The quest for light: How plants compete to survive

Plants are known to engage in fierce competition for essential growth elements – light, water, and nutrients. And one of the most fascinating phenomena observed in the green world is the “shade avoidance” response.

This is an instinctive survival mechanism where plants do everything possible to intercept light in high-density environments. The concept has been studied extensively, and yet, the world of science never ceases to surprise us.

A team in the Laboratory of Molecular Biology at Wageningen University has recently unveiled a brand new shade avoidance mechanism revolving around the crucial role of the hormone cytokinin.

Plants fight for the light

So how do plants even realize that they’re getting crowded? The answer lies in the minute details of light absorption.

“In densely planted crops, red light is absorbed faster than far-red light, which is instead reflected. The red-to-far-red ratio therefore decreases with greater density. Plants ‘see’ this through the light-sensitive pigment phytochrome,” explained Professor Ronald Pierik.

Just think of this pigment as a light switch operated by the red-to-far-red light ratio. As the far-red light increases, likely in densely planted crops, responses such as elongating stems or leaves shifting from horizontal to vertical positions are triggered.

The objective is simple: the plants must rise above their neighbors to intercept more light.

Plant competition beyond light

While light competition among plants has been well-documented, Professor Pierik and postdoctoral researcher Pierre Gautrat studied these interactions from another angle.

They considered how plants compete for nutrients like nitrogen, and whether the plant’s response to far-red light is affected if it does not receive sufficient nutrition.

The fine details of plant communication are mind-boggling. But a simplified version is that plant tissues need to know the nitrogen availability in soil. They receive this information through a “message” passed from the roots.

The message carrier is cytokinin, a hormone produced in the roots that travels to the above-ground part of the plant. More nitrogen equals more cytokinin.

The Wageningen University team found that the shade avoidance response reduced when nitrogen was low. However, by adding extra cytokinin, even with low nitrogen, the length growth was significantly triggered by the far-red light.

This was a breakthrough discovery, indicating that cytokinin has a crucial role in shade avoidance.

The role of cytokinin

Even more intriguing is that previous research labeled cytokinin as a growth inhibitor.

“Looking back, all the trials on which that conclusion was based involved seedlings raised in the dark,” noted Professor Pierik. “You only get that response when you grow them in the light. And not with ordinary white light, but only with an excess of far-red light.”

The research also shed light on the genetic level of this mechanism. Certain proteins inhibit plant sensitivity to cytokinin, and these proteins are inhibited when exposed to far-red light.

It’s a fascinating game of inhibition which ultimately stimulates sensitivity.

Impact on crop cultivation

The architecture of crops has a significant bearing on their productivity. For example, dwarf wheat and rice varieties of the Green Revolution proved to be highly productive as they put less energy into length growth and more into grains.

These novel findings could help agronomists and growers improve yields in barley, wheat, maize, and rice.

The research ultimately highlights the ongoing enigma of plant biology and its potential to enhance our food production systems.

New era in sustainable agriculture

The implications of these findings extend far beyond the lab, hinting at a future where crop yields could be optimized by leveraging our understanding of shade avoidance and cytokinin.

For farmers, this research offers the possibility of tailoring crop growth under high-density planting conditions, especially as the demand for efficient food production continues to rise.

With the right balance of cytokinin, crops can potentially be coaxed into maximizing growth even in nutrient-poor soils or densely populated fields.

This breakthrough could inspire a new era in sustainable agriculture, where crop architecture is finely tuned for resilience and productivity, reducing the need for excessive fertilizer and supporting global food security efforts.

The study is published in the journal Nature Communications.

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