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