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Reproduction and Flowering in Plants LO´s • Know main parts of a flower • Know how flowering is induced and controlled • Know the seed structure and how the process of germination works Flowering in plants • What is the environmental cue that synchronizes flowering in plants? • What are the advantages of synchronization of flowering? • Which substance causes a plant to produce a flowering hormone that causes a plant to produce flowers? Control of flowering • Photoperiodic activities are controlled through the action of a pigment called phytochrome. • Phytochrome acts as a signal for some biological clocks in plants and exists in two forms, Pr (inactive) and Pfr (active). • It is important in the flowering response in plants but is also involved in other light initiated responses, such as germination and shoot growth. Phytochrome • Pfr interacts with genes that maintain the plant´s biological clock (e.g. by producing a flowering hormone) • Pfr promotes flowering in long day plants and inhibits flowering in short day plants. • How does the plant measure day length? Development of the Flower • In order to flower, a plant must pass through several stages of development with several changes in gene expression occurring at the shoot meristem. – The plant must first pass from an immature to a sexually mature stage. – The apical meristem must change from a vegetative meristem to a floral meristem, – The organs of the flower must grow and develop. • Apical meristem Environmental cues perceived in the leaves are transmitted to the apical meristem by hormonal messengers. – The messengers activate the genes LEAFY and FLOWERING LOCUS T which results in flowering. Dartmouth Seeds • A seed is an entire reproductive unit, housing the embryonic plant in a state of dormancy. • During the last stages of maturing, the seed dehydrates until its water content is only 5-15% of its weight. • The embryo stops growing and remains dormant until the seed germinates. • At germination, the seed takes up water and the food store is mobilized to provide the nutrients for plant growth and development. Energy source in the seed • Monocots: Endosperm • Dicots: Cotyledon