The developmental origin of leaves 1. Earliest vascular plants had no leaves 2. Leaves have evolved at least twice -- microphylls and megaphylls 3. Microphyll origins a. small projections formed called enations b. later, single vascular strand grew toward and into the enation c. result is a microphyll, with single unbranched vein d. found only in one group of plants (Lycophyta) 4. Megaphyll origins a. ancestors had dichotomous branching b. ferns & all seed plants
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The developmental origin of leaves 1. Earliest vascular plants had no leaves 2. Leaves have evolved at least twice -- microphylls and megaphylls 3. Microphyll.
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The developmental origin of leaves
1. Earliest vascular plants had no leaves 2. Leaves have evolved at least twice -- microphylls
and megaphylls
3. Microphyll origins a. small projections formed called enations b. later, single vascular strand grew toward and into the
enation c. result is a microphyll, with single unbranched vein d. found only in one group of plants (Lycophyta)
4. Megaphyll origins a. ancestors had dichotomous branching b. ferns & all seed plants
http://www.ualr.edu/~botany/leaf_types.gif
Leaf Shapes and Functions
• Photosynthesis• Evapotranspiration• Minimizes
desiccation via cutin, epidermal hairs, and stomata
2. palisade mesophyll a. located on adaxial side b. may contain more than 80% of the leaf's plastids c. controls light intensity and damage by reducing light
passing through
3. spongy mesophyll a. spongy appearance because of air spaces, allowing free
gas flow b. primary site of photosynthesis in vascular plants
1. Pine leaves ("needles") - low moisture (e.g. frozen ground in winter)
2. epidermis 3. hypodermis -beneath the
epidermis– one or more layers of thick-walled
cells – support and rigidity– protection
4. mesophyll - not divided into palisade and spongy layers.
5. transfusion tissue - surround xylem and phloem
6. endodermis - outer boundary of the transfusion tissue
7. resin canals - circular to elliptical cells in mesophyll (cells lining canal secrete resin)
8. sunken stomatal pores (common in desert plants)
Internal Anatomy of a Pine Leaf
http://www.ualr.edu/~botany/leaf_lab.html
Krantz Anatomy in C4 Plants Two stages of carbon fixation
1. Stage 1 - in MESOPHYLL CELL temporary fixation of CO2 cytoplasm into C4 molecule (no direct involvement of chloroplasts)• Transferred through plasmodesmata to the
bundle sheath cells
2. Stage 2 - in BUNDLE SHEATH CELL• C4 molecules broken down to CO2 again. • chloroplasts fix the CO2 into C3 intermediates to
build sugars
Diagram of a typical leaf. Typical C3 leaf, that is.
C4 typical leaf with photosynthetic cells in concentric rings around the vascular bundles.
Esau 1977
Krantz Anatomy
vascular bundle
bundle sheath cell
palisade mesophyll (Kranz-mesophyll) cell
water-storage parenchyma
cuticle
stomata
Esau 1977
Examples of Xeromorphic Leaves (Esau 1977)
Leaf Functions and Specializations, continued
3. Other leaf specializations – tendrils - elongated leaves for climbing
and attaching – spines - sharp stiff leaves for defense – bracts - floral leaves; often colorful to
attract pollinators– carnivory - leaf is modified to trap