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 Germination Biology 104 Authors: Lucy Morgan Becka Carrie.

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1  Germination Biology 104 Authors: Lucy Morgan Becka Carrie

2 What is germination?  Germinate- To begin to grow or develop, to develop into a plant or individual as a seed spore or bulb. To put forth shoots; sprout; pullulate.  Pullulate- to send forth sprouts, buds or to sprout.

3 What conditions required for germination? Period of Dormancy Germination begins with imbibition, as the seed absorbs water to make the seed coat permeable. Imbibition is when a seed absorbs enough water to soften the seed coat and break dormancy. This allows germination to begin. Seeds need moisture, proper temperature, darkness and light. Biology: Life on Earth

4 Example: Arabidopsis Germination Requirements  Arabidopsis plants are winter annuals, which means the seeds germinate in fall, survive winter, flower in spring and seeds are dormant in the summer.  Dormancy can be broken by a imbibing seeds at 4 degrees Celsius for 2-4 days.  For germination seeds must have a high humidity, about 25-75%  The photoperiod must also be around 8 hrs of light and 16 hrs of dark Arabidopsis: A Laboratory Manuel

5 Importance of Dormancy Period  Often, seeds require a preceding period of dormancy.  Dormant- inactive, latent, but capable of being activated, suspension of metabolic process.  Seeds of many temperature-climate angiosperms will germinate only after a prolonged period of cold. An inhibitor within the seed usually abscisic acid, or ABA, is gradually broken down at a low temperature until finally there is not enough to prevent germination when other conditions become favorable.  This is an obvious mechanism of survival, preventing seeds from germinating during an unseasonably warm spell in the autumn.  ABA- plant hormone that maintains a water balance of plants, prevents seed embryos from germinating, induces the dormancy of seeds. Biology: Life on Earth

6 Why don’t all seeds germinate at the same rate?  Seeds require different ideal germination conditions  Time delays between ideal conditions cause variations in germination rates.  Growing days- a certain number of days when growing conditions are favorable.  If the plant does not get enough growing days it will die before flowering.

7 Consequences of germinating too soon or too late.  If a seed germinates too early it might exhaust its food reserves before its roots are fully developed to support the plant.  Environmental conditions that are suitable for seedling growth might not coincide with seed maturity. Example: if a seed germinates in late summer then it will have to face the cold of winter. Biology: Life on Earth

8 Common Causes of Germination Failure  Soil: being too heavy, wet or cold  Drying out: slow seeds not having long enough to come up. Reasons of burning out are due to placing seeds in full sun, or outdoor conditions too quickly. Pests eating the seeds  Dormant seeds not receiving proper pre-treatment, poor air circulation, and over-watering.

9 Why do germinated seeds produce roots first? Why not leaves first?  The part of the plant that emerges from the seed first is the embryonic or primary root. This allows the seedling to become anchored in the ground, and start absorbing water.  After the roots absorb water, the embryonic shoot emerges from the seed.  The shoot then grows and begins to photosynthesize Biology: Life on Earth

10 Where does the energy and material come from to create the growing root?  The seed has energy and raw material stored in the cotyledons or the endosperm  This energy supports the growth of the plant until it is able to photosynthesize. Biology: Life on Earth

11 Sources:    Biology: Life on Earth   Arabidopsis: A Laboratory Manuel

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