| The hypersensitive response (HR) in plants is a highly effective, rapid and intense activation of numerous defense reactions against invading pathogens. HR is often accompanied by an oxidative burst and rapid programmed cell death. Research supports that one of the events that occurs during the HR is a reduction in photosynthesis. The work presented here is an investigation of the possible rote of photosynthesis inhibition in the HR in soybean and involved: (1) surveying global gene expression of plants treated with photosystem II (PSII) inhibiting herbicides, atrazine and bentazon, (2) examining protein expression of the PSII reaction center subunit D1 in leaves infected with the bacterial pathogen Pseudomonas syringae, (3) analyzing the effect of the PSII inhibiting herbicides on defense against P. syringae, (4) cross comparing the genomic transcriptional response to HR and PSII inhibiting herbicide and (5) studying expression of chloroplast-encoded genes in plants infected with P. syringae. In addition, transcript profiling of soybean in response to the shikimate pathway inhibitor, glyphosate, was analyzed and cross compared with that from HR and bentazon treatments. The gene expression profiling from HR and bentazon treatment shared similar patterns in many aspects, including the efforts to relieve oxidative stress. The differences included distinct regulation of phenylpropanoid production in response to two treatments. The infection of P. syringae resulted in decreased transcript of D1 but did not affect the steady state level of D 1 protein. Bentazon treatment benefited bacterial multiplication in planta and aggravated disease symptoms in soybean infected virulent bacteria. Bentazon also promoted phenolic accumulation in soybean infected with avirulent bacteria. The infection with P. syringae led to repression of all 15 chloroplast-encoded genes investigated, especially in soybean leaves infected by HR inducing pathogen. The overall results suggested that PSII inhibition through D1 degradation is probably not playing a major role in HR, but were not conclusive enough to rule out the possibility of a minor role. |
