An Investigation of the Bioactivity of Cyanobacterial Exometabolites in Plant Stress Tolerance

  • Oral Presentation
  • Plant Cell Biology and Biochemistry
  • 13 Jun 2018 12:10
  • FS-G01, UCD Agriculture and food science Centre
  • View all IPSAM abstracts

Alysha Chua*
Department of Science, Waterford Institute of Technology

Cara Daly
Department of Science, Waterford Institute of Technology

Laurence Fitzhenry
Department of Science, Waterford Institute of Technology

*Presenting Author

Cyanobacteria are part of the plant growth promoting rhizobacteria (PGPR) consortium. Previous work showed that Nostoc muscorum conditioned media (CM) inhibits stress-induced programmed cell death (PCD) in Arabidopsis thaliana root hairs. Here, a novel Root Hair Assay (RHA) was used to investigate Nostoc CM bioactivity in heat-stressed Arabidopsis seedlings in terms of cell viability, PCD and necrosis. Nostoc CM increased stress tolerance by suppressing PCD but not necrosis, indicating that the bioactive compound was specifically affecting the PCD pathway and not a general stress response. A framework developed to find the bioactive candidate(s) identified proline as one compound of interest. Proline is a stress-responsive amino acid that accumulates in plants under stress. Proline was detected in Nostoc CM using a ninhydrin assay and subsequent testing with exogenous proline showed a remarkably similar performance when compared to Nostoc CM; a dose-dependent effect was observed across Nostoc CM and exogenous proline treatments, with similar levels of PCD suppression and negligible changes in necrosis levels. However, the correlation between proline accumulation and plant stress tolerance applied only to a certain point; low concentrations conferred plant stress tolerance in a dose-dependent manner, but excessively high doses (100-1000 μM) induced cell death. In addition, the bioactivity of proline appears to be active only at a narrow range; effective PCD-suppression was only observed at medium stress levels (50 °C), but not low (25-45 °C), or mid-high (52-55 °C) stress levels. Interestingly, exogenous proline suppressed PCD in wheat and barley root hairs but not in a dose-dependent manner. We provide preliminary evidence that the passive leakage of proline by cyanobacteria is assimilated by plants and can stimulate the stress-acclimatisation response. This has unique implications for the use of cyanobacterial inoculants (or PGPR isolates with elevated proline production) as novel alternatives for enhancing plant stress tolerance.