Leaf Anatomy

Venation is classified by:

"order" starting with primary and continuing through fifth order for the finest gauge veins.

The process by which deciduous trees shed their leaves annually.

Abscisission.

The above is a cross section of a hydrophytic (found in wet habitats) leaf.

Hydrophytic plants normally have thin cuticles because water loss is usually not a problem. They usually have plenty of aerenchyma (the spongy mesophyll layer). Because the abaxial (lower) epidermis of the leaf is in contact with water, the stomata occur only on the adaxial (upper) epidermis. It has a dense palisade mesophyll layer.

Cells that surround the stomata and have a different morphology than the regular epidermal cells.

Subsidiary cells

The network for feeding an immature leaf or for collecting photosynthesis products from a mature leaf.

Vascular tissue

The separation event of abscission occurs when cells walls are degraded by

enzymes

Describe the anatomy of Tmesipteris leaves, a pendulous fern closely related to Psilotum that naturally occurs in parts of Australia, New Zealand, and New Caledonia, and some other South Pacific islands.

-Mesophyll is not differentiated into palisade vs spongy -Only 3-4 layers of cells present w/ sm. intercellular spaces -Epidermal cells have thick external wall -Chloroplasts in the mesophyll cells - Guard cells on both surfaces -One single, very simple vascular bundle

Characterize the mesophyll of conifers.

-Plicate mesophyll-not differentiated into palisade vs. spongy -Resin ducts present -Single vascular bundle in the center -Xylem located adaxially(above) -Phloem located abaxially(below) -Vascular tissue surrounded by transfusion tissue

Zamia floridana (coontie) is a cycad with compound leaves. Describe the hypodermal layer, the mesophyll, venation, the type of xylem and phloem cells, vascular bundle, leaflet margins and its significance.

-hypodermal fibers forming a solid layer are a layer of cells beneath the epidermis that are distinct from the underlying ground tissue -mesophyll is differentiated into palisade and spongy -parallel venation -the vascular bundle has extensions in the form of fibers that connect the bundle with the upper & lower epidermis -xylem contains tracheids (no vessels) -phloem no companion cells -each vascular bundle has extensions i the for of fibers that connect the bundle with the upper and lower epidermis -leaflet margins are slightly rolled down

One or more layers of cells that surround a vascular bundle in a leaf composed of parenchyma and sclerenchyma.

A bundle sheath.

What is a cleared leaf?

A modern leaf that have been bleached and stained to make their venation patterns more visible.

Draw and describe an actinocytic stomata complex.

Actinocytic- Several subsidiary cells that radiate from the center of the stoma form a ring.

Draw and describe an amphiparacytic stomata complex.

Amphiparacytic- Two subsidiary cells on each side of the guard cells oriented parallel to the stoma.

Draw and describe an anisocytic stomata complex.

Anisocytic-Guard cells surrounded by three subsidiary cells of unequal size.

Draw and describe an anomocytic stomata complex.

Anomocytic- no subsidiary cells. Cells surrounding guard cells are not different than other epidermal cells.

Many grasses have these enlarged epidermal cells in their adaxial (upper) surface. When the plant becomes dehydrated, these cells lose water and cause the leaf to become rolled inward. If the plant becomes hydrated again, these cells gain water, and the leaf expands.

Bulliform cells

How is the type of stomata complex classified?

By the arrangement of guard cells and subsidiary cells.

Agave, a xerophyte, uses this type of photosynthetic pathway.

CAM Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2).

Draw and describe an cyclocytic stomata complex.

Cyclocytic- Several unevenly sized subsidiary cells that radiate from the center of the stoma form a ring.

Draw and describe an diacytic stomata complex.

Diacytic- One subsidiary cell on each side of the guard cells oriented perpendicular to the stoma.

The outermost single cell layer of the leaf.

Epidermis

Chloroplasts are only present in the mesophyll cells closer to the surface in xerophytic leaves, while the internal mesophyll cells are enlarged for this reason.

For water storage

Plants in arid environments are particularly vulnerable to _____ that seek water in addition to nutrients. Thus, many xerophytes develop _____ or other forms of protection.

Herbivores/spines

Podocarpus is a gymnosperm, but its leaves are flat. Describe the cuticle, epidermal layers, mesophyll, vascular bundles, and stomata.

Hint: Look at this photograph of Podocarpus and see answers below.

A layer of cells (of any type) located between the epidermis and the mesophyll usually lacking chloroplasts.

Hypodermis

This layer may appear below the epidermis and act to strengthen the leaf structure.

Hypodermis

What is the significance of a leaf rolling inward?

It reduces the area exposed to the sun.

The adaptation of slightly rolled down leaf margins is common in many plant species. Why might this adaptation have developed?

It seems to be an adaptation for preventing raindrops from touching the abaxial (lower) leaf surface, where they would obstruct the stomata and impede gas exchange.

Describe the mesophyll.

Just below the epidermis Composed of parenchyma Filled with chloroplasts Photosynthesis occurs here Arranged to maximize light efficiency and CO2 diffusion Arrangement species & environmental condition dependent Two types: Palisade mesophyll & Spongy mesophyll

The most important photosynthetic structure in the plant body.

Leaves

These can usually be found on one side of each vascular bundle in xerophytes.

Massive fiber caps

Describe the differences between the arrangement of stomatal complexes in monocots and gymnosperms vs. what is found in the leaves of "dicots."

Monocots and gymnosperms (This does not always apply to monocots)-The stomata are often in rows parallel to the long axis of the leaf. In "dicots" stomata are most often scattered throughout the epidermis.

_______ vascular elements are common in xerophytes.

Narrow

Draw and describe C4 anatomy-vein spacing - # of photosynthetic cell types - chloroplast types

Narrow vein spacing Two photosynthetic cell types Dimorphic chloroplasts

PIne leaves are long and narrow, and commonly called:

Needles

In the mesophyll of the leaf, a region in which the chlorenchyma cells are elongate and are arranged parallel to each other, perpendicular to the epidermis; usually located in the upper half of the leaf.

Palisade parenchyma

Draw and describe an paracytic stomata complex.

Paracytic- One subsidiary cell on each side of the guard cells oriented parallel to the stoma.

Monocots normally have this type of leaf venation.

Parallel

Draw and describe an paratetracytic stomata complex.

Paratetracytic- Guard cells surrounded by four subsidiary cells of unequal size.

Draw and describe an pericytic stomata complex.

Pericytic- Guard cells surrounded by one subsidiary cell.

Podocarpus is a gymnosperm, but its leaves are flat. Describe the cuticle, epidermal layers, mesophyll, vascular bundles, transfusion tissue, and stomata.

Podocarpus: -Thick cuticle covering the epidermis -Layer of subepidermal fibers -palisade and spongy mesophyll Central vascular bundle (midvein) -Xylem -Phloem -Transfusion tissue around the vascular bundle Transfusion tissue -tracheids -parenchyma cells (Secondary vascular bundles, secondary veins, are present with their tracheid visible in longitudinal view almost perpendicular to the midvein Stomata -somewhat sunken -mostly on the abaxial (lower) epidermis

Draw and describe an polocytic stomata complex.

Polocytic- One subsidiary cell that encloses one end of the guard cells.

Zamia floridana (coontie) is a cycad with compound leaves. Describe the hypodermal layer, the mesophyll, venation, the type of xylem and phloem cells, vascular bundle, leaflet margins and its significance.

See answers provided below .

Zamia floridana (coontie) is a cycad with compound leaves. Describe the hypodermal layer, the mesophyll, venation, the type of xylem and phloem cells, vascular bundle, leaflet margins and its significance.

See photo below for leaflet margins and venation.

A portion of the leaf mesophyll characterized by the cells having little contact among themselves; the apoplast constitutes as much as one-half or more of the volume of the tissue.

Spongy mesophyll

What is the function of bundle extensions?

The bundle extensions provide support and mechanical protection to the vascular tissues in the bundle.

The epidermis is covered with what and why?

The cuticle or wax to prevent water loss.

Answers to Kalanchoe question above.

The epidermal cells do not appear to have pigments. It contains chloroplasts within the guard cells. The arrangement of the subsidiary cells is cyclocytic.

Answers to Tradescantia question above.

The epidermal cells do not appear to have pigments. It contains chloroplasts within the guard cells. The arrangement of the subsidiary cells is paratetracytic.

Elodea is an extreme hydrophyte, an aquatic angiosperm that grows completely submerged. Give a brief description of the layers.

The leaf is extremely thin (only 1-2 layers) and lacks an epidermis and does not have a cuticle.

The above is a cross section of a mesophytic ("normal" habitat) leaf.

There are 2-3 layers of palisade mesophyll cells, and the number of layers of spongy mesophyll cells is more difficult to determine.

Characterize the stomata on conifer leaves.

They occur on all sides of the leaf, but are sunken.

The epidermis and hypodermis act in concert to perform these functions.

They protect the inside tissue from physical damage and can occasionally absorb nutrients.

Characterize the epidermis of conifer leaves.

Thick with a heavy cuticle.

What is the function of the aerenchyma in hydrophytic leaves?

To transport oxygen to the air spaces in the roots from plant parts above the water surface, and they give the plant buoyancy to enable the leaves to gather enough light to photosynthesize.

What does transfusion tissue in a gymnosperm contain?

Tracheid and parenchya cells

These are less specialized than the vessel members and are the only type of water-conducting cells in most gymnosperms and seedless vascular plants. Water moving from one to another must pass through a thin modified primary cell wall known as the pit membrane, which serves to prevent the passage of damaging air bubbles.

Tracheids

What are the circled structures on this Coleus leaf and what type are they?

Trichomes. Multicellular uniseriate.

Why doesn't Elodea have a cuticle?

Water loss is not an issue.

Draw and describe C3 anatomy-vein spacing - # of photosynthetic cell types - chloroplast types

Wide vein spacing Single photosynthetic cell type Single chloroplast type

The above is a cross section of a xerophytic (found in dry habitats) leaf.

Xerophytic leaves typically have a thick cuticle to minimize water loss through transpiration and enlarged parenchyma cells for water storage that lack chloroplasts (water cells). Leaves are often small and compact (high ratio of volume to surface area) and have a thick mesophyll. Sometimes water cells form a hypodermis. Abundant fibers surround the vascular bundles to protect them from herbivores.

The cells near the base of the petiole change in a region known as the:

abscission zone

What surrounds the vascular bundle and transfusion tissue in a gymnosperm?

cylindrical endodermis, which has Casparian strips during the early stages of development of the pine needle.

The protective layer includes deposits of protective substances to prevent the introduction of parasites until the __________ can grow over that spot.

periderm

The abscission zone consists of:

the abscission (or separation zone) and the protective layer.