Exam 1 Lectures 5-6 Flashcards
What is a seed?
A plant structure consisiting of an embryonic plant, the food supply necessary for germination and a protective coat.
What is an Embryo?
The rudimentary (undeveloped) plantlet within a seed
What is Germination?
Beginning of growth by an embryo
What is a Cotyledon?
- Leaf that forms part of a seed embryo
- In the case of a legume the major portion of the two halves of a seed that emerges from the soil
- In grasses the cotyledon remains in the soil
What is an Epicotyl?
The stem of the young seedling above the cotyledon
What is a Hypocotyl?
The stem of the young seedling below the cotyledon
What is a Radicle?
The part of the seed which at initation of germination becomes the root
What is a Coleoptile?
The sheath covering the first leaf of a grass seedling as it emerges from the soil
What is a Plumule?
- Terminal bud of the embryo
- In grasses it emerges from the coleoptile after the coleoptile emerges from the soil
- In legumes emerges above the cotyldonary node
What is a seedling?
The juvenile stage of a plant grown from seed
What is necessary from external conditions in order for germination to occur?
- Ample moisture
- Oxygen
- Suitable temperature
- Specific light conditions
How does the initial processes in germination occur?
- Seed absorbs water and after about 3 days their mositure concentration may be more than 60%. During this process (called imbibition) the seed coat softens and the seed swells
- Soluble nutrients in the seed go into solution and are transported to growing sprout
- Proteins are broken down into amides and amino acids and incorportated into seedling proteins
- Fats are broken down by lipases and are used to form sugars and fats in the seedling
- Energy for the germination process is supplied by respiration, the biological oxidation of carbo and hydron into carbon dioxide and water
What occurs in grass seedling emergence?
- Radicles emerges from seed
- Coleoptile emerges from seed
- Coleoptile pushed through soil by elongation of growing point below ground
- Coleoptile merges from soil as a pale tube-like structure that ecnloses true leaf
- Slit develops at tip of coleoptile & leaf emerges through it.
- Photosynthesis begins & seedling establishes independence from stored food
- Cotyledon & apical meristem (growing point) remain underground
What is a legume seedling emergence ?
- Radicle emerges from seed and elongates
- Hypococtyl elongates, forms an arch, arch is forced through the soil
- Arch emerges followed by cotyledons
- Cotyledons open & photosynthesis begins
- Plumate (true leaves) emerges from between Cotyledons
What are the advantages of grass compared to legumes?
- Grass has pointed colyoptile
- Keeps gorwing point underground longer
When it comes to vegetative propogation what does it consist of?
- Some plants are sterile and do not produce seeds, while others do not produce uniform offspring from seed
- A vegetative stem can reproduce itself since its contains:
* A meristematic tissue exists at the base of the internode-axillary bud (intercalary meristem)
* Can produce new shoots & roots
When it comes to vegetative propogation what does it consist of? (part 2)
- Vetitative propogation consists of putting nodes in contact with soil in the presence of adequate moisture, temperature, and light, resulting in the production of new shoots and roots
- The new plant is identical in genetic composition to the plant it was derived from (clone)
What does Photosynthesis consist of?
- Primary mechanism of energy input into the living world
- Directly or inderictly resposible for all life on earth
- In essence photosynthesis is a two-phase process:
* Harvesting energy from light and producing ATP and NADPH
* Uptake of CO2 from the atmosphere and synthesis of organic acids using the energy from ATP and reducing power of NADPH
What is the formula for photosynthesis?
nCO2+H20+light -> (CH2O)n+nO2
What pathways make up the carbon dioxide fixation pathways in forage plants?
The Two major pathways are:
* C-3: First product is a three-carbon compound first
* C-4:First product is a four-carbon compound
How is the process of carbon fixation?
- CO2 from atmosphere diffuses through stomata into the leaf
- In C-3 CO2 enters mesophyll cell and goes to chloroplast encountering Rubisco, a five-carbon compound & oxygen
- CO2 and Oxygen compete for binding sites in C-3 if CO-2 wins 6 carbon compounds turn into 2 3-carbon compounds. If oxyegn weins photorespiration occurs
- In C-4, CO2 enters mesophyll and is fixed or added to a 3-carbon compound using PEP carboxylase. (It does not bind with oxygen)
What is a generla description of plants represented by each pathway?
1.Almost all grasses of tropical origin and most sedges are C-4
2.Temperate grasses and both temperate and tropical legumes are C-3 plants. Most trees & trees are C-3
What is the significance of different pathways?
- C-4 plants have kranz anatomy
-Tights rings of mesophyll surrounding a well-defined bundle sheath
-More structural component in leaf (sclerenchyma fibers & vascular bundles - C-3 plants have loosely arranged mesophyll, open spaces between cells, & less structural support & vascular tissue.
When it comes to C-4 how come it is much more capable of higher growth rates than C-3 plants?
- C-4 plants contain enzyme that fixes on carbon dioxide (PEP) does not bind with oxygen
- Rubisco in C-3 essentially binds with oxygen and CO2
- Plants produce more dry matter per unit of nitrogen and per unit of water than C-3 making it more efficient
- C-4 optimum temperature is 90-95 degrees F, in C-3 it is about 65-75 degress F
How does one determine forage nutritive value?
- More structural support & vascular cells in C-4 grass leaves lower digestiblity
- Tightly packed leaf cells provide less surface area for attachment by bacteria, digestion is lower and less complete. strong structural components slow breakdown of leaf particles.
- Efficient nitrogen use by C-4 grasses means lower crude protein contentrations than found in C-3 grasses.
What is the use of fixed carbon by plants?
- Growth and maintenance
- Reserve storage
When it comes to prioritization of growth versus reserves what occurs?
- Growth has priority over storage for carbyohydrate use. (uncontrolled grazing can deplete a plant’s reserve & kill it)
- Storage occurs when leaf area is more than adequate to meet growth demand.
- Storage is reduced when leaf area cannot supply all needed energy for growth
What are the contributions of legumes to forage-livestock systems?
- Fix atmospheric N2
- May improve seasonal distribution of frage DM (may be more productive during dry periods)
- Utilize more of the soil rooting zone ( deep rooted)
Why do Legumes fix atmopsheric N2?
- Legumes produce high crude protein forage
- Legumes improve soil fertility for subsequent crops
What factors make legumes a limited use in Florida?
- Requires greater managment inputs in fertilizer and control of grazing
- Difficult/unreliable estblishment (low seedling vigor in some cases, unpredictable weather causes failures in others)
- Lack of persisten perennials for grazed pasture
What would be an overview of nitrogen relationships?
- In most grassland systems, nitrogen is the most limiting nutrient for plant growth.
- Occurs despite 79% if the atmosphere is N2
- N2 is inert, very stable, and a large amount of energy is required to break the triple bond
- Bacteria can break the N2 bond at room temperature and atmospheric pressure
What are the bacteria involved in biological N fixation in forage legumes?
- Rhizobium - Often associated with temperate legumes
- Bradyrhizobium - Often associated with tropical legumes
What is the nature of the association between rhizobia and legumes?
- Both parties benefit
* Rhizobia use carbohydrates from plant
* Plants obtain N compounds from the bacteria
How is the nature of symbiosis?
- Rhizobia traditionally were classified based on their host
- Some bacterial species are host specific and others will inoculate a large number of hosts
How does the establishment of association of infection and nodulation occur?
- Bacteria is the root zone attach to root hairs
- Bacteria release a compound that causes the root hairs to curl
- Rhizobia are trapped in the curled root hair and an opening is formed in the root hair cell wall
- Rhizobia enters the opening in the root hair cell wall and travel to the root cortex
How is the process of nitrogen fixation?
- Energy demanding
- Nitrogenase - enzyme complex (two seperate enzymes) that reduces N2 to NH4
- Pratically field test to determine if nodules are fixing N (cut nodule in half, if actively fixing N, will have burnt red color, gray if not fixing)
What factors affect quantity of N fixed? (negative effect)
- Drought
- Flooding
- Very acid soils
- Low soil fertility
- N fertilization
- Shading
- Extreme temperatures
What is the reason for seed inoculation?
- Maximize growth & N fixation
- Reduce risk of seedling failure
When should legume seeds be inocuulated?
- Always when planting a legume in a new field
- Always, as it is cheap insurance to ensure your legumes thrive!
What are the requirements for succesful seed inoculation?
1.Use correct inoculant
2.Use viable inoculant (expiration date, storage)
3.Sticker - Used to attach inoculum to seed
4.Plant immediately (heat & UV sensitive)
What are forms of inoculant?
- Peant humus- peat serves as the carrier
- Granule flowable- put in a granular form to flow through a seeder, often used for large seeded legume
- Coated seed- seed seller adds a coating to the seed that includes inoculant and coudl also include lime and fertilizer
