Lab Talk: plant chemistry, agriculture, biology and genetics
We ask four researchers to tell us about the recent papers that have excited them the most.
Phosphorus-poor plants turn to cyanide
It’s bad enough that global reserves of phosphate are running low but we may have another problem – phosphate-starved plants can produce toxic cyanide. Thousands of species do it as a form of self-defence. Sorghum, for example, produces it as a young plant or if stunted by drought. The cyanide content can reach levels high enough to kill a cow.
Our group at Monash University tested to see how low phosphate levels in the soil affected cyanide production. The deprived plants not only ended up smaller, but their stems produced higher levels of cyanide than plants stunted by other means. Surprisingly their roots showed the opposite effect, cyanide levels were lower. But when plants were grown together with mycorrhizae – fungi that help roots extract phosphate – the toxicity was lower.
Paper: Age versus stage: does ontogeny modify the effect of phosphorus and arbuscular mycorrhizas on above- and below-ground defence in forage sorghum?
Plant, Cell and Environment, 2013, DOI: 10.1111/pce.12209
Shade-loving insects cut the cost of cocoa
Traditionally, cocoa has been grown under other shady tree crops on farms that resemble simplified forests. Insects and larger fauna use them as stepping-stones between wild forest remnants. This set up also maintains ecological functions such as pollination and pest predation. Cocoa-farming trends, however, are towards full-sun monoculture cropping for higher yields and reduced fungal infections.
This pioneering study in West Africa, where most cocoa is grown, confirmed that the diversity of beneficial insects that help control the pests of cocoa, increases with shade, particularly under native trees. Although farms with less shade yielded substantially more cocoa, the extra income was negated by increased costs of pest control. The authors’ findings support policies that encourage ecologically complex agroforestry alongside farmer education.
Paper: Shade Tree Diversity, Cocoa Pest Damage, Yield Compensating Inputs and Farmers’ Net Returns in West Africa, PLOS One, 2013, vol 8, e56115
New pain drug from centipede venom
Spiders, scorpions, and centipedes evolved complex venoms that paralyse their insect prey by blocking electrical signals across nerves. Containing up to 1,000 small proteins (peptides), the venoms work by blocking the ion channels that keep the electrical signal moving. A peptide storm simultaneously blocks many different types of ion channels to ensure rapid paralysis.
In vertebrates, pain-sensing nerves rely on similar ion channels to transmit signals. So for many years now, researchers have prospected in venoms, looking for new peptides that might relieve pain.
Analysing centipede venom, we discovered a remarkable peptide called Ssm6a that selectively blocked an ion channel relaying all pain signals to the human brain. In some rodent tests, the peptide was more effective than morphine but without the side effects.
Paper: Discovery of a selective NaV1.7 blocker from centipede venom with analgesic efficacy exceeding morphine in rodent pain models. Proc. Natl. Acad. Sci. USA, 2013, vol 110, p17534–39.
Smashing the DNA time barrier
DNA is a powerful tool for studying evolutionary history. Unfortunately, an organism’s DNA begins to break down after it dies, and until recently it was thought there would be no readable DNA left after about 100,000 years.
This barrier has now been smashed in a paper by Matthias Meyer and colleagues, who have retrieved DNA from a 400,000-year-old fossil hominin from a cave in northern Spain. Comparison of this new DNA sequence with DNA from modern humans and other hominins suggests a very complex evolutionary history, with different hominin populations, including different species, interbreeding repeatedly.
Hopefully, the same techniques for ancient DNA analysis will be applicable to remains of the Australian megafauna that died out 50-200,000 years ago. This would provide fundamental new insights into their evolution and extinction.
Paper: A Mitochondrial Genome Sequence of a Hominin from Sima de los Huesos
Nature, 2013, vol 505, p403.