LIGHT SWITCH: The active form of the photoreceptor phytochrome B (phyB) suppresses stem growth in seedlings. In lab experiments, low light inactivates phyB, triggering growth. Warm temperatures turn out to also inactivate phyB, evidence that this pathway monitors temperature as well as light to coordinate growth. This may explain why plants grow the most in warmer, shady conditions compared to cooler shade, and why plants in full light—a growth-slowing condition—grow more if it’s warm.
© KIMBERLEY BATTISTA
The paper
M. Legris et al., “Phytochrome B integrates light and temperature signals in Arabidopsis,” Science, 354:897-900, 2016.
Researchers discovered in the 1930s that they could cause lettuce seeds to germinate just by shining red light on them. It turns out, as scientists later revealed, that the proteins responsible for this phenomenon are photoreceptors called phytochromes, now appreciated for their roles in regulating many aspects of plant development beyond germination, from stem growth to the sprouting of leaves to bud flowering. A pair of papers published last October in Science, however, describes an entirely new role for one of the pigments: sensing temperature.
The experiments were conducted on phytochrome B (phyB), which, like other phytochromes, is activated by red light but deactivated by light on the far-red end of the visible light spectrum. When turned on, phyB shuts off a class of transcription factors needed for stem growth in seedlings. If the seedling is in the shade of another plant—a potentially fatal situation—far-red light filters through the leaves and triggers a growth spurt.
Jorge Casal, a researcher at the Agricultural Plant Physiology and Ecology Research Institute in Argentina and a coauthor on one of the papers, initially hypothesized that phyB would be unaffected ...
