Plant resources for teaching & learning

Vocabulary plants

Stem is the main part or stalk of a plant or shrub, typically above ground but occasionally underground. It can also refer to the stalks that support a fruit, flower, or leaf, and attach it to a larger branch, twig, or stalk.

Hypogeal - is a plant that when the seed germinates the cotyledons remain below ground. Example is the Peas. Advamtages protected from frost, animals can't graze on it, usually has more nutrients so will grow in less fertile soils and need less sunlight. Diseadvantages is grows slower at first and can be infected with diseases.

Epigeal - is a plant that when the seed germinates the cotyledons and seed leaves, grow above ground, throw off the seed coat or shell, and begin photosynthesis. Example is the Beans. Advantage it starts photosynthesis sooner thant hypogeal seeds so can grow in less fertile soil and more dependant of sunlight.

Root is the part of a plant which attaches it to the ground or to a support, typically underground, moves water and nourishment to the rest of the plant with numerous branches and fiber. Roots can be the persistent underground part of a plant, especially when fleshy and enlarged and used as a vegetable. Examples potato, turnip, carrot.

Flower

Stem - holds up the flower

Sepals - the outermost ring of flower parts. It protect the bud; usually green but can be the same color as the petals.

Petals - Often in a ring of flower parts. They attract pollinators, often giving them a landing place; often colorful, may also make scent to attract pollinators.

Stamens - Often inside the ring of flower parts. Produce and hold the pollen. Made of

• Filament (the stem),
• Anther (the canoe-shaped structure at the tip that holds the pollen, and
• Pollen, the tiny grains on the anthers.

Pistil(s) - At center of the flower, may be one or more. They act as catcher for pollen, container for the ovule(s). Pistil is made up of

• Ovary - A vase-like structure
• Style - the stem-like structure
• Stigma is at the top of the style and has a sticky substance. to catch and hold the pollen.
• Ovules (found inside the ovary, often look like tiny white beads) – become the seeds when fertilized by pollen that has landed on the stigma.

Nectar - Is the sweet reward for pollinators. It is located in the nectaries that can be located:

• At the base of the Stamen, the male pollen-producing stalks.
• Base of the Ovary. At the very bottom of the female central structure.
• Petal Spurs. Inside long, hollow tubes or pockets formed by the petals.
• Extrafloral Nectaries: Are outside the flower entirely, such as on stems or leaves, to attract insects like ants.

Fruit - The seed-bearing structure of a plant. The sweet and fleshy product of a plant that contains seeds and can be eaten as food. Fruit types.

Seeds

Seed Coat (Testa) is the hard or tough outer protective layer of a seed.

Hilum A small scar on the seed coat where it was attached to the ovary wall or stalk

Micropyle is the tiny pore in the seed coat that lets water in for the seed to germinate.

Embryo is a small, undeveloped plant, that can include the

• Radicle is the embryonic root that emerges first during germination.
• Plumule is the embryonic shoot/tip that develops into leaves.
• Hypocotyl is the portion of the stem below the cotyledons.
• Epicotyl is the portion of the stem above the cotyledons.

Cotyledons are the seed leaves that either store or absorb food for the embryo (two in dicots, one or scutellum in monocots).

Endosperm is the part of a seed that is a food store for the developing plant embryo, usually containing starch with protein and other nutrient rich substances. It is often triploid storage tissue that feeds the embryo (present in many seeds at maturity or absorbed into the cotyledons).

Germination is the process that starts the development of a seed or spore into a plant after a period of being inactive. This activation is usually caused by water hydration

Germination

Germination is the process that starts the development of a seed or spore into a plant after a period of being inactive. This activation is usually caused by water hydration.

The information in this box is for those intereseted in a more detailed description of germination and the beginning of plant growth.

Seed hydration and metabolic activation (the wake-up call)

Before growth can begin, a dormant seed must activate its metabolic machinery through a sequence driven by hydration, hormones, and enzymes.

1. Imbibition (The Physical Trigger)

• A dry seed rapidly absorbs water through a tiny pore called the micropyle.
• This physical influx causes cells to become saturated, the seed to swell, and the rigid seed coat to crack.
• Hydration reactivates cellular structures suspended during dormancy.

2. Hormonal Signaling

• Once hydrated, the embryo cells synthesize and release the hormone Gibberellic Acid (GA).
• GA migrates out of the embryo into the aleurone layer, the protein-rich tissue jacket surrounding the central food storage (endosperm).

3. The Molecular Unlock

• In dormant seeds, DELLA proteins sit on top of the DNA and physically block the DNA genes responsible for growth and enzyme production.
• When gibberellin arrives, the GA binds to the internal cellular receptor GID1.
• This GA-GID1 complex attacks the DELLA proteins and completely destroys them.
• With DELLA gone it allows the transcription factors GAMyb to begin transcribing genes for hydrolytic enzymes.

4. Enzyme Action and Energy Production

• With the genes unlocked the aleurone cells manufacture and secrete the enzyme Alpha-Amylase.
• Alpha-Amylase breaks down the endosperm's insoluble starch reserves into soluble sugars (maltose and glucose).
• The embryo absorbs these simple sugars, utilizing them in aerobic respiration to generate a massive burst of cellular energy (ATP).
• This ATP provides the necessary fuel to drive the seeds growth, beggining with structural cell elongation.

Fuel & organization for growth - embryo polarity (the apical-basil axis)

With fuel provided by the metabolic activation, it can be is used to drive highly organized growth. Without structural coordination, the cell mass would expand into a chaotic clump.

For a seed to germinate and becomea a functioning plant, it is necessary that top and bottom (polarity) is established in the embryo so the seed can position the root and shoot accurately.

This polarity can be thought of as a biological axis from top to bottom (apical-basal ) or near and far (proximal-distal) axis within the embryo, which is created during the development of the embryo. This axis will determine exactly where the root and shoot will form and their directions of growth.

In the embryo, the proximal zone represents the central region of the axis, or the point where the root and shoot meet (between the hypocotyl/embryonic stem). The distal ends of the axis (point out) toward the extreme tips: the radicle (embryonic root tip) at the far bottom end, and the plumule/epicotyl (embryonic shoot tip) at the other far top end.

This polarity is controlled by the plant hormone auxin with specialized PIN proteins (cellar pumps) that transport auxin directionally, based on the vaarying amount of auxin along the axis, with the most at the distal tip of the radicle.

When a seed absorbs water and begins germination, polarity directs cell expansion. Cellular elongation in the central proximal hypocotyl zone (the middle), physically pushes the distal radicle tip (the far bottom tip) out through the seed coat emerging as the primary root.

Without internal distal-proximal cellular polarity, a seed would grow into an unorganized mass of cells rather than sending roots down and shoots up.

Up and down with environmental guidance

Once the seedling breaks free of the seed coat, it relies on environmental cues to guide its directional growth via a single hormone with dual capabilities.

After the distal radicle tip emerges from the seed coat, the internal proximal-distal axis interacts with external gravity to guide the seedling.

A process called gravitropism (or geotropism). The internal proximal-distal axis acts as a roadmap, but gravity tells the seedling which way is up and down.

How the distal root senses gravity.

At the very furthest edge of the distal root tip is a protective structure called the root cap. Inside its central cells (the columella), are heavy cellular structures called statoliths (dense starch granules). Because they are heavy, they sink to the bottom of the cell, like plumb bobs, they signal to the cell, up and down.

If the root is sideways in the dirt, the sinking statoliths will cause PIN to redistribute auxin to the lower side of the root. Because high concentrations of auxin actively slow cell elongation in root tissue, the top side of the root grows faster than the bottom side. This differential growth causes the root to curve downward into the soil (positive gravitropism). Likewise, the proximal hypocotyl responds oppositely, elongating upward away from gravity (negative gravitropism) to push the shoot upward.

How the shoot senses light.

Once the shoot emerges into the open air, the seedling transitions from gravity-guided growth to light-guided growth (phototropism).

Blue-light receptors called phototropins at the distal shoot tip sense the direction of incoming sunlight. This triggers PIN proteins to laterally redistribute auxin to the shaded side of the stem.

Because auxin stimulates cell elongation in shoots, the cells on the shaded side grow faster than those on the lit side. This differential growth rate forces the shoot to bend toward the light source, optimizing the young plant's capacity for photosynthesis.