Natures wonders:new phototropism mechanism (Introduction)

by David Turell , Monday, November 27, 2023, 18:22 (152 days ago) @ David Turell

Air spaces in stems interpret light:

https://www.science.org/doi/10.1126/science.adl2394?utm_source=sfmc&utm_medium=emai...

"Plants sense and respond to light through photoreceptors—for example, by using directional growth to bend toward strong light (phototropism). Decades of work has identified the molecular mechanisms that underlie phototropism, but whether plants also physically alter beams of light to enhance their ability to respond was not known. Nawkar et al. report that plants can use intercellular air spaces to actively modify the path of light and perform accurate phototropism. This finding highlights the importance of physical organ structure in environmental sensing and opens new avenues to understand the role of air spaces in other contexts.

"Nawkar et al. show that intercellular air spaces in the hypocotyl (embryonic stem) of the model plant Arabidopsis thaliana scatter light and are necessary for phototropism. To do this, they identified a mutant line of the plant with a transparent hypocotyl that does not bend toward light. In this mutant, imaging methods including transmission electron microscopy revealed that the intercellular spaces in the hypocotyl and roots that are normally filled with air are instead full of water. These water-filled spaces allowed light to pass through the stem without scattering, making the stem appear transparent. Mutant plants responded normally in response to gravity, which shows that this is a specific response to light rather than a more general defect in environmental sensing or directional growth.

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"Previous work has identified the abcg5 mutant, has shown that hypocotyls contain intercellular air spaces, and has shown that water infiltration enhances light transmission in several plant species. Nawkar et al. have linked these three observations to identify the molecular basis of tissue-level optical properties and to show that these properties confer the ability to respond to environmental cues.

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"The identification of ABCG5 as a regulator of air space formation is also an avenue to understand the broader role of air spaces in other tissues and species. If other ABCG family members control air space formation in organs, such as leaves or flowers, then plants with mutations in these genes would allow the function of air spaces throughout the plant to be investigated. Questions include whether air spaces affect light scattering in petals to make them more attractive to pollinators and whether there are cell type–specific roles for air spaces in the leaf. It would also be interesting to establish whether ABCG proteins evolved to maintain the enlarged air spaces that allow many aquatic plants to float.

"Such a clear function for air spaces in the stem may pose an answer to the questions of how and why plants evolved to have these spaces. It has long been appreciated that air spaces function in leaves to promote gas exchange and light scattering (10), but intercellular spaces can be observed in the stems of 400-million-year-old fossil plants in early Devonian rocks of the Rhynie Chert in Scotland—which is long before plants evolved to have leaves (11). The function of these stem intercellular spaces is not clear, but it may be that, as in the A. thaliana hypocotyl, they are air-filled channels that allow effective phototropism. This interpretation suggests that plants evolved to have air spaces in stems, at least in part, to regulate light sensing and that these spaces were co-opted to perform secondary functions in leaves.

"Overall, the study by Nawkar et al. demonstrates the importance of looking in unexpected places to answer long-standing questions and is a reminder to look beyond molecular mechanisms and consider the physical structure of an organism when thinking about function. It is also a reminder that, like animals, plants actively modify their sensory inputs to better respond to their environment. (my bold)

Comment: note the bold. Work by a designer, who understands how to bend light, or adaptation by the plants themselves?