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.”