Download Lab 05-Leaf stem root

Lab 05: Leaf development in Pisum sativum (pea), Stems and Roots
Pea leaf mutants demonstrate the plasticity of leaf development. A change in one gene product
results in the conversion of compound leaves to simple leaves (unifoliata-uni), the conversion of
leaflets to tendrils (afila-af), tendrils to leaflets (tendril-less-tl), partial loss of stipules (reduced
stipules-st), change in leaflet and stipule shape (sinuate leaf-sil), and crinkling of leaves due to
loss of adaxial identity (crispa-cri). To prepare for this lab, you need to read sections 4.16-4.18
in your book (Cronk, 2010).
For the leaf development section of this lab you will:
-describe wild-type pea leaves
-identify which genes are defective in a series of mutant plants
-make predictions of the phenotypes of additional mutant combinations
-make predictions of the effects of mutations in other plants
-contrast pea mutants with other plants with compound leaves
Characterizing mutants
Obtain a pot with a wild-type pea plant to share with your table. In the space below, sketch one
leaf, including its attachment to the stem. Include the petiole, rachis, stipules, the correct number
of leaflets and tendrils. Label each part of the leaf.
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We will typically have four to five single mutants (may vary year-to-year). Describe and
illustrate the plant’s appearance (leaf phenotype) and attempt to determine which of the genes
described in the introduction is mutated (genotype) in each case.
When you are done, you may check your answers with your TA.
1. Phenotype:
Genotype:
2. Phenotype:
Genotype:
3. Phenotype:
Genotype:
4. Phenotype:
Genotype:
5. Phenotype:
Genotype:
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The pots labeled with letters are mutant combinations. These may be a bit trickier. Refer to the
descriptions in the introduction and the mutants you just observed. Attempt to identify at least 3
of the mutant combinations.
A. Phenotype:
Genotype:
B. Phenotype:
Genotype:
C. Phenotype:
Genotype:
When you are done reasoning your own mutant characterization, consult the mutant
key available in lab
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As you examine the pea plants, answer the following questions:
Do mutations that affect the compound leaf also affect the stipules? If so, which ones?
___________________________________________________
Do mutations that affect the stipules also affect the compound leaf? If so, which ones?
___________________________________________________
Do any mutations have similar effects in the leaflets and stipules? If so, which ones?
____________________________________________________
Do regions of stipules and the compound leaf share a developmental program?
Compound leaves in other lineages
Compound leaves are characteristic of the legume family (Fabaceae). Bean plants (Phaseolus
vulgaris) have compound trifoliate leaves, but do not have stipules or tendrils. Given what you
know about each of the pea leaf mutants observed, predict the effect of similar mutations on bean
leaves.
afila
tendril-less
unifoliata
crispa
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Simple leaves are most certainly ancestral in Angiosperms, and compound leaves have evolved
many times. Compound leaf development has been well studied in the tomato family
(Solanaceae). Observe available tobacco (Nicotiana tabacum) and two species of Solanum, one
with simple leaves (Solanum cheesmanii) and compound-leaf tomato plants (S. lycopersicon).
Use your lecture notes and readings to help answer the following questions:
How is the development of compound leaves different in pea and tomato plants at a
morphological level?
How is the development of compound leaves different in pea and tomato plants at a molecular
level?
What are the underlying molecular mechanisms for compound leaf evolution?
Is there evidence that small changes in gene expression can lead to large changes in leaf
morphology?
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Stems
Goals:
1. Identify short shoots and long shoots in gymnosperms
2. Become familiar with shoot morphology in angiosperms
3. Observe histological sections of dicot and monocot stems.
1-Branching Patterns in seed plants: Gymnosperms
Pine and related conifers – Some conifers such as Douglas fir only have one kind leaf and
shoot system. However, two kinds of branches may be found in many conifer species. Long
shoots, as the name implies, are shoots in which the internodes are relatively long. Short shoots
produce leaves in a tight cluster so that internodes are scarcely detectable. Short shoots are very
conspicuous in the pines (Pinus), larches (Larix) and "true" cedars (Cedrus). With the exception
of Pinus, branches that have been growing for a number of years as a long shoot may convert to
short shoot growth and vice versa.
Cedrus deodara. Cedrus is the genus of "true" cedars. They have long shoot/short shoot
morphology (LS/SS). The morphology of Larix (larch) is similar to that of Cedrus, but the
former is deciduous and may already lack leaves at this time of year.
Glance over an entire branch system and notice that some of the new growth (lighter green at the
tips of main and side branches) is LS growth (relatively long internodes between needles) and
some of it is SS growth (needles in apparent whorls).
A terminal bud on the major branch axis usually opens to produce further LS growth, but you
may find a major branch axis in which the terminal bud has reverted to SS growth (you may have
to look at branches on other benches).
Terminal buds on the short shoots usually open to produce further SS growth, but not always.
Find a short shoot that has shifted from SS to LS growth. Does this seem to happen frequently?
(Look at a number of different branch systems.)
__________________________________________________________________
On long shoots, does every needle have an axillary bud associated with it? _________________
Ginkgo biloba
Obtain a branch showing LS/SS morphology. Find a region of LS growth for the current
year. Study the SS, noting the almost nonexistent internodes. Do SS ever shift to LS growth?
_____________
Do LS ever shift to SS growth? ______________
Look at a number of branches before attempting to answer these questions.
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2-Branching Patterns in Angiosperms
Herbaceous shoot– Begin your observations by looking at an herbaceous plant such as Coleus,
locate the following, a) apical meristem (shoot tip with leaf primordia), b) axillary bud, c) node
and internode, d) lateral branches, and f) leaves
What is the leaf arrangement? (alternate, opposite, whorled)_______________________
Woody Twig of Horse Chestnut – On the benches in the lab there will be a number of woody
twigs of Horse Chestnut, obtain one. Using the illustration below, label the following: a) terminal
bud, b) terminal bud scale scars, c) axillary (lateral) bud, d) leaf scar, e) leaf vein scars, and
lenticels.
What was the leaf arrangement on this plant?____________________________________
What happened to the leaves? Are they deciduous?_______________________________
Home many years of growth can you see on your twig?___________________________
(Clue: look at terminal bud scale scars!)
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3-Cross sections of stems
Observe a cross section of a corn stem (monocot) and a Coleus stem (dicot herb, primary growth
only). Illustrate each below, identifying: epidermis, cortex, vascular bundles, primary xylem and
phloem, cambium and pith.
Stems vocabulary:
Terminal bud- dormant bud found at the tip of the shoot (includes apical meristem).
Lateral/ axillary buds- usually dormant meristems surrounded by leaf primordia/bud scales
found in the axil of a leaf
Adventitious bud- a bud initiated from a location other than an axil.
Apical dominance- inhibition of axillary bud growth by the terminal bud.
Indeterminate growth- continued growth from a long-lived meristem (most vegetative
growth).
Determinate growth- defined amount of growth before termination of meristem (most
reproductive).
Dichotomous branching- apical meristem splits to form two branches.
Monopodial growth- growth associated with a persistent apical meristem.
Sympodial growth- cessation of growth by apical meristem allows axillary branches to
grow. Phyllotaxy- geometric arrangement of leaves on stem.
Alternate, spiral- single leaf at each node, each occurring at about 135° from last leaf.
Opposite, decussate- two leaves at each node, with each pair occurring at 90° from last pair.
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Roots
Goal: Identify and label anatomical and morphological structures of angiosperm roots.
Branch (lateral) root initiation. Obtain a slide of Lupinus branch roots l.s. There will be branch
roots of various ages, some of which are tiny primordia at the periphery of the vascular cylinder
and others that have pushed through the cortex and emerged at the surface of the parental root
(Fig. 8.6).
a
b
Cross section of roots showing lateral root initiation: a, two lateral roots mid- through
the cortex of the parent root; b, two lateral roots, growing through the cortex of the parent root.
Eudicot Mature root x-section. Obtain a slide of Ranunculus. Use the diagrams below to help
you find all of the following tissues on the slide:
a. epidermis
b. cortex. In many roots, the cortical cells are filled with starch.
c. endodermis. In a stained cross-section of young root tissue, the casparian strip is seen as red
dots in the radial walls of endodermal cells. But, in most of your slides, an old region of the root
has been sectioned and the endodermal wall is more uniformly thickened.
d. stele. The stele refers to the primary vascular tissue. e. xylem. Xylem is a tissue easy to pick
out because it contains the large water-conducting cells in the stele. Note the four xylem "arms".
f. protoxylem. Notice that the smallest water-conducting cells are toward the outside (at the tips
of the xylem arms.)
g. metaxylem. These xylem elements are the larger, more centrally located vessels and tracheids.
f. phloem occurs in discrete regions between the xylem arms.
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a, root cross section; b, detail of root stele.
Monocot mature root cross section
In the space below draw and label a root cross section of corn (Zea), include the following: a)
root hairs, b) epidermis, c) cortex, d) endodermis, f) vascular bundles, and g) pith. Compare to
the dicot root above.
Root Morphology
Fibrous and Tap roots
To get an idea of how the morphology of the root system differs in monocots and dicots,
examine available examples of each. Tap root systems are common in dicots. Fibrous root
systems are characteristic of monocots; note the absence of a dominant root. Also note where the
fibrous roots originate. Roots originating from stem tissue are adventitious roots (a.k.a. nodal
roots, crown roots, prop roots). For both examples identify: root cap, root hairs, primary root,
lateral roots. You may also detect the slimy mucigel secreted by the roots.
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Each root hair is an outward extension of a single specialized epidermal cell. Are the root hairs
randomly distributed over the surface, or do they have a defined arrangement?
Why are the root hairs longer farther from the root tip? _________________________________
Hand-section of dicot root. Obtain a carrot longitudinal and cross section. Compare to the dicot
cross section viewed previously. What is the function of this part of the carrot?
Are root hairs evident on your carrot? Why or why not? Is the root cap evident on your carrot?
Why or why not? Can you see lateral roots on the outside of the carrot? On the inside of the
carrot? Is the stele evident?
Root vocabulary Rhizoid- root-like structure with no vascular tissue (seedless plant
gametophytes)
Primary root- root arising from the embryonic RAM
Lateral root- root arising from the pericycle (endogenous origin, in contrast to branch stems)
Pericycle- meristem just exterior to stele, which produces lateral roots
Adventitious roots- root arising from the shoot
Root hairs- single-cell extensions of root epidermal cells, which greatly increase surface area
(occur just behind zone of elongation and are ephemeral)
Fibrous root- highly branched root system with many lateral roots of equal size
Taproot- large, dominant primary root with reduced branching and strong gravitropism
Endodermis- sheath of cells surrounding stele which function as barrier between root and soil
environment
Casparian strip- waterproof, waxy (suberin) layer found in the radial walls of epidermal
cells Mycorrhizae- fungal symbionts that aid in plant absorption of nutrients
Root nodules- modified lateral roots that allow for symbiotic association with nitrogen- fixing
bacteria
Prop roots- roots which function in support of the stem
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