2 results
Assessment of sulphur deficiency in commercial oilseed rape crops from plant analysis
- X. SARDA, S. DIQUELOU, M. ABDALLAH, N. NESI, O. CANTAT, P. LE GOUEE, J. C. AVICE, A. OURRY
-
- Journal:
- The Journal of Agricultural Science / Volume 152 / Issue 4 / August 2014
- Published online by Cambridge University Press:
- 01 March 2013, pp. 616-633
-
- Article
- Export citation
-
Sulphur (S) is one of the six main macroelements required to sustain the growth of plants. Sources include soil, fertilizer and atmospheric deposition, which has been reduced by 85% over the last three decades. Risks of S deficiencies are now recognized in high S-demanding species such as Brassica napus L. With the aims of evaluating the risk of excessive or insufficient fertilization and identifying robust relationships that may be used as plant S status indicators, 57 commercial crops of oilseed rape were selected among contrasting soils and along a rainfall gradient that may affect soil S availability. Cultivation practices were investigated and the S and nitrogen (N) concentrations of soil, senescing leaves, stems and seeds were analysed. Despite an excessive organic N supply and large variation in S supply (from 0 to 112 kg S/ha), principal component analysis using 43 parameters indicated that seed yield was poorly related to N and S fertilization rates. While the N and protein-N concentrations in seeds were inversely related to oil and glucosinolate concentrations, they were linked to S and sulphate (SO42−) accumulation in the seeds. Sulphate concentrations in senescing leaves, stems or seeds could be deduced from total S concentrations, as they were positively and highly correlated. Sulphate accounted for on average 0·69 of total S in senescing leaves with minimum and maximum values of 0·007 and 0·94, which revealed conditions of limited and excess supply of S, respectively. This high variation of SO42− concentration in leaves can be interpreted as the result of its mobilization triggered by S deficiency, but cannot be used alone as an indicator of plant S status. A comparison with plants grown in controlled conditions under different S supplies suggests that the intensity of S starvation affects N metabolism, leading to NO3− (nitrate) accumulation. It is further suggested that dual evaluation of SO42− and NO3− concentrations in senescing leaves could be used at the vegetative stage as a field indicator to adjust S fertilization.
Fructan biosynthesis in Lolium perenne: appraisal of soluble and insoluble enzymatic pathways
- D. GUERRAND, J. C. AVICE, N. PAVIS, M. P. PRUD'HOMME, J. BOUCAUD
-
- Journal:
- The New Phytologist / Volume 141 / Issue 1 / January 1999
- Published online by Cambridge University Press:
- 01 January 1999, pp. 109-118
- Print publication:
- January 1999
-
- Article
- Export citation
-
Previous work on Lolium perenne showed that sucrose[ratio ]sucrose fructosyltransferase (SST) activity did not increase concomitantly with fructan synthesis in regrowing leaves or in mature leaf blades of plants that have been subjected to carbohydrate-accumulating conditions. This was contrary to the pattern of SST activity in roots and stubble. To obtain further insight into the fructan synthesizing activities and to explain this discrepancy, total fructosyltransferase activity (FT) was assayed by increasing the sucrose and the soluble enzyme concentrations and was compared to sedimentable phlein sucrase activity (PS) throughout the regrowth period following defoliation in leaves, stubble and roots. Before analysis on 2-month-old plants, PS activity was characterized in dark-grown coleoptiles, using [U-14C]sucrose. PS activity had a pH optimum of 6.0 and produced 1-kestose in addition to high molecular weight fructans with a mean DP of 9. In 2-month-old plants, sedimentable PS and FT soluble reactions contained an initial sucrose concentration of 160 mM and 400 mM and proteins equivalent to 1.4 and 2.1 g f. wt of tissue, respectively. In stubble and roots, the FT preparation catalysed the synthesis of large fructans, and the overall pattern resembled the native fructans when separated by anion exchange HPLC. In regrowing leaves, the FT preparation produced low-DP fructans relatively more than in vivo but synthesized the high-DP fructan characteristic of the tissue. Moreover, FT activity did not remain at a low level like SST activity but increased from day 5 after defoliation when fructans began to accumulate. PS activity formed very few low- DP fructans and 1-kestose was the main product. Trisaccharides generated by PS activity represented 2–5% of the total trisaccharide synthesis. High-DP fructans were detectable only when the products of the reaction were concentrated 100 times. Results are discussed with respect to the relative contribution of FT and PS activities for the synthesis of 1-kestose and fructans in roots, stubble and leaves of Lolium perenne.