BIO3082 Lecture Notes - Lecture 14: Calcium Oxalate, Cytochrome C Oxidase, Cassava
Lecture 14: Climate Change and Food Security
• Cassava produces cyanide → toxic
Predictions for Changes at Elevated CO2
• Increased photosynthesis → boosts C
o Increased soluble carbohydrates
o Increase in phenolics
• More efficient use of N → boosts available N
o Less Rubisco needed for same unit leaf rate
o Reallocation of nitrogen to defence
Problem with Cyanide
• Cayanogenic glycosides (marzipan)
o Chewing it releases glucose → HCN + benzaldehyde → binds to
cytochrome oxidase
• Effects of excess cyanide in humans
o Acute poisoning
▪ Depending on dose, ingestion rate and diet
o Konzo
▪ Paralysis of legs
▪ More common in children and pregnant women – high
metabolic rate
▪ Increasing
▪ Epidemics
Effects of Drought on Cassava
• High HCN levels in droughted Cassava
• Konzo epidemics
• WHO limit – 10 ppm of cyanide
• Normal year – 15-20 ppm
• But in drought year - >200 ppm
• Rewatering can reverse high HCN in drought
Effects of Elevated CO2 on Taro and Cassava
• Photosynthesis is limited
• Resource allocation in tuberous crops in roots → more storage
• Taken taro – has small traces of HCN
o Have calcium oxalate as defence → causes swelling of throat
o Grown at high levels of CO2
o Get more corn numbers – root material at higher CO2
▪ Increased biomass
• Biomass increases at 700 ppm of CO2
o Doesn’t downregulate its photosynthesis – keeps growing
o Makes more side chains – more corms
o Increases its growth in elevated CO2 – better for future
• Biomass of Cassava increases at elevated CO2 – at 700ppm
o More corms
o Limited in where its carbohydrates can grow
o Downregulates its photosynthesis
o Effects limited to <700 ppm
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