Into the fourth dimension

Abstract

The influence of time on the drought response of Brassica rapa, an agriculturally important species of plant, has been clarified.

Keywords: Brassica rapa; abiotic stress; daily rhythms; drought; photosynthesis; plant biology; transcriptomic network analysis.

Figure 1.. Cyclic behavior in the plant Brassica rapa (schematic).

Greenham et al. exposed the plants to mild drought over four days, with the level of drought slowly increasing over time, and measured a number of traits over the last 48 hours; results for well-watered plants are shown in green, drought-stressed plants are shown in brown. Mild drought had a negligible effect on the rate of photosynthetic carbon reduction (top). However, mild drought led to increased leaf sugar content overnight (middle); it is possible that this helps to maintain favourable 'water relations' between cells and the external environment. The presence of two types of sample variation in the experiment – the increase in the level of drought with time, and the natural circadian cycle – allowed Greenham et al. to identify the genes that respond to drought (bottom). They did this by identifying genetic modules with levels of expression that correlate with variations in the rate of carbon fixation over time, and differ slightly in well-watered plants (green) and plants exposed to mild drought (brown).