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Control of shoot elongation and hormone physiology in poinsettia by light quality provided by light emitting diodes – a minireview

Islam, M. A., Gislerod, H. R., Torre, S., Olsen, J. E.
Acta horticulturae 2015 no.1104 pp. 131-136
Euphorbia pulcherrima, abscisic acid, adverse effects, auxins, cryptochromes, cultivars, flowering, gibberellins, greenhouse production, hormone metabolism, hormones, human health, imports, lamps, light quality, ornamental plants, phytochrome, receptors, sodium, supplementary lighting
In greenhouse culture of poinsettia, which is among the economically most import ornamentals worldwide, control of shoot elongation is essential. Plant growth retardants (PGR) are commonly used in this respect. However, due to the potential negative effects of PGR on human health and the environment, limitation of their use is desirable. Recent developments in light emitting diode (LED) technology provide interesting possibilities for optimizing greenhouse cultures by precise manipulation of supplementary lighting regimes. Aiming at exploitation of light quality responses as an alternative to PGR in poinsettia, we have studied responses to blue (B) light and end of day (EOD) treatments with red (R) and far-red (FR) light from LEDs and effects on hormone metabolism. Here, recent studies of light quality responses and profiling of involved hormones in poinsettia are reviewed. Exposure to LED with 20% B (80% R) inhibited shoot elongation up to 35% compared with traditional high pressure sodium lamps providing 5% B. The phytochrome photostationary state was similar in these treatments, indicating that B light receptors such as cryptochromes control elongation in poinsettia. Furthermore, poinsettia was sensitive to manipulation of the phytochrome status at the EOD. Depending on cultivar, 30 min EOD-R suppressed elongation by up to 55% compared to EOD-FR. This was associated with alterations in metabolism of gibberellin, auxin and abscisic acid. Time to flowering was not affected by the B and EOD treatments. In conclusion, exploiting light quality responses may be a useful tool to reduce shoot elongation in poinsettia without affecting flowering time.