Plant Physiology

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Plant growth and Development

• By
• Dr. EMAD ELDIN ABBAS
• ?????? ??????? ???? (? 501)

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Growth, morphogenesis, and differentiation
produce the plant body

• Growth is the irreversible increase in mass that
• results from cell division (number) and cell
  expansion (size).
• An increase in mass, or growth, during the life
  of a plant results from both cell division and
  cell expansion.
• The development of body form and organization,
  including recognizable tissues and organs is
  called morphogenesis.
• The specialization of cells with the same set
  of genetic instructions to produce a diversity of
  cell types is called differentiation.

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Growth involves both cell division and cell
expansion

• Cell division in meristems, by increasing cell
  number, increases the potential for growth.
• However, it is cell expansion that accounts for
  the actual increase in plant mass.
• Together, these processes contribute to plant
  form.

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SEED DORMANCY

• It is a phenomenon in certain seeds in which they
  would not germinate if given an optimal condition
  ( water, oxygen, optimum temperature ).
• Dormancy can be seen in seeds ( e.g legumes ),
  buds, spore food storage organs ( tubers ).
• Due to many factors include
• Lack of oxygen
• Dryness
• Presence of substances that inhibit germination

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GROWTH UNDER EXTREME CONDITION

• DORMANCY
• A period in the life cycle of many animals
  plants when their metabolic activities become
  minimum growth stop.
• Is a resting stage
• It can occur in the adult, egg, pupa, spore or
  seed stage.
• A way of protecting an organism against
  unfavourable conditions such as insufficient
  food, cold ( winter ) dry ( drought ).
• It is controlled by hormones that
• response to physiological in plants
  animals
• affecting the behaviour in animals

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What physiological changes lead to dormancy

• Metabolism falls
• Number of organelles per cell falls
• Dehydration water content falls
• Vacuoles in cells deflate
• Food reserves become dense crystalline bodies

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SEED Germination

• Dormancy of these seeds may be broken by one or
  more of the following
• light, sunlight being the most effective
• low temperatures (1 to 5 degrees Celsius 33.8 to
  41 degrees Fahrenheit) for several weeks
• day/night fluctuating temperatures of 1 to 10
  degrees Celsius (41 to 50 degrees Fahrenheit)
• chemicals, such as nitrate in the soil, or
  applied hormones (gibberellins) in the
  laboratory and
• fire.

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Maintaining dormancy

• Physical barriers The seed coat (testa) is waxy
  waterproof and impermeable to oxygen
• Physical state dehydrated
• Chemical inhibitors present e.g. salts, mustard
  oils, organic acids, alkaloids
• Growth promoters absent

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The breaking of dormancy
Break down of barriers Abrasion of seed coat
(soil particles) Decomposition of seed coat (soil
microbes, gut enzymes) Cracking of seed coat
(fire)
Change in physical state - rehydration
Destruction and dilution of inhibitors Light,
temperature, water
Production of growth promoters
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Seed Germination(Emergence of Radicle through
Seed Coat)

• To break dormancy seeds need
• Water
• Warm Temperature
• So if you want to store seeds what are the
  conditions?
• Dry Cold

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Dormant seeds need more than moisture and warmth
Example Is overcome by Dormancy is caused by
Kentucky Coffee Tree Scarification??? Thick Seed Coat
Lettuce or Pea Light or Dark Thin Seed Coat
Orchids Soil Fungus Association Insufficient Development
Most CT feral plants Stratification Vernalization 6 weeks at 4 C 20 C Inhibitor Abscisic Acid
Cacti?????? Leaching by Repeated Rain Inhibitor Phenolics
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Germination of seeds

• 1. Utilization of stored reserves
• In cotyledons or endosperm tissue
• During germination, enzymes are made that convert
  stored reserves (large molecules) into compounds
  that can be used by the seedling (smaller
  molecules)
• starches ? sugars
• lipids, fats ? sugars
• proteins ? amino acids

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Germination of seeds

• 2- Transport of compounds into growing seedling
  through vascular system
• These compounds have two functions
• Support respiration in the embryo
• Provide a source of building blocks (carbon,
  nitrogen, etc.) for the seedling
• 3- Expansion and growth of seedling
• Root radicle elongates down, hypocotyl expands up
• Establishment of root system and emergence of
  shoot

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Seedling establishment

• Shoot emerges and is exposed to light
• Chlorophyll is produced and seedling starts to
  perform photosynthesis
• Seedling is no longer dependent on reserves from
  the seed
• If stored reserves are consumed before
  photosynthesis is established, the seedling will
  die

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Seed germination
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Seedling establishment

• Growth of the seedling can be measured in many
  ways
• Length
• Increases after seed imbibes
• Fresh weight
• Increases as seedling grows
• Dry weight
• Declines initially as stored reserves are
  consumed by respiration, increases
• once photosynthesis is established

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Conclusions

• Seeds are alive but dormant
• Comprise an embryonic plant and stored reserves
• Germination requires
• Water - for imbibition
• Oxygen - for respiration
• Suitable temperature
• Outcome of successful germination is a seedling
  capable of independent growth

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• Dont eat green potatoes.
• Potatoes belong to the nightshade family, and
  most green portions of plants in this family
  contain an alkaloid poison called solanine

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Flowering 

• Light perception is often involved in the control
  of flowering. When plants flower at a particular
  time of year it is usually because they respond
  to day-length.
• Not all plants are regulated in this way "day
  neutral" plants will flower at any time that they
  are able to grow. So-called "free flowering"
  garden plants like Petunia and Impatiens have
  been selected for this feature.

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Flowering is controlled by daylength

• oaks flower in spring, lettuce flowers in summer,
  asters flower in autumn production of seeds,
  fruit must be properly timed to physiology of
  plant and rigors of environment

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• Flowering is also regulated by temperature. In
  herbaceous perennials and biennials, trees and
  shrubs that grow in temperate areas, flower buds
  develop or become fully differentiated during the
  winter months.
• This cold requirement for flowering is exploited
  in vernalization treatments where plants like
  Easter lilies are exposed to low temperatures in
  order to induce flowering at a particular time.

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• In some plants flowering can be induced either by
  long days or by cold exposure, whereas others
  require both for optimum flower development.
• Vernalization is a response to low temperature.
•  exposure of buds of some perennials to low
  winter temperature stimultes flowering
• Treatments with gibberellins can often be
  substituted for the photoperiodic (long or short
  day) or temperature requirements.

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Flower anatomy
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From Flower to Fruit

• After fertilization the following takes place
• the fertilized egg within the ovule develops into
  a seed.
• The ovary surrounding the ovule develops into a
  fruit.
• The fruit swells and ripens while holding and
  protecting the developing seeds.
• The seeds represent the next generation once
  germinated and looking like a plant

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Fruit and seed development

• Fruit development is usually dependent on a
  signal from the developing seeds, although some
  plants such as banana can develop parthenocarpic
  fruit that lack seeds.
• Parthenocarpic fruit set can be induced in many
  species by auxin, GA or cytokinin or some
  combination of these hormones.

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• Early seed development is associated with cell
  division and synthesis, so that immature seeds
  contain hormones associated with growth, auxin,
  GA and cytokinin.
• As seeds mature they usually begin to desiccate,
  abscisic acid increases and dormancy sets in.

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Ethylene and Fruit Ripening

• The gaseous plant hormone ethylene plays a key
  regulatory role in ripening of many fruits,
  including some representing important
  contributors of nutrition and fiber to the diets
  of humans.
• Examples include banana, apple, pear, most stone
  fruits, melons, squash, and tomato.

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Senescence

• Senescence is a natural part of plant
  development, and, like other aspects of
  development it is under genetic and hormonal
  control.
• Patterns of senescence vary from one plant to
  another.

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• - Senescence processes leading to the death of
  plant parts or whole plant often occurs when
  nutrients are funneled into reproductive parts of
  plant- plants withdraw nutrients from leaves,
  roots, stems and redistribute them to form new
  flowers, fruits and seeds- as an outcome of this
  redistribution, leaves generally wither and die
  (Note abscission triggered by ethylene, not
  abscissic acid)

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Senescence

• In monocarpic senescence the whole plant dies
  after seed formation. This is frequently observed
  in annuals (therophytes in Raunkiaer's
  terminology) and biennial plants, but some
  perennials such as the century plant Agave
  americana show monocarpic senescence.
• Senescence of all above ground plant parts is a
  feature of many herbaceous perennials (or
  geophytes and hemicryptophytes). An underground
  storage organ of some kind persists in a dormant
  state and produces new above ground structures in
  the following season.

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• Woody plants (phanerophytes) in temperate regions
  often show a deciduous pattern of senescence in
  which all of the leaves die at the same time as
  the meristems become dormant. The leaves are
  replaced by a whole new set at the end of
  dormancy in the spring.

• The "century plant" Agave americana takes about
  30 years (not 100) to grow to maturity and
  flower. It then dies after setting seed

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Senescence

• Sequential senescence is a feature of evergreen
  plants, particularly those that grow throughout
  the year. Leaves are continuously produced and
  shed in order of age.
• However senescence occurs, the underlying changes
  are very similar.

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Senescence

• There is a switch from synthesis to breakdown of
  cell structure.
• Photosynthesis declines as the chloroplast
  becomes a chromoplast.
• Proteins and other polymers are broken down by
  digestive enzymes.
• In perennial plants some of the amino acids and
  other small molecules are withdrawn from the
  leaves before they are shed.
• In this way the plant recovers some of its
  investment.

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Seasonal Changes in Leaves

• All trees lose their leaves
• Evergreens and Deciduous Trees
• Evergreen trees shed their needle leaves a little
  at a time
• Deciduous trees lose their leaves at the same
  time each year.
• Usually in the fall and winter
• Tropics or areas near the Equator have only wet
  and dry seasons so the deciduous trees shed
  leaves before the dry season begins.

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Abscission

• Like senescence, abscission is a natural and
  necessary part of plant development.
• Plant parts like flower petals, mature fruits
  and senescent leaves are detached form the plant
  along a clearly defined abscission zone.
• This zone is differentiated early in
  development usually it is a region of smaller
  cells at the base of the petiole, petal or
  pedicel.

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Abscission

• Prior to abscission cell-wall degrading enzymes
  are secreted into the zone the middle lamella is
  broken down between cortical parenchyma cells.
• The secondary walls of xylem elements are
  resistant to these enzymes and these cells simply
  break when the others have separated.

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Abscission

• Ethylene produced by the senescing organ
  stimulates the synthesis of cellulase and
  pectinase ethylene (or ethrel) treatment can be
  used to promote abscission.
• This is particularly useful for mechanically
  harvested crops like coffee or for thinning
  excess crop on fruit trees.

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• This cabbage was stored in the same room as
  apples, which produce large amounts of ethylene.
  The ethylene stimulated abscission of the leaves
  from the stalk, even though they were immature.

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Thank you