Insect-pollinated flowers Often yellow or blue Have a scent Bird-pollinated flowers Often yellow, orange, or red Do not have a strong scent

Ultraviolet markings on insect-pollinated flowers

Bat-pollinated flowers Often have dusky white petals Are scented Wind-pollinated flowers Often have smaller petals or none at all Have neither scent nor nectar Make large amounts of pollen

Animal pollinators: Archilochus colubris obtains nectar

Animal pollinators: Leptonycteris curasoae obtains nectar

Wind pollination

Coevolution Reciprocal adaptation Caused by two species Forming interdependent relationship Affecting the course of each other’s evolution E.g., certain showy flowers + bees

Pollination Fertilization Transfer of pollen grains from anther to stigma Fertilization Fusion of gametes Occurs after pollination

Double fertilization In the ovule, egg fuses with first sperm cell Zygote is formed Zygote develops into a multicellular embryo in the seed

Double fertilization, cont. Two polar nuclei fuse with second sperm cell Triploid nutritive tissue (endosperm) is formed

Mature flowering plant embryo consists of A radicle A hypocotyl A plumule Cotyledons (one in monocots, two in dicots)

For use during germination, a mature seed contains both A young embryo Nutritive tissue (stored in endosperm or cotyledons)

Ovules Ovaries Structures with the potential to develop into seeds Structures with the potential to develop into fruits

Simple fruits Develop from a single pistil consisting of Either a single carpel Several fused carpels Some are fleshy at maturity Others are dry

Aggregate fruits Multiple fruits Develop from a single flower with many separate ovaries Multiple fruits Develop from the ovaries of many flowers growing close together on a common axis

Dispersal methods of seeds and fruits include Accessory fruits The major part of the fruit consists of tissue other than ovary tissue Dispersal methods of seeds and fruits include Animals Wind Water Explosive dehiscence

An accessory fruit

Plant growth and development are controlled by Internal factors like location of cell in plant body Causes some genes in cell to be turned off and others to be turned on, thus affecting gene expression during development Environmental factors like changing day length

Germination and seedling growth

Germination is the process of seed sprouting Internal factors affecting germination Maturity of the embryo Presence or absence of chemical inhibitors Presence or absence of hard, thick seed coats

Germination, cont. External environmental factors affecting germination include requirements for Oxygen Water Temperature Light

Photoperiodism is any response of plants to the duration and timing of light and dark In many plants, flowering is a photoperiodic response Short-day plants Long-day plants Intermediate-day plants

Photo-periodic responses of short-day and long-day plants Light treatment Photo-periodic responses of short-day and long-day plants Short-day plant Long-day plant

Photoperiodism, cont. Day neutral plants Flowering is not affected by photoperiod

Phytochrome is The photoreceptor in photoperiodism A family of ~5 blue-green pigments Each type has two forms named by the wavelength of light they absorb Pr Pfr

Phytochrome, cont. Pfr is the active form, triggering or inhibiting physiological responses such as Flowering Shade avoidance A light requirement for germination

Phytochrome This pigment occurs in two forms, Pr and Pfr, and readily converts from one to the other. Red light (660 nm) converts Pr to Pfr, and far-red light (730 nm) converts Pfr to Pr

Circadian rhythm A regular period in the growth or activities of a plant or organism That approximates the 24-hour day Is reset by the rising and setting of the sun

Circadian rhythm, cont. Examples are The opening and closing of stomata Sleep movements

Plant movements occurring in response to external stimuli Tropisms Directional growth responses (i.e., the direction of growth is dependent on the direction of the stimulus)

Phototropism Gravitropism Thigmotropism Heliotropism Response to the direction of light Gravitropism Response to gravity Thigmotropism Response to contact with a solid object Heliotropism Ability of leaves or flowers to track the sun across the sky

Gravitropism

Heliotropism

Plants produce and respond to hormones that Act as highly specific chemical signals Elicit a variety of responses that regulate Growth Development

Hormones Are effective in very small concentrations Functions of some overlap Many physiological activities are regulated by interactions of several at once

General mechanism of action of plant hormones

Plant hormones bind to specific receptor proteins in or on target cells Binding may trigger production of a second messenger (e.g., Ca2+) Second messenger may bind to and activate or inactivate certain enzymes

Hormones affecting plant growth and development Auxin is involved in Cell elongation Tropisms Apical dominance Inhibition of axillary buds by the apical meristem

Isolating auxin from coleoptiles

Phototropism and the unequal distribution of auxin

Hormones, cont. Gibberellins are involved in Stem elongation Flowering Germination

Gibberellin and stem elongation

Hormones, cont. Cytokinins Promote cell division and differentiation Delay senescence Interact with auxin and ethylene in apical dominance Induce cell division in tissue culture

Auxin-cytokinin interactions in tissue culture

Hormones, cont. Ethylene plays a role in Ripening fruits Apical dominance Leaf abscission Wound response Thigmomorphogenesis Senescence

Hormones, cont. Abscisic acid is an environmental stress hormone involved in stomatal closure caused both By water stress In seed dormancy

Abscisic acid and seed germination Arrows show where some of the kernels have germinated while still on the ear, producing roots

Salicylic acid Helps defend plants against Pathogens Insect pests May bind to a cell receptor to switch on genes to Fight infection Promote wound healing