Detailed Study Notes on Growth and Development of Pasture Plants

G R A S 2 6 1 4 : C H A P T E R 1 - G R O W T H A N D D E V E L O P M E N T O F P A S T U R E P L A N T S

Instructor: Mrs. Jamie Paulse-Ross

Endosperm: Nutrient-rich tissue found in the seeds.
Scutellum: The structure that absorbs nutrients from the endosperm during germination.
Coleoptile: The protective sheath covering the emerging shoot in monocotyledons.
Plumule: The part of the embryo that develops into the shoot.
Radicle: The embryonic root that emerges first during germination.
Coleorhiza: The sheath protecting the radicle.
Aleurone Layer: A layer of protein-rich cells that provides enzymes for seed germination.

Coleoptile: A structure serving to protect the shoot as it emerges.
Radicle: Emerges as the first root, crucial for anchoring.
Seminal Roots: Root system that consists of the first roots that emerge during germination.
Lateral Roots: Roots that extend horizontally from the primary root for stability and nutrient acquisition.
Mesocotyl: The part of the plant that connects the seed with the shoot and provides additional support.

Meristems: Regions of cells capable of division and growth within plants.
- Classification by Location:
- Apical Meristems: Found at the root and shoot tips; responsible for primary growth (lengthening).
- Basal/Intercalary Meristems: Located at the internodes and leaf bases; they contribute to growth in length.
- Lateral Meristems: Include vascular and cork cambia; promote secondary growth in woody plants, leading to an increase in girth.

Zone of Cell Division: Area where the most rapid cell division occurs.
Zone of Elongation: Cells here elongate, contributing to the plant's growth.
Promeristem: The initial undifferentiated tissue of the meristematic region.
Zone of Maturation: Cells differentiate into distinct cell types, contributing to the mature structure of the plant.
Leaf Primordia: Early formations of leaves that will develop from the meristem.
Axil: The angle between the upper side of a leaf stalk and the stem.

Leaf Primordia: The early stages of leaf development that emerge from the meristem.
Basal Leaves: Leaves that develop at the base of the plant.
Collar: The boundary between the leaf sheath and blade.
Sheath: The part of the leaf that wraps around the stem.
Blade: The flat part of the leaf that is involved in photosynthesis.
First Leaf: The initial leaf produced by the plant.
Adventitious Roots: Roots arising from non-root tissues.
Primary Root: The first root that emerges from the seed.
Germination: The process by which a seed develops into a new plant.
Initial Tillering: Early stages of producing new shoots.
Vegetative Phase: The stage of growth where the plant focuses on leaf and shoot development rather than reproduction.

Intravaginal Branching: Secondary shoots grow upwards within the leaf sheath. Example: Themeda triandra.
Extravaginal Branching: Shoots grow horizontally and penetrate through the leaf sheath; associated with forms of branching that create stolons. Benefits include increased resistance against defoliation.

Three types of shoots based on lifespan:

Influencing Leaf Formation:
- Leaf area and size can affect overall health and production.
- Leaf age influences nutrient absorption and photosynthesis efficiency.
Factors Influencing Shoot Formation:
1. Genetic differences among species.
2. Temperature impacts growth rates.
3. Light intensity affects photosynthesis and energy availability.
4. Water and mineral supply are essential for optimal growth.

Transition Process:
- Shoots form as small growth points in axillary positions of basal leaves.
- The apical meristem switches from vegetative to reproductive growth.
- The development of secondary shoots is inhibited due to auxin action (apical dominance).
- Leaf primordia production stops, and flower primordia formation begins.
- The growth point elevates above the soil during reproduction.
Apical Dominance: The phenomenon where the main central stem of a plant suppresses the growth of lateral branches.
Effects of Removing the Growing Point: Can enhance lateral branch growth by lifting apical dominance.

Stages:
- Flag Leaf: The last leaf that predominates in flower formation.
- Boot Stage: The period before the flower head fully emerges from the sheath.
- Anthesis: The flowering stage when pollination occurs, including early anthesis and peak anthesis stages.
- Reproductive Phase: Characterized by flower and seed head emergence.

Classes of Root Systems:
1. Superficial Root System: Present in annuals and certain species (e.g., Eragrostis, Cymbopogon).
2. Deep Root System: Typically observed in perennial species such as Digitaria tricholaenoides and Elionurus muticus.
3. Double Root System: Both deep and shallow roots, present in species like Cynodon dactylon and Tetrachne dregei.

Root growth primarily occurs under conditions of excess carbohydrate production.
There exists a negative correlation between root growth and aboveground growth.
- Timing: Root growth is expected in early spring before vegetative growth and after seed maturation in autumn.
Impact of Grazing: Severe grazing in autumn can adversely affect grass root systems and overall health.

Examines how limited water availability affects both aboveground and underground development of grasses.