Essa Ali

The alleviation of cadmium toxicity in oilseed rape (Brassica napus) by the application of salicylic acid

To assess the potential role of salicylic acid (SA) in plants under cadmium (Cd) stress, a study was conducted on three different oilseed rape (Brassica napus) genotypes. Gas exchange parameters, photosynthetic pigments, antioxidant enzymes activities, mineral nutrients concentration, and ultrastructural analysis were carried out for assessment. Interestingly, cadmium treatment reduced gas exchange parameters, photosynthetic pigments, mineral elements [calcium (Ca), magnesium (Mg), and iron] and the activity of catalase (CAT) enzyme. Whereas, a pronounced increase was observed in malondialdehyde content and antioxidant enzymes, cadmium and zinc accumulation. Impressively, SA played its role as an alleviatory agent by reducing the damage to all parameters caused by Cd except internal CO2 concentration which was further decreased by SA. Even more, Cd and SA showed synergistic effects by increasing superoxide dismutase, peroxidases, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and decreasing CAT. Apart from affecting the enzyme activities of oilseed rape, both Cd and SA had the same inhibitory effects on Ca and Mg concentrations. Damage caused by Cd to chloroplast and other internal organelles were almost rectified by SA. Effective role of SA, in alleviating Cd toxicity, could be attributed to the SA-induced improvement of photosynthetic activities, enhancement of antioxidant enzymes activities, reduction in lipid peroxidation and Cd uptake. These findings reflect the possible role of SA as a potential inhibitor of cadmium toxicity by strengthening the internal immunity in oilseed rape.

TRANSPARENT TESTA8 Inhibits Seed Fatty Acid Accumulation by Targeting Several Seed Development Regulators in Arabidopsis

A maternal factor affects seed fatty acid biosynthesis and inhibits seed lipid accumulation by targeting seed development and down-regulating a group of genes critical to embryonic development. Fatty acids (FAs) and FA-derived complex lipids play important roles in plant growth and vegetative development and are a class of prominent metabolites stored in mature seeds. The factors and regulatory networks that control FA accumulation in plant seeds remain largely unknown. The role of TRANSPARENT TESTA8 (TT8) in the regulation of flavonoid biosynthesis and the formation of seed coat color is extensively studied; however, its function in affecting seed FA biosynthesis is poorly understood. In this article, we show that Arabidopsis (Arabidopsis thaliana) TT8 acts maternally to affect seed FA biosynthesis and inhibits seed FA accumulation by down-regulating a group of genes either critical to embryonic development or important in the FA biosynthesis pathway. Moreover, the tt8 mutation resulted in reduced deposition of protein in seeds during maturation. Posttranslational activation of a TT8-GLUCOCORTICOID RECEPTOR fusion protein and chromatin immunoprecipitation assays demonstrated that TT8 represses the activities of LEAFY COTYLEDON1, LEAFY COTYLEDON2, and FUSCA3, the critical transcriptional factors important for seed development, as well as CYTIDINEDIPHOSPHATE DIACYLGLYCEROL SYNTHASE2, which mediates glycerolipid biosynthesis. These results help us to understand the entire function of TT8 and increase our knowledge of the complicated networks regulating the formation of FA-derived complex lipids in plant seeds.

Removal of DELLA repression promotes leaf senescence in Arabidopsis

Leaf senescence is an integrated response of leaf cells to developmental age and various internal and environmental signals. However, the role of gibberellins (GA) in leaf senescence is not clear. In the current study, we investigated the effect of DELLA on leaf senescence. Compared with the wild type (WT), leaf senescence occurred earlier in the mutant ga1-3 gai-t6 rga-t2 rgl1-1 rgl2-1 (abbreviated as Q-DELLA/ga1-3) whose DELLA repression was removed, whereas leaf senescence was retarded in the mutant ga1-3 whose GA biosynthesis was blocked and whose DELLA proteins accumulated abnormally. During leaf senescence, SAG12 and SAG29 were upregulated in Q-DELLA/ga1-3 and downregulated in ga1-3 plants. The Q-DELLA/ga1-3 senescent leaves contained more sugar but less chlorophyll and fatty acids (FAs) than those of ga1-3 and WT. Both absolute and relative contents of C18:3 in Q-DELLA/ga1-3 senescent leaves were lower compared with those of the WT and ga1-3 leaves. The genes regulating FA β-oxidation in Q-DELLA/ga1-3, such as KAT2, LACS6, LACS7, ACX1, ACX2 and MAP2, were significantly upregulated. The removal of DELLA repression highly upregulated certain genes on various hormone pathways, suggesting that GA signaling acts upstream of the jasmonic acid, salicylic acid, and ethylene pathways in regulating leaf senescence.

Correlations between Tocopherol and Fatty Acid Components in Germplasm Collections of Brassica Oilseeds

To date, little is known about the correlations among the tocopherol (T) and fatty acid (FA) components in rapeseed oils. In the current study, a germplasm collection of landraces from the species Brassica juncea , Brassica rapa , and Brassica napus and a collection of low erucic acid (EA) breeding lines from B. napus were analyzed for FA and T contents. In the groups comprising landraces, the most notable correlation was the significantly positive one between α-T and the sum of C18:1 and C18:2, whereas neither positive correlations were found between α-T and C18:3 nor were positive correlations observed between α-T and very long chain FAs (VLCFA). Hardly any association between γ-T and FA components was observed, indicating the possible function of α-T beyond its antioxidant property. The complexity of correlation between T and FA components in Brassica oils may arise from the role of α-T in the FA metabolism of endoplasmic reticulum (ER).

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

Tocopherols (Tocs) are vital scavengers of reactive oxygen species (ROS) and important seed oil quality indicators. Nitrogen (N) is one of the most important fertilizers in promoting biomass and grain yield in crop production. However, the effect of different sources and application rates of N on seed Toc contents in oilseed rape is poorly understood. In this study, pot trials were conducted to evaluate the effect of two sources of N fertilizer (urea and ammonium nitrate). Each source was applied to five oilseed rape genotypes (Zheshuang 72, Jiu-Er-1358, Zheshuang 758, Shiralee, and Pakola) at three different application rates (0.41 g/pot (N1), 0.81 g/pot (N2), and 1.20 g/pot (N3)). Results indicated that urea increased α-, γ-, and total Toc (T-Toc) more than did ammonium nitrate. N3 was proven as the most efficient application rate, which yielded high contents of γ-Toc and T-Toc. Highly significant correlations were observed between Toc isomers, T-Toc, and α-/γ-Toc ratio. These results clearly demonstrate that N sources and application rates significantly affect seed Toc contents in oilseed rape.

Nitrogen (N) metabolism related enzyme activities, cell ultrastructure and nutrient contents as affected by N level and barley genotype

Abstract Development of the new crop cultivars with high yield under low nitrogen (N) input is a fundamental approach to enhance agricultural sustainability, which is dependent on the exploitation of the elite germplasm. In the present study, four barley genotypes (two Tibetan wild and two cultivated), differing in N use efficiency (NUE), were characterized for their physiological and biochemical responses to different N levels. Higher N levels significantly increased the contents of other essential nutrients (P, K, Ca, Fe, Cu and Mn), and the increase was more obvious for the N-efficient genotypes (ZD9 and XZ149). The observation of ultrastructure showed that chloroplast structure was severely damaged under low nitrogen, and the two high N efficient genotypes were relatively less affected. The activities of the five N metabolism related enzymes, i.e., nitrate reductase (NR), glutamine synthetase (GS), nitrite reductase (NiR), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) all showed the substantial increase with the increased N level in the culture medium. However the increased extent differed among the four genotypes, with the two N efficient genotypes showing more increase in comparison with the other two genotypes with relative N inefficiency (HXRL and XZ56). The current findings showed that a huge difference exists in low N tolerance among barley genotypes, and improvement of some physiological traits (such as enzymes) could be helpful for increasing N utilization efficiency.

Comprehensive genomic analysis of the CNGC gene family in Brassica oleracea: novel insights into synteny, structures, and transcript profiles.

BackgroundThe cyclic nucleotide-gated ion channel (CNGC) family affects the uptake of cations, growth, pathogen defence, and thermotolerance in plants. However, the systematic identification, origin and function of this gene family has not been performed in Brassica oleracea, an important vegetable crop and genomic model organism.ResultsIn present study, we identified 26 CNGC genes in B. oleracea genome, which are non-randomly localized on eight chromosomes, and classified into four major (I-IV) and two sub-groups (i.e., IV-a and IV-b). The BoCNGC family is asymmetrically fractioned into the following three sub-genomes: least fractionated (14 genes), most fractionated-I (10), and most fractionated-II (2). The syntenic map of BoCNGC genes exhibited strong relationships with the model Arabidopsis thaliana and B. rapa CNGC genes and provided markers for defining the regions of conserved synteny among the three genomes. Both whole-genome triplication along with segmental and tandem duplications contributed to the expansion of this gene family. We predicted the characteristics of BoCNGCs regarding exon-intron organisations, motif compositions and post-translational modifications, which diversified their structures and functions. Using orthologous Arabidopsis CNGCs as a reference, we found that most CNGCs were associated with various protein–protein interaction networks involving CNGCs and other signalling and stress related proteins. We revealed that five microRNAs (i.e., bol-miR5021, bol-miR838d, bol-miR414b, bol-miR4234, and bol-miR_new2) have target sites in nine BoCNGC genes. The BoCNGC genes were differentially expressed in seven B. oleracea tissues including leaf, stem, callus, silique, bud, root and flower. The transcript abundance levels quantified by qRT-PCR assays revealed that BoCNGC genes from phylogenetic Groups I and IV were particularly sensitive to cold stress and infections with bacterial pathogen Xanthomonas campestris pv. campestris, suggesting their importance in abiotic and biotic stress responses.ConclusionOur comprehensive genome-wide analysis represents a rich data resource for studying new plant gene families. Our data may also be useful for breeding new B. oleracea cultivars with improved productivity, quality, and stress resistance.

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.概要目的本研究目的在于了解:(1)喷施外源茉莉酸对受 到镉胁迫油菜的作用;(2)是否茉莉酸能够通过增强气体交换,从而保护受到氧化胁迫的地上部分组织的叶绿体,进而通过减少镉的吸收来维持 离子平衡;(3)是否通过喷施茉莉酸来对具有减 缓镉毒害效应的抗氧化酶的活性进行调节。创新点茉莉酸能够调节响应胁迫的抗氧化酶的活性,从而通过保护叶绿体免受活性氧(ROS)伤害而提高光合产物的能力,最大限度地缓解油菜植株受到的镉毒害。方法(1)叶片气体交换;(2)叶片光合色素分析;(3) 丙二醛与抗氧化酶活性分析;(4)营养成分分析; (5)透射电镜亚细胞水平观察。结论茉莉酸对于植物受镉毒害的缓解作用的机理在于减少叶片中镉的积累,从而减轻氧化胁迫过程中产生的ROS 对于膜系统的损害程度。

Growth and physiological characterization of low nitrogen responses in Tibetan wild barley (Hordeum spontaneum) and cultivated barley (Hordeum vulgare)

ABSTRACT Development of crop cultivars with high yield under low nitrogen (N) supply is a basic approach for the enhancement of agricultural sustainability. The previous studies showed that Tibetan wild barley shows wider genetic diversity in abiotic stress and poor fertility tolerance. In this study, four barley genotypes (two Tibetan wild and two cultivated), differing in N use efficiency (NUE), were characterized for their growth and physiological responses to low N stress. The genotypes ZD9 (cultivated) and XZ149 (wild) with high NUE performed better in terms of shoot dry weight (DW) and photosynthetic parameters under both low and normal N levels and had higher antioxidative enzyme activities, N concentration, and accumulation in both shoots and roots under low N stress. The current results showed the substantial difference among barley genotypes in low N tolerance and verified the significance of Tibetan wild barley in the genetic improvement of cultivated barley in NUE.

Plant Cell Signaling in Metal Stress

Signal pathways accountable for the sensing and transduction of the metal stress signal in the cell, eventually leads to the induction of signaling molecules especially transcription factors and enzymes, followed by the expression of genes involved in the neutralization of metal stress. In order to respond to stress signals, plant cells are equipped to perceive these signals and switch them into appropriate responses, which in turn confer on plants the competence to tolerate, avoid or escape unfavorable conditions. Generally, Plant signaling pathways can be classified on the bases of their response to internal and external stimuli. Tolerance to unfavorable conditions entails harmonization of complex physiological, biochemical and molecular processes such as changes in global gene expression, protein modification and metabolite compositions. The aim of this chapter is to present: (1) the nature of chemicals which are produced following perception of metal stress and carry the message in the cell to respond either directly or indirectly by regulating the expression of genes leading to altered functions or enhance the capacity of the already existing defense metabolites; (2) to dissect the pathways in order to find the function of each component in metal stress signal. Thus, stress signaling is a vital spot in order to boost crops yield under sub-optimal conditions.