Downsizing in plants - UV induces pronounced morphological changes in cucumber in the absence of stress

Ultraviolet (UV)-A- or UV-B-enrichment of growth light resulted in a stocky cucumber (Cucumis sativus L.) phenotype exhibiting decreased stem and petiole lengths and leaf area. Effects were larger in plants grown in UV-B- than in UV-A-enriched light. In plants grown in UV-A-enriched light, decreases in stem and petiole lengths were similar independently of tissue age. In the presence of UV-B radiation, stems and petioles were progressively shorter the younger the tissue. Also, plants grown under UV-A-enriched light significantly reallocated photosynthate from shoot to root and also had thicker leaves with decreased specific leaf area. Our data therefore imply different morphological plant regulatory mechanisms under UV-A and UV-B radiation. There was no evidence of stress in the UV-exposed plants, neither in photosynthetic parameters, total chlorophyll content, nor in accumulation of damaged DNA (cyclobutane pyrimidine dimers). The ABA content of the plants also was consistent with non-stress conditions. Parameters such as total leaf antioxidant activity, leaf adaxial epidermal flavonol content and foliar total UV-absorbing pigment levels revealed successful UV acclimation of the plants. Thus, the stocky UV-phenotype was displayed by healthy cucumber plants, implying a strong morphological response and regulatory adjustment as part of UV acclimation processes involving UV-A and/or UV-B photoreceptors.