Is the remobilization of S and N reserves for seed filling of winter oilseed rape modulated by sulphate restrictions occurring at different growth stages?

How the remobilization of S and N reserves can meet the needs of seeds of oilseed rape subject to limitation of S fertilization remains largely unclear. Thus, this survey aims to determine the incidence of sulphate restriction [low S (LS)] applied at bolting [growth stage (GS) 32], visible bud (GS 53), and start of pod filling (GS 70) on source–sink relationships for S and N, and on the dynamics of endogenous/exogenous S and N contributing to seed yield and quality. Sulphate restrictions applied at GS 32, GS 53, and GS 70 were annotated LS32, LS53, and LS70. Long-term 34SO42− and 15NO3− labelling was used to explore S and N partitioning at the whole-plant level. In LS53, the sulphur remobilization efficiency (SRE) to seeds increased, but not enough to maintain seed quality. In LS32, an early S remobilization from leaves provided S for root, stem, and pod growth, but the subsequent demand for seed development was not met adequately and the N utilization efficiency (NUtE) was reduced when compared with high S (HS). The highest SRE (65±1.2% of the remobilized S) associated with an efficient foliar S mobilization (with minimal residual S concentrations of 0.1–0.2% dry matter) was observed under LS70 treatment, which did not affect yield components

Effect of mineral sulphur availability on nitrogen and sulphur uptake and remobilization during the vegetative growth of Brassica napus L.

Because it has a high demand for sulphur (S), oilseed rape is particularly sensitive to S limitation. However, the physiological effects of S limitation remain unclear, especially during the rosette stage. For this reason a study was conducted to determine the effects of mineral S limitation on nitrogen (N) and S uptake and remobilization during vegetative growth of oilseed rape at both the whole-plant and leaf rank level for plants grown during 35 d with 300 μM 34SO42– (control plants; +S) or with 15 μM 34SO42– (S-limited plants; –S). The results highlight that S-limited plants showed no significant differences either in whole-plant and leaf biomas or in N uptake, when compared with control plants. However, total S and 34S (i.e. deriving from S uptake) contents were greatly reduced for the whole plant and leaf after 35 d, and a greater redistribution of endogenous S from leaves to the benefit of roots was observed. The relative expression of tonoplast and plasmalemma sulphate transporters was also strongly induced in the roots. In conclusion, although S-limited plants had 20 times less mineral S than control plants, their development remained surprisingly unchanged. During S limitation, oilseed rape is able to recycle endogenous S compounds (mostly sulphate) from leaves to roots. However, this physiological adaptation may be effective only over a short time scale (i.e. vegetative growth)

Differences in the photosynthetic response of three tomato cultivars to different salinity sources and their effect on vegetative growth parameters

[EN] Abstract Previous works into photosynthesis regulation under salt stress have focused on the effect of NaCl, although other salts may significantly contribute to the toxicity of saline soils. In this paper, the effects of different salt sources (NaCl, Na2SO4, MgCl2 and MgSO4) on photosynthesis and vegetative growth in three tomato (Solanum lycopersicum L.) cultivars (Marmande RAF, Leader and Daniela) are presented. Differences were found in the net photosynthetic rate and vegetative growth among the studied cultivars and salinity treatments. Cultivar photosynthetic performance related not only to capability for toxic ion exclusion, but also to the maintenance of appropriate essential macronutrient concentrations in leaves. In addition, the role of metabolic and diffusion limitations in regulating photosynthesis varied depending on the studied genotypes. These data, along with variation in biomass and ion distribution in leaves and roots, show that distinct tomato cultivars can address salt tolerance differently, which should be considered when designing strategies to overcome plant sensitivity to salt stress. Highlights ► Photosynthesis and growth were more affected by Na2SO4, MgCl2 and MgSO4 than by NaCl. ► Photosynthetic limitations under salt stress were cultivar-dependent. ► Salinity differentially affected photo-assimilate utilisation among tomato cultivars. ► Salt tolerance has been related to toxic ion exclusion and macroelement homeostasis.This research has been supported by the Spanish Ministry of Education and Science (GEN2006-27772-C2-2-E/VEG). We thank Dr. Jaume Flexas and Dr. Miquel Rivas for their assistance with photosynthetic parameters modelling, and Dr. A. Calatayud for her assistance in the mineral content determinations. We thank Helen Warburton for revising the language in the manuscript.González Nebauer, S.; Sánchez Perales, M.; Martinez, L.; Lluch Gomez, YP.; Renau Morata, B.; Molina Romero, RV. (2013). Differences in the photosynthetic response of three tomato cultivars to different salinity sources and their effect on vegetative growth parameters. Plant Physiology and Biochemistry. 63:61-69. https://doi.org/10.1016/j.plaphy.2012.11.006S61696

Remobilization of leaf S compounds and senescence in response to restricted sulphate supply during the vegetative stage of oilseed rape are affected by mineral N availability

The impact of sulphur limitation on the remobilization of endogenous S compounds during the rosette stage of oilseed rape, and the interactions with N availability on these processes, were examined using a long-term 34SO42− labelling method combined with a study of leaf senescence progression (using SAG12/Cab as a molecular indicator) and gene expression of the transporters, BnSultr4;1 and BnSultr4;2, involved in vacuolar sulphate efflux. After 51 d on hydroponic culture at 0.3 mM 34SO42− (1 atom% excess), the labelling was stopped and plants were subject for 28 d to High S-High N (HS-HN, control), Low S-High N (LS-HN) or Low S-Low N (LS-LN) conditions. Compared with the control, LS-HN plants showed delayed leaf senescence and, whilst the shoot growth and the foliar soluble protein amounts were not affected, S, 34S, and SO42− amounts in the old leaves declined rapidly and were associated with the up-regulation of BnSultr4;1. In LS-LN plants, shoot growth was reduced, leaf senescence was accelerated, and the rapid S mobilization in old leaves was accompanied by decreased 34S and SO42−, higher protein mobilization, and up-regulation of BnSultr4;2, but without any change of expression of BnSultr4;1. The data suggest that to sustain the S demand for growth under S restriction (i) vacuolar SO42− is specifically remobilized in LS-HN conditions without any acceleration of leaf senescence, (ii) SO42− mobilization is related to an up-regulation of BnSultr4;1 and/or BnSultr4;2 expression, and (iii) the relationship between sulphate mobilization and up-regulation of expression of BnSultr4 genes is specifically dependent on the N availability

Isolation and characterization of low-sulphur-tolerant mutants of Arabidopsis

Sulphur is an essential element for plant growth and development as well as for defence against biotic and abiotic stresses. Increasing sulphate utilization efficiency (SUE) is an important issue for crop improvement. Little is known about the genetic determinants of sulphate utilization efficiency. No gain-of-function mutants with improved SUE have been reported to date. Here the isolation and characterization of two low-sulphur-tolerant mutants, sue3 and sue4 are reported using a high-throughput genetic screen where a ‘sulphur-free’ solid medium was devised to give the selection pressure necessary to suppress the growth of the wild-type seedlings. Both mutants showed improved tolerance to low sulphur conditions and well-developed root systems. The mutant phenotype of both sue3 and sue4 was specific to sulphate deficiency and the mutants displayed enhanced tolerance to heavy metal and oxidative stress. Genetic analysis revealed that sue3 was caused by a single recessive nuclear mutation while sue4 was caused by a single dominant nuclear mutation. The recessive locus in sue3 is the previously identified VirE2-interacting Protein 1. The dominant locus in sue4 is a function-unknown locus activated by the four enhancers on the T-DNA. The function of SUE3 and SUE4 in low sulphur tolerance was confirmed either by multiple mutant alleles or by recapitulation analysis. Taken together, our results demonstrate that this genetic screen is a reasonable approach to isolate Arabidopsis mutants with improved low sulphur tolerance and potentially with enhanced sulphate utilization efficiency. The two loci identified in sue3 and sue4 should assist in understanding the molecular mechanisms of low sulphur tolerance