Trends in Plant Science
SpotlightPhytochrome Responses: Think Globally, Act Locally
Section snippets
Local Hyponastic Response
Two recent papers 8, 9 address shade avoidance responses to localized FR treatments in Arabidopsis plants at the rosette stage, which are structurally more complex than tiny seedlings. Both studies measured the upward leaf movement (hyponasty) caused by supplemental FR radiation. Leaf hyponasty is a classical shade avoidance response because it allows the plant to push leaf blades into well-illuminated areas of the canopy. The hyponastic movement depends on differential growth rates between the
How Is the Local Hyponastic Response Generated?
Interestingly, FR treatment of a small area of the leaf tip is sufficient to elicit a strong hyponastic response, which is equivalent to the response elicited by illuminating the whole leaf with FR. By contrast, FR delivered to the petiole, which is the part of the leaf that bends to generate upward leaf movement, results in increased petiole elongation, but fails to elicit a hyponastic response 8, 9. Therefore, the local response, which is restricted to the treated leaf, requires
The Advantages of Being Modular
Higher plants are modular organisms comprising interconnected repeated units or modules. Within the aerial part of the plant, organ-specific responses to local R:FR signals (Figure 1) can be important to maximize light capture and whole-plant fitness. For example, the fact that the internodes of plants with vertical stems can autonomously detect and respond to lateral FR allows the plant to efficiently use FR radiation coming from the sides of the plant as an early signal of competition. This
Concluding Remarks
Plants have a reputation for not allocating resources to ‘subprime’ functional units. Each leaf is responsible for its own carbon budget, because mature leaves do not import photoassimilates from other leaves even if they become shaded or carbon starved. As such, it makes sense that each leaf has the sensory systems and transduction elements to ensure its proper positioning for optimal light capture. This is what allows plants as a whole to efficiently forage for light in complex environments,
Acknowledgments
Work in my laboratory is supported by CONICET and grants from UBACyT and FONCyT. I thank Amy Austin for helpful comments on the manuscript.
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