Response of cotton and sorghum to several levels of subambient solar UV-B radiation: A test of the saturation hypothesis

Robert S. Coleman, Thomas Day

Research output: Contribution to journalArticle

20 Scopus citations

Abstract

Some have proposed that plant responses to above-ambient or supplemented levels of solar ultraviolet-B radiation (UV-B; 280-315 nm) are typically subtle because targets or receptors in plants become saturated. If true, in solar UV-B filter exclusion experiments we would expect that plant responses would level off or 'saturate' as doses approached ambient levels. To test this so-called 'saturation hypothesis' we examined the response of Gossypium hirsutum (cotton) and Sorghum bicolor (sorghum) to filter exclusions that provided five levels of biologically effective UV-B, ranging from 36 to 91% of ambient solar levels in Arizona, USA. UV-B dose had no effect on biomass production of either species. As UV-B dose increased or approached ambient, individual leaves of S. bicolor were smaller, but plants produced more tillers and leaves. In G. hirsutum, individual leaves as well as total plant leaf area were smaller, but plants produced more branches. Bulk concentrations of soluble UV-B absorbing compounds increased with UV-B dose in both species. Leaf epidermal UV-B transmittance, assessed with the chlorophyll fluorescence technique, declined with increasing UV-B dose, and was well correlated with bulk concentrations of soluble UV-B screening compounds. Bulk concentrations of insoluble or wall-bound UV-B absorbing compounds were not affected by UV-B dose. The intensity of UV-induced blue fluorescence from leaf surfaces was strongly correlated with bulk concentrations of wall-bound UV-B absorbing compounds, and this signal has the potential to provide a rapid, non-invasive method to estimate concentrations of these compounds, which are time-consuming to extract. While both species were responsive to solar UV-B, responses did not appear to become saturated as doses approached ambient levels. Rather, responses required a threshold dose of >70% of solar ambient UV-B levels before they became apparent.

Original languageEnglish (US)
Pages (from-to)362-372
Number of pages11
JournalPhysiologia Plantarum
Volume122
Issue number3
DOIs
StatePublished - Nov 1 2004

ASJC Scopus subject areas

  • Physiology
  • Genetics
  • Plant Science
  • Cell Biology

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