Abstract
Sulfur is an essential macronutrient for growth of higher plants. The entry of the sulfate anion into the plant, its importation into the plastids for assimilation, its long-distance transport through the vasculature, and its storage in the vacuoles require specific sulfate transporter proteins. In this study, mycorrhizal and non-mycorrhizal maize plants were grown for 60 days in an S-deprived substrate, whilst iron was provided to the plants in the sparingly soluble form of FePO4. On day 60, sulfate was provided to the plants. The gene expression patterns of a number of sulfate transporters as well as sulfate assimilation enzymes were studied in leaves and roots of maize plants, both before as well as after sulfate supply. Prolonged sulfur deprivation resulted in a more or less uniform response of the genes’ expressions in the roots of non-mycorrhizal and mycorrhizal plants. This was not the case neither in the roots and leaves after the supply of sulfur, nor in the leaves of the plants during the S-deprived period of time. It is concluded that mycorrhizal symbiosis modified plant demands for reduced sulfur, regulating accordingly the uptake, distribution, and assimilation of the sulfate anion.
Highlights
Sulfur is an essential macronutrient for growth of higher plants
Phylogenetic comparison of the protein sequences discovered in maize to those of the Arabidopsis thaliana sulfate transporters has revealed that the maize putative sulfate transporter homologs (ZmSULTR) correspond well to the known classifications in other species and can be sorted into 4 distinct groups (Figure 1)
Group 3 can be further divided into two subgroups: the first includes transporters ZmSULTR3.1 and ZmSULTR3.5, and the other is comprised of ZmSULTR3.3 and ZmSULTR3.4
Summary
Plants take up sulfate mainly from the soil solution in order to synthesize essential organic sulfur compounds. It composes a part of proteins in the form of cysteine and methionine. The influx of sulfate occurs against the inside-negative gradient of the membrane potential, requiring a driving force for transport. In this line, sulfate transporters are pH-dependent proton/sulfate co-transporters containing 10–12 membrane-spanning helices. In Arabidopsis thaliana, sulfate transporters have been classified into 4 groups according to their phylogenetic relationships, tissue-specific expression, and kinetic properties; twelve proteins have been characterized in total
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