How plants know where to find the light

In a remarkable fusion of biology and engineering, the team led by Prof Christian Fankhauser at the University of Lausanne (UNIL), in collaboration with EPFL, has made a significant breakthrough in understanding how plants perceive light.

This study reveals how plants, devoid of visual organs, determine the source of light using the unique optical properties at the air-water interface within their tissues.

Phototropism in plants

Phototropism, the orientation of plants towards light, is a critical phenomenon for their survival. As Prof Fankhauser explains, “The majority of living organisms (micro-organisms, plants and animals) have the ability to determine the origin of a light source, even in the absence of a sight organ comparable to the eye.”

This ability is crucial for plants to optimally position their organs for maximum sunlight exposure, facilitating efficient photosynthesis, the process by which they convert light energy into chemical energy.

Light detection mechanism

The key to this discovery was the observation of a mutant variety of Arabidopsis thaliana, a model plant species, with a uniquely transparent stem. Prof Fankhauser’s team, in conjunction with DrSc. Andreas Schüler and the UNIL’s Electron Microscopy Centre, found that the normal, milky appearance of plant stems is due to air-filled channels in their tissues.

In contrast, the mutant plants had these channels filled with water, giving them a translucent appearance. These channels, it turns out, are crucial for establishing a light gradient within the plant, a mechanism previously unknown.

Martina Legris, a postdoctoral fellow in Prof Fankhauser’s group, sheds light on the underlying science. She clarifies, “More specifically, air and water have different refractive indices. This leads to light scattering as it passes through the seedling.”

This scattering of light, akin to the formation of rainbows, enables the plant to ‘read’ the light gradient and determine the light source’s direction.

Broader implications of phototropism

This fascinating research elucidates a novel mechanism for light perception in plants, and also provides insights into the formation and functions of air-filled intercellular channels. These channels are known to aid in gas exchange and offer resistance to hypoxia during flooding.

Understanding their development from embryonic stages to adulthood remains an area ripe for exploration. The genetic resources utilized in this study promise to further our understanding of these intricate structures.

In summary, the collaborative efforts of UNIL and EPFL have unveiled a fascinating aspect of plant biology, opening new avenues in our understanding of plant physiology and their interaction with the environment. This study not only enriches our scientific knowledge but also underscores the importance of interdisciplinary research in unraveling the complexities of nature.

The full study was published in the journal Science.

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