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Dryad

Time-lapse images of Arabidopsis thaliana photoreceptor mutants under darkness and blue-light conditions

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Dec 09, 2024 version files 179.52 MB

Abstract

Rapid cell expansion pushes the Arabidopsis hypocotyl (juvenile stem) through the soil until blue light acting first through phototropin 1 (phot1) and then through cryptochrome 1 (cry1) suppresses elongation to produce the short hypocotyl characteristic of established, photosynthetically capable seedlings.

To determine where these two different blue light receptors act to suppress hypocotyl elongation, we measured relative elemental growth rate specifically along the hypocotyl midline at 5-minute intervals before and during blue light using a machine learning-based image analysis pipeline designed specifically for this kinematic analysis of growth.

In darkness, hypocotyl material expanded most rapidly (approximately 4% h⁻¹) in a zone from 0.4 to 1.5 mm below the apical terminus of the hypocotyl (cotyledonary node). Blue light acting through phot1 rapidly inhibited expansion in this zone, while simultaneously stimulating unexpanded cells in a more apical region only 0.1–0.3 mm below the cotyledonary node. Nuclear cry1, and not its cytoplasmic pool, counteracted the phot1-initiated expansion of the small cells in this apical region, preventing them from entering the more basal elongation zone. In a cry1 mutant, activation of these apical cells proceeded unchecked, reaching rates as high as 6% h⁻¹ to produce the iconic cry1 long-hypocotyl phenotype.

In addition to showing where future cell and molecular studies of cry1 and phot1 signaling mechanisms should focus, the new spatial information indicates that a seedling may use an apical reservoir of elongation potential to reenter a lit environment should a natural darkening event such as soil disturbance deactivate cry1