Regulation of sulfate uptake and expression of sulfate transporter genes in Brassica oleracea as affected by atmospheric H(2)S and pedospheric sulfate nutrition

Abstract

Demand-driven signaling will contribute to regulation of sulfur acquisition and distribution within the plant. To investigate the regulatory mechanisms pedospheric sulfate and atmospheric H(2)S supply were manipulated in Brassica oleracea. Sulfate deprivation of B. oleracea seedlings induced a rapid increase of the sulfate uptake capacity by the roots, accompanied by an increased expression of genes encoding specific sulfate transporters in roots and other plant parts. More prolonged sulfate deprivation resulted in an altered shoot-root partitioning of biomass in favor of the root. B. oleracea was able to utilize atmospheric H(2)S as S-source; however, root proliferation and increased sulfate transporter expression occurred as in S-deficient plants. It was evident that in B. oleracea there was a poor shoot to root signaling for the regulation of sulfate uptake and expression of the sulfate transporters. cDNAs corresponding to 12 different sulfate transporter genes representing the complete gene family were isolated from Brassica napus and B. oleracea species. The sequence analysis classified the Brassica sulfate transporter genes into four different groups. The expression of the different sulfate transporters showed a complex pattern of tissue specificity and regulation by sulfur nutritional status. The sulfate transporter genes of Groups 1, 2, and 4 were induced or up-regulated under sulfate deprivation, although the expression of Group 3 sulfate transporters was not affected by the sulfate status. The significance of sulfate, thiols, and O-acetylserine as possible signal compounds in the regulation of the sulfate uptake and expression of the transporter genes is evaluated.

Figure 1.

Sulfate and total water-soluble nonprotein thiol content of B. oleracea as affected by pedospheric and atmospheric sulfur nutrition. B. oleracea was grown on a 25% Hoagland nutrient solution (0.5 mm sulfate) in a climate controlled room for 7 d and subsequently transferred to a fresh nutrient solution at 0 (−S) or 0.5 mm sulfate (+S) and simultaneously exposed to 0 or 75 nL L⁻¹ H₂S for 1, 2, 3, 6, and 10 d. Sulfate contents represent the means of two experiments with three to five measurements on one (day 10) to three plants in each (± sd). Thiol content represents the means of three measurements with three or six plants in each (± sd).

Figure 2.

OAS content of B. oleracea as affected by pedospheric and atmospheric sulfur nutrition. B. oleracea was grown on a 25% Hoagland nutrient solution (0.5 mm sulfate) in a climate controlled room for 7 d and subsequently transferred to a fresh nutrient solution at 0 (−S) or 0.5 mm sulfate (+S) and simultaneously exposed to 0 or 75 nL L⁻¹ H₂S for 3, 6, and 10 d. Data represent the means of three measurements with three plants in each (± sd). Breaks in the chart indicate two different scales of OAS concentrations.

Figure 3.

Sulfate uptake capacity of B. oleracea as affected by pedospheric and atmospheric sulfur nutrition. B. oleracea was grown on a 25% Hoagland nutrient solution (0.5 mm sulfate) in a climate controlled room for 7 d and subsequently transferred to a fresh nutrient solution at 0 mm sulfate (−S) or 0.5 mm sulfate (+S) and simultaneously exposed to 0 or 75 nL L⁻¹ H₂S for 1, 2, 3, 6, and 10 d. Sulfate uptake was measured over a 24-h period (see “Materials and Methods”) and represents the mean of three to six measurements with three plants in each (± sd).

Figure 4.

Phylogenetic analysis. Neighbor-joining tree (MEGA V.2.1; Kumar et al., 2001) from the multiple alignment (ClustalX V.1.81; Thompson et al., 1997) of the coding cDNAs of the Arabidopsis: AB018695, AB042322, AB049624, AB003591, D85416, D89631, AB004060, AB023423, AB054645, AB061739, AB008782, AB052775, AC018848, and AC006053; and Brassica oleracea sulfate transporter family: AJ416460, AJ311388, AJ633707, AJ633705, AJ581745, AJ601439, AJ704373, AJ704374, AJ633706, AJ416461, AJ555124 (this report), and AJ223495 (Heiss et al., 1999).

Figure 5.

Expression analysis by northern hybridization of the Brassica sulfate transporter gene family in root tissues of B. oleracea as affected by pedospheric and atmospheric sulfur nutrition. B. oleracea was grown on a 25% Hoagland nutrient solution (0.5 mm sulfate) in a climate controlled room for 7 d and subsequently transferred to a fresh nutrient solution at 0 (−S) or 0.5 mm sulfate (+S) and simultaneously exposed to 0 or 75 nL L⁻¹ H₂S for 1, 2, 3, 6, and 10 d.

Figure 6.

Expression analysis by northern hybridization of the Brassica sulfate transporter gene family in stem tissues including petioles of B. oleracea as affected by pedospheric and atmospheric sulfur nutrition. For details see legend Figure 5.

Figure 7.

Expression analysis by northern hybridization of the Brassica sulfate transporter gene family in leaf tissues of B. oleracea as affected by pedospheric and atmospheric sulfur nutrition. For details see legend Figure 5.