Growth and Growth hormones

Dr. Sarita SrivastavaChaudhary Mahadeo Prasad Degree College

Allahabad

Animal vs. plant growth

Development: is a series of change which an organism goes through in his life cycle.

Development is associated with morphogenesis and differentiation

During growth New cells are added by cell division Organism grows in size Increase in weigh Protoplasm multiplicates Irreversible permanent increase in volume takes

place

Development leads to growth

Growth and Development

Definition-Growth: permanent and irreversible change in size of the cell, organ or whole organism usually accompanied with increase in dry weight .

Types of Plant Growth1. Determinate growth : As you grow and develop from childhood you get taller and bigger overall. But at some point you reach a maximum height. This type of limited growth is called determinate growth. What it means is that once you have reached your maximum height (which is determined by your genetics), you can't grow any taller. This is something that you have no control over.2. Indeterminate growth: Plants, unlike animals, have indeterminate growth. This means that they can continue to grow taller as long as they are alive. Most plants tend to slow their growth at some point, but as long as they wish to keep growing they may do so.

All plants experience what is called primary growth. Primary growth is the upward growth of the stem and the downward growth of the roots. It is the type of growth that makes a plant longer.

Some plants experience an additional type of growth called secondary growth. This occurs in plants known as dicots, such as trees, shrubs, and vines. Secondary growth is the outward or lateral growth of a plant, which makes it thicker and wider. Dicots need secondary growth because they tend to grow taller than other plants and need the extra support. Without secondary growth, a tall pine tree would be just like a very long blade of grass.

Process of growthGrowth involves meristematic changes1.Cell division :

occurs due to meristems, apical intercalary and lateral

2.Cell enlargement: 3.Cell maturation

Meristematic and physiological changes during the process of growth

Cell is metabolically highly active Cellular mass of cell increases Replication of genetic material takes place Growth basically due to the mitotic cell

division Mitochondria and chloroplast duplicate on

their own Two daughter cells are formed which are

half the size of the mother cell These cells proceed for cell enlargement

Cell division:

Cells increase in size due to vacuolation i.e. absorption of water

The central vacuole pushes the cytoplasm to the periphery of cell

The cell wall becomes thin New wall material is being synthesized to cope up with

the cell enlargement It is said that cell enlargement is governed by osmosis DPD=OP-TP Wall pressure is reduced in the vacuolating cells due

to increased plasticity of cell walls this results in absorption of water from the neighboring cells

Cell enlargement is associated with absorption of water, synthesis of new cytoplasm and cell wall material

Cell enlargement

Development of specialized mature tissues E.g. meristematic cells of leaf epidermis

differentiates to form: Guard cells Trichomes Glands Epidermal cells Cell differentiation depends upon the

growth factors

Cell maturation

Phases of growth Growth Curve is Sigmoid

Growth Curve : Lag Phase Log Phase Steady Phase

Instruments An auxanometer (Gr. auxain, "to grow" + metron, "measure") is an apparatus for measuring increase or rate of growth in plants.

A crescograph is a device for measuring growth in plants. It was invented in the early 20th century by Sir Jagadish Chandra Bose - a Bengali polymath, physicist, biologist, botanist, archaeologist.

Factors affecting growth

Light : Etiolation Photomorphogenesis Seedling growth, seed germination,

flowering Temperature: thermoperiodicity-fluctuation in temp

affectin growth 25 ˚C day temp-12˚C night Water: water stress stops growth

Environmental factors

C/N ratio More nitrogen : more protoplasm, less mechanical tissues, vigorous vegetative growth, shoot is large in compared to roots leaves are large and soft Succulent and dark green in colour Less nitrogen and more carbohydrate

favors more wall synthesis, less protoplasm and more roots as compared to shoot

Nutritional factors

The genes of an individual determines its type

Hormonal factors: Growth is regulated by growth

hormones

Genetic factors

What is difference between Growth hormones and growth regulators

Definition of Growth hormones:

Growth hormonesWent and Thinmann 1937

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