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Title: Bimodal effect of hydrogen peroxide and oxidative events in nitrite-induced rapid root abscission by the water fern Azolla pinnata

In the genus Azolla rapid abscission of roots from floating fronds occurs within minutes in response to a variety of stresses, including exposure to nitrite. We found that hydrogen peroxide, though itself not an inducer of root abscission, modulates nitrite-induced root abscission by Azolla pinnata in a dose-dependent manner, with 2 mM H 2O 2 significantly diminishing the responsiveness to 2 mM NaNO 2, and 10 mM H 2O 2 slightly enhancing it. Hypoxia, which has been found in other plants to result in autogenic production of H 2O 2, dramatically stimulated root abscission of A. pinnata in response to nitrite, especially for plants previously cultivated in medium containing 5 mM KNO 3 compared to plants cultivated under N 2-fixing conditions without combined nitrogen. Plants, including Azolla, produce the small signaling molecule nitric oxide (NO) from nitrite using nitrate reductase. We found Azolla plants to display dose-dependent root abscission in response to the NO donor spermine NONOate. Treatment of plants with the thiol-modifying agents S-methyl methanethiosulfonate or glutathione inhibited the nitrite-induced root abscission response. Synchrotron radiation-based Fourier transform infrared spectromicroscopy revealed higher levels of carbonylation in the abscission zone of dropped roots, indicative of reaction products of polysaccharides with potentmore » free radical oxidants. Lastly, we hypothesize that metabolic products of nitrite and NO react with H 2O 2 in the apoplast leading to free-radical-mediated cleavage of structural polysaccharides and consequent rapid root abscission.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [2]
  1. Sonoma State Univ., Rohnert Park, CA (United States); Okinawa Inst. of Science and Technology, Okinawa (Japan)
  2. Univ. of the Ryukyus, Nishihara (Japan)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Frontiers in Plant Science
Additional Journal Information:
Journal Volume: 6; Journal ID: ISSN 1664-462X
Publisher:
Frontiers Research Foundation
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; root abscission; apoplast; free radical cleavage; FTIR spectromicroscopy; hydrogen peroxide; nitric oxide; nitrite; plant cell wall loosening
OSTI Identifier:
1257258