Crop Science

1. Plant Growth and Development
Hanzel L. Pedrosa

2. What is Growth?
 irreversible permanent increase in size of an organ or
its parts or even of an individual cell.
 as accompanied by metabolic processes (both
anabolic and catabolic), that occur at the expense of
energy

3. Terms
Morphogenesis is the process of development of shape
and structure of an organism
Differentiation is the process of change in cells, tissues
or organs to carry out different functions
Development is the whole series of qualitative and
quantitative changes such as growth, differentiation
and maturation, which an organism undergoes
throughout its life cycle

4. STAGES OF CELLULAR GROWTH
 Cell division : The number of cells
increases due to mitosis
 Cell enlargement: The size of individual
cell increases after cell division due to
increase in the volume of its protoplasm
 Cell differentiation: In this stage, structure
of the cells changes to perform specific
functions. And similar type of cells having
same functions form a group, which is
known as tissue

5. GROWTH CURVE
 Lag Phase – This is the initial phase of
growth when the rate of growth is very
slow.
 Log Phase – It shows rapid growth and
is maximum during the entire life span.
 Stationary Phase – Here the rate of
growth starts decreasing and finally it
stops

6. Growth
 Plant Growth Generally is Indeterminate
• Plant growth is unique because plants retain the capacity
for unlimited growth throughout their life
• This ability of the plants is due to the presence of
meristems at certain locations in their body

7. Growth
 Growth is Measurable
• Growth, at a cellular level, is principally a consequence of
increase in the amount of protoplasm
 increase in fresh weight
 dry weight
 length
 area
 volume and cell number

8. Measurement of Growth
 Increase in length or growth – in case of stem and
root;
 Increase in area or volume – in case of leaves and
fruits;
 Increase in the number of cells – in algae, yeast and
bacteria.

9. Phases of Growth
 Meristematic - The constant dividing phase of cells at the shoot
and root apex
 Elongation - The cells that are present close to meristematic
cells are in the elongation phase
- These cells elongate due to the growth of the
vacuole within the cell, and this zone is known as the zone of
elongation
 Maturation - The cells in this region reach their maximum size
with respect to their protoplasm and cell wall thickening.

10. Growth Rates
a. Arithmetic growth - following
mitotic cell division, only one
daughter cell continues to divide
while the other differentiates and
matures
b. Geometrical growth - the initial
growth is slow (lag phase), and it
increases rapidly thereafter – at an
exponential rate (log or exponential
phase)

11. Factors Affecting Plant Growth
 External growth factors
 External factors are those factors present in the environment that
affect the growth of the plants directly or indirectly.
(i) Light
(ii) Temperature
(iii) Water
(iv) Mineral nutrients

12. Factors Affecting Plant Growth
 External growth factors
(i) Light
• for the process of photosynthesis
• seed germination
• growth of seedling
• differentiation of various tissues and organs
• reproduction

13. Factors Affecting Plant Growth
 External growth factors
(ii) Temperature
• optimum temperature required for growth of plants ranges
between 28-30°C, but it may occur in the temperature range of
4-45°C
• very low temperature causes injuries to the plant due to chilling
and freezing, and very high temperature stops its growth

14. Factors Affecting Plant Growth
 External growth factors
(iii) Water
• primary component in photosynthesis and respiration
• Responsible for turgor pressure in cells
• A solvent for minerals and carbohydrates moving through the plant
• Responsible for cooling leaves as it evaporates from leaf tissue during
transpiration
• A regulator of stomatal opening and closing, thus controlling transpiration
and, to some degree, photosynthesis
• The source of pressure to move roots through the soil
• The medium in which most biochemical reactions take place

15. Factors Affecting Plant Growth
 External growth factors
(iv) Mineral nutrients
• Soil minerals serve as both sources and sinks of essential plant
nutrients

16. Factors Affecting Plant Growth
 Internal Growth Factors
• are substances produced in the plant body itself, which affects
the growth of the plant. These are called plant hormones or
phytohormones or growth hormones.
 a phytohormone is an organic substance produced in a small
quantity in one part of plant body and capable of moving to other
parts to influence the growth of that part

17. Factors Affecting Plant Growth
 Internal Growth Factors
The naturally produced growth hormones are broadly grouped
under five major classes
(i) Auxin
(ii) Gibberellins
(iii) Cytokinins
(iv) Ethylene
(v) Abscissic acid

18. Factors Affecting Plant Growth
PLANT GROWTH REGULATORS
(PLANT HORMONES)
• Internal and external signals that regulate plant growth are
mediated, at least in part, by plant growth-regulating
substances, or hormones (from the Greek word hormaein,
meaning "to excite")

19. PLANT GROWTH REGULATORS
(PLANT HORMONES)
Plant hormones differ from animal hormones in that:
 No evidence that the fundamental actions of plant and animal
hormones are the same.
 Unlike animal hormones, plant hormones are not made in tissues
specialized for hormone production. (e.g., sex hormones made in
the gonads, human growth hormone - pituitary gland)
 Unlike animal hormones, plant hormones do not have definite
target areas (e.g., auxins can stimulate adventitious root
development in a cut shoot, or shoot elongation or apical
dominance, or differentiation of vascular tissue, etc.).

20. Factors Affecting Plant Growth
 Internal Growth Factors
Auxin
 growth promoter
 generally produced by the growing apex of stem and root of the
plants
 helps in the elongation of shoot and root tips behind apical
meristem

21. Functions of Auxin
(a) It promotes cell elongation;
(b) It suppresses the growth of lateral bud. If the tip of a plant is
removed, the lateral branches begin to grow; In most of the
plants apical bud suppresses the development of lateral buds.
This is called apical dominance.
(c) It delays fall of leaves. (leaf abscission)
(d) NAA (Naphthalene acetic acid) is used for preventing fruit drop
in apples before they are ripe.
(e) 2, 4-D (2, 4-dichlorophenoxy acetic acid) acts as a dicot
weedicide

22. Internal Growth Factors
 Gibberellin Gibberellin or Gibberellic Acid (GA)
 initially isolated from a fungus Gibberella fujikuroi
 In plants, it is produced in embryos, roots, and young
leaves and it enhances growth

23. Functions of Gibberellins
(a) It helps in elongation of stems in genetically dwarf plants.
By using gibberellin the height of the dwarf plants can be
increased
(b) It breaks dormancy of seeds and buds
(c) It induces parthenocarpy. (Formation of seedless fruits
without fertilization) or provides stimulus received by
pollination

24. Internal Growth Factors
 Cytokinins
 They were extracted from coconut milk
 Heredity Cytokinins are synthesized in root apex,
endosperm of seeds, and young fruits where cell division
takes place continuously

25. Functions of Cytokinins
(a) They stimulate cell division, cell enlargement and cell
differentiation
(b) They prevent aging of plant parts
(c) They inhibit apical dominance and help in growth of lateral
buds into branches

26. Internal Growth Factors
 Ethylene
 Ethylene is a gaseous hormone
 It is found in ripening fruits, young flowers and young
leaves

27. Functions of Ethylene
(a) It induces ripening of fruits
(b) It promotes senescence and abscission of leaf, and flowers
(c) In cells it only increases the width not the length

28. Internal Growth Factors
 Abscissic acid
 Abscissic acid also known as Dormin is a naturally
occurring growth inhibitor found in wide variety of plants
 It is synthesised in leaves

29. Functions of Abscissic acid
(a) It induces dormancy of buds and seeds as opposed to
Gibberellin, which breaks dormancy
(b) It promotes the senescence of leaf, i.e., fall of leaves
happen due to abscissic acid
(c) It inhibits seed germination and development
(d) It causes closing of Stomata

30. Practical Application of Growth Regulators
 With the help of auxins and gibberellins seedless varieties of
fruits can be produced. You might have seen seedless
grapes and papayas in the market
 Early flowering in some plants is possible by applying growth
regulators

31. Practical Application of Growth Regulators
 With the use of hormones some fruits can be ripened at an
early stage
 Germination in seeds can be possible by applying auxins
 Germination of potatoes and onions can be stopped in
storage by application of growth inhibitors

32. Summary

33. HOW PLANTS RESPOND TO ENVIRONMENTAL
STIMULI
Tropisms - plant growth toward or away from a stimulus
such as light or gravity.
Nastic Movements - response to environmental stimuli
that are independent of the direction of the stimulus. Pre-
determined response.

34. HOW PLANTS RESPOND TO ENVIRONMENTAL
STIMULI
Phototropisms - Phototropic responses
involve bending of growing stems toward
light sources.
 Individual leaves may also display
phototrophic responses.
 auxin most likely involved

35. HOW PLANTS RESPOND TO ENVIRONMENTAL
STIMULI
Gravitropism is the response of a plant
to the earth’s gravitational field.
 present at germination
 auxins play primary role

36. Gravitropism
• Increased auxin concentration on the lower side in
stems causes those cells to grow more than cells on
the upper side.
 stem bends up against the force of gravity
 negative gravitropism
• Upper side of roots oriented horizontally grow more
rapidly than the lower side
 roots ultimately grow downward
 positive gravitropism

37. HOW PLANTS RESPOND TO ENVIRONMENTAL
STIMULI
Thigmotropism is directional growth
response to contact with an object.
 tendrils

38. HOW PLANTS RESPOND TO ENVIRONMENTAL
STIMULI
SEISMONASTY - a nastic response
resulting from contact or mechanical
shaking
Mimosa pudica L. (sensitive plant)

39. HOW PLANTS RESPOND TO ENVIRONMENTAL
STIMULI
NYCTINASTY
 sleep movements
 prayer plant - lower leaves during
the day and raises leaves at night
 legumes

40. Topics
1. Flower and Fruit Development
2. Seed and Seed Germination
3. Plant-water Relations
4. Physiological Processes Affecting Crop Production
5. Soil Fertility and Plant Nutrition
6. Genetics
7. Agronomic Principles
8. Principles of Crop Protection
9. Conservation Farming

41. Topics
1. Flower and Fruit Development
a. Flower initiation and fertilization
b. Fruit set and seed development
2. Seed and Seed Germination
a. Seed structure
b. Seed germination
3. Plant-water Relations
a. Water properties
b. Water movement
c. Water potential

42. Topics
4. Physiological Processes Affecting Crop Production
a. Photosynthesis
b. Respiration
c. Transpiration
d. Translocation
5. Soil Fertility and Plant Nutrition
a. Soil composition
b. Soil characteristics
c. Plant nutrition

43. Topics
6. Genetics
a. Genetic terms
b. Mitosis
c. Meiosis
d. Mendelian laws of inheritance
7. Agronomic Principles
a. Agro-ecological zones
b. Tillage practices
c. Plant population
d. Crop rotation

44. Topics
8. Principles of Crop Protection
a. Weed management
b. Pest management
c. Diseases management
9. Conservation Farming
a. Principles and practices