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SULTR2;1 is a low-affinity sulfate transporter expressed in the vascular tissues of roots and leaves for interorgan transport of sulfate in Arabidopsis thaliana. Transgenic Arabidopsis carrying a fusion gene construct of SULTR2;1 5′-promoter region and β-glucuronidase coding sequence (GUS) demonstrated that within the reproductive tissues, SULTR2;1 is specifically expressed in the bases and veins of siliques and in the funiculus, which connects the seeds and the silique. The antisense suppression of SULTR2;1 mRNA caused decrease of sulfate contents in seeds and of thiol contents both in seeds and leaves, as compared with the wildtype (WT). The effect of antisense suppression of SULTR2;1 on seed sulfur status was determined by introducing a sulfur-indicator construct, p35S::βSRx3:GUS, which drives the expression of GUS reporter under a chimeric cauliflower mosaic virus 35S promoter containing a triplicate repeat of sulfur-responsive promoter region of soybean β-conglycinin β subunit (βSRx3). The mature seeds of F1 plants carrying both the SULTR2;1 antisense and p35S::βSRx3:GUS constructs exhibited significant accumulation of GUS activities on sulfur deficiency, as compared with those carrying only the p35S::βSRx3:GUS construct in the WT background. These results suggested that SULTR2;1 is involved in controlling translocation of sulfate into developing siliques and may modulate the sulfur status of seeds in A. thaliana. [ABSTRACT FROM AUTHOR]

Analysis of the Arabidopsis genome has indicated that the gene families encoding for specific solute transporters are surprisingly large. An example is the sulphate transporter family, which in Arabidopsis, consists of 14 isoforms showing homology to one another. H+‐sulphate co‐transport has been demonstrated for some, but not all, of these Arabidopsis isoforms. Occurrence of the sulphate transporter is ubiquitous and many examples have been cloned from a variety of plant species, animals and yeast. This is a unique transporter family with no apparent homology to any other transporter type. Phylogenetic analysis of the plant gene or amino acid sequences indicates that there are 5 or more distinguishable clusters within the family of sulphate transporters. Analysis of functional characteristics and patterns of regulation together with localization data, suggests that these groups have specific roles, such as high affinity uptake in the root, translocation in vascular tissues and cell to cell transfer in leaves and seeds. Additionally, some members of this sulphate transporter family may have discrete subcellular locations in plastid or tonoplast membranes. Within individual groups, there are often multiple isoforms from the same species, indicating an even greater degree of specialization or alternatively, redundancy. This mini‐review will summarize the available data to distinguish between specialization and redundancy. [ABSTRACT FROM AUTHOR]

The myrosinase-glucosinolate system is considered to be a major component of the preformed defence system of Brassicaceae species. This hypothesis has influenced the belief that the components of the myrosinase-glucosinolate system are present at fixed levels which are independent of environmental factors. In the present study we show that external availability of nutrients can modulate the expression levels of myrosinase enzymes (EC 3.2.3.1). Nutrients such as sulphate, iron, copper, zinc and manganese were tested for their modulation effect on myrosinase expression levels and activity in roots, stems, cotyledons and buds of Sinapis alba seedlings at four different developmental stages. The most sensitive organ was the bud where iron deficiency approximately doubled the myrosinase activity. Removal of sulphate and all four micronutrients reduced the myrosinase activity to approximately half of the activity in plants supplemented with all these nutrients. The myrosinase polypeptides can be divided into classes based on molecular mass after reduction. The nutritional status influenced mainly the 68-kDa class of myrosinases as revealed by western blot and laser scan densitometry of the immunolabelled blots. [ABSTRACT FROM AUTHOR]

Rosa Paul's Scarlet’cell suspension cultures were used as a test system for working out a method of viability and drug‐sensitivity determination based on plating efficiency. High plating efficiencies (80–95%) were obtained on a simple synthetic medium when aggregates of a mean size of c. 100 cells/unit from exponential phase cultures were plated at a density of 1500 units/plate in the middle layer (5 ml) of three layers of the agar‐solidified medium (total = 30 ml). This 3‐layer plating technique produces homogeneous colony growth and simplifies the microscopical evaluation of plating efficiencies. The reduction of plating efficiencies seen when the smaller aggregates of stationary phase cultures were plated was mainly due to low cell density and could be overcome by enriching the medium with various supplements. Reconstitution experiments using mixtures of inactivated and non‐inactivated aggregates demonstrated that plating efficiency can be taken as a goodmeasure of viability. The described plating technique was found to be more sensitive and reliable compared to two other methods for determining p‐fluorophenylalanine‐sensitivity of Rosa cells. [ABSTRACT FROM AUTHOR]

The efficiency of sulfate uptake was evaluated in excised roots of 22 maize genotypes, 12 inbreds and 10 hybrids, in order to study the relationship between the kinetic characteristics of the uptake and the grain productivity. During root elongation, the uptake capacity showed a pulse which appeared when the root reached ⅓ to ½ of its final length. The size of the accumulated pool of sulfate was significantly correlated with the productivity. The kinetic parameters of the uptake, Vmax and Km, followed the same trend, showing pulses, whose maximum had the same position for Vmax and Km in each genotype. The variability with the genotype of the size and duration of the Vmax pulse was not strictly connected with that of Km. The main correlation between Vmax and Km patterns was the following: inhreds were generally characterized by low Vmax and low Km: hybrids by high Vmax and high Km. As a consequence, in most cases, the benefit of the heterotic stimulation of Vmax was contrasted by the loss of affinity of the transport system or the nutrients. [ABSTRACT FROM AUTHOR]

Petiole explants from 17 cultivars of Begonia × hiemalis were grown on a basal agar medium with different combinations of NAA and BA as well as on media lacking microelements or vitamins. The stock plants were kept either under short days (7-8 h of light per day) at 15°C or under long days (15-16 h of light) at 18-21°C. The day length during the in vitro culture was 20 h of light and the temperature 2 1°C. Explants from short-day treated stock plants did not show any differentiation. In explants from long-day treated stock plants, the percentage of explants with shoot, root and with both shoot and root initiation were recorded after 55 days. Explants forming both shoots and roots were transferred to soil, and plantlet formation was observed after another 55 days. The percentage of explants with organ and plantlet formation differed between cultivars. With increasing NAA and decreasing BA concentrations, the percentage of explants forming only roots increased, whereas the percentage of explants with only shoots decreased. Plantlet formation was most frequent in explants from NAA : BA ratios of 2: 1 and 10: 1, and a variation was found between different cultivars. When the vitamin fraction was not added to the medium, this did not influence formation of shoots, roots and plantlets. When the microelements were omitted, shoots, roots and callus were formed, but no plantlets. [ABSTRACT FROM AUTHOR]

Sulphate uptake in the blue-green alga Anacystis nidulans appears based upon an active mechanism with a Km of 0.75 μM and Vmax of 0.7 pmol/min × 106 cells. sulphate uptake is competitively inhibited by thiosulphate and sulphite. The sulphate uptake has a pH optimum at 8 and a temperature optimum at 40°C. By increasing the extracellular sulphate concentration from 0.1 to 10 μM the sulphate pool in Anacystis was altered from 8.3 ·10-5 M to 5.9 · 10-4 M. [ABSTRACT FROM AUTHOR]

Shikimate dehydrogenase (SKDH, EC 1.1.1.25) was extracted from seedlings of pepper (Capsicum annuum L.) and purified 347-fold. The purification procedure included precipitation with ammonium sulphate and chromatography in columns of Reactive Red-agarose, Q-Sepharose and Sephadex G-100. Pepper SKDH isozymes are separable only using PAGE. The purified enzyme has a relative molecular mass of 67 000 as estimated by gel filtration. The optimum pH of enzyme activity is 10.5 and the optimum temperature is 50°C, but the enzyme is quickly inactivated at temperatures higher than 40°C. The purified enzyme exhibited typical Michaelis-Menten kinetics and Km values are 0.087 mM for shikimic acid and 0.017 mM for NADP. The mechanism of reaction is sequential considering NADP as a cosubstrate. Ions such as Ca2+, Mg2+ and Mn2+ activate the enzyme, but Zn2+ and Cu2+ are strong inhibitors. Some phenolic compounds such as guaiacol, protocatechuic acid and 2,4-D are competitive inhibitors of pepper SKDH, showing Ki values of 0.38 mM, 0.27 mM and 0.16 mM, respectively. [ABSTRACT FROM AUTHOR]

15N-Nitrate and 35S-sulphate labelling experiments were performed with spring wheat (Triticum aestivum L. cv. Timmo) 44, 64, 79, 95 and 115 days after sowing (growth stages arbitrarily denoted I to V). Label was fed to the plants via a fraction of the root system, termed “donor root”, whereas the rest of the root (“receiver root”) was fed non-labelled nutrient solution. Net uptake rates for both nitrate and sulphate per unit root weight changed little from growth stage I to IV, but were considerably lower at stage V. On a whole-plant weight basis, uptake declined from stage I to IV, because root contribution to total plant weight declined. Between 80 and 95% of absorbed label was translocated to the shoot at all growth stages. At stage V, up to 30% of absorbed label was recovered in the ears. Labelling of the receiver root indicated that, at all growth stages, 10 to 17% of N and 12 to 32% of S translocated to the shoot was retranslocated to the root. This corresponds to between 35 and 85% of the label actually recovered in the roots. Analysis of 15N-labelling of xylem sap collected from receiver roots at growth stages I to IV indicated that about half of the reduced N in the sap is derived from cycling through roots of recently assimilated N. Evidence of cycling was also obtained at stage V. Labelled sulphate was the only form of S cycled in the plant, but it accounted for only 1 to 7% of the sulphate in the xylem sap. [ABSTRACT FROM AUTHOR]

The uptake of K+ ion was studied in the roots of wheat (Triticum aestivum L. cv. GK Szeged) and cucumber (Cucumis sativus L. cv. Budai csemege) seedlings grown in nutrient solution under nitrogen and sulfate stress conditions. Seedlings pretreated with 1 or 10 mM NaNO3, absorbed more K+ than those treated with 0.1 mM NaNO3. However, the posteffect of NaNO3 was considerably influenced by the Na2SO4, treatment. The results suggest that, at least partly, a feed‐back regulation of K+ uptake may occur. However, due to the high Na+ contents of the roots, a Na+ effect in this process cannot be excluded. The growth and dry matter yields of the roots and shoots were strongly influenced by the SO2−/4 and NO−/3 supply of the plants. Appreciable differences were experienced between wheat and cucumber seedlings. The optimum SO2−/4 concentration of the growth solution for maximal growth varied considerably between the species, and was also different for the roots and the shoots in a given species. [ABSTRACT FROM AUTHOR]

In heterotrophic tobacco cells (Nicotiana tabacum L. cv. Samsun) inhibition of sulfate transport by reduced glutathione (GSH) is a reversible process. When GSH was removed from the culture medium subsequent to a 10-h treatment with 1 mM GSH, sulfate transport began to recover after a lag period of ca 4 h and reached the transport rates of controls without GSH within another 3-4 h. Recovery was pre-vented when inhibitors of protein synthesis, i.e. cycloheximide or puromycin, were added to the medium upon removal of GSH, even if low concentrations (cycloheximide 1 μM; puromycin 250 μM) were applied. At these low concentrations the rate of synthesis of sulfate transport entities was maintained at the rate of degradation in the absence of GSH. The post-transcriptional polyadenylation inhibitor cordycepin and the transcription inhibitor α-amanitin only slightly reduced recovery of sulfate transport from inhibition by GSH. Apparently, protein synthesis is required for this recovery, suggesting that inhibition of synthesis of sulfate carrier entities is the mechanism of action of GSH on sulfate transport in heterotrophic tobacco cells. An initial rate of net increase in sulfate transport during recovery from inhibition of GSH of 3.6 ± 0.2 U h-1 was calculated [1 U = 1 nmol sulfate (g DW)-1 min-1]. This rate of increase is small compared with the rate of decrease in sulfate transport at maximum inhibition by cycloheximide (110 ± 3 U h-1). However, with increasing time of exposure without GSH, the net increase in sulfate transport was enhanced to a maximum rate of 96 ± 3 U h-1, measured 5-7 h after GSH had been removed from the media. Apparently, the rate of synthesis of sulfate transport entities in heterotrophic tobacco cells is about twice its rate of degradation. [ABSTRACT FROM AUTHOR]

Exposure of spinach (Spinacia oleracea L. cv. Monosa) to 0.25 μl l-1 H2S reduced the relative growth rate by 26, 47 and 60% at 15, 18 and 25°C, respectively. Shoot to root ratio decreased in plants fumigated at 18 and 25°C. Growth of spinach was not affected by a 2-week exposure to 0.10 or 0.25 μl l-1 SO2. Both H2S and SO2 fumigation increased the content of sulfhydryl compounds and sulfate. A 2-week exposure to 0.25 μl l-1 H2S resulted in an increase in sulfhydryl and sulfate content of 250 to 450% and 63 to 248% in the shoots, respectively, depending on growth temperature. Exposure to 0.15 and 0.30 μl l-1 H2S at 20°C for 2 weeks resulted in a 46% increase in sulfate content of the shoots at 0.30 μl l-1 and no detectable increase at 0.15 μl l-1 H2S; the sulfate content of the roots increased by 195 and 145% at 0.15 and 0.30 μl l-1 H2S, respectively. Fumigation with 0.25μl l-1 SO2 at 20°C for 2 weeks resulted in an increase in sulfhydryl content and sulfate content in the shoots of 285% and 300 to 1100%. H2S fumigation during the 12 h light period or only during the dark period resulted in identical growth reduction and accumulation of sulfhydryl compounds; they were about 50 and 67% of those observed in continuously exposed plants. H2S- and SO2-exposed plants showed an increased transpiration rate, which was mainly caused by an increased dark-period transpiration. No effect of H2S and SO2 on the water uptake of the plants and the osmotic potential of the leaves was detected. Plants fumigated with 0.25 μl l-1 H2S for 2 weeks were smaller and differed morphologically from the control plants by slightly more abaxially curved leaf margins. Cross sections of the leaves showed smaller cells at the margins and smaller and fewer air spaces. The increased transpiration in the H2S-exposed plants is discussed in relation to the observed morphological changes. [ABSTRACT FROM AUTHOR]

A 24 h incubation of leaf discs of spinach (Spinacia oleracea L. cv. Estivato) in darkness with 50 and 100 mM sulfate resulted in a two‐ to three‐fold increase in the level of glutathione (GSH), a compound which may serve as storage of excess reduced sulfur in the plant. The accumulated GSH was a small fraction (around 1%) of the sulfate taken up in the spinach leaf discs. Incubation of spinach leaf discs with 50 and 100 mM chloride resulted in only a 30% increase of the water‐soluble non‐protein‐SH; the uptake of electrolytes was comparable to that observed with sulfate. This indicated that the increase of the GSH level upon incubation with sulfate was rather specific and not due to salinity. Incubation with 50 mM Na2SO4 did not affect water‐soluble protein‐SH content after 24 h. Addition of 1 and 10 mM selenate, an inhibitor of sulfate reduction, strongly reduced sulfate‐induced GSH accumulation in spinach leaf discs, both in light and darkness. It was concluded that the sulfate‐induced SH accumulation was due to a substantial de novo reduction of sulfate in darkness and subsequent incorporation of the reduced sulfur into GSH. The role of the sulfate concentration at the reaction site of ATP sulfurylase in the regulation of sulfur assimilation in the plant is discussed with respect to the low affinity of the enzyme for sulfate. [ABSTRACT FROM AUTHOR]

The accumulation of labelled ions was measured in seedlings of Arabidopsis thaliana (L.) Heynh. grown in submerged cultures. Genotypes used were wild type and the nitrate-uptake mutant B1, which is altered in the uptake of nitrate and chlorate from concentrations above 1 mM when grown under normal conditions. At low and high concentrations of chlorate, chloride, and K+, significantly less radioactivity was accumulated in seedlings of B1 than in seedlings of wild type. The influx of sulphate did not decrease in B1. The results indicate that the effect of the mutation in B1 is restricted to the uptake of monovalent ions. [ABSTRACT FROM AUTHOR]

Sulfate and nitrate uptake capacity, ATP sulfurylase (ATPS) and nitrate reductase (NR) activity were determined in a set of maize hybrids representative of selection cycles carried out during the period 1930 through 1975. All the above metabolic parameters together with the grain yield were improved by the selection. The annual rate of the improvement was higher (double) for sulfate uptake than for ATPS and similar for NR and nitrate uptake. Significant correlations were evidenced between the uptake efficiency of the roots and the enzyme activity in the leaves both for sulfate and nitrate pathways, and also between the uptake and enzyme steps of nitrate and those of sulfate. This offered good evidence of a coupled genetic regulation between nitrogen and sulfur metabolism in maize. [ABSTRACT FROM AUTHOR]

Water-extractable sulfhydryl content of spinach leaf discs increased up to four-fold when, they were incubated with sulphate (10-100 mM) for 20 h in light or darkness. The accumulated sulfhydryl compound was reduced glutathione. An increased glutathione content did not result in a higher frost-tolerance of the spinach leaf discs. Both freezing temperature and time of exposure to freezing, determined as the point at! which 50% of the cells were killed, remained unchanged after incubation with sulphate. These observations suggest that a sulfhydryl compound as glutathione does not play a direct role in protection of plants against freezing injury. [ABSTRACT FROM AUTHOR]

The polar movement of IAA has been examined in 5-mm root segments of Brassica oleracea and Helianthus annuus. The movement was studied partly with IAA-1-14C and partly with IAA-5-³H In both plants a slight acropetal flux of 14C and IAA-³H was found through the segments. The recovered radioactivity in the agar receiver blocks and in the receiver end of the segments increased as a function of time. A large portion of the applied IAA was converted on the cut surfaces and in the tissues of the segments. Chromatographic analysis indicated different destruction products when estimated by scintillation counting and by spraying with indole reagent (DMCA). Chromatograms run in isopropanol : ammonia : water, 8 : 1 : 1, yielded three different substances, one spot near the starting line and one near the front, neither of which has been identified. Finally there was a spot with Rf 0.4-0.6, probably representing IAA.

Gradients of tritiated water, 35S-sulphate and 32P-phosphate, were established in isolated segments of willow stems. Sieve tube exudate was collected as honeydew from the high activity end of the segment. After girdling the stem a few centimeters from the site of sieve tube puncture, the specific activity of 35S and 32P in the honeydew rose, whilst the specific activity of tritium remained constant. These findings indicate that prior to girdling, unlabelled sulphates and phosphates were contributing to the honeydew, whilst there had been no detectable contribution by unlabelled water from the low activity end of the segment. The data support the conclusions drawn from previous experiments by Peel et al. (1969), that water is relatively immobile in sieve tubes of willow when compared to solutes. [ABSTRACT FROM AUTHOR]

A simple tissue culture protocol was used to examine phloem differentiation. Sieve tube elements differentiated from Coleus blumei Benth. pith parenchyma when pith blocks were explanted on to an agar medium containing sucrose and indole acetic acid. Growth regulator concentration had surprisingly little influence on the production of phloem cells. Increasing the availability of sucrose, however, resulted in an enhancement of phloem differentiation. Evidently phloem and xylem differentiation began at the same time in this system, and the concentration of sucrose determined the relative production of phloem cells. [ABSTRACT FROM AUTHOR]