Colour, smell and taste – the beautiful world of plants and chemistry Alison Foster, University of Oxford Botanic Garden Dubrovnik, Croatia, 2012

Plants and Chemistry Colour Smell Taste

Colour Main pigment types –Porphyrins (nitrogen containing) –Flavonoids (incl. anthocyanins) –Carotenoids (terpenes) –Betalains (nitrogen containing)

Colour β-carotene cyanidin-3- glucoside betanidin

Colour Anthocyanins: Found in many plant families – except those in Caryophyllales Found in all plant tissues 10 9 tonnes produced per year in nature 2% of all carbon fixed via photosynthesis is converted to anthocyanins

Ferns (and Fern allies) Gymnosperms Angiosperms

Colour Functions of anthocyanins: Pollinator attractant Sunscreen – succulents and autumn leaf colouration Anti-feedants – bitter tasting

Colour Anthocyanins as pollinator attractant? Bromeliaceae

Colour Anthocyanins as sunscreen or antifeedant or both?

Colour Anthocyanins as antifeedant ?

Colour Metasequoia glyptostroboides dawn redwood Rhodoxanthin:

Colour Daucus carrota carrot beta-carotene

Colour Solanum lycopersicon tomato lycopene:

Colour Betalains: Amino-acid derived Nitrogen containing – metabolically more expensive Yellow to red pigments (betaxanthins and betacyanins) Only present in plants in order Caryophyllales

Caryophyllales

Colour Betalains: Caryophyllales: Beetroot (Amaranthaceae) Bougainvillea (Nyctaginaceae) Pokeweed (Phytolaccaceae) Carnations (Caryophyllaceae)

Smell Nicotiana attenuata from the SW United States –Releases benzyl acetone when flower opens at night –Attracts hawkmoth pollinators Pollinators are also herbivores (larval stage) Upon herbivore attack, flowers no longer produce benzyl acetone nor open at night Day opening flowers are then hummingbird pollinated

Smell Lavandula angustifolia camphorcineole linalyl acetate linalool

Smell Amorphophallus titanum Spadix emits smell of rotting flesh Pollinators are attracted –Carrion-eating beetles –Flesh flies Smell made up of amines and disulfides putrescine cadaverine

Smell Cercidiphyllum japonicum –Senescing and abscising leaves –Green leaves contain maltol glucosides –Yellow brown/fallen leaves contain maltol

Taste Chilli peppers (Capsicum species) contain capsaicin “Hotness” measured on the Scoville scale Test method devised in 1912 by Wilbur Scoville Now measured by HPLC

Taste 0 Jalapeño pepper Scotch Bonnet 5, ,000 Naga jolokia1,040,000 Sweet pepper Chilli pepper Scoville Heat Units

Taste Euphorbia resiniferatoxin Resiniferatoxin 16 Billion SHU

Taste Ginger – Zingiber officinalis, Zingiberaceae Active constituent of fresh ginger is gingerol Cooking ginger transforms it into zingerone

Taste Ginger – Zingiber officinalis, Zingiberaceae Dried ginger contains more of another molecule, shogaol The Japanese name for ginger is shōga

Taste Ginger – Zingiber officinalis, Zingiberaceae Dried ginger contains more of another molecule, shogaol The Japanese name for ginger is shōga

Taste Vanilla– Vanilla planifolia, Orchidaceae

Taste

caffeine theophylline theobromine

Taste theobrominecaffeinetheophylline

Conclusions