The roles of glutathione in the control of plant growth, development and signalling in Arabidopsis thaliana

Reduced glutathione (GSH) is an abundant low molecular weight thiol that fulfils multiple functions in plants, many of which remain poorly characterised. The following studies were undertaken in order to characterise the roles of GSH in growth, development and signalling in Arabidopsis thaliana. In the first experiments, a phenomics approach was used to investigate the effects of GSH deficiency on growth and stress tolerance using mutants that are either defective either in GSH synthesis (cad2-1, pad2-1 and rax1-1) or the export of -glutamylcysteine and GSH from the chloroplast (clt1clt2clt3). Whereas the clt1clt2clt3 mutant had a greater rosette area than the wild-type under low light growth conditions, the GSH deficient mutants were significantly smaller. Moreover, lateral root densities were significantly decreased in GSH deficient and clt1clt2clt3 mutants. The redox potentials of the nucleus and cytosol in the root cells of the wild-type seedlings measured using roGFP were over -300mV. However, in roots grown in the presence of the GSH synthesis inhibitor buthionine sulfoximine (BSO), the redox potentials of the nucleus and cytosol increased to approximately -260mV. Low GSH-responsive genes were identified by transcript profiling analysis of the GSH-deficient root meristemless 1-1 (rml1-1) mutant. These included a large number of transcription factors, proteins involved in cell division, redox regulation and auxin signalling. Many transcripts modified by low GSH influence plant growth and development, and explain the altered root development observed the low GSH mutants. These results demonstrate that low GSH leads to significant increases in the redox states of the nucleus and cytosol and results in specific responses in gene expression that are distinct from those observed under oxidative stress. Moreover, the findings suggest that the cytosolic/nuclear GSH pool is important in the control of root development and that low GSH per se does not enhance overall sensitivity to abiotic stresses.