Module 1: Flowering and Seeds

Cut flowers have a limited shelf (vase) life as reserves of moisture and carbohydrates present at the time of harvest decline over time

This results in:

Wilting

Flower and foliage deterioration

Leaf and flower abscission

Flower senescence

Programmed cell death

How does respiration result in physiological changes in cut flowers

Respiration is the oxidative breakdown of complex substrates (starch, sugars, organic acids) to simpler molecules (CO2 and H2O) for production of energy and intermediate molecules such as ATP.

This results in a loss of substrates, requirement for oxygen, production of heat and CO2

How does transpiration result in physiological changes in cut flowers

Transpiration is water movement through plant stems with evaporation through stomata and some petals

Stomata open to allow uptake of CO2

How does ethylene production and sensitivity result in physiological changes in cut flowers

Involved in several phases of flowering from bud induction through to growth of floral tissues, petal senescence and flower abscission

How does maintenance of cell membranes result in physiological changes in cut flowers

Cell turgor, osmotic potential

Practical measures to prolong shelf life

Supplemental reserves of carbohydrates

• Supplying sugars in vase water

Reducing loss of water

• Cooling and storage at high humidity

• Reducing leaf area

• Packaging

Slowing cell metabolism

• Cooling and storage in low light or darkness

Reducing contaminants

• Treating with antifungal and antibacterial solutions or sprays

• Placing stems into acidic water

Promoting/increasing water uptake

• Placing stems into water as soon as possible after harvest

• Cutting stem at 45 degree angle

• Removing stem embolism (‘bubbles’) or other blockages by cutting stem underwater

• Change water in vase regularly

Chemical methods to prolong shelf life

Distilled water (DW)

Sucrose thiosulfate solution (Suc) → as a source of energy

8-Hydroxy quinoline sulphate (HQS) → acts of ethylene receptors and production sites

Kinetin (Kin) → plant hormone that slows processes associated with both senescence and stress

E.g. shelf-life of cut flowers of anthurium

Shelf-life of 15-49 days

Shelf-life determined by browning of peduncle base; spathe floppiness, discolouration and loss of lustre and necrosis of spathe and spadix

Predictors of anthurium shelf-life

High abaxial stomatal density related to short shelf-life

• Increased transpiration and water loss

Spathe colour green related to long shelf-life

• Due to presence or absence of chlorophyll

• On-going photosynthesis and continued carbohydrate supply

Spathe colour white related to long shelf-life

• Due to presence or absence of flavones (white pigments) which have a strong antioxidant capacity

Large spathe (surface area and thickness) related to short-life

• Increased loss of water (transpiration) from tissues

Thick cuticle on spathe related to long shelf-life

• Reduced loss of water (transpiration) from tissues

Stages of flowers after being cut

Stage 1: small green bud

Stage 2: bud at full colour, ready to open

Stage 3: half open flower

Stage 4: fully opened flower

Stage 5: wilted flower

How do soluble sugars, soluble proteins and malondialdehyde change over time of development

Soluble sugars decrease over development

• They are an energy source, a structural constituent of cells, and act as signals to regulate processes associated with plant growth and development

Soluble proteins decrease with development

• They provide nutrition to buds and developing flowers and are involved in transport, structural support, and ion regulation during flowering

Malondialdehyde increase with development

• This is an indicator of oxidative stress

Electrolytic leakage increase with development

• is an indicator of breakdown of cell membranes

Effect of plant hormones

Ethylene

• is a plant hormone (phytohormone) produced by all plants

• influences growth and development of plants throughout their life cycle

• is active at very low concentrations

• Cut flowers with sensitivity: Astroemeria, Asiatic Lily, Oriental Lily, Carnation, Lisianthus, Daffodil, Freesia, Stock

External supply of ethylene

• For some species causes wilting, petal and flower abscission, flower fail to open and senescence of open flowers

• For other species there is little or no effect

Internal formation of ethylene

• Triggers ripening and senescence of flowers and fruits

• Activation of bulbs

• Produced when plants are wounded

Why is Saffron so valuable

Each flower produces three stigmas/styles

150,000-250,000 flowers required to produce 1 kg of saffron

Stigmas only harvested mid-morning when the flowers are fully opened

Reproduction biology of Saffron

Long history of cultivation so it no longer grows in the wild

Male flowers are sterile due to inability to pair chromosomes during meiosis

Flowers are self-incompatible so fail to produce viable seeds

Unique climatic conditions are need to grow Saffron

Biochemistry of Saffron

Crocin is responsible for the distinctive colour of saffron

Safranal creates the aroma of saffron

Picrocrocin imparts the flavour (grassy or hay-like) of saffron

What is phenology

A natural cyclic and seasonal phenomena

e.g. leaf emergence, leaf fall, flowering and fruiting, seed germination

Environmental factors in timing of flowering

Floral evocation: the conditions required for an apical meristem to become a flower

Environmental cues includes:

• Photo period (day length)

• Temperature

• Competition from other plants

• Nutrient availability

• Interactions with animals

Internal cues include:

• Plant age

• Plant size

• Hormonal signals

How does photoperiod affect timing of flowering

Short-day plants flower when an uninterrupted period of darkness exceeds a critical night length

Long-day plants flower when a period of darkness is less than critical night length

How does vernalisation affect timing of flowering

Vernalisation is prolonged cold temperature

• Ensures that reproductive development and seed production occurs in winter or spring, rather then in autumn

• Flowering is promoted with cold periods; effective range between freezing and 10 degrees, optimum range between 1-7 degrees

Plant in warm climates

• Other environmental cues are more important

• E.g. fire-induced flowering

Phenology and climate change

Increased temperature and more unpredictable weather events will impact flowering