Short-term UV Light Exposure Can Lead to Long-term Plant Growth Regulation

Ultraviolet light, especially in the UV-B region (280–315 nm), is a high-energy stressor of plants, causing darker, thicker leaves, increased secondary metabolite production, plant stunting, DNA damage, reductions in photosynthesis, and cell death. In greenhouse environments, production, UV-B is eliminated and UV-A (315–400 nm waveband) is significantly reduced. We sought to determine if short-term doses on seedlings of UV-A + UV-B from an electric lamp have a predictable long-term response in altering plant growth and form. In a series of experiments, we treated 10 species of plants, including both vegetable and ornamentals, at the plug stage with extremely high doses of UV light, and evaluated their immediate and long-term performance.  Most species showed an immediate reduction in photosystem II efficiency upon exposure to UV light, and in a few cases, they could not recover long-term.  Generally, recovery in growth, based on projected leaf area measurements, occurred seven to 14 days after treatment.  In only a few species, UV treatment caused delays in flowering.  Based on these results, we believe brief intense doses of UV-A + UV-B lead to immediate changes in plant growth and function, but the effects are largely reversible after several weeks.  This approach or using multiple, shorter-term treatments, may have potential in modifying plant growth in greenhouse production.