Lecture 20: Seeds & Seedlings

List 3 reasons why seeds are important.

dispersal, protection for embryo, food for embryo

seeds can have food storage tissue called ______, which is rich in _____, ____, and _______

endosperm, lipids, proteins, starch

the embryonic root is called the _____

radicle

the embryonic stem is called the ______

hypocotyl

the embryonic leaves are called the ________

cotyledons

the tip of the embryonic shoot is called the _______

plumule

When the embryo inside a seed dehydrates, it becomes _____.

For the seed to germinate, it must ______. It also needs ____, and correct _____

dormant, hydrate, oxygen, temperature

When a seed doesnt germinate even when all conditions are met, it is called ______

dormancy

What are 2 ways dormancy can be good for a seed.

can help seed travel farther, or wait for good conditions

if a new seed doesnt germinate even when conditions are good, its called ______

primary dormancy

if a seed moves past primary dormancy but still wont germinate because conditions are bad, its called ______

secondaey dormancy

Within ______ dormancy, there are ______ and _____ dormancy.

secondary, exogenous, endogenous

exogenous dormancy is ____-imposed

coat

list 3 examples of exogenous dormancy

water impermeability, gas exchange interference, mechanical contstraint

endogenous dormancy is ___-imposed

hormonal

list 3 examples of endogenous dormancy

ratio of ABA to GA, lack of sucrose, arrested embryogenesis

when low temps can trigger dormancy, its called ______, which is most important for species in _____ climates

cold stratification, temperate

when a dormant seed needs a dry period to germinate, its called _______, and is most important for species in ____ climates

after-ripening, tropical

germination begins with ______, and ends with ______

water uptake, root emergence

____ is the single most important resource needed for germination

water

when a dry seed takes up water very quickly, its called _____

imbibition

What are the 3 phases of germination?

imbibition, lag, growth

When water uptake slows down, and metabolic processes restart is the _____ phase

lag

When water uptake resumes and food reserves are mobilized is the ____ phase

growth

Seeds have food stored in _______, but if its small, food will also be in _______

endosperm, cotyledons

In endosperm, starches are stored in ________, oils are stored in ______, and proteins are stored in _______

amyloplasts, oleosomes, vacuoles

Overall, what causes endogenous dormancy?

ABA to GA ratio

In a seed, ABA ______ germination, and GA _____ germination

inhibits, promotes

In a seed, _____ promotes germination, but _____ inhibits germination

GA, ABA

When a seed is young and still developing, its very sensitive to _____, and less sensitive to _____, keeping it from ______

ABA, GA, germinating

As a seed matures, it becomes _____ sensitive to ABA, ____ sensitive to GA, and ____ sensitive to the environment

less, more, more

For a seed to germinate, the _____ must be favorable, and _____ to ____ and ____ must be correct.

environment, sensitivity, ABA, GA

When a seed is germinating, the embryo produces more _____

GA

When a seed is germinating, more GA produces ______ that break down ______

amylases, starch

GIve an example of primary cross regulation in seed germination.

GA is produced to make amylases to mobilize food reserves, after germination ABA stops GAs from making amylases

Give an example of secondary cross regulation.

ethylene influences the production pathway of auxin

Give an example of tertiary cross regulation.

auxin controls cell wall extension, but brassinosteroids control how far the cell walls extend

Which type of cross-regulation is the most common?

secondary

Once a seedling can photosynthesize, has differentiated tissue, and can respond to environment, it is considered to be _____

established

_____ absorb red and far red light, whereas ______ absorb blue light

phytochromes, cryptochromes

_____ interact with GAs to regulate development of seedlings

phytochromes

auxin _____ growth in stems, _____ growth in roots

promotes, inhibits

A plant in the shade will have more _____ light than _____ light

far red, red

A plant in sunlight will have more ____ light then _____ light

red, far red

Far red light makes plants _____ sensitive to gibberellins, which makes the plant ____ and ____

less, tall, skinny

Plants in the shade get tall and skinny because they have more _____ light, which makes them less sensitive to ________

far red, gibberellins

When plants become long and skinny from having more far-red light, its called a _____ response

etoliation

directional growth stimulated by movement is called a ______

tropism

tropisms are caused by ______ growth of the stem or root, _______ growth

asymmetrical, anisotropic

What are the 4 kinds of tropisms?

phototropism, gravitropism, thigmotropism, hydrotropism

Phototropism is caused by _____ sensing light, causing _____ to move to the _____ side of the plant, causing those cells to grow ______

phototropins, auxin, shaded, longer

Gravitropism is caused by movement of ______, causing ____ to be on the ____ side of a stem

statoliths, auxin, lower

In a root tip, thigmotropism is caused by _______ sensing stretching or compression, causing a signal cascade of ____, then _____, which makes ____ accumulate on the _____ side of touch

mechanoreceptors, Ca2+, ROS, auxin, opposite

Hydrotropism is movement in response to ____ water potential _____

soil, gradient

During hydrotropism, water is sensed by a change in root cell _____ potential.

_____ is then produced on the side with ____ water, making _____ accumulate, causing the root to grow towards wet soil

osmotic, ABA, less, cytokinins