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? Night length

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? Concentration of Pr and Pfr (Pr rapidly converted to Pfr in daylight), Pfr converts slowly to Pr in dark of far red light.

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. 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 Apical meristem

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