Abstract
Plants growing in high densities experience a reduced red (R) to far‐red (FR) light ratio and shade‐intolerant species respond with accelerated elongation growth to reach the top of the canopy: the shade avoidance syndrome (SAS). FR‐enriched light inactivates phytochrome photoreceptors, which results in subsequent action of several plant hormones regulating growth. SAS is adaptive for shade‐intolerant plants, but is suppressed in shade‐tolerant plant species. Inspired by a previously published transcriptome analysis, we use two species of the genus Geranium here to study the involvement of auxin, brassinosteroids (BRs), and gibberellins (GAs) in supplemental FR‐induced elongation growth. G. pyrenaicum, a shade‐avoiding species, strongly induces auxin and gibberellin levels, but not BR, in elongating petioles. We show that, in this species, FR light perception, hormone synthesis, and growth are local and restricted to the petiole, and not the leaf lamina. Using chemical hormone inhibitors, we confirm the essential role of auxin and GAs in supplemental FR‐induced elongation growth. Shade‐tolerant G. robertianum does not display the change in hormone levels upon FR light enrichment, resulting in the lack of a shade avoidance response.
Highlights
Shade‐intolerant plants growing in dense stands, for example, a grassland or agricultural field, compete with neighbors to secure light interception
shade avoidance syndrome (SAS) is a favorable strategy for shade‐intolerant species, but it is suppressed by shade‐tolerant plants in the forest understory that are unable to outgrow neighboring trees (Gommers, Visser, St Onge, Voesenek, & Pierik, 2013; Gommers et al, 2017)
We aimed to look for differences in hormone synthesis and signaling upon plant neighbor detection through FR light enrichment in two species with opposite growth strategies during shade
Summary
Shade‐intolerant plants growing in dense stands, for example, a grassland or agricultural field, compete with neighbors to secure light interception. To do so, they enhance the elongation of stems and leaves, growing taller than surrounding plants. They enhance the elongation of stems and leaves, growing taller than surrounding plants This adaptive trait is referred to as the shade avoidance syndrome (SAS) and largely depends on the modulation of the homeostasis of several plant hormones
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