The postembryonic phase of plant development begins with germination. Some dormant seeds require a period of after-ripening during which low-level metabolic activities continue to prepare the embryo for germination. Highly evolved interactions between the seed and its environment increase the odds that the germinating seedling will survive to produce another generation. Temperature, water, light, and oxygen are all key in determining the success of germination. Stratification is the requirement for chilling (5°C) to break dormancy in some seeds. In temperate climates, this adaptation ensures germination only after the winter months have passed. In addition, seeds have maximum germination rates at moderate temperatures of 25°–30°C and often will not germinate at extreme temperatures. Seeds such as lettuce require light (specifically, the red wavelengths) for germination; thus seeds will not germinate so far below ground that they use up their food reserves before photosynthesis is possible.
Desiccated seeds may be only 5–20% water. Imbibition is the process by which the seed rehydrates, soaking up large volumes of water and swelling to many times its original size. The radicle (primary embryonic root) emerges from the seed first to enhance water uptake; it is protected by a root cap produced by the root apical meristem. Water is essential for metabolic activity, but so is oxygen. A seed sitting in a glass of water will not survive. Some species have such hard protective seed coats that they must be scarified (scratched or etched) before water and oxygen can cross the barrier. Scarification can occur by the seed being exposed to the weather and other natural elements over time, or by its exposure to acid as the seed passes through the gut of a frugivore. The frugivore thus prepares the seed for germination, as well as dispersing it to a site where germination can take place.
During germination, the plant draws on the nutrient reserves in the endosperm or cotyledons. Interactions between the embryo and endosperm in monocots use gibberellin as a signal to trigger the breakdown of starch into sugar. As the shoot reaches the surface, the differentiation of chloroplasts is triggered by light. Seedlings that germinate in the dark have long, spindly stems and do not produce chlorophyll. This environmental response allows plants to use their limited resources to reach the soil surface, where photosynthesis will be productive.
The delicate shoot tip must be protected as the shoot pushes through the soil. Three strategies for protecting the shoot tip have evolved (Figure 20.19):
Meristems have delicate cells that are susceptible to damage during germination. A variety of strategies have evolved for protecting the shoot meristem during germination. (A) Some cotyledons protect the meristem as the shoot emerges from the soil. (B) (more...)
- 1.
Cotyledons protect the shoot tip.
- 2.
The epicotyl (the stem above the cotyledons) bends so that stem tissue, rather than the shoot tip, pushes through the soil.
- 3.
In monocots, a special leaflike structure, the coleoptile, forms a protective sheath around the shoot tip.
FAQs
Germination is the process of development of a new plant from a dormant embryo within the seed under the availability of suitable conditions like temperature, water, air, and light. During germination, the seed absorbs water and swells up, this results in the rupture of the seed coat.
What is the trick for germination? ›
5 Gardening Tips to Improve Seed Germination
- Pre-Soak Your Seeds Before Planting. Plants lie dormant until the seeds detect enough regular moisture to be able to grow. ...
- Begin by Starting Your Seeds Indoors. ...
- Monitor Your Seed's Environment. ...
- Keep Them Well-Watered. ...
- Change Seed Sources.
Seed germination refers to the process by which a seed, which is a fertilized plant ovum, effectively sprouts and grows into a baby plant.
Why won't my zinnia seeds germinate? ›
The soil was too wet or too dry:
Too dry, and your seeds won't germinate. Too wet, and they're liable to rot. Ensure that seeds are kept evenly moist by thoroughly wetting and draining the compost before you begin.
What is germination? ›
Germination is the process by which a plant grows from a seed into a seedling. Seeds remain dormant until conditions are favorable for germination. All seeds need water, oxygen and optimal temperature to germinate. When a seed is exposed to the proper conditions, water and oxygen are taken in through the seed coat.
What are the 7 steps of seed germination? ›
Firstly, the seed grows roots below the soil to get water under the earth. Once the roots appear, the seed starts to grow shoots above ground. Next, a seed sends a shoot to the surface and grows leaves to absorb sunlight. In a process known as photomorphogenesis, the leaves grow toward the light source.
How long to soak seeds before planting? ›
Examples of seeds that benefit from soaking include peas, beets, cucumber, corn, squash, pumpkin and beans. In a bowl, cover your seeds with warm water and leave to soak for 6-24 hours. Smaller seeds and those with thinner coats need the shorter time, and larger seeds with thicker coats need the longer period.
How to germinate seeds with paper towel and ziplock bag? ›
Dampen a paper towel and fold it into the bag. Place the seeds along one side of the bag, pressing them against the paper towel. Seal the bag tightly and hang in a window using tape. Make sure the beans are visible on the side of the window where your child will be observing their seeds sprout.
Which grows first, root or shoot? ›
The primary root, or radicle, is the first organ to appear when a seed germinates. It grows downward into the soil, anchoring the seedling.
What three things are necessary for germination to begin? ›
Seeds remain dormant or inactive until conditions are right for germination. All seeds need water, oxygen, and proper temperature in order to germinate.
The radicle is the first part of a seedling (a growing plant embryo) to emerge from the seed during the process of germination. The radicle is the embryonic root of the plant, and grows downward in the soil (the shoot emerges from the plumule). Q. Radicle emerges out of the seed earlier than plumule.
Why are my seeds not germinating after 7 days? ›
Too much or too little water is the most likely reason for seeds not germinating. With too little or no water, seeds remain dormant. With too much water, seeds become susceptible to rot or infection from soil-borne fungi (also referred to as "dampening off").
Why are none of my seeds germinating? ›
Mostly, extreme temperature and lack of consistent moisture are likely causes of seeds not sprouting or seedlings withering. Here is a list of factors that affect seed germination and the condition can be fairly avoided by taking care of these small things.
Can I just scatter zinnia seeds? ›
Even the planting process is easy. I put down fresh mulch, then sprinkle the Zinnia seeds where I want them. I don't worry about spacing or anything, I just scatter them. When the seeds are down, I sprinkle just a little more mulch over the area for cover.
What is the germination of seeds called answer? ›
Germination of seeds is known as sprouting.
What is germination one word? ›
Definitions of germination. the process whereby seeds or spores sprout and begin to grow. synonyms: sprouting. type of: development, growing, growth, maturation, ontogenesis, ontogeny.
What is an example of germination? ›
A common example of seed germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm.
What happens during germination responses? ›
In the process of seed germination, water is absorbed by the embryo, which results in the rehydration and expansion of the cells. Shortly after the beginning of water uptake, or imbibition, the rate of respiration increases, and various metabolic processes, suspended or much reduced during dormancy, resume.
