AGRONOMY ENGINEERING

ENGLISH I

LCDA. ARACELIS TORRES

INTRODUCTION

Reproductive structure in plants that consists of a plant embryo, usually

accompanied by a supply of food (endosperm, which is produced during

fertilization) and enclosed in a protective coat. Seed embryos contain one

or more cotyledons. In typical flowering plants, seed production follows

pollination and fertilization. As seeds mature, the ovary that enclosed the

ovules develops into a fruit containing the seeds. Most seeds are small,

weighing less than a gram; the smallest contain no food reserve. At the

opposite extreme, the seed of the double coconut palm may weigh up to

about 60 lb. (27 kg). Seeds are highly adapted to transportation by

animals, wind, and water. When circumstances are favorable, water and

oxygen penetrate the seed coat, and the new plant begins to grow (see

germination). The longevity of seeds varies widely: some remain viable

for only about a week; others have been known to germinate after

hundreds or even thousands of years.

DEFINITION

A seed is a small embryonic plant enclosed in a covering called the seed

coat, usually with some stored food. It is the product of the ripened ovule

of gymnosperm and angiosperm plants which occurs after fertilization

and some growth within the mother plant. The formation of the seed

completes the process of reproduction in seed plants (started with the

development of flowers and pollination), with the embryo developed

from the zygote and the seed coat from the integuments of the ovule.

Seeds have been an important development in the reproduction and

spread of flowering plants, relative to more primitive plants such as

mosses, ferns and liverworts, which do not have seeds and use other

means to propagate themselves. This can be seen by the success of seed

plants (both gymnosperms and angiosperms) in dominating biological

niches on land, from forests to grasslands both in hot and cold climates.

The term "seed" also has a general meaning that antedates the above —

anything that can be sown, e.g. "seed" potatoes, "seeds" of corn or

sunflower "seeds". In the case of sunflower and corn "seeds", what is

sown is the seed enclosed in a shell or husk, whereas the potato is a tuber.

Ontogeny of the Seed-Coat

The bitegmic, anatropous ovule develops into an exalbuminous, partially

pachychalazal and endotegmic seed. In the mature seed-coat the

extensive chalazae with associated tanniniferous hypostases sensu lato

manifests externally as a characteristic brown patch. The walls of the

cells of the hypostases are impregnated with callose and lipidic

substances, which most probably represent cutin. Ultimately the outer

integument and outer parts of the inner integument are more or less

squashed. However, the cell walls of the inner epidermis of the inner

integument show distinct secondary thickening and lignifications. The

pachychalazal seed with undifferentiated seed-coat characterizes not only

a number of the genera of the tribe Anacardieae, but also occurs in

Heeria of the tribe Rhoeae. A number of genera of the tribe Spondiadeae

have a partially pachychalazal seed. The seed-coat of the latter shows

varying degrees of traces of an exo-, meso- and/or endotestal

lignifications. The seed of certain genera of the Rhoeae is partially

pachychalazal and endotegmic, or probably only endotegmic.

Origin

The seed is a reproductive unit complex, characteristic of higher vascular

plants, which is formed from the egg plant, usually after fertilization. It is

found in flowering plants (angiosperms) and gymnosperms. In

angiosperms the eggs develop within an ovary, while in gymnosperms,

the structure that contains them is very different, as not a real flower, but

the structure of the seeds of these plants is basically similar to that of

flowering plants.

Function

Seeds serve several functions for the plants that produce them. Key

among these functions is nourishment of the embryo, dispersal to a new

location, and dormancy during unfavorable conditions. Seeds

fundamentally are a means of reproduction and most seeds are the

product of sexual reproduction which produces a remixing of genetic

material and phenotype variability that natural selection acts on.

DOUBLE FERTILIZATION

Double fertilization is a complex fertilization mechanism that has

evolved in flowering plants (angiosperms). This process involves the

joining of a female gametophyte (mega gametophyte, also called the

embryo sac) with two male gametes (sperm). It begins when a pollen

grain adheres to the stigma of the carpel, the female reproductive

structure of a flower. The pollen grain then takes in moisture and begins

to germinate, forming a pollen tube that extends down toward

the ovary through the style. The tip of the pollen tube then enters the

ovary and penetrates through the micropyle opening in the ovule. The

pollen tube proceeds to release the two sperm in the mega gametophyte.

STRUCTURE OF EXTERNAL AND INTERNALOF THE SEED

OF MONOCOTYLEDONS AND DICOTYLEDONS

A seed consists of three parts: a Dormant Embryo, a Storage Tissue, and

a Seed Coat. Not every seed that has evolved on this planet has precisely

the same structure. In some seeds, the endosperm is retained as the

storage tissue. In other seeds, the endosperm is more or less used up to

put storage chemicals into the embryo itself (commonly in the

cotyledons). Below is a diagram of two hypothetical seeds. The upper

seed shows a dicot that lacks endosperm; its storage material (blue) is

held in the cotyledons, the lower seed shows a monocot that has a well-

developed endosperm (also blue). Both of these examples qualify as true

seeds because they possess all three parts needed to make a true seed.

Below is a photomicrograph of a longitudinal section of a Capsella seed.

The seed coat is the three-layered outer covering. The outermost and

innermost layers of the seed coat pick up a red dye used in the

preparation of this sample. That dye is preferentially held by parts of the

specimen that have waxy or brittle biomolecules. Cutin, sabering, lignin

are three components of plant cells that pick up the red dye. This leads us

to the idea that the integument has a waterproofing (cutin/sobering)

function and also possibly a mechanical strengthening (lignin) function

that could impede herbivore.

Looking toward the inside of the seed coat, there is a bent embryo (dark

looking) surrounded by some loose and light

colored cells of the remaining endosperm?

Indeed the paucity of endosperm leads us to the

conclusion that much of the storage material

has been moved to the embryo itself...perhaps

much of that in the cotyledons. However, this

seed is clearly somewhere between the two

extremes diagrammed above.

The embryo has an axis (on the left) with a

downward-pointing radicle including a root

apex. The radicle ultimately penetrates the seed

coat in seed germination, branches profusely,

and becomes the primary root system. Toward the top of the embryonic

axis, the radicle becomes hypocotyl...transitioning from root-type

anatomy into stem-type anatomy as we shall see later. In seeds with

hypogenous germination, this hypocotyl is too short and does not grow

above the soil. In species with epigeous germination, the hypocotyl

elongates rapidly, lifting the cotyledon(s) out of the soil and into the air.

The axis has two appendages, the cotyledons; as there are two

cotyledons, Capsella is a dicotyledonous plant. There are two classes of

flowering plants, the dicots and the monocots, and they are distinguished

(in part) on the basis of the number of cotyledons found on their dormant

embryos. The part of the axis where the cotyledons attach is called a

node because this zone of the axis does not elongate. At the extreme top

of the axis is a shoot apex; after germination this shoot apex will

elongate, and make appendages to produce the collection of stems and

leaves that constitute the plant shoot.

MORPHOLOGICAL DIFFERENCES BETWEEN SEEDS OF

ANGIOSPERMSPES AND GYMNOSPERMS

Gymnosperms

A gymnosperm (Greek for "naked seed") is a vascular plant that produces

seeds that are not protected by fruit but are hidden in a woody cone. They

do not have flowers, but most retain their leaves year round.

Gymnosperms include over 600 species in four divisions: Conifers,

Cycads, Ginkgoes, and Gnetophytes. Most of today's gymnosperms

belong to the conifer division. Gymnosperms are found in most of the

world's regions and take most of the credit for timber and paper products.

Angiosperms

Angiosperms are vascular plants that produce flowers and fruit with one

or more seeds. Angiosperms make up two classes: monocotyledonous

and dicotyledonous plants. Angiosperms make up more than 80% of all

plant species, ranging from roses to palm trees.

Gymnosperm - 'naked seed'

The endosperm is (n haploid)

Reproduction is achieved through male and female cones

Mainly represented by tree species

Phylem coniferophyta

Phylem Gnetophytes

Phylem Cycadophyta

Phylem Ginkgophyta

Angiosperm - flowering plant

The endosperm is (3n triploid)

Male pollen and female ovules are produced

Fruits and flowers

Phylem anthophyta

Read more:

http://wiki.answers.com/Q/What_is_the_difference_between_angiosperm

s_and_gymnosperms#ixzz21Mg5yjuo

TYPES AND MODIFICATION OF THE SEEDS

We have seen the basic features that are common to most types of seeds.

However, different plant species have their own modifications. In stone

fruits, for example, the seed is surrounded by a hardened fruit layer,

known as the endocarp. More broadly, the seeds of angiosperm plants

differ from those produced by gymnosperm plants. ‘Angiosperm’

literally means ‘enclosed seed’, and gymnosperm ‘naked seed’.

Angiosperm seeds are enclosed by a hard or fleshy fruit, whereas

gymnosperm seeds are usually exposed to the outside world, for example

on the cone of a conifer.

Seeds also vary a lot in size. Orchid seeds look like tiny dust particles,

whereas other seeds are much larger, such as the giant (over 20kg) seeds

produced by the coco of palm tree. As a rule, larger seeds are produced in

smaller quantities, as more energy goes into their production.

ADAPTATION OF THE SEEDS TO SPREAD OR DISPERSION

For plant species to survive, it's critical that its seeds are spread over the

landscape. Otherwise, the seeds would drop in a clump at the base of the

plant. To grow, the seeds would then have to compete with the mature

plant and all the other seeds for water, sunlight and nutrients. To avoid

this fate, plants have developed seed adaptations.

Wind

Some plants depend on the wind to spread their

seeds. In these cases, the seeds are often

attached to fine, fluffy threads that catch the

breeze, enabling them to float to a new patch of

land. Examples of plants with these seed

adaptation are dandelions and cattails. Some

tree seeds, such as those from maples and ashes,

also depend on the wind. These seeds will often have a propeller shape.

Water

Plants also use water to transport their seeds to new

locations. Coconuts -- which are a seed -- are an

example. The thick shells keep the salt water out

and the buoyant coconuts can float on the sea for

hundreds of miles without being damaged.

Animals

Animals are another way seeds are dispersed.

Plants that use this method have seeds that attract

animals, such as berries. After the seeds have

passed through an animal's digestive tract, they

can take root at the site of the animal dropping

containing the seed. Other seeds are adapted to

stick to animal fur. Such seeds, often known to

humans as burrs, eventually fall off and take root.

Germination

Some seeds have extra adaptations that help

control when the seeds are germinated no matter

how the seeds were dispersed. For example,

some seeds will not germinate -- or begin to

grow -- until after a fire. Those seeds depend on

the heat to crack the shell or open the pine cone,

allowing the seeds to drop to the ground. Other

seeds depend on the wind to scratch their casings, allowing water to seep

into the seed and begin the germination process.

Read more: What Are Three Seed Adaptations? | eHow.com

http://www.ehow.com/info_8494069_three-seed

adaptations.html#ixzz21MtpS4pH

http://www.ehow.com/info_8494069_three-seed-

adaptations.html#ixzz21MuQOkyY

http://www.ehow.com/info_8494069_three-seed-

adaptations.html#ixzz21MvZQlni

http://www.exploringnature.org/db/detail.php?dbID=45&detID=2792

IMPORTANT AGRICULTURAL SEED LEVEL

Seed production is an essential

process in agriculture. Thanks to it,

peasants have been domesticated plant

species we consume today, creating a

huge variety within each

species to be adapted to the different

environmental conditions and cultural

needs. This process has continued in

some regions for at least ten

thousand years. From the twentieth century, there is

a current tech industrial production and seed varieties designed to

create work with chemicals and mass

production conditions.

At the beginning of XXI century, this

trend has shifted in many regions of

the planet to the traditional production of

seeds. The industry argues that the industrial

seeds are more productive and free

of pests. Peasant movements like

Via Campesina argue that such

production depends on the application of

agrochemicals and overall energy subsidy on

oil and traditional seeds that are more robust and suitable

for local food. The marketing of seed industry is one of the causes of

genetic erosion.

BIBLIOGRAPHY

PRISCILA ANDRESSA CORTEZ1 and SANDRA MARIA

CARMELLO-GUERREIRO 1,2(received: November 10, 2006;

accepted: January 17, 2008) Revista Brasil. Bot., V.31, n.1, p.71-79, jan.-

mar. 2008 Ontogeny and structure of the pericarp and the seed coat of

Miconia albicans (Sw.) Triana (Melastomataceae) from “cerrado”, Brazil

http://www.scielo.br/pdf/rbb/v31n1/a08v31n1.pdf

Website Gerhard Leubner Lab Royal Holloway, University of

London 2005. The Seed Biology Place

http://www.seedbiology.de/structure.asp

The World of the Plants

http://www.botanical-online.com/llavorangles.htm

Catherine Steinbauer, eHow Contributor What Are Three Seed

Adaptations?

http://www.ehow.com/info_8494069_three-seed-adaptations.html

Amsel, Sheri. “Adaptations.” Pollination and Seed Dispersal

Adaptations. Exploring Nature Educational Resource. © 2005 - 2012.

July 22, 2012.

http://exploringnature.org/db/detail.php?dbID=45&detID=2792