March 6, 2015

Tutorial: Mass spectrometry in plant science, part 2 – using isotopic labels to study plant metabolism

In this second entry on the use of mass spec in plant research, I want to introduce isotopic labeling and its power to inform us about plant metabolic processes quantitatively. By feeding an isotopically labeled substrate into the metabolic stream of an organism and observing it later in some downstream metabolic intermediate, we can gain insights into the rates at which these transformations take place inside the cell. Experimentally, we observe these isotopic labels as shifts to heavier m/z values in the mass spectrum of molecules that incorporate them. As isotopically labeled atoms introduced in our labeling experiment migrate through the different metabolites in a biochemical pathway, we see specific mass peaks rise and fall in a spectrum over time that are indicative of the turnover of that pool of metabolites. This is a complex subject that has been covered in detail with precisely the mathematical rigor you might expect (see for example publications by Wolfgang Wiechert on metabolic flux analysis). In this short monograph, I can only hope present how well mass spectral analysis lends itself to quantifying plant metabolism.

March 5, 2015

Zhang et al. "Full crop protection from an insect pest by expression of long double-stranded RNAs in plastids"

Jiang Zhang, Sher Afzal Khan, Claudia Hasse, Stephanie Ruf, David G. Heckel, Ralph Bock*

Science 27 February 2015:Vol. 347 no. 6225 pp. 991-994 DOI:10.1126/science.1261680

Crop protection in large scale agriculture is a necessity given the many unintended consequences of traditional breeding. One of these consequences was the elimination of many natural plant defenses against insects, which consisted partly of the accumulation of bitter and poisonous secondary metabolites which made them unappealing for insects to eat. In our aeons long quest to make a better tasting tomato, our breeding experiments naturally resulted in food that tasted better to us by eliminating those same bitter, poisonous metabolites. And insects could not thank us more for our efforts, as they find our domesticated plants even tastier than their wild type cousins. A considerable amount of scientific energy has therefore been invested in devising strategies that protect crops intended to fill our pantries from their natural enemies: the rest of nature.