Germinative and Post-Germinative Behaviours of Brassica napus Seeds Are Impacted by the Severity of S Limitation Applied to the Parent Plants

In oilseed rape (Brassica napus L.), sulphur (S) limitation leads to a reduction of seed yield and nutritional quality, but also to a reduction of seed viability and vigour. S metabolism is known to be involved in the control of germination sensu stricto and seedling establishment. Nevertheless, how the germination and the first steps of plant growth are impacted in seeds produced by plants subjected to various sulphate limitations remains largely unknown. Therefore, this study aimed at determining the impact of various S-limited conditions applied to the mother plants on the germination indexes and the rate of viable seedlings in a spring oilseed rape cultivar (cv. Yudal). Using a 34S-sulphate pulse method, the sulphate uptake capacity during the seedling development was also investigated. The rate of viable seedlings was significantly reduced for seeds produced under the strongest S-limited conditions. This is related to a reduction of germination vigour and to perturbations of post-germinative events. Compared to green seedlings obtained from seeds produced by well-S-supplied plants, the viable seedlings coming from seeds harvested on plants subjected to severe S-limitation treatment showed nonetheless a higher dry biomass and were able to enhance the sulphate uptake by roots and the S translocation to shoots.

ATP stimulates lysosomal sulphate transport at neutral pH: evidence for phosphorylation of the lysosomal sulphate carrier

ATP markedly stimulated sulphate uptake by rat liver lysosomes that had been treated with N-ethylmaleimide to block the effects of the lysosomal proton-translocating ATPase (H+-ATPase). Maximal stimulation required millimolar concentrations of ATP and neutral buffer pH. ATP-stimulated transport exhibited saturation kinetics with a Km of 175 μM, identical with the Km for lysosomal sulphate uptake at pH 5.0, a process that does not require ATP. The requirement for ATP was specific: other nucleotides such as AMP, ADP, CTP, GTP, ITP and UTP failed to stimulate transport. Adenosine 5ʹ-[β,γ-imido]triphosphate, the non-hydrolysable analogue of ATP, also failed to stimulate sulphate uptake, suggesting a requirement for ATP hydrolysis. Lysosomal pH, membrane potential and glucose transport were unchanged by the presence of ATP under the experimental conditions, consistent with a direct effect of ATP on the sulphate transporter. Exposure of lysosomes to protein kinase A and protein kinase C inhibitors did not alter the stimulation of sulphate transport by ATP. The lysosomal sulphate transport protein might be subject to regulation by a phosphorylation pathway that is not dependent on protein kinase A or protein kinase C.

Synergism of GH and IGF-I in stimulation of sulphate uptake by teleostean branchial cartilage in vitro

The combined effects of teleostean GH and human IGF-I in the regulation of teleost branchial cartilage growth were examined. Ceratobranchial cartilages were dissected from the common carp (Cyprinus carpio) and maintained in a defined culture medium supplemented with recombinant striped bass GH (sbGH), human IGF-I (hIGF-I) or both, and the uptake of [35S]sulphate by cartilage explants was measured. sbGH alone in the culture medium did not exhibit a significant stimulatory effect on the uptake of [35S]sulphate when compared with the controls. However, with hIGF-I in the culture medium, as low as 1 ng/ml, the stimulatory effect of sbGH was apparent and dose-dependent. The synergism of sbGH and hIGF-I was observed at the concentrations of 1 and 10 ng IGF/I/ml tested. At a constant hIGF-I concentration (10 ng/ml), a maximum stimulatory effect was detected with 3 μg recombinant sbGH/ml, at which point a 2·3-fold increase in sulphation activity was obtained when compared with the treatment with hIGF-I alone. A similar dose-dependent stimulatory effect was observed when native common carp and bonito GHs were tested using this assay system. These results suggest that the synergistic effect of sbGH and hIGF-I on sulphation activity is a common biological function of teleost GH, thus ruling out the possibility of experimental artifacts resulting from utilization of heterologous GH. Furthermore, experiments were conducted to test whether the synergism between sbGH and hIGF-I occurred between sbGH and insulin. Results showed that although bovine insulin was less effective than hIGF-I on the stimulation of [35S]sulphate uptake, the synergistic effects of sbGH with hIGF-I and sbGH with insulin were similar at the concentrations tested. The concept of a 'dual effector' mechanism for GH action in teleosts is supported by these findings. Journal of Endocrinology (1995) 147, 67–73