Supplementary UV-A and UV-B radiation differentially regulate morphology in Ocimum basilicum

UV-A- or UV-B-enriched growth light was given to basil plants at non-stress-inducing intensities. UV-A-enriched growth light gave rise to a sharp rise in the expression of PAL and CHS genes in leaves, an effect that rapidly declined after 1-2 days of exposure. On the other hand, leaves of plants grown in UV-B-enriched light had a more stable and long-lasting increase in the expression of these genes and also showed a stronger increase in leaf epidermal flavonol content. UV supplementation of growth light also led to shorter more compact plants with a stronger UV effect the younger the tissue. The effect was more prominent in plants grown under UV-B-enriched light than in those grown under UV-A. Parameters particularly affected were internode lengths, petiole lengths and stem stiffness. In fact, the bending angle of the 2nd internode was found to increase as much as 67% and 162% for plants grown in the UV-A- and UV-B-enriched treatments, respectively. The decreased stem stiffness was probably caused by both an observed smaller internode diameter and a lower specific stem weight, as well as a possible decline in lignin biosynthesis due to competition for precursors by the increased flavonoid biosynthesis. Overall, at the intensities used, UV-B wavelengths are stronger regulators of morphology, gene expression and flavonoid biosynthesis than UV-A wavelengths. [GRAPHICS]

Automated summary

Basil plants were exposed to UV-A or UV-B-enriched growth light at non-stress-inducing intensities. The expression of PAL and CHS genes in leaves significantly increased under UV-A-enriched light, but rapidly declined after 1-2 days. In contrast, plants grown under UV-B-enriched light had a steady and long-lasting increase in gene expression, along with a stronger increase in leaf flavonol content. UV supplementation also affected the morphology of plants, resulting in shorter and more compact growth, with a stronger effect on younger tissue. UV-B wavelengths were found to be more influential than UV-A wavelengths in regulating morphology, gene expression, and flavonoid biosynthesis.