Nitrogen Limited Red and Green Leaf Lettuce Accumulate Flavonoid Glycosides, Caffeic Acid Derivatives, and Sucrose while Losing Chlorophylls, Β-Carotene and Xanthophylls

PLoS One. 2015 Nov 16;10(11):e0142867. doi: 10.1371/journal.pone.0142867. eCollection 2015.

Abstract

Reduction of nitrogen application in crop production is desirable for ecological and health-related reasons. Interestingly, nitrogen deficiency can lead to enhanced concentrations of polyphenols in plants. The reason for this is still under discussion. The plants' response to low nitrogen concentration can interact with other factors, for example radiation intensity. We cultivated red and green leaf lettuce hydroponically in a Mediterranean greenhouse, supplying three different levels of nitrogen (12 mM, 3 mM, 0.75 mM), either in full or reduced (-50%) radiation intensity. In both red and green lettuce, we found clear effects of the nitrogen treatments on growth characteristics, phenolic and photosynthetic compounds, nitrogen, nitrate and carbon concentration of the plants. Interestingly, the concentrations of all main flavonoid glycosides, caffeic acid derivatives, and sucrose increased with decreasing nitrogen concentration, whereas those of chlorophylls, β-carotene, neoxanthin, lactucaxanthin, all trans- and cis-violaxanthin decreased. The constitutive concentrations of polyphenols were lower in the green cultivar, but their relative increase was more pronounced than in the red cultivar. The constitutive concentrations of chlorophylls, β-carotene, neoxanthin, all trans- and cis-violaxanthin were similar in red and green lettuce and with decreasing nitrogen concentration they declined to a similar extent in both cultivars. We only detected little influence of the radiation treatments, e.g. on anthocyanin concentration, and hardly any interaction between radiation and nitrogen concentration. Our results imply a greater physiological plasticity of green compared to the red lettuce regarding its phenolic compounds. They support the photoprotection theory regarding anthocyanins as well as the theory that the deamination activity of phenylalanine ammonia-lyase drives phenylpropanoid synthesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Caffeic Acids / metabolism*
  • Carbohydrates / analysis
  • Carbon / analysis
  • Chlorophyll / metabolism*
  • Flavonoids / metabolism*
  • Genotype
  • Glycosides / metabolism*
  • Lactuca / genetics
  • Lactuca / growth & development
  • Lactuca / metabolism*
  • Nitrates / analysis
  • Nitrogen / analysis
  • Nitrogen / deficiency*
  • Phenols
  • Phenylalanine Ammonia-Lyase
  • Photosynthesis
  • Plant Leaves
  • Sucrose / metabolism*
  • Xanthophylls / metabolism*
  • beta Carotene / metabolism*

Substances

  • Caffeic Acids
  • Carbohydrates
  • Flavonoids
  • Glycosides
  • Nitrates
  • Phenols
  • Xanthophylls
  • beta Carotene
  • Chlorophyll
  • Sucrose
  • Carbon
  • Phenylalanine Ammonia-Lyase
  • Nitrogen
  • caffeic acid

Grants and funding

CB received a grant from the German Academic Exchange Service (project ID: 54388867; www.daad.org) and was supported by the German Federal Ministry of Agriculture, Food, and Consumer Protection (http://www.bmel.de/EN/Homepage/homepage_node.html;jsessionid=3E5F5B0D3C4DE2F534ED66C2DCF995A7.2_cid376) and the Croatian Ministry of Science, Education and Sports (http://public.mzos.hr/Default.aspx?sec=2428). The funders had no role in study design, data collection and Analysis, decision to publish, or preparation of the manuscript.