gases

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Dimensions of light influence on growth and
development

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

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ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH
(Continues)

• 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

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Continues

• 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

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Continues

• 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

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Plant growth Regulators

• 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

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Definition of phytohormones

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

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Characteristics of Phytohormones

• They are required in small quantity,
• Transported from the site of synthesis to mediate
  physiological response in other parts of the
  plant.
• The have organic origin
• They are naturally occurring or synthetic
• Non-nutrient chemicals
• Brassinosteroids
• Jasmonic Acid
• Salicylic Acid
• Polyamines

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Classification

• Growth promoters
• Auxins
• Gibberellins
• Cytokinins

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Continues

• Growth Inhibitors
• Ethylene
• Abscisic acid

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Comparative evaluation of hormones

• See table 3 of the lecture note

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Respiration

• 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

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Definition of Respiration

• 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

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Biological importance of respiration

• 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)

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Where does respiration takes place?

• Cytosol
• Mitochodria

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When does it takes place

• Throughout the life of the plant

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Conceptual framework of respiration

• Initial degradation (hydrolysis)
• Partial degradation (glycolysis/EMP/oxidative
  pentose phosphate pathway/Enter-Doudoroff
  pathway)
• Total degradation (Krebs cycle and electronic
  transport system)

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Flow chat of Respiratory process
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Aerobic respiration

• It is common to all plants
• It goes on throughout the life
• Energy is liberated in larger quantity. In total,
  38 ATP molecules are formed
• The process is not toxic to plants
• Oxygen is utilised during the process
• The carbohydrates are oxidised completely and are
  broken down into CO2 and H2O
• The end-products are CO2 and H2O
• The process takes place partly in cytosol
  (glycolysis) and partly inside mitochondria
  (Krebs cycle)

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Anaerobic respiration

• It is a rare occurrence
• It occurs for a temporary phase of life
• Energy is liberated in lesser quantity. Only 2
  ATP molecules are formed
• It is toxic to plants
• It occurs in the absence of oxygen
• The carbohydrates are oxidised incompletely and
  ethyl alcohol and carbon dioxide are formed
• The end-products are ethyl alcohol and carbon
  dioxide
• The process occurs only in the cytosol

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Functional Classification of Respiration

• Growth Respiration
• Maintenance Respiration

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Model of respiration

• R grG mrW
• Where
• R Respiration
• gr Coefficient of Growth Respiration
• G Growth Respiration
• Mr Coefficient of Maintenance Respiration
• W Maintenance Respiration

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Scope of Maintenance respiration

• Structural maintenance of the cellular structures
• Gradient of ions and metabolites across the
  membrane
• Phenotypic plasticity
• Turnover of macromolecules

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Scope of growth respiration

• Active uptake of ions
• Assimilation and reduction of NO3 and SO4
• Synthesis of biological monomers
• Polymerisation of biological monomers
• Translocation of assimilates
• Tools maintenance

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Implication of this functional model on crop
performance

• Relationship between photosynthesis, respiration
  and growth on crop performance

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Finish. Thank you for listening