Fields of yellow: getting the nutrient balance right in oilseed rape

How plants take up, mobilise and use the mineral elements they require is key to how plants thrive in dynamic environmental conditions, and to maximising the potential of commercially-important plants. Brassica napus, better known as oilseed rape or rapeseed, will be a familiar sight and smell to anyone who grew up in the countryside of many nations. In their recent paper in Annals of Botany, Wang and colleagues investigate how exposure to different levels of phosphorous affects the abundance and distribution of other mineral elements in B.napus. They then identify genetic loci that may further our understanding how important crop species balance their nutrient levels in dynamic conditions.

Widespread production of oilseed rape is no accident, it is now the third largest supply of vegetable oil in the world and is also a significant feedstock for production of animal feeds and biofuels. Like all commercially-important crops, mineral availability is of key importance to maximising yields and productivity of oilseed rape and it has particularly been shown to be susceptible to low phosphorous conditions. One often-recorded consequence of phosphorous deficiency is alteration in the composition and distribution of other essential plant minerals.

Wang and colleagues record the difference in concentrations and distribution changes of various mineral elements in B.napus grown in either high or low concentrations of phosphorous. The concentration of the majority of other mineral elements were reduced at the whole-plant level in low phosphorous conditions, something that Wang and colleagues speculate is possibly due to reduced growth of B.napus in the low phosphorous conditions. The main exception to this trend was iron, which was significantly increased in concentration in low phosphorous B.napus. This may be due to the fact that iron can precipitate with phosphorous at high concentrations of the latter, reducing the ability of plants to take the iron up. This highlights an important point – high concentration does not necessarily correlate to high availability.

Analysis of changes in mineral concentration and distribution in response to phosphorous conditions also gives insights into the possible mechanisms underpinning these changes. For example, Wang and colleagues note that partitioning of calcium and manganese to the shoot in both high and low phosphorous conditions follows similar patterns. This possibly indicates shared mechanisms in uptake or translocation of these ions. To investigate this further, Quantitative Trail Loci (QTLs – basically changes in a DNA sequence that correlate with the presence or absence of a certain phenotype or trait) are identified by Wang and colleagues that correlate with the changes in mineral concentration and distribution. Amongst other things, analyses indicated similar QTL positions for certain minerals, supporting shared possible mechanisms for uptake or translocation encoded at the genetic level. Interestingly, QTLs identified differed between the high phosphorous and low phosphorous conditions, reinforcing the notion that plant nutrient uptake is complex and sophisticated, and capable of responding to a variety of conditions including the availability of other minerals.

The patterns and genetics described in this paper will be important to understanding how the commercially important B.napus responds to dynamic environments, and how we can perhaps make best use of it in the future.