Metabolization of elemental sulfur in wheat leaves consecutive to its foliar application

The qualitative and quantitative aspects of elemental sulfur metabolization in wheat leaves and its effect upon photosynthetic metabolism were studied through the application of micronized sulfur upon the third leaf. Energy-dispersive x-ray analysis combined with scanning electron microscopy emphasized the existence of a sulfur peak associated with a strong potassium peak in the spectra of different tissue regions for treated leaves only, supplying an original evidence of sulfur uptake. Experiments with³⁵S-labeled micronized sulfur showed that about 2% of the labeled S was absorbed and metabolized into cystine, methionine, glutathione, and sulfate. The close correlation between the excess of oxygen uptake and oxygen needs for sulfur oxidation in conjunction with the absence of hydrogen sulfide released by treated leaves support direct and fast oxidation of sulfur into sulfate according to a pathway still unclear but independent of photosynthetic CO₂ metabolism in treated leaf. The mechanisms involved in the primary metabolism of element sulfur in wheat therefore appear to be different from those in fungi.     

Responses of rape genotypes to boron application

Pot and field experiments were conducted to examine the effect of boron on the yield and quality of different rape genotypes and to identify cultivar variation in some physiological responses to boron. B fertiliser can significantly increase the yields of both traditional and high-quality rape. Significant differences in yield response to boron application were found between cultivars. High quality varieties were more sensitive to boron deficiency than a traditional variety. Application of boron increased plant height, net photosynthetic rate, activity of nitrate reductase (NRA) and dry-weight yield, and decreased the contents of erucic acid and glucosinolate in both traditional and high-quality rape varieties. Boron plays a positive role in keeping the stability of the good characteristics of high quality cultivars.     

Differential response of oilseed rape (Brassica napus L.) cultivars to low boron supply

Three experiments were carried out on an alluvial sandy loam (Udifluvent) at Tonglu, Zhejiang Province, P.R. China from 1992 to 1995, to determine the genotypic range in boron (B) efficiency of 16 oilseed rape (Brassica napus L.) cultivars, to identify the B-efficient cultivars and to identify specific responses which can be utilised for selection in a breeding program. The 16 cultivars which included high-quality and conventional types differed significantly in survival, plant height, leaf area, shoot dry weight and seed yield; however, the ranking of the cultivars for their seed yield or other plant traits differed with B treatment. With severe B deficiency (CaCl2 extractable B < 0.26 mg/kg) and no boron applied, none of the cultivars exhibited significant B efficiency, with seed yield <300 kg/ha. With moderate B deficiency (CaCl2 extractable B 0.34 mg/kg or 0.17 kg B/ha applied), seed yield varied significantly among the cultivars from 397 to 1889 kg/ha in year 1 and from 616 to 1260 kg/ha in year 3. Zhongyou 821 and 92-13 were the most B-efficient and Wanyou 324, Huashuang 2 and Su 2051 were the most B-inefficient cultivars under moderate B deficiency. Significant differences were found among the cultivars in leaf B concentration; however, there was no close relationship between leaf B concentration and seed yield responses to B of oilseed cultivars. Of all the growth parameters measured, leaf area was the early indicator best correlated with subsequent seed yield and may be useful for evaluating the response of cultivars to low B supply. Contrary to current opinion, it was also found that high-quality oilseed rape cultivars were not all sensitive to low B supply nor were all conventional cultivars B-efficient.     

The importance of sampling immature leaves for the diagnosis of boron deficiency in oilseed rape (Brassica napus cv. Eureka)

Plant analysis can diagnose boron (B) deficiency when the standards used have been properly developed by establishing that a close relationship exists between B concentration in a plant part and its physiological function. The purpose of the present study was to demonstrate the importance of choosing the growing immature leaves for B deficiency diagnosis and for establishing critical B concentrations for the diagnosis of B deficiency in oilseed rape (Brassica napus). In Experiment 1, the plants were subject to seven levels of B supply using programmed nutrient addition, for the estimation of critical B concentrations in plant parts for shoot growth. In Experiment 2, the plants were treated with two levels of B supply in solution: 10 (+B) and 0 (-B) M B, for the estimation of functional B requirements for leaf elongation. The results showed that critical B concentrations varied amongst the plant parts sampled and decreased with leaf age. As B taken up by roots is largely phloem-immobile, B concentrations in mature leaves are physiologically irrelevant to plant B status at the time of sampling, giving rise to a significant over- or underestimation of the B requirement for plant growth. By contrast, a growing, immature leaf, in this case the youngest open leaf (YOL), was the most reliable plant part for B deficiency diagnosis. Critical B concentrations developed from both methods were comparable-i.e. 10–14 mg B kg^–1 dry matter in the YOL at vegetative growth stages up to stem elongation.     

Effects of triazole growth retardants on oilseed rape; photosynthesis of single leaves

Rates of CO₂ exchange were measured for single leaves on oilseed rape plants after application of triapenthenol and BAS111. For leaves which expanded after treatment, there was no detectable change in the rate of photosynthesis per unit leaf area compared with the control for either chemical about 3 wk after application. For fully expanded leaves at the time of application a reduction in the rate of photosynthesis per unit leaf area occurred and was sustained for at least 2 wk. The reduction in the rate of photosynthesis is explained by decreased stomatal conductance.     

Photosynthesis in leaves and siliques of winter oilseed rape (Brassica napus L.)

The rate of photosynthesis and its relation to tissue nitrogen content was studied in leaves and siliques of winter oilseed rape (Brassica napus L.) growing under field conditions including three rates of nitrogen application (0, 100 or 200 kg N ha^-1) and two levels of irrigation (rainfed or irrigated at a deficit of 20 mm). The predominant effect of increasing N application under conditions without water deficiency was enhanced expansion of photosynthetically active leaf and silique surfaces, while the rate of photosynthesis per unit leaf or silique surface area was similar in the different N treatments. Thus, oilseed rape did not increase N investment in leaf area expansion before a decline in photosynthetic rate per unit leaf area due to N deficiency could be avoided. Much less photosynthetically active radiation penetrated into high-N canopies than into low-N canopies. The specific leaf area increased markedly in low light conditions, causing leaves in shade to be less dense than leaves exposed to ample light. In both leaves and siliques the photosynthetic rate per unit surface area responded linearly to increasing N content up to about 2 g m^-2, thus showing a constant rate of net CO₂ assimilation per unit increment in N (constant photosynthetic N use efficiency). At higher tissue N contents, photosynthetic rate responded less to changes in N status. Expressed per unit N, light saturated photosynthetic rate was three times higher in leaves than in silique valves, indicating a more efficient photosynthetic N utilization in leaves than in siliques. Nevertheless, from about two weeks after completion of flowering and onwards total net CO₂ fixation in silique valves exceeded that in leaves because siliques received much higher radiation intensities than leaves and because the leaf area declined rapidly during the reproductive phase of growth. Water deficiency in late vegetative and early reproductive growth stages reduced the photosynthetic rate in leaves and, in particular, siliques of medium- and high-N plants, but not of low-N plants.     

The effects of freezing on membrane electric potential in winter oilseed rape leaves

Extracellular ice formation in winter oilseed rape leaf discs (Brassica napus L. var. oleifera L. cv. Jantar) at different temperatures resulted in a transient membrane depolarization, which was followed by a decrease in membrane electric potential. In discs which underwent supercooling (no extracellular ice was formed), no membrane depolarization was observed. The inhibitors of calcium ion channels, gadolinium and lanthanum, decreased to some extend the amplitude of the frost-induced (−6 °C) depolarization and completely eliminated the decrease in membrane potential. Changes in membrane potential were associated with the increased electrolyte efflux, measured after thawing of the discs. No efflux from supercooled discs was observed. Application of calcium channel blockers decreased the level of the efflux induced by freezing at −6°C. It is suggested that membrane depolarization is one of the primary events induced by ice formation at a leaf surface. The possible reasons for changes in the membrane electric potential and their physiological consequences are discussed.     

Competitiveness of transgenic oilseed rape

The competitiveness of two transgenic oilseed rape (Brassica napus ssp.napus) lines and their fertile transgenic hybrid was tested in field trials in Belgium and Denmark. The lines contained genes for male sterility, restoration of fertility and herbicide resistance. The competitiveness of the three transgenic lines was related to three non-transformed commercially-grown oilseed rape varieties: Drakkar, Topas and Line. As a reference of a more aggressive crucifer, white mustard (Sinapis alba) was also included in the experiment. The experimental design was a complete block design with two locations, monocultures and mixtures with barley (Hordeum vulgare), three plant densities, four harvest times and four blocks. The yield density relationship of the transgenic oilseed rape lines was not different from that of the non-transgenic varieties in either location. The first harvest times showed a vigorous biomass production of white mustard, which in turn produced a significant difference in the competitive ability between oilseed rape and white mustard. Later, this difference decreased, and in Belgium there was no difference at the last harvest time. Variations within populations may blur actual differences between lines and varieties, and it is argued that unless the experimental design covers a range of competitiveness for which it is possible to detect significant differences, test results reporting a lack of difference between transgenic and non-transgenic plants are of little value.     

Modifications of abscisic acid level in winter oilseed rape leaves during acclimation of plants to freezing temperatures

An almost twofold increase in abscisic acid (ABA) content was observed in the leaves of winter oilseed rape plants (Brassica napus L., var. oleifera L., cv. Jantar) grown in the cold (>0°C). This ABA increase took place during the first three days of cold treatment. After 6 days of plant growth in the cold, the level of ABA started to decline or remained constant, depending on the calculation basis: dry weight or disc area units, respectively. The exposure of cold-acclimated plants to night frost (–5°C for 18 h) induced a further increase (65%) in the ABA level, which begun during the first few hours after thawing. The comparison of time courses of frost resistance increments and ABA content changes showed that modifications of ABA level in the cold-treated leaves preceded those of frost resistance, whereas in the frost-pretreated tissues the ABA increase occurred later than that of frost tolerance. Possible interrelations between ABA content, frost tolerance and tissue water potential modifications in the low temperature-affected tissues are discussed.     

Salicylic acid-induced accumulation of glucosinolates in oilseed rape (Brassica napus L.) leaves

Applying a salicylic acid soil drench to oilseed rape plantsincreased the concentration of glucosinolates in their leaves.The intensity of this ‘induction’ depended on theconcentration of salicylic acid applied and the age of the leaf:developing leaves retained enhanced levels of glucosinolateslonger than mature leaves. 2-Phenylethylglucosinolate showedthe greatest increase in concentration, with only minor increasesin other glucosinolates in developing leaves. This responseto salicylic acid is more specific than that observed followingfungal infection or damage by herbivores. The results presentedhere are among the first to demonstrate an increase in secondarymetabolite content in response to salicylic acid. The implicationsof this response are discussed in terms of the role of salicylicacid and glucosinolates in plant defence. Key words: Salicylic acid, oilseed rape, Brassica napus, glucosinolates     

Variation in the glucosinolate content of oilseed rape (Brassica napus L.) leaves

The glucosinolate content of oilseed rape {Brassica napus) leaves was monitored over the growth period 30–70 days after planting, and a comparison made between a single-low cultivar (low in erucic acid), Bienvenu, and a double-low cultivar (low in erucic acid and glucosinolate), Cobra. In older, fully-expanded leaves the glucosinolate concentration was very low (< 0.3 μmol/ml tissue water) and did not alter during the course of the experiment. In developing sixth leaves glucosinolate content increased rapidly and reached a maximum concentration (4–5 μmol/ml tissue water) 40 days after planting (6 days after leaf emergence). The concentration then declined, to about 1 μmol/ml after 60 days although the total glucosinolate content in leaves continued to increase until 50 days; much of the reduction in concentration was simply a result of leaf expansion. No major differences were seen between the two varieties in total glucosinolate content or in the individual compounds present. Cv. Cobra developed more quickly than cv. Bienvenu so direct comparison between leaves of the two cultivars was complex. When comparing the glucosinolate content of oilseed rape leaves, between cultivars or between treatments, it is vital to ensure that carefully matched leaves of comparable developmental age are selected.     

Feeding preferences of woodpigeons and flea-beetles for oilseed rape and turnip rape

Winter turnip rape Brassica rapa ssp. oleifera was shown to have reduced palatability to woodpigeons, enhanced susceptibility to adult flea beetle feeding and reduced susceptibility to larval flea-beetle infection when compared with winter oilseed rape (B. napus) cultivars in field trials. Levels of leaf waxes were negatively correlated with feeding preferences of adult flea beetles. Analysis of volatiles from damaged leaves showed that while all cultivars produce a similar range of nitriles, cyanoepithioalkanes and isothiocyanates, derived from 3-butenyl, 4-pentenyl and phenylethyl glucosinolates, B. rapa leaves produced relatively high levels of 1-methylpropyl isothiocyanate, although there was significant plant-to-plant variation. The possible involvement of this mustard oil glycoside and variation in epicuticular waxes in plant-herbivore interactions are discussed.     

Pollination efficiency of wild bees and hoverflies provided to oilseed rape

• 1 Declining numbers in honeybees and various wild bee species pose a threat to global pollination services. The identification and quantification of the pollination service provided by different taxa within the pollinator guild is a prerequisite for the successful establishment of nature conservation and crop management regimes.
• 2 Wild bees and hoverflies are considered to be valuable pollinators in agricultural and natural systems. Although some information on pollination efficiency of individual pollinator species is available, comparative studies of both taxa at different densities are rare. In the present study, the efficiency of the solitary mason bee Osmia rufa and two hoverfly species (Eristalis tenax and Episyrphus balteatus) as pollinators of oilseed rape Brassica napus was examined in a standardized caged plant breeding regime. Honeybee Apis mellifera colonies were used as a reference pollinator taxon.
• 3 Yield parameters responded differently to pollinator density and identity. Fruit set and number of seeds per pod increased with increasing pollinator density, although these were stronger in the mason bee than the hoverfly treatment. Weight per 1000 seeds did not respond to any pollinator treatment, indicating that seed quality was not affected. Oilseed rape yield in the highest tested densities of both pollinator taxa resulted in yield values close to the efficiency of small honeybee colonies.
• 4 Hoverflies required approximately five‐fold densities of the red mason bees to reach a similar fruit set and yield. Thus, mason bees are more efficient in plant breeding and managed pollination systems. Both natural pollinator taxa, however, are of potential value in open and closed crop production systems.

     

氮磷钾、硼水平对不同基因型油菜硼吸收及某些生物学性状的影响

采用温室土培试验,研究了不同氮磷钾复合型（NPK肥）施用水平下,油菜对B的吸收及其耐缺B机理以及缺B对某些生物学性状的影响,结果表明,缺B时,随NPK肥施用量的增加,油菜植株缺B症状加重,苗期叶面积及其生长速率减小,叶绿素含量增加,硝酸还原酶活性下降,成熟期单株有效分枝,有效角果数减少,籽粒产量降低,可以认为,油菜大苗期最新展开叶（YOL）与最新成熟叶（YML）的B浓度比值可作为不同基因型油菜植株体内B移动性大小的判氟指标,B移动性及B利用率的大小是不同基因型油菜耐缺B的重要营养机理之一。     

Photorespiratory NH(4)(+) production in leaves of wild-type and glutamine synthetase 2 antisense oilseed rape

Exposure of oilseed rape (Brassica napus) plants to increasing leaf temperatures between 15 degrees C and 25 degrees C increased photorespiratory NH(4)(+) production from 0.7 to 3.5 micromol m(-2) s(-1). Despite the 5-fold increase in the rate of NH(4)(+) production, the NH(4)(+) concentration in root and leaf tissue water and xylem sap dropped significantly, whereas that in the leaf apoplastic fluid remained constant. The in vitro activity of glutamine synthetase (GS) in both leaves and roots also increased with temperature and in all cases substantially exceeded the observed rates of photorespiratory NH(4)(+) production. The surplus of GS in oilseed rape plants was confirmed using GS2 antisense plants with 50% to 75% lower in vitro leaf GS activity than in the wild type. Despite the substantial reduction in GS activity, there was no tendency for antisense plants to have higher tissue NH(4)(+) concentrations than wild-type plants and no overall correlation between GS activity and tissue NH(4)(+) concentration was observed. Antisense plants exposed to leaf temperatures increasing from 14 degrees C to 27 degrees C or to a trifold increase in the O(2) to CO(2) ratio did not show any change in steady-state leaf tissue NH(4)(+) concentration or in NH(3) emission to the atmosphere. The antisense plants also had similar leaf tissue concentrations of glutamine, glycine, and serine as the wild type, whereas glutamate increased by 38%. It is concluded that photorespiration does not control tissue or apoplastic levels of NH(4)(+) in oilseed rape leaves and, as a consequence, that photorespiration does not exert a direct control on leaf atmosphere NH(3) fluxes.     

Identification of endogenous gibberellins from oilseed rape

Oilseed rape (Brassica napus, canola variety `Westar') plants were grown in greenhouse conditions and shoots were harvested during the final stages of shoot elongation. Leaves and immature pods were removed and the remaining stem tissue was extracted and purified. The extract was chromatographed on sequential, step-eluted silica gel partition and reverse-phase C<sub>18</sub> HPLC columns, and gibberellin (GA)-like substances were detected using the `Tan-ginbozu' dwarf rice microdrop assay. Purified fractions showing GA-like activity were analyzed by capillary gas chromatography-mass spectrometry (GC-MS) and GC-selected ion monitoring (GC-SIM). Gibberellins A₁, A₃, and iso-A₃ were identified by full spectrum GC-MS with GA₁ being the most abundant GA in the stem tissue. Gibberellins A₁₉ and A₂₀ were identified by GC-SIM and are logical precursors of the GA₁.     

Lipid biosynthesis in cultures of oilseed rape

Summary This review focuses on how microspore-derived (MD) embros and cell suspension cultures of oilseed rape have been used to advance our understanding of the biochemistry and molecular biology of lipid biosynthesis in plants. Both types of cultures are easily maintained and circumvent the difficulties associated with using developing seeds for investigations of lipid biosynthesis. Developing MD embryos exhibit a similar storage lipid accumulation profile and fatty acid composition to developing seed. The use of dihaploids derived from plantlets of MD embryos have accelerated breeding programs and have proven useful in the detection of recessive mutations. MD embryos and MD cell suspension cultures have been particularly useful in investigating the properties of key enzymes involved in triacylglycerol (TG) bioassembly. MD cell suspension cultures, however, offer the advantage of being able to study lipid metabolism in the absence of cellular differentiation. TG accumulation can be induced in MD cell suspension cultures by increasing the sucrose concentration of the growth medium thereby providing a useful system to investigate gene expression and the proteomics of lipid biosynthesis.     

Availability of different forms of sulphur fertilisers to wheat and oilseed rape

A pot experiment was conducted to compare the availability and efficiency of three sulphur (S) fertilisers to wheat in the first year and oilseed rape in the second year, using six agricultural soils. Four treatments were applied in the initial year: control (no S), two forms of elemental S (either micronised S° particles or a bentonite + S° mixture) and a sulphate fertiliser (ammonium sulphate). In the first year, the micronised S° was as effective as the sulphate fertiliser, both producing similar increases of wheat grain yield (on average 36%) and S uptake (on average 164%) over the control. In contrast, responses to the bentonite + S° form were minimal, indicating a limited S supply. In the second year the control treatment failed to produce seeds in most soils, whereas the micronised S° and sulphate treatments increased seed yields of oilseed rape to an average of 13.4 and 12.9 g pot^-1, respectively. The performance of the bentonite + S° varied between soils: two soils produced yields similar to those of the other S fertilisers, while the remaining soils had low yields. To test whether the poor performance of the bentonite clay + S° fertiliser was due to the lack of exposure of the prills to physical weathering in the glasshouse, the effect of freeze-thaw action on the fertilisers performance was assessed in a separate pot experiment. The responses in wheat yield and S uptake showed that freeze-thaw did not enhance the physical disruption of the prills or fertiliser effectiveness. These results suggest that the release of available S from the bentonite + S° mixture was too slow to meet the requirement of wheat and oilseed rape. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrogen metabolism and seed composition as influenced by foliar boron application in soybean

The physiological effects of foliar boron application (FB) on nitrogen metabolism and seed composition have not been well established in soybean [(Glycine max(L.)Merr.)]. Therefore, the effect of FB on nitrogen metabolism and seed composition was investigated. Nitrate assimilation was evaluated by measuring nitrate reductase activity (NRA) and nitrogen fixation was evaluated by measuring nitrogenase activity and natural abundance of ¹⁵N/¹⁴N. NRA were significantly (P?≤?0.05) higher in plants that received FB than the control plants. Higher rate of FB (One application of four times of commercial rate) inhibited nitrogen fixation as measured by natural abundance of ¹⁵N/¹⁴N ratio, but increased NRA. The higher activities of NR and nitrogenase by FB were accompanied with a higher B concentration in leaves. The significant (P?<?0.0001) enrichment of ¹⁵N/¹⁴N, accompanied with a higher rate of FB, suggested a possible mechanism where nitrate assimilation may compensate for the decrease in nitrogen fixation. FB increased seed protein by 13.7% and oleic acid by 30.9% compared to the control plants. This alteration was accompanied by a higher B concentration in leaves and seed. The results suggest that FB affects nitrogen metabolism and alters seed compositions, especially protein and unsaturated fatty acids.