The response of tomato roots (Lycopersicon esculentumMill.) to iron deficiency stress: alterations in the pattern of protein synthesis

Abstract

Dicotyledon plants adapt to iron (Fe) deficiency through a series of reactions that increase the ability of the plant to assimilate Fe and to increase the efficiency of Fe utilization. In an attempt to gain an insight into these adaptive processes, the specific changes in protein synthesis associated with the onset of the Fe deficiency response in tomato roots (Lycopersicon esculentum Mill cv. Rutgers) have been investigated. Roots were grown under Fe-sufficient and -deficient conditions, and the pattern of protein synthesis was analysed by in vitro translation of root mRNA and by in vivo labelling of root proteins. Polypeptides were resolved by two-dimensional polyacrylamide gel electrophoresis. Seven polypeptides were identified by in vitro translation, whose synthesis was significantly increased during Fe deficiency. The increase was probably specific to Fe deficiency in that the polypeptide synthesis was not increased during phosphate deficiency stress, was less prominent following prolonged Fe deficiency and was decreased following re-supply of Fe to the hydroponic medium. The pattern of in vitro translation of mRNA isolated from Fe-deficient roots was compared to the results obtained in vivo following radiolabelling of proteins. In these analyses, eight polypeptides were identified, tentatively including the seven polypeptides previously identified by in vitro translation. All polypeptides were characterized with regard to molecular mass and pl and their localization in the cell, whether being membrane bound or soluble. It is suggested that members of this group of polypeptides are involved in the response of the root to Fe deficiency; although their functions remain to be identified.