Chapter-15
Plant Growth and Development
- Points to Remember
- Seed Germination : The seed germinates only when favourable conditions for growth exists in the enviroment. in absence of favourable condition it goes into a period of suspended growth or rest, called dormancy.
- Abscission : Shedding of plant organs like leaves, flowers and fruits etc. from the mature plant.
- Apical dominance : Supperssion of the growth of lateral buds in presence of apical bud.
- Dormancy : A period of suspended activity an growth usually associated with low metabolic rate. Some, seeds undergo a period of dormancy and can germinates only after dormancy period gets over.
- Phytohormone : Chemicals secret by plants whic control the light dependent developmental process.
- Senescene : The last phase of growth when metabolic acitivities decrease.
- Vernalisation : A method of promoting flowering by exposing the young plant to low temperature.
- Growth : Am irreversible permanent increase in size, volume and wight of an organ or its parts or even of an individual.
- Quiescence : Non germination of a viable seed due to non-availability of proper enviromental conditions
- Vivipary : It is the germination of seed while it is still attached to the parent plant and is nourised by it. e.g., Rhizophora and Sonneratia. As the germinating seed forms a seedling. It fall down into the mud due to increase in weights. In the mud, lateral roots develop for anchorage.
- Heterophyll : Occurrence of more than one type of leaves in plants e.g., larkspur, coriander leaves of Juvenile plant are different in shape form mature plant.
- Bolting : Elongation of internodes prior to flowering in plants like Cabbage.
- Photoperidism : Response of plants to relative periods of day/night to induce flowering.
- According to duration of exposure of plants to light, plants are divided in 3 categories :
- 1. Long Day Plant (LDP) -- Plants which need exposure to light for period exceeding critical duration e.g., wheat, rice, cucumber.
- 2. Short Day Plant (SDP) -- Plants that need exposure to light for period less than the critical lenght e.g., Cabbage.
- 3. Day Neutral Plants (DNP) -- There is no correlation between exposure to light duration & induction of flowering e.g., Tomato.
| IAA | Indole acetic acid |
| NAA | Napththalene acetic acid |
| ABA | Abscisic acid |
| IBA | Indole-3 butyric acid |
| 2.4D | 2.4 dichlorophenoxy acetic acid |
| PGR | Plant growth regulator |
- Measurement of Growth : Plant growth can be measured by a variety of parameters like increase in fresh weights, dry wight, lenght, area, volume and cell numbre.
- Phases of Growth : The period of growth is generally divided into three phases, namely, meristematic, elongation and maturation.
- (i) Meristematic : New cell produced by mitotic division at root-tip and shoot-tip thereby show increase in size. Cells are rich in protoplasm and nuclei.
- (ii) Elongation : Zone of elongation lies just behind the meristematic zone of roots and concerned with enlargement of cells.
- (iii) Maturation : The portion lies proximal to the zone fo elongation in roots. The cells of this zone attain their maximum size in terms of wall thicking and protoplasmic modification.
- Growth rate : The increased growth per unit time is termed as growth rate. The growth rate shows an increase that may be arithmetic or geometrical.
Sigmoid Growth Curve chart :
Sigmoid Growth Curve :
- Lag Phase : Growth is slow in initial stage.
- Exponential Phase : Period of maximum growth.
- Stationary Phase : When the nutrients become limiting, growth slows down.
- Differentiation : A biochemiacal or morphological change in meristemic cell (at root apex and shoot apex) ot differentiate into permanent cell is called differentiate. e.g., loss of protoplasm by tracherary elements.
- Dedifferentiation : The phenomenon of regeneration of permanent tissue to become meristematic is called dedifferentiation. e.g, formation of interfascicular crmbium and cork combium form parenchymatous cells.
- Redifferentiation : Meristematic/ tissue are able to produces new cells that once again lose the capacity to divide but nature to perform specific fucntions. e.g. secondary cortex, secondary xylem etc.
Conditions or factor influencing Growth
- 1. Nutrition 2. Availability of water 3. Temperature 4. Oxygen 5. Light 6. Gravity 7. Stress factors like minerals, water or temperature etc.
- Phytohormone or Plant Growth-Regulator
- Growth promoting hormones : These are involved in growth promoting acitivities such as cell division, cell enlargement, flowering, fruiting and seed formation. e.g., Auxin, gibberellins, cytokinins.
- Growth inhibitor : Involved in growth inhibiting acitivities such as dormancy and abscission. e.g., Abscisic acid and Ethylene.
- Vernalisation : The phenomenon in which flowering is either quantitatively or qulitatively dependent on exposure ot low temperature. e.g., wheat, barley, rye, bi-ennial plants like sugarbeet Cabbage, Carrots. It prevents precocious reproductive development late in the growing season and enables the plant to have sufficient time to reach maturity.
