9.4 Reproduction in Angiospermophytes

I. Flower Structure & Function Flowers are the reproductive structure of plants (4 parts) 1. sepals 2. petals 3. stamens 4. carpels Flowering involves a change in gene expression in the shoot apex. The switch to flowering is a response to the length of light and dark periods in many plants.

B. All 4 floral parts are important but only stamens (“male” organs) and carpels (“female” organs) produce gametes C. A flower with all 4 parts is called “Complete”, if it doesn’t have all 4 parts it is called “incomplete” D. A flower with both stamens & carpels is said to be “perfect”, whereas an “imperfect” flower has one or the other but not both Complete flower

E. Functions of flower parts Sepal Protect flower Petals Colored leaves that attract pollinators Anther Male part of the flower that produces pollen Filament Males part of flower that hops up the anther Stigma Female part that contains sticky substance that pollen adheres to Style Female part that holds up the stigma and transfers sperm from pollen grain to ovary Ovary Female part that holds ovules (eggs) Stamen Collective male parts of the flower: anther and filament Pistil Collective female parts of the flower: stigma, style and ovary

Male & Female Flower Parts

II. Pollination & Fertilization Pollination: placement of pollen onto the stigma of a carpel by wind, water or animal carriers; a pre-requisite to fertilization 1. Self Pollination 2. Cross pollination

B. Fertilization: the union of haploid gametes (pollen and egg) to produce a diploid gamete 1. Occurs within the ovary of a plant 2. Pollen tube grows down from the stigma to the ovary through the style 3. the gamete is now the seed

C. Seed Dispersal: action of the seed moving from its place of origin to another site where it will grow

III. Seed Structure Seed Part Function Testa (seed coat) Tough, protective outer coat Cotyledons Embryonic leaves that function as nutrient storage structures Micropyle Scar of the opening where the pollen tube entered the ovule Embryonic root Becomes plants root system Embryonic shoot Becomes plants first leaves Hilum Scar left on seed from where it is attached to the ovary

IV. Germination Germination is the development of a new plant Conditions needed for Germination 1. water to rehydrate dried seed tissues 2. Oxygen aerobic respiration to produce ATP. 3. Ideal temperature and pH for enzyme activity 4. Some seeds need special conditions to germinate a. fire b. testa disruption c. freezing

5. Seeds do not carry out photosynthesis Seeds use used energy stored in cotyledons for cellular processes This is in the form of amylose Seed Germination

V. Seed Metabolism during Germination Water is absorbed & activates cells Synthesis of gibberelins (plant growth hormones) Gibberelins cause synthesis of amylase Amylase hydrolyses stored starch to maltose Maltose is further broken down into glucose which is used for cellular respiration and converted into cellulose

VI. Phytochrome & Flowering A. Photoperiodism: reaction of plants to the length of daylight (night is the critical time). Plant Type Flowering & Light Examples Long-Day Plants Bloom when days are longest and nights shortest (midsummer) Radishes, spinach and lettuce Short-Day Plants Bloom in spring, late summer and autumn when days are shorter Poinsettias, chrysanthemums, and asters Day-Neutral Plants Flower without regard to day length Roses, dandelions and tomatoes

B. Phytochrome: photoreceptor, a pigment in plants used to detect light. Sensitive to light in the red and far-red region -inactive form by red light (Pr) (660nm) -active form by far-red light (Pfr) (730nm) -moonlight produces a greater percentage of far-red light than sunlight, so during the night the phytochrome is slowly converted to its inactive form -more phytochrome is converted in a longer night, allowing the plant to measure the length of the night.

Monocots Dicots One cotyledon Two cotyledons (embryonic leaves) Parallel veins in leaves Netlike veins in leaves Floral organs in multiples of 3 Floral organs in multiples of 4 or 5 Vascular tissue in stems scattered Vascular tissue in stems distributed in rings Fibrous roots Taproots with lateral branches One pollen grain opening 3 pollen grain openings