Role of sulphate transporter systems in sulphur efficiency of mustard genotypes Altaf Ahmad, Ishart Khan, Nasar A. Anjum, Yash P. Abrol, Muhammad Iqbal * Department of Botany, Faculty of Science, Hamdard University, New Delhi 110 062, India Received 19 February 2005; received in revised form 27 May 2005; accepted 31 May 2005 Available online 21 June 2005 Abstract Fourteen genotypes of mustard [Brassica juncea (L.) Czern. & Coss.] were grown for 30 days in complete nutrient solution with 50 mM (S- insufficient) and 1 mM (S-sufficient) sulphur levels, and sulphur efficiency (SE) was analysed. SE, the ability of a plant to maintain good growth on S-limited condition, was calculated as the ratio of dry matter production at low and high S supply. There was 2–10-fold differences in SE of the genotypes. Of the 14 genotypes, Pusa Bold was identified as the most S-efficient, while Pusa Jai Kisan the most S-inefficient. SE of Pusa Bold was about 10-fold higher than Pusa Jai Kisan. To find out the physiological basis of this difference, we investigated the possible role of SO 4 2 influx across the root cell plasma membrane in conferring SE by measuring the short-term 35 SO 4 2 uptake in two contrasting genotypes, S-efficient Pusa Bold and S-inefficient Pusa Jai Kisan. This was done by quantifying sulphate uptake over two different concentration ranges: a high-concentration range (50–500 mM) and a low-concentration range (5–50 mM). Uptake experiments revealed the presence of two separate sulphate transporter systems mediating high- and low-affinity sulphate uptake. Interestingly, the sulphate uptake by the roots of Pusa Bold is mediated by both high- and low-affinity sulphate transporter systems, while that of Pusa Jai Kisan by only low- affinity sulphate transporter system. The study suggests that root SO 4 2 uptake rate may play an important role in conferring S efficiency of mustard genotypes under S-limiting condition. This information may be useful in breeding mustard varieties more efficient in acquiring S from soil solution. # 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Brassica juncea; Sulphur efficiency; S uptake; Sulphate transporter systems 1. Introduction Sulphur (S) is an essential element needed for plant growth. Sulphur requirement of plants varies with the developmental stage and with species. S concentration in plants varies between 0.1 and 1.5% of dry weight. Nitrogen (N) and S are necessary for the synthesis of amino acids, proteins and various other cellular components, including thiol compounds and the so-called secondary sulphur compounds, which have a significant bearing on protection of plants against stress and pests. Sulphur deficiency in the agricultural soils has been reported frequently over the past several years [1]. Among different regions, Asia has the highest S fertilizer require- ment. In Asia, India and China alone currently account for about 60% of the total estimated deficit. Continuous mining of S from soils has led to widespread S deficiency and negative soil budget [2]. Correction of S deficiency via fertilization is not always the ideal solution because of the influence of agronomic, environmental and economic factors. Therefore, identification and cultivation of S- efficient genotypes that could use soil S efficiently is a realistic alternative to S fertilizer application in some edaphic environments. Mustard, an important oilseed crop, is particularly sensitive to S deficiency because of its high demand for S [3–6]. S deficiency in the soil, where these crops are raised, is considered as a major factor responsible for low mustard production. This study aims (a) to determine as to how mustard genotypes respond to S deficiency under defined conditions of S supply and (b) to understand the physiological mechanisms that confer S-efficiency in www.elsevier.com/locate/plantsci Plant Science 169 (2005) 842–846 * Corresponding author. E-mail address: miqbal@jamiahamdard.ac.in (M. Iqbal). 0168-9452/$ – see front matter # 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2005.05.036