Differential protein synthesis in response to sulphate and phosphate deprivation: Identification of possible components of plasma-membrane transport systems in cultured tomato roots

Abstract

Isolated roots of Lycopersicon esculentum Mill., cultured in axenic conditions were starved of sulphate or phosphate, and uptake capacities for the respective oxyanion-transport systems were observed for several days after sulphate or phosphate withdrawal. Sulphate-uptake capacity of the intact roots, measured in a 20-min period, increased from a control level of 100 nmol · g(-1) · h(-1) to 1100 nmol · g(-1) · h(-1) in 10 d, and phosphate-uptake capacity increased from 500 to 1400 nmol · g(-1) · h(-1) over 4 d. Newly synthesised polypeptides of these root cultures were pulse-labelled in vivo for 2 h, by adding [(3)H]leucine to the culture medium. The tissue was immediately homogenised and soluble and membrane fractions were prepared. A highly purified plasma-membrane fraction was separated from the crude microsomal membrane fraction using an aqueous two-phase partitioning technique. All fractions were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography. A 28-kilodalton (kDa) soluble polypeptide, and 36-, 43-, and 47-kDa plasma-membrane polypeptides were observed to have increased labelling after 4 d of sulphate deprivation. Longer periods resulted in additional polypeptides with increased [(3)H]leucine incorporation. The synthesis of a 25-kDa membrane polypeptide and a 65-kDa soluble polypeptide was increased after 4 d of phosphate deprivation. Two-dimensional electrophoresis afforded greater resolution of the plasmamembrane polypeptides, confirming increased synthesis of the 36-kDa polypeptide and the presence of the 28-kDa polypeptide in the plasma-membrane preparation from sulphate-starved roots. These polypeptides were also observed in protein-stained two-dimensional gels as low-abundant protein components of the plasmamembrane fraction. It is suggested that the 36-kDa polypeptide may be a component of the plasma-membrane sulphate-transport system and that the 25-kDa polypeptide may be a component of a phosphate-transport system.

Demand-Driven Control of Root ATP Sulfurylase Activity and SO42- Uptake in Intact Canola (The Role of Phloem-Translocated Glutathione)

“…Under S deficiency, S0,'-uptake rates in canola increased considerably (Fig. l), which is consistent with previous reports ( e g Lee, 1982Lee, , 1993Hawkesford and Belcher, 1991;Bell et al, 1995). This positive effect is readily reversible upon restoration of S0,'- (Fig.…”

“…The rate of S uptake by plant roots, especially those of crop species, which have been bred for their fast growth capacity and high harvest potential, is controlled by regulatory processes that operate in such a way that the needs of the whole organism are matched by rates of S uptake. A good illustration of this behavior is provided by the severalfold enhancement of S0: -uptake observed in plants previously deprived of S for periods of a few hours to a few days (Smith, 1975(Smith, , 1980Lass and Ullrich-Eberius, 1984;Clarkson and Saker, 1989;Hawkesford and Belcher, 1991;Hawkesford et al, 1993;Lee, 1993). Conversely, S0, '-uptake decreased steadily upon restoration of S0,'-availability (Smith, 1980;Clarkson et al, 1983Clarkson et al, , 1992Clarkson and Saker, 1989).…”

“…Demand-driven regulation of ion uptake (see Imsande and Touraine, 1994) has two important traits: (a) it affects the transport rate of one specific ion in roots (Datko and Mudd, 1984;Lee and Rudge, 1986;Clarkson and Saker, 1989;Hawkesford and Belcher, 1991;Lee, 1993); and (b) the underlying process involves a remote control of root activity by shoots. In the case of SO,2-, this has been shown by experiments in which enhancement of S0,'-uptake in a given root had been obtained by depriving other roots of S, and the root under observation was continuously fed with S0,'- (Clarkson et al, 1983).…”

Cross-Effects of Nitrogen and Sulphur Starvation in <i>Chlorella sorokiniana</i> 211/8K

“…These effects of N-starvation recall in many aspects those observed following S-deprivation. Indeed, S-starvation causes de-repression of enzyme systems involved in sulphate transport, metabolism and cysteine synthesis [5]- [7]. In addition, microalgae have been reported to synthesize arylsulphatase to recover 2 4 SO − [8].…”

Sac3, an Snf1-like Serine/Threonine Kinase That Positively and Negatively Regulates the Responses of Chlamydomonas to Sulfur Limitation

“…We are using the genetically tractable, unicellular green alga Chlamydomonas ( Chlamydomonas reinhardtii ) as a model system to investigate how photosynthetic organisms acclimate to changes in nutrient availability (de Hostos et al, 1988(de Hostos et al, , 1989Davies et al, 1994Davies et al, , 1996Yildiz et al, 1994Yildiz et al, , 1996Quisel et al, 1996;Wykoff et al, 1998). Several responses of Chlamydomonas to nutrient limitation are similar to those exhibited by vascular plants and soil-dwelling microbes (Marzluf and Metzenberg, 1968;Harder and Dijkhuizen, 1983;Hawkesford and Belcher, 1991;Tsay et al, 1993;Smith et al, 1995;Trueman et al, 1996;Davies and Grossman, 1998;Wykoff et al, 1998). Much of our work has focused on the ways in which Chlamydomonas adjusts to limiting sulfur levels.…”