Response of seed tocopherols in oilseed rape to nitrogen fertilizer sources and application rates

The Effect of Nitrogen Fertigation and Harvesting Time on Plant Growth and Chemical Composition of Centaurea raphanina subsp. mixta (DC.) Runemark

The aim of the present study was to evaluate the effect of nitrogen fertigation (0, 200, 400, and 600 ppm of total nitrogen) and harvesting time (9 March 2018 and 19 April 2018) on the plant growth, chemical composition, and bioactive properties of Centaurea raphanina subsp. mixta plants. The highest yield of fresh leaves was observed for the treatment of 200 ppm of N without compromising nutritional value. The increasing nitrogen levels resulted in an increase of α- and total tocopherols and sugars content, especially in the second harvest for tocopherols and in the first harvest for sugars. Similarly, total organic acids and oxalic acid content increased with increasing nitrogen levels in both harvests, while fatty acids composition had a varied response to the tested factors. Pinocembrin neohesperidoside and pinocembrin acetyl neohesperidoside isomer II were the most abundant phenolic compounds with the highest content being observed in the control treatment of the first and second harvest, respectively. The highest antioxidant activity was observed for the control and the 600 ppm treatments of the second harvest for the OxHLIA and TBARS assays, respectively, probably due to the high content of pinocembrin acetyl neohesperidoside isomer II and α-tocopherol, respectively. Finally, cytotoxic effects and antimicrobial properties showed a varied response depending on the treatment. In conclusion, C. raphanina subsp. mixta has low requirements of nitrogen to achieve the highest yield, while a varied response to the tested fertigation treatments and harvesting time was observed in terms of the chemical composition and the bioactive properties.

Role of jasmonic acid in improving tolerance of rapeseed (Brassica napus L.) to Cd toxicity

The well-known detrimental effects of cadmium (Cd) on plants are chloroplast destruction, photosynthetic pigment inhibition, imbalance of essential plant nutrients, and membrane damage. Jasmonic acid (JA) is an alleviator against different stresses such as salinity and drought. However, the functional attributes of JA in plants such as the interactive effects of JA application and Cd on rapeseed in response to heavy metal stress remain unclear. JA at 50 µmol/L was observed in literature to have senescence effects in plants. In the present study, 25 µmol/L JA is observed to be a "stress ameliorating molecule" by improving the tolerance of rapeseed plants to Cd toxicity. JA reduces the Cd uptake in the leaves, thereby reducing membrane damage and malondialdehyde content and increasing the essential nutrient uptake. Furthermore, JA shields the chloroplast against the damaging effects of Cd, thereby increasing gas exchange and photosynthetic pigments. Moreover, JA modulates the antioxidant enzyme activity to strengthen the internal defense system. Our results demonstrate the function of JA in alleviating Cd toxicity and its underlying mechanism. Moreover, JA attenuates the damage of Cd to plants. This study enriches our knowledge regarding the use of and protection provided by JA in Cd stress.

Exogenous Glycine Nitrogen Enhances Accumulation of Glycosylated Flavonoids and Antioxidant Activity in Lettuce (Lactuca sativa L.)

Glycine, the simplest amino acid in nature and one of the most abundant free amino acids in soil, is regarded as a model nutrient in organic nitrogen studies. To date, many studies have focused on the uptake, metabolism and distribution of organic nitrogen in plants, but few have investigated the nutritional performance of plants supplied with organic nitrogen. Lettuce (Lactuca sativa L.), one of the most widely consumed leafy vegetables worldwide, is a significant source of antioxidants and bioactive compounds such as polyphenols, ascorbic acid and tocopherols. In this study, two lettuce cultivars, Shenxuan 1 and Lollo Rossa, were hydroponically cultured in media containing 4.5, 9, or 18 mM glycine or 9 mM nitrate (control) for 4 weeks, and the levels of health-promoting compounds and antioxidant activity of the lettuce leaf extracts were evaluated. Glycine significantly reduced fresh weight compared to control lettuce, while 9 mM glycine significantly increased fresh weight compared to 4.5 or 18 mM glycine. Compared to controls, glycine (18 mM for Shenxuan 1; 9 mM for Lollo Rossa) significantly increased the levels of most antioxidants (including total polyphenols, α-tocopherol) and antioxidant activity, suggesting appropriate glycine supply promotes antioxidant accumulation and activity. Glycine induced most glycosylated quercetin derivatives and luteolin derivatives detected and decreased some phenolic acids compared to nitrate treatment. This study indicates exogenous glycine supplementation could be used strategically to promote the accumulation of health-promoting compounds and antioxidant activity of hydroponically grown lettuce, which could potentially improve human nutrition.

Effects of a controlled-release fertilizer on yield, nutrient uptake, and fertilizer usage efficiency in early ripening rapeseed (Brassica napus L.)

BACKGROUND

Nitrogen (N), phosphorous (P), and potassium (K) are critical nutrient elements necessary for crop plant growth and development. However, excessive inputs will lead to inefficient usage and cause excessive nutrient losses in the field environment, and also adversely affect the soil, water and air quality, human health, and biodiversity.

METHODS

Field experiments were conducted to study the effects of controlled-release fertilizer (CRF) on seed yield, plant growth, nutrient uptake, and fertilizer usage efficiency for early ripening rapeseed (Xiangzayou 1613) in the red-yellow soil of southern China during 2011-2013. It was grown using a soluble fertilizer (SF) and the same amounts of CRF, such as SF1/CRF1 (3750 kg/hm²), SF2/CRF2 (3000 kg/hm²), SF3/CRF3 (2250 kg/hm²), SF4/CRF4 (1500 kg/hm²), SF5/CRF5 (750 kg/hm²), and also using no fertilizer (CK).

RESULTS

CRF gave higher seed yields than SF in both seasons by 14.51%. CRF4 and SF3 in each group achieved maximum seed yield (2066.97 and 1844.50 kg/hm², respectively), followed by CRF3 (1929.97 kg/hm²) and SF4 (1839.40 kg/hm²). There were no significant differences in seed yield among CK, SF1, and CRF1 (P>0.05). CRF4 had the highest profit (7126.4 CNY/hm²) and showed an increase of 12.37% in seed yield, and it decreased by 11.01% in unit fertilizer rate compared with SF4. The branch number, pod number, and dry matter weight compared with SF increased significantly under the fertilization of CRF (P<0.05). The pod number per plant was the major contributor to seed yield. On the other hand, the N, P, and K uptakes increased at first and then decreased with increasing the fertilizer rate at maturity, and the N, P, and K usage efficiency decreased with increasing the fertilizer rate. The N, P, and K uptakes and usage efficiencies of the CRF were significantly higher than those of SF (P<0.05). The N accumulation and N usage efficiency of CRF increased by an average of 13.66% and 9.74 percentage points, respectively, compared to SF. In conclusion, CRF significantly promoted the growth of rapeseed with using total N as the base fertilizer, by providing sufficient N in the later growth stages, and last by reducing the residual N in the soil and increasing the N accumulation and N usage efficiency.

Enhanced accumulation of phytosterols and phenolic compounds in cyclodextrin-elicited cell suspension culture of Daucus carota

In this work, suspension-cultured cells of Daucus carota were used to evaluate the effect of β-cyclodextrins on the production of isoprenoid and phenolic compounds. The results showed that the phytosterols and phenolic compounds were accumulated in the extracellular medium (15100μgL(-1) and 477.46μgL(-1), respectively) in the presence of cyclodextrins. Unlike the phytosterol and phenolic compound content, β-carotene (1138.03μgL(-1)), lutein (25949.54μgL(-1)) and α-tocopherol (8063.82μgL(-1)) chlorophyll a (1625.13μgL(-1)) and b (9.958 (9958.33μgL(-1)) were mainly accumulated inside the cells. Therefore, cyclodextrins were able to induce the cytosolic mevalonate pathway, increasing the biosynthesis of phytosterols and phenolic compounds, and accumulate them outside the cells. However, in the absence of these cyclic oligosaccharidic elicitors, carrot cells mainly accumulated carotenoids through the methylerythritol 4-phosphate pathway. Therefore, the use of cyclodextrins would allow the extracellular accumulation of both phytosterols and phenolic compounds by diverting the carbon flux towards the cytosolic mevalonate/phenylpropanoid pathway.

Effect of Gibberellin on the biosynthesis of tocopherols in Oilseed rape (Brassica napus L.) and arabidopsis

Elevating the yield and altering the composition of seed tocopherols (Toc’s) are important to rapeseed breeding and production. However, little is known about the biosynthesis of Toc’s in response to environmental signals. In this study, we investigated the effects of exogenous gibberellin (GA3) and paclobutrazol (PAC) on Toc biosynthesis. We also explored the interactive effects between the two plant growth regulators (PGRs) and other factors, such as PGR treatment duration, genotype, and growing location on the total Toc yield and composition in oilseed rape seed. GA3 significantly enhanced the production of Toc’s and elevated the α-/γ-Toc ratio in a time- and genotype-dependent manner. By contrast, PAC significantly reduced Toc yield. Genotypic differences were observed in the effects of GA3 on Toc yield and composition in the seeds. GA3 significantly increased the Toc yield and α-/γ-Toc ratio in Zheyou-50, a genotype with a low proportion of very long chain fatty acids (VLCFAs). However, GA3 did not significantly influence these parameters in Jiu-Er-13Xi, a genotype with a high VLCFA proportion. The increased Toc yield induced by GA3 was mediated by the upregulation of genes (BnPDS1 and BnVTE1) that catalyze the production of Toc precursors. Therefore, applying GA3 can improve rapeseed quality by increasing Toc yield and improving Toc composition.