Growth inhibition is one of the most consistent plant responses to Ultraviolet-B (UV-B) exposure; this radiation, both as part of the solar spectrum in the field and from UV-B lamps in controlled environments. In this work, Fina et al. () demonstrate that the UV-B levels present in solar radiation inhibit maize (Zea mays) leaf growth without causing any other visible stress symptoms, including the accumulation of DNA damage. So how does UV-B inhibit leaf growth? To answer this question, the authors conducted kinematic analyses of cell division and expansion to understand the impact of UV-B radiation on these cellular processes. Their results demonstrate that the decrease in leaf growth in UV-B-irradiated leaves is a consequence of a reduction in cell production and a shortened growth zone. To determine the molecular pathways involved in UV-B inhibition of leaf growth, they performed RNA sequencing on isolated growth zone tissues of control and UV-B-exposed plants. Their results show a link between the observed leaf growth inhibition and the expression of specific cell cycle and developmental genes, including growth-regulating factors (GRFs) and transcripts for proteins participating in different hormone pathways. Interestingly, the decrease in the growth zone size correlates with a decrease in the concentration of gibberellic acid-19 (GA19), the immediate precursor of the active gibberellin, GA1, by UV-B in this zone. This decrease is regulated, at least in part, by the expression of GRF1 and possibly other transcription factors of the GRF family.
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