Germinating sunflowers, turgor and nutation From: http://sunflower.bio.indiana.edu/~rhangart/plantmotion Nutation is Sunflower due to unequal Germination rates of growth in that continuous is dependent on light cell turgor.
Leaves parallel veins Eudicot (or dicot) leaf blade petiole stem Monocot leaf blade bud node sheath midrib node
The leaf blade is the thin flat part of the leaf. Leaves of most dicots have a petiole. This attaches the leaf blade to the stem. The petiole determines the distance of the leaf from the stem. This decreases shading of the blade by other leaves. It also allows the position of the leaf to be changed. The base of the leaf blade of monocot leaves wraps around the stem to form the sheath. The sheath may contain a ligule or auricles.
node blade stem sheath Crabgrass, no ligules, no auricles
node ligule Corn sheath
blade stem ligule auricles Barley sheath
The main function of leaves is photosynthesis. Leaves are generally thin and flat with a high surface area. This allows optimal light absorption for photosynthesis. It also promotes water loss that needs to be regulated. The cuticle prevents excessive water loss. Stomatal pores allow regulated water lose and CO 2 uptake. Photosynthesis requires CO 2 and light. Open stomatal pores are required for CO 2 uptake but also allow water evaporation (called transpiration). Regulation of stomatal pores provides a balance between CO 2 uptake and water loss. Transpiration is essential for many reasons: Evaporative cooling of the leaves. Generating the negative pressure in the xylem. Getting nutrients from a large volume of soil solution.
midrib blade poplar (Populus) oak (Quercus) maple (Acer) petiole a Simple leaves leaflets red buckeye (Aesculus) b Compound leaves black locust (Robinia) honey locust (Gleditsia) This is called bicompound or doubly compound
Figure 6.07ab: Compound leaves: Two types of compound leaves. The petiolule is attached to the rachis in (a) and to the end of the petiole in (b).
Figure 6.08: Mimosa, double compound leaf.
Figure 6.09: Myriophyllum heterophyllum (two-leaf water milfoil) dissected leaves of submerged plant.
When two-leaf water milfoil grows above the surface of the water, it produces thicker and tougher leaves shown here. Hence the name heterophyllum = different or other leaf.
Figure 6.12: Several common types of leaf margin.
Leaf Margins Serrate: having sharp, forward-pointing teeth on the margin Serrulate: serrate with very small teeth Dentate: with sharp, outward-pointing teeth on the margin Undulate: wavy From: http://www.calflora.net/botanicalnames/botanicalterms.html
Monocot leaves have parallel venation, the veins are parallel to each other.
Eudicot leaves have net venation.
Ginkgo leaves have dicotomous venation. Ginkgo is a gymnosperm.
The functions of leaf veins: - Leaf veins are vascular bundles composed of xylem and phloem. - The xylem carries water and nutrients from the soil to mesophyll cells. - The phloem carries fixed carbon and other metabolites to sink tissues. Sink tissues are net importing tissues such as roots, flowers, developing leaves etc. - In the leaf vein Xylem in upper part of bundle Phloem in lower part of bundle - Bundle sheath Single layer of cells surrounding vascular bundle Loads sugars into phloem Unloads water and minerals out of xylem
upper epidermis cuticle bundle sheath palisade mesophyll spongy mesophyll water moves from roots to stems, and into the leaf through the xylem lower epidermis guard cell Oxygen and water vapor depart from the leaf through stomata. xylem phloem carbon dioxide from the air enters the leaf through stomata vascular bundle (vein) sugars and other products of photosynthetic cells enter the phloem in the vascular bundle and depart from the leaf
Cross section of a lilac leaf (dicot) palisade parenchyma xylem phloem upper epidermis spongy parenchyma lower epidermis midrib
Cross section of a maize leaf (monocot)
Close-up view of a leaf vein in Zea mays showing the bundle sheath
Two types of parenchyma cells in the mesophyll pallisade parenchyma or pallisade mesophyll - in the upper part of the leaf spongy mesophyll - usually in the lower part of the leaf, less regular arrangement of cells. The mesophyll is the primary site of photosynthesis. Pallisade parenchyma cells are separated as shown in (b) so that there is airspace between the cells to allow CO 2 uptake
stoma epidermal cell guard cell
Leaf structure and regulation of water loss: What structures are important for the regulation of water loss from leaves? The cuticle prevents direct water loss from the epidermal cells. Guard cells regulate the aperture of stomatal pores and thereby control water loss - also called transpiration. Plants require transpiration to bring nutrients from the soil. But too much transpiration and water loss causes wilting. So water loss must be tightly regulated.
There is generally a greater density of stomata on the underside of the leaf (lower epidermis). Table 6.T02: Frequency of Stomata in Leaf Upper and Lower Epidermis
Dionaea - venus flytrap Drosera - sundew Modified leaves of carnivorous plants Sarrecenia - pitcher plant
Different types of trichomes on the same plant. Simple, glandular and stalked-glandular trichomes are visible on this Croton leaf.
Glandular secreting trichomes from tomato, there are five types. Glandular trichomes
Leaf initiation, in the shoot apical meristem. leaf primordium SAM
next leaf primordium leaf primordium procambium young leaves
Heterophylly: different leaf shapes on the same plant. The bean plant is an example in lab this week. first leaf (simple) cotyledons mature leaf (compound) withered cotyledon
Figure 6.11a: Two types of leaves on beans.
Two types of leaves on Azara lanceolata. This is an evergreen from Chile that has small round leaves and large lanceolate leaves.
Heterophylly depends on plant age and enviroment. In this example, the leaves of white water buttercup (Ranunculus aquatilis) are more more deeply lobed when submerged. Similar to the example of two-leaf milfoil.
Leaf acclimation to light intensity, leaves of same species under different light intensity Shade leaf Leaves of plants grown in the shade will have thinner leaves and more chlorophyll per reaction center Sun leaves are thicker.
Leaf adaptations to dry climates: sunken stomata. This adaptation maximizes CO 2 uptake per water that evaporates. Figure 6.38b: Yucca leaves, fiber bundles, high mag.
Figure 6.38c: Yucca leaves, groove with stomata, high mag.
Leaf adaptations to dry climates: multiple epidermis Fig
Leaf adaptations to dry climates: less air space in leaf mesophyll cells Jade
Trichome development trichomeless mutant phenotype
Similarities between trichome development and root hair development, also an overlap in genes responsible.
Cactus spines tendril plantlets More leaf modifications
Figure 6.39a: Many conifers have needle-shaped leaves.
Figure 6.41a: Pine needle, low mag of whole xs.
Figure 6.41b: Pine needle, mag of vascular bundle with secondary phloem.
Figure 6.41c: Pine needle, mag of resin canal.
Leaf senescence (death) is a developmental process that usually culminates in abscission. Abscission is the process of plant organ separation. axillary bud xylem phloem abscission zone separation