Abstract
Photons during the dark period delay flowering in short-day plants (SDP). Red photons applied at night convert phytochromes to the active far-red absorbing form (Pfr), leading to inhibition of flowering. Far-red photons (greater than 700 nm) re-induce flowering when applied after a pulse of red photons during the dark period. However, far-red photons at sufficiently high intensity and duration delay flowering in sensitive species. Mechanistically, this response occurs because phytochrome-red (Pr) absorbance is not zero beyond 700 nm. We applied nighttime photons from near infrared (NIR) LEDs (peak 850 nm) over a 12 h dark period. Flowering was delayed in Glycine max and Cannabis sativa (two photosensitive species) by 3 and 12 days, respectively, as the flux of photons from NIR LEDs was increased up to 83 and 116 μmol m-2 s-1. This suggests that long wavelength photons from NIR LEDs can activate phytochromes (convert Pr to Pfr) and thus alter plant development.
Highlights
Phytochromes are a class of plant photoreceptors that modulate development throughout the life cycle of a plant
They interconvert between two major forms upon photon absorption: the inactive form (Pr), which is most sensitive to red photons, and the active form (Pfr), which is most sensitive to far-red photons [1]
PPE is an estimate of the fraction of active Pfr to the total phytochrome pool, and it is calculated from the spectral photon distribution (SPD) of the incident light and photoconversion cross-sections for Pr and Pfr at each wavelength [2,3,4,5,6,7,8]
Summary
Phytochromes are a class of plant photoreceptors that modulate development throughout the life cycle of a plant. It is important to choose species known to be sensitive to night-break/nighttime photons when investigating the ability of photons from NIR LEDs to activate phytochromes and inhibit flowering.
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