Control of Plant Morphology by UV-B and UV-B-Temperature Interactions

Chemical plant growth retardants (PGRs) are used to control height of greenhouse grown plants. Increasing environmental awareness has strongly promoted interest in alternative methods. Since UV-B is known to reduce shoot elongation, the use of supplemental UV-B radiation or UV-B and UV-A-transmitting cladding material such as F-clean appears highly interesting. Substantially reduced shoot elongation was observed in a variety of bedding and pot plants produced in the spring in Norway at 59 degrees N under F-clean compared to polyethylene. Furthermore, although natural UV levels are low in the autumn at 59 degrees N, a 30% reduction in the use of PGRs as a consequence of reduced shoot elongation was then observed in poinsettia (Euphorbia pulcherrima) under F-clean. Poinsettia exposed to short diurnal periods of UV-B radiation in the night, also showed reduced internode lengths and increased branching. Effect of UV-B and its interaction with temperature on morphology was investigated using pea (Pisum sativum) as a model system. The UV-B stimulated reduction in shoot elongation was substantially enhanced when given in combination with a temperature drop treatment. Also, plants were then less susceptible to UV-B-induced damage, indicating an effect of temperature reduction on UV-protective mechanisms.