2 May 2019

‘Pinch of salt’ keeps crops from growing too tall

A little bit of salt in the soil attenuates plant height growth at high planting densities. Biologists from Utrecht, Wageningen, Amsterdam and Madrid have unravelled the molecular route that guides this process.

Plants in a field or a greenhouse often grow close together, and therefore in shade from nearby plants. In order to catch the life-giving sunlight, they tend to quickly grow to great heights. Unfortunately, investing in a long stem weakens the plant and lowers the yield of desired parts like tubers, fruits and seeds. The challenge is to find a way to prevent plants from growing unnecessarily tall.

Opposite influences

Until now, plant biologists had only investigated the influence of individual abiotic factors on the growth of plants. Professor of Plant Photobiology at Utrecht University (UU) Ronald Pierik: “For plants, the difference between sun and shade is the proportion of two types of light; the colours red and far-red. The greater the proportion of far-red light a plant receives, the faster it will grow to reach the sunlight.” Salt, however, has the opposite effect: plants don’t grow well on saline soils. “Salt hampers the plant’s absorption of water from the soil, and sodium, which is a component of salt, is even toxic”, says Pierik.

Arm against stress

To be able to determine how light and salt combine to influence plant growth, the UU biologists sought cooperation with colleagues from other universities. Pierik: “We discovered that just a pinch of salt in the soil keeps a plant from growing out of the shade, but it doesn’t die either. Perhaps it is important for plants to attenuate their growth rate instead of boosting it, when they have to arm themselves against stress.” First author Scott Hayes, who now works in Madrid, determined how that happens at the genetic and molecular level: “In situations without salt stress, the plant hormone brassinosteroid helps the plant to grow out of the shade. However, with salt stress, another hormone called abscisic acid is activated, which in turn mitigates the response to the aforementioned hormone. As a consequence, the plant no longer responds well to shade.”

Arabidopsis seedling with a drop of the hormone application fluid.
A salty soil attenuates the growth response to shade: Arabidopsis in control conditions (upper left), in shade (upper right), on salty soil (lower left) and in combined shade and salt conditions (lower right).

Improving crops

The findings could influence both agriculture and science, according to Pierik. “Agricultural plants always grow in high densities, and now we know much better how to manage the undesired growth in height. But apart from that, our research shows that it is important to not just to study separate processes, but also the complex interactions between those processes. And that’s the knowledge we need to be able to improve our crops.”

Publication

Soil salinity limits plant shade avoidance
Scott Hayes*, Chrysoula K. Pantazopoulou*, Kasper van Gelderen*, Emilie Reinen*, Adrian Louis Tween*, Ashutosh Sharma, Michel de Vries, Salomé Prat, Robert C. Schuurink, Christa Testerink, and Ronald Pierik*
*Affiliated to Utrecht University
Current Biology, 2 May 2019

Researchers

Response of plants to light: Scott Hayes and Ronald Pierik (Utrecht University)
Plan salt stress: Christa Testerink (Wageningen University & Research)
Specific analyses: Rob Schuurink (University of Amsterdam) and Salomé Prat (Centro Nacional de Biotecnologia, Madrid)