PLB 105 Developmental Plant Biology

CONTENTS:

• Study Objective List 3
• Laboratory 3 - Parenchyma, Collenchyma, Sclerenchyma.
• Laboratory 4 - Sclerenchyma and Epidermis.

Parenchyma Read:

Fahn, Chapter 4

Collenchyma Read:

Fahn, Chapter 5

Sclerenchyma Read:

Fahn, Chapter 6

Epidermis Read:

Fahn, Chapter 10

Student will be able to:

1. PARENCHYMA
   1. Recognize, draw, and describe the structures, shapes and functions of the following parenchyma tissues and cell types. Give an example of where each type might be found.
      1. Chlorenchyma

      2. Aerenchyma

      3. Sclerified parenchyma

      4. Branched parenchyma

      5. Folded parenchyma

      6. Storage parenchyma

      7. Parenchyma

   2. List at least 4 substances which are known to be stored in parenchyma cells or their cell walls.

   3. Discuss all of the possible meristematic origins of parenchyma tissues, and describe the difference between parenchyma cells and parenchyma tissues.

   4. Describe the structure and function of "transfer cells." Give several examples of places in the plant body where transfer cells are found.

2. COLLENCHYMA

   1. Recognize, draw and describe the following types of collenchyma:
      1. Angular collenchyma

      2. Lamellar collenchyma

      3. Lacunar collenchyma

   2. Describe the location, meristematic origin and distribution of collenchyma in plant organs. Where in the plant body would you expect to find collenchyma?

   3. Discuss the general characteristics of a collenchyma cell, including its cell contents, structure and function.

3. SCLERENCHYMA

   1. Draw, recognize and describe the following sclereid types and give an example of tissues and/or organs in which they occur.
      1. Brachysclereid

      2. Macrosclereid

      3. Astrosclereid

      4. Osteosclereid

      5. Trichosclereid

      6. Filiform sclereid

   2. Define the concept of an idioblast with regard to sclereid development.

   3. Draw, recognize, and describe the general structure and function of a sclerenchyma fiber. What kind of pits do they usually have?

   4. Differentiate by their structure and distribution each type or classification of fiber:
      1. Xylary fibers

      2. Extra xylary fibers
         • Cortical fiber

         • Phloic fiber (bast fibers)

         • Perivascular fiber

      3. Fiber-tracheids

      4. Libriform fibers

      5. Septate fibers

      6. Gelatinous fibers

   5. Describe the differentiation of fibers, in terms of their coordinated and intrusive growth. (See the diagram at the end of the Objectives)

   6. List at least three plants which produce economically important fibers.

   7. Discuss the developmental reason why the elasticity of fiber walls and the plasticity of collenchyma walls makes them ideally suited for their anatomical roles.

4. EPIDERMIS
   1. Describe two regions of the primary plant body which do not have a differentiated epidermis.

   2. List at least five functions of the epidermis and/or its cells.

   3. Diagram a shoot tip and indicate the position of the three primary meristems. You should also be able to describe the tissues which are derived from each.

   4. Do the same for the root tip.

   5. List at least three substances which may be found in epidermal cell walls in addition to normal wall components.

   6. Draw and describe the structure and possible functions of bulliform cells.

   7. List the possible components of the cuticle, and discuss its formation and functions.

   8. Describe the anatomical and developmental differences between uniseriate and multiseriate epidermis. Define the term - velamen.

   9. Describe the stomatal apparatus in terms of its general structure and function.

   10. Define and identify the following terms which relate to stomatal distribution and other characteristics of the epidermis:
       1. Amphistomatic

       2. Epistomatic

       3. Hypostomatic

       4. Abaxial

       5. Adaxial

   11. Define the following terms which relate to stomatal development:
       1. Mesogenous

       2. Perigenous

       3. Mesoperigenous

   12. Define and recognize the following stomatal apparatus types found in dicotyledonous plants:
       1. Anomocytic

       2. Anisocytic

       3. Diacytic

       4. Paracytic

       5. Actinocytic

       6. Cyclocytic

       7. Tetracytic

   13. Define and recognize the four types of stomatal apparatus found in monocot plants.
       1. Type 1 - 4-6 subsidiary cells. (Radial type)

       2. Type 2 - 4-6 subsidiary cells with end cells rounded. (Round-end type)

       3. Type 3 - parallel sided. (Grass type)

       4. Type 4 - No subsidiary cells. (No-sub type)

   14. Discuss the structure and function of root hairs.

   15. Diagram, describe, and recognize the trichomes listed below. Give examples of locations where they occur in the plant body.
       1. Unicellular and multicellular hairs.

       2. Peltate hairs (scales)

       3. Glands

       4. Branched hairs (stellate and dendroid)

       5. Hooked hairs

       6. Stinging hairs

       7. Papillae

1. Fundamental Tissues

   In this lab you will begin to investigate the first of three tissue systems. The fundamental tissue system is composed of three tissues - parenchyma, collenchyma and sclerenchyma. These tissues are found in the pith and cortex of roots and stems, the mesophyll of leaves, as a component of the fleshy and storage tissues of fruit and seeds, and as a component of complex tissues such as xylem and phloem. Parenchyma, collenchyma and sclerenchyma are referred to as simple tissues when they are found in aggregates (as in the cortex) and they also occur as individual cell types when they occur alone as part of complex tissues like xylem. We will examine all of these instances in the following examples.

   1. PARENCHYMA - Parenchyma cells have a variety of shapes, depending upon their functions. Photosynthesis, storage, support, and aeration are examples of their numerous roles. Parenchyma cells may also redifferentiate to form meristematic cells which further differentiate into other cell types, as in the beginning of secondary growth in stems.
      1. Callus - Parenchyma - Mount a small mass of cells in a drop of water; examine unstained first, and then stain with toluidine blue. Why are these cells interpreted as parenchyma? [Note: Sometimes we skip this example when we fail to find and available tissue cultures.]

      2. Eichhornia - Cut T.S. of petiole. Note the large air spaces in the center and throughout the cortex. This tissue is called aerenchyma. What other name might be applied to the chloroplast-containing parenchyma near the epidermis? Note the large "styloid" crystals which are formed in long, narrow cells.

      3. Sansevieria leaf - Cut T.S. and stain with toluidine blue. Note the parenchyma cells in mesophyll with a reticulate (net-like) pattern of secondary wall material. Do you see any other types of parenchyma cells in these leaves.

      4. Smilax root - Prepared slide of mature root. Note the thick-walled parenchyma in the pith and within the xylem. This is an example of sclerified parenchyma.

      5. Pinus leaf (prepared slide) - Note the parenchyma cells with invaginations or folds around their edges - these are folded parenchyma, characteristic of some gymnosperm species.

      6. DiospyrosPersimmon endosperm (prepared slide) - This is an example of a unique kind of storage parenchyma in that carbohydrate is stored in the cell walls. Note also the plasmodesmata between adjacent cells. These can be seen as faint black lines crossing the yellowish cell walls, by turning the condensor diaphragm down and focusing carefully.

      7. Simmondsia seed coat (prepared slide) - The cotyledon parenchyma cells in this seed store protein (the large bodies you see) and wax.

      8. Juncus stem (fresh material) - Examine dark green, rather stiff stems for branched parenchyma in the pith.

      9. Medicago stem - Cut T.S. and stain with toluidine blue. Examine for chlorenchyma and storage parenchyma with starch grains.

   2. COLLENCHYMA - This is a supporting tissue, distinguishable by its thick primary walls which characteristically stain dark purple with toluidine blue and do not react with phloroglucinol. Collenchyma is usually found distributed around the periphery of young stems and petioles. It is a supporting tissue, because its walls are plastic - they can elongate or stretch without trying to regain their original shape. This allows the plant organ to grow or to move in the wind without damage. There are three common types of collenchyma, illustrated in the examples below. Remember that intergradations between types occur and that the classification is primarily for convenience.
      1. Sambucus - young twigs - Cut T.S. and examine the lamellar collenchyma.

      2. Petasites - petioles - Cut T.S. This is a classic example of lacunar collenchyma. Notice the intercellular spaces or lacuna between the corner thickenings of adjacent cells.

      3. Cucurbita stem - Cut T.S. and note the angular type of collenchyma.

   3. SCLERENCHYMA - This is another supporting and protecting tissue. It differs from collenchyma in the fact that its walls are lignified secondary walls, and therefore they give a characteristic red staining reaction with phloroglucinol. There are two basic types of sclerenchyma: sclereids and fibers.

      Sclereids are primarily protective or supportive. They are found in several shapes and sizes, and comprise such diverse tissues as the seed coat in beans and the stone cells which give pears a gritty texture.

      Sclereids - Stain with phloroglucinol and draw representative examples of each type.

      1. Pyrus (pear) - Scrape some of the flesh, especially from just under the skin, onto a slide and examine. These are brachysclereids, commonly called "stone cells."

      2. Trochodendron leaf clearing - Look for astrosclereids.

      3. Monstera leaf (prepared slide) - Focus up and down to see trichosclereids with very long, thin, tapered "arms."

      4. Simmondsia seed coat (prepared slide) - The seed coat is composed of an outer layer of macrosclereids and an inner layer of crushed cell remnants.

      5. Castalia ordorata (TS) waterlily leaf - Astrosclereids with crystals embedded in cell walls in leaf mesophyll. (Demonstration)

      6. Hakea leaf (prepared slide) - Notice the osteosclereids between the palisade parenchyma cells. Examine the macerated material for individual osteosclereids.

      7. Olea leaf (clearing) - Examine the trichosclereids forming a tangled mass in the leaf mesophyll.

2. CELL AND TISSUE IDENTIFICATION

   Plant anatomists need to be able to identify cell types, tissues and organs from photographs and small tissue fragments. This will be the first exercise in helping you to learn this skill. [NOTE: This exercise is sometimes done in laboratory #4 if we run out of time.]

   This is simply a verbalization of techniques used by some students who have good visual recognition skills. You should be able to follow this strategy to help identify cell types and tissues used in lab quizzes. It isn't quite that simple, however, because you must first have a firm grounding in the theory of plant structure, function and development, and solid knowledge of the possible shapes, colors, sizes and distri-butions of many cell types before you will be able to successfully identify these structures.

   1. The first thing most people do is to evaluate the overall appearance of the photograph. Ask yourself leading questions about the distribution of cells, their general shapes, orientation and planes of view. The pattern of cell distribution should trigger some ideas automatically-e.g. is the photo of primary or secondary growth, is it phloem or xylem, etc.

   2. Next, examine the color and texture of the cells and tissues in the photo. Thick lignified secondary walls usually stain red with safranin; thin primary cell walls usually stain green with fast green, the usual counterstain used with safranin. If toluidine blue is used, the lignified walls stain light blue and the thinner primary walls are darker. Never make a judgment only on the wall color, however, since an atypical stain might be used; color is only one clue.

   3. Now look for other more explicit clues. a. Are the walls thick or thin? b. If they are thick, what kind of pits do they have? Border-ed pits are only found in tracheary elements and fibers, etc. c. Is there any evidence of the cells being alive, before they were killed and fixed? Look for cytoplasmic contents - nuclei, chloroplasts, etc. Living cells could only be parenchyma, collenchyma, etc. d. Look for cell shape clues. Fibers are long, tapered cells; sclerified parenchyma cells are short and stumpy.

   4. It is helpful to take yourself through a dialog when you look at photographs of plant structures. Sort out the clues one at a time, and reason out your response.

   At quiz time, if you can't come to a single answer, then write down a statement to show your reasoning, and we will then rule on your logic. Remember to always be as specific as you can be in coming to a conclusion. Starting with the next lab, we will look at review slides at the end of each laboratory.

1. Sclerenchyma

   Fibers are supportive; they are found in various parts of the plant body, are commonly associated with vascular tissue, but are also found in the cortex and other parts. Sclerenchyma fibers are especially suited to their role for support in older, more mature tissues because, unlike collenchyma, their walls are elastic, they tend to snap back into original shape when bent or stretched. This characteristic makes them unsuitable for young growing tissues, as they would resist growth; in older tissues, however, it is more important to recover from loading stresses.

   1. Phloem fibers
      1. Juglans or Robinia phloem macerations from young twigs -look for individual fibers.
      2. Sansevieria leaf-Cut T.S. and L.S. and stain with phloroglucinol. Note the distribution of bundles of fibers.

   2. Xylem fibers
      1. Quercus -Examine macerations for individual fibers (libriform type). Also examine prepared slides of T.S. and L.S. of wood.
      2. Vitis stem (prepared slide)-Look at L.S. for septate fibers with several cross-walls along their length.
      3. Aristolochia (macerations)-Examine for gelatinous fibers which appear to have contents.

      Demonstration of commercially-important fibers.

      Fiber bundles stripped from monocot leaves are hard, stiff, and heavily lignified. These are "hard fibers." "Soft fibers" may or may not be lignified and are very soft and flexible. Make a list of both types from the demonstration.

2. Epidermis

   The DERMAL tissue system is composed of two tissues, EPIDERMIS and PERIDERM. The periderm is derived from a secondary meristem, the cork cambium or phellogen, and the epidermis is derived from a primary meristem, the protoderm. Since they both have the same function, protection from loss of water and from pathogen entry, and the same position on the plant body, they are in the same tissue system. Epidermis will be studied in this and the next laboratory, periderm will be examined later when we look at stems and roots.

   Epidermal cells comprise the outer covering of the entire primary plant body with the exception of the tip of the shoot apex and the root cap. Their function includes mechanical protection, restriction of transpiration, gas exchange, and occasionally photosynthesis and/or storage. They are variable in shape, and commonly covered on their exposed walls with a waxy cuticle. Stomata occur among the epidermal cells in some plant organs and consist of a pore surrounded by two guard cells. Stomata, together with associated subsidiary cells, form the stomatal apparatus. A stoma is a controllable opening in the plant's surface to allow the escape of water vapor and the exchange of CO2 and O2 with the tissues inside. Stomata are commonly found on leaves, and often on stems as well. Certain terminology is associated with their location; if they occur on both surfaces of a leaf, the plant is amphistomatic; if they occur on the upper surface only, it is epistomatic; and lower surface only is hypostomatic.

   In this lab you will be looking at different stomatal types, other features of the epidermis will be examined next time.

   1. Stomatal types-Dicotyledonous plants-Make epidermal peels or clearings of small pieces of the leaves listed below. Observe the following stomatal types: Diacytic, Paracytic, Anisocytic, Anomocytic, Actinocytic, or Tetracytic.
      1. Gossypium hirsutum (cotton) leaf-Malvaceae

      2. Begonia leaf-Begoniaceae

      3. Phaseolus vulgaris leaf-Fabaceae

      4. Dianthus sp.-Caryophyllaceae

   2. Stomatal types-Monocotyledonous plants-In one classification scheme (see your textbook - Fahn, 4th ed., pg. 169), four different types have been distinguished in monocot families.
      1. Guard cells surrounded by 4 to 6 subsidiary cells. (Type1 or Radial type)

      2. Guard cells surrounded by 4 to 6 subsidiary cells, but two of them are round, smaller than the rest, and located at the ends of the guard cells. (Type 2 or Round-end type)

      3. Guard cells accompanied by two parallel subsidiary cells, one on each side. (Type 3 or Grass type)

      4. Guard cells not associated with any subsidiary cells. (Type 4 or No-sub type)

      Examine the monocot leaves listed below and determine which of the four types above are applicable.
      1. Musa sapientum (banana) leaf-Musaceae

      2. Iris sp. leaf-Iridaceae

      3. Zea mays (corn) leaf-Poaceae

      4. Pandanus sp. leaf-Palmaceae

3. Xylem Regeneration Experiment

   Part #1. (Lab. #4)

   1. Each group of 2 or 3 students should obtain 3 similar Coleus plants. Counting from the bottom find the 5th set of leaves on each plant and the flat surface of the internode below this pair of leaves. If your plant doesn't have 5 nodes, use the uppermost set of fully developed leaves. Now carry out the following treatments. (see diagram)
      1. Plant 1. Make a small incision in the 5th internode, but otherwise leave the plant intact. A small scalpel should be inserted in the middle of one of the flat sides of the internode, in order to sever the fairly small central vascular bundle and not the large bun-dles at the corners of the stem. The would should be approxi-mately 2-3 mm deep and 1-2 mm wide. This treatment will be performed in the lab with the lights off and with the stem illuminated from behind in order to reveal the silhouette of the vascular bundle to be severed.

      2. Plant 2. Make a wound in the 5th internode as described above, then remove all leaves and buds from the shoot above and below the wound. Decapitate the plant several mm above the 5th internode. You should be left with the bare stem, wounded at the uppermost internode. Now treat the cut stump of the stem with plain lanolin paste. Also smear a little lanolin on the wounded sur-faces of all the leaves and buds.

      3. Plant 3. Proceed as for plant 2, but treat the cut stump with lanolin paste containing 1% indoleacetic acid (IAA). Smear the wounds with plain lanolin paste without IAA.

   2. Identify your plants with a labeled stick or string tag (write with pencil) with your name and lab room number. Place your plants as directed by the TA. They will be returned to you during lab. #6.

   Part #2. (Lab. #6)
   1. Find your own plants, and excise the wounded region by making a horizontal cut across the entire stem about 1/4 inch above and below the wound.

   2. Cut the segment in half lengthwise and discard the unwounded half.

   3. Place the wounded half in a vial containing 70% ethanol. Be sure to label each vial for the treatment used. At the end of the period today, decant the ethanol, rinse in water, and pour on the NaOH/Basic Fuchsin suspension.

   4. Place your vials in the container provided, and the TA will put them into a 60 degree C oven.

   5. Tomorrow morning your TA will pour off the NaOH mixture and will start to rinse the tissues repeatedly in water until lab tomorrow.

   Part #3. (Lab. #7)
   1. Find your labeled vials. The lignified secondary walls of regenerated tracheary elements will now be stained bright red.

   2. Place the segment wound-side-up on a slide under a dissecting microscope. You should be able to see the red-stained cells without further treatments. If you can't see them, then carefully scrape away the epidermis with a razor blade to make the segment thinner.

   3. What are your results? What did you expect? If things didn't work as you expected, can you suggest why not?

PLANT ANATOMY: A STUDY GUIDE AND LABORATORY MANUAL

Thomas L. Rost
Section of Plant Biology
University of California
Davis, California 95616-8537

23rd Edition (1998) Copyright (C); 1975 by Thomas L. Rost
Revised: August, 1998
URL: http://trc.ucdavis.edu/CoursePages/PLB105/HTML/Lab3.html