Leaves Chapter 7 Copyright Mc GrawHill Companies Permission

Outline • • Structure/Function Leaf Arrangements and Types Internal Structures of Leaves v Stomata

Structure/Function • There are different types of leaves with different functions: v Foliage leaves

Structure • All leaves originate as primordia in the buds. v ~200 cells in

Structure • • At maturity, most leaves have a stalk (petiole) and a flattened

Structure Simple and Compound lamina Vascular bundle Petiole/ rachis Stern - Introductory Plant Biology:

Structure Compound leaves • • Pinnately compound leaves have leaflets in pairs along the

Structure Pinnate Simple Bipinnate Palmate Stern - Introductory Plant Biology: 9 th Ed. -

Leaf forms Figure 7. 4 in Stern - Introductory Plant Biology: 9 th Ed.

Leaf Arrangements and Types • Arrangement of veins in a leaf or leaflet blade

What is the arrangement of VEINS? Palmate Pinnate Stern - Introductory Plant Biology: 9

What is the arrangement of VEINS? Parallel Palmate monocot Palmate dicot Stern - Introductory

Structure/Function—Cells and Tissue • Green leaves capture sunlight and thus go through photosynthesis. v

Structure/Function—Cells and Tissue Stomata Guard cells Stern - Introductory Plant Biology: 9 th Ed.

Guttation water forced out Stern - Introductory Plant Biology: 9 th Ed. - All

Internal Structure of Leaves • Epidermis is a single layer of cells covering the

Fig. 7. 6 Stern - Introductory Plant Biology: 9 th Ed. - All Rights

Stomata • • Lower epidermis of most plants is perforated by numerous stomata, upper

Fig. 7. 8 Stern - Introductory Plant Biology: 9 th Ed. - All Rights

• Which surface of these leaves have the most stomata? Stern - Introductory

Mesophyll and Veins • • Most photosynthesis takes place in the mesophyll between the

Mesophyll and Veins Stern - Introductory Plant Biology: 9 th Ed. - All Rights

Fig. 7. 11 Stern - Introductory Plant Biology: 9 th Ed. - All Rights

Specialized Leaves • • Shade Leaves (see Fig. 7. 11!) v Leaves in the

Specialized Leaves • Tendrils v Modified leaves that curl around more rigid objects helping

Tendrils Modified leaves Stern - Introductory Plant Biology: 9 th Ed. - All Rights

Specialized Leaves • Spines, Thorns, and Prickles v Spines - Modified leaves designed to

Specialized Leaves • • • Storage Leaves - Succulents Window Leaves - Leaves buried

Autumnal Changes in Leaf Color • • Chloroplasts of mature leaves contain several groups

Abscission • Deciduous plants drop their leaves seasonally. v Occurs as a result of

Leaf Abscission Zone Stern - Introductory Plant Biology: 9 th Ed. - All Rights

Review • • • Overview Leaf Arrangements and Types Internal Structures of Leaves v

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Outline • • Structure/Function Leaf Arrangements and Types Internal Structures of Leaves v Stomata v Mesophyll and Veins Specialized Leaves Autumnal Changes in Color Abscission Relevance of Leaves Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Structure/Function • There are different types of leaves with different functions: v Foliage leaves - food manufacturing or photosynthesis Bud scales - protection of vegetative bud v Floral bracts - protection of floral bud v Sepals - protection of floral bud v v Cotyledons/swollen leaves – storage food/water Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Structure • All leaves originate as primordia in the buds. v ~200 cells in the bud that develop into leaf in response to: - Spring, day length, - temp, - water, - Hormones - Etc…. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Structure • • At maturity, most leaves have a stalk (petiole) and a flattened blade (lamina) with a network of veins (vascular bundles). Leaves of flowering plants are associated with leaf gaps and have an axillary bud at the base. v May be simple (single blade) or compound (divided into leaflets). Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Structure Compound leaves • • Pinnately compound leaves have leaflets in pairs along the rachis Palmately compound leaves have all the leaflets attached at the same point at the end of the petiole. v Pinnately compound leaves may be further subdivided an thus be referred to as bipinnately compound. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Leaf Arrangements and Types • Arrangement of veins in a leaf or leaflet blade may also be pinnate or palmate. v Pinnately veined leaves have a main midvein within a midrib. - Secondary veins branch from midvein. v Palmately veined leaves have several primary veins that fan out from the base of the blade. - Parallel in monocots - Divergent in dicots (reticulate venation) Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Structure/Function—Cells and Tissue • Green leaves capture sunlight and thus go through photosynthesis. v Lower surfaces of leaves are dotted with stomata which allow carbon dioxide to enter and oxygen and water to diffuse out. - Guard Cells control stomatal opening. v Transpiration occurs when water evaporates from the leaf surface. v Guttation - Root pressure forces water out hydathodes. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Internal Structure of Leaves • Epidermis is a single layer of cells covering the entire surface of the leaf. v Epidermal cells are devoid of chloroplasts - (no photosynthsis!) v Waxy cuticle often present. v Different glands may also be present in the epidermis. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Stomata • • Lower epidermis of most plants is perforated by numerous stomata, upper epidermis has fewer stomata. 3 6 2 - 1 x 10 to 1 x 10 stoma/cm Guard cells unlike other epidermal cells contain chloroplasts. - Primary function includes regulating gas exchange between leaf interior and the atmosphere, and the evaporation of water. Ø Cell water pressure regulates guard cells which in turn regulate stomata. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Mesophyll and Veins • • Most photosynthesis takes place in the mesophyll between the two epidermal layers. v Palisade Mesophyll - Uppermost layer Contain 80% of leaf’s chloroplasts. v Spongy Mesophyll - Lower layer, lots of air spaces Veins (Vascular bundles) are scattered throughout the mesophyll. v Consist of xylem and phloem tissues surrounded by the bundle sheath. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Leaves • • Shade Leaves (see Fig. 7. 11!) v Leaves in the shade receive less total light, thus tend to be thinner and have fewer hairs than leaves on the same tree exposed to direct light. Leaves of Arid Regions v Many have thick, leathery leaves and few stomata. v Some have succulent, water-retaining leaves, or dense, hairy coverings. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Leaves • Tendrils v Modified leaves that curl around more rigid objects helping the plant to climb or support weak stems. - Become coiled like a spring as they develop. Ø When contact is made, the tip curls around the object, and the direction of the coil reverses. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Leaves • Spines, Thorns, and Prickles v Spines - Modified leaves designed to reduce water loss and protect from herbivory. v Thorns - Modified stems arising in the axils of leaves of woody plants. v Prickles - Outgrowths from the epidermis or cortex. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Leaves • • • Storage Leaves - Succulents Window Leaves - Leaves buried in ground. Reproductive Leaves - New plants at tips. Floral Leaves – Bracts (Fig. 7. 19 and 7. 20) Insect trapping leaves Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Autumnal Changes in Leaf Color • • Chloroplasts of mature leaves contain several groups of pigments. v Chlorophylls - Green v Carotenoids - Yellows - In fall, chlorophylls break down and other colors are revealed. Water soluble anthocyanins (red or blue) and betacyanins (red) may also be present in the vacuole. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Abscission • Deciduous plants drop their leaves seasonally. v Occurs as a result of changes in an abscission zone near the base of the petiole of each leaf. - Cells of the protective layer become coated and impregnated with suberin. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Review • • • Overview Leaf Arrangements and Types Internal Structures of Leaves v Stomata v Mesophyll and Veins Specialized Leaves Autumnal Changes in Color Abscission Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies