Early iron deficiency stress response in leaves of sugar beet

Abstract

Iron nutrient deficiency was investigated in leaves of hydroponically grown sugar beets (Beta vulgaris) to determine how ribulose1,5-bisphosphate carboxylase/oxygenase (Rubisco) gene expression is affected when thylakoid components of photosynthesis are diminished. Rubisco polypeptide content was reduced by 60% in severely iron-stressed leaves, and the reduction was directly correlated to chlorophyll content. The concentration of Rubisco protein in ironstressed leaves was found to be regulated by availability of mRNAs, and CO2 fixation by Rubisco was reduced from 45 μmol CO2 m-2 s-1 in extracts from iron-sufficient leaves to 20 μmol CO2 m-2 s-1 in extracts from severely stressed leaves. The rate of CO2 fixation was directly correlated to leaf chlorophyll content. Rubisco in iron-sufficient control leaves was 59% activated, whereas in severely stressed leaves grown under the same light, Rubisco was 43% activated. RNA synthesis was reduced by about 50% in iron-deficient leaves, but 16S and 25S rRNA and ctDNA were essentially unaffected by iron stress.