Floral Color Changes in Boswellia sacra Flueck

Botany 2110 Samantha Kane

Flora-Morphology, Distribution, Functional Ecology of Plants Volume 206, Issue 9, September 2011

Facts about Boswellia sacra

Also known as Frankincense; found in the Bible

Part of the Burseraceae family

Used for perfume and medicine

Popular in trade

Facts about Boswellia sacra

Found in South Arabia and North East Asia

Found in extreme locations

Population is decreasing because of overgrazing and human destruction

National Park in Wadi Dowkha

Boswellia sacra

Flowering stage begins in the winter until April

Fruiting bodies are ripe by March

Characteristics: green calyx radial symmetry five white petals ten stamens that have yellow anthers one pistil nectariferous ring is present in the ovary and

can change colors from yellow to red to black

Purpose & Hypothesis

Purpose: to figure out why the nectariferous ring changed colors

Hypothesis: the color change helped lure pollinators towards the flower with the reward of nectar

The Study

Took place along the coasts of Dhofar and in the Wadi Dowkha National Park

Flowers were collected in February and March from 2006-2010

Nectar and pollination were observed in the morning (7:30-8am) and sunset (6-6:30) for a week

Microscopical observations were observed in labs in Florence

Under the Microscopes

Different stains were used to see detail under the light microscopes including:

Toluidine Blue for testing lignin

Mercuric Bromophenol Blue for proteins

Acriflavine stain for total polysaccharides

Alcian Blue for acidic polysaccharides

Fluorol Yellow-088 for lipids

Methods

The pistils and nectariferous discs were covered in glutaraldehyde (a disinfectant and preservative)

stained with PAS (Periodic Acid Schiff) to see undissolvable polysaccharides

stained with Blue Nile Sulfate to see the neutral and acidic lipids

The nectariferous rings were cut off and covered in an alkaline and an acidic solution to test for anthocyanins. (may appear in different colors depending on pH)

Results of Flower Organs

(Nectariferous Ring) Located between the stamens and the ovary (3mm in diameter)

Changes color from yellow to red depending on the maturity of the flower

Before anthesis, (flower opens its petals) the nectariferous ring is fully developed

Trichomes are covered in a cuticle layer where nectar drops can be found

The drops show a positive response to the PAS reagent, Alcian Blue, and Mercuric Mromopenol Blue. (shows polysaccharides exist!)

Stomata always open with guard cells appearing outward

Results of Flower Organs(Pistil)

The stigma (top of pistil) has a positive response towards the Alcain Blue, and Blue Nile Sulfate stains (test acidic polysaccharides and neutral lipids)

After fertilization, the ovary swells transforms into a fruit with a seed in each open compartment

Results of Flower Organs

(Anthers)Anthers on the flower are all the same size

with longitudinal dehiscence (spontaneously opening)

yellow in color with trichomes sparsely located

anthers swell due to the large amount of pollen

dehiscence takes place

Color Changes

The nectariferous ring is already a yellow color when the petals begin to open; many liquid drops found

Changes to orange and few drops are present. Nectar begins to be reabsorbed. Largest amount of pollen germination occurs. Anthers empty and the stigma changes its green color to a brown

Changes to red and is completely dry and lacking nectar. Anthers begin to fall and stigma dry up and darken

Only fifteen hours are needed for the color changes

Color Changes

Lastly, the nectariferous ring will turn brown with black patches. The surface is wilted and rough. The ovary is growing into the fruit

Takes two days to change from yellow to brown

Red stage changes to a green-blue color once dipped into an alkaline medium and will change back to red once rinsed in acid showing that there are many anthocyanins present.

Field Observations(Pollinators)

Many pollinators

Main pollinators in the day-bees, wasps, and ants

Other visitors-butterflies and little flies

pollinators preferred flowers with the yellow nectariferous ring , the red were not visited at all

Conclusions

Color changes help lead the pollinators towards the rewarding flowers

Mutualistic relationship (plants get pollinated and pollinator gets pollen and nectar as nutrients)

Insects are attracted to the yellow and orange phase; no nectar reward in the red phase

The color change occurs because of high amounts of anthocyanins

that flowers with nectar rewards and an attractive color for pollinators have a greater chance of reproducing and outcompeting other plants