Bioactive natural products from marine angiosperms:abundance and functions

This review explores the natural products of seagrass that are to be exploited for their bioactive potential.Beside from portraying the presence of a wide array of secondary compounds such as phenols,flavonoids,sterols and lipids from different seagrass species,the focus is on novel natural products projecting towards their biological applications.Though there are a significant number of reports on the abundance of secondary metabolites from seagrass and their bioactive derivatives,only a small number of reports explore their functional and defensive characteristics.Efforts have been made to collate the available information on seagrass natural products and clarify their function and metabolic pathway’s.It is emphasized that metabolic profiling of seagrass should be extensively progressed to obtain a deeper knowledge about the specific roles of each natural product.The investigation of seagrass natural products for their bioactive potential would most likely result in the detection of surprising and unexpected novel chemical structures and clinical leads that may be useful to mankind.

New Insights into the Shikimate and Aromatic Amino Acids Biosynthesis Pathways in Plants

The aromatic amino acids phenylalanine, tyrosine, and tryptophan in plants are not only essential components of protein synthesis, but also serve as precursors for a wide range of secondary metabolites that are important for plant growth as well as for human nutrition and health. The aromatic amino acids are synthesized via the shikimate pathway followed by the branched aromatic amino acids biosynthesis pathway, with chorismate serving as a major intermediate branch point metabolite. Yet, the regulation and coordination of synthesis of these amino acids are still far from being understood. Recent studies on these pathways identified a number of alternative cross-regulated biosynthesis routes with unique evolutionary origins. Although the major route of Phe and Tyr biosynthesis in plants occurs via the intermediate metabolite arogenate, recent studies suggest that plants can also synthesize phenylalanine via the intermediate metabolite phenylpyruvate （PPY）, similarly to many microorganisms. Recent studies also identified a number of transcription factors regulating the expression of genes encoding enzymes of the shikimate and aromatic amino acids pathways as well as of multiple secondary metabolites derived from them in Arabidopsis and in other plant species. .

The Metabolic Response of Arabidopsis Roots to Oxidative Stress is Distinct from that of Heterotrophic Cells in Culture and Highlights a Complex Relationship between the Levels of Transcripts, Metabolites, and Flux

Metabolic adjustments are a significant, but poorly understood, part of the response of plants to oxidative stress. In a previous study （Baxter et al., 2007）, the metabolic response of Arabidopsis cells in culture to induction of oxidative stress by menadione was characterized. An emergency survival strategy was uncovered in which anabolic primary metabolism was largely down-regulated in favour of catabolic and antioxidant metabolism. The response in whole plant tissues may be different and we have therefore investigated the response of Arabidopsis roots to menadione treatment, analyzing the transcriptome, metabolome and key metabolic fluxes with focus on primary as well as secondary metabolism. Using a redox-sensitive GFP, it was also shown that menadione causes redox perturbation, not just in the mitochondrion, but also in the cytosol and plastids of roots. In the first 30 min of treatment, the response was similar to the cell culture： there was a decrease in metabolites of the TCA cycle and amino acid biosynthesis and the transcriptomic response was dominated by up-regulation of DNA regulatory proteins. After 2 and 6 h of treatment, the response of the roots was different to the cell culture. Metabolite levels did not remain depressed, but instead recovered and, in the case of pyruvate, some amino acids and aliphatic glucosinolates showed a steady increase above control levels. However, no major changes in fluxes of central carbon metabolism were observed and metabolic transcripts changed largely independently of the corresponding metabolites. Together, the results suggest that root tissues can recover metabolic activity after oxidative inhibition and highlight potentially important roles for glycolysis and the oxidative pentose phosphate pathway.

The ARABIDOPSIS Accession Pna-10ls a Naturally Occurring sngl Deletion Mutant

Sinapoylmalate is the major sinapate ester found in leaves of Arabidopsis thaliana, where it plays an important role in UV-B protection. Metabolic profiling of rosette leaves from 96 Arabidopsis accessions revealed that the Pna-10 accession accumulates sinapoylglucose instead of sinapoylmalate. This unique leaf sinapate ester profile is similar to that of the previously characterized sinapoylglucose accumulator1 （sngl） mutants. SNG1 encodes sinapoylglucose：malate sinapoyltransferase （SMT）, a serine carboxypeptidase-like （SCPL） enzyme that catalyzes the conversion of sinapoylglucose to sinapoylmalate. In the reference Columbia genome, the SNG1 gene is located in a cluster of five SCPL genes on Chro- mosome II. PCR and sequencing analysis of the same genomic region in the Pna-10 accession revealed a 13-kb deletion that eliminates the SNG1 gene （At2g22990） and the gene encoding sinapoylglucose：anthocyanin sinapoyltransferase （SAT） （At2g23000）. In addition to its sinapoylmalate-deficient phenotype, and consistent with the loss of SAT, Pna-10 is unable to accumulate sinapoylated anthocyanins. Interestingly, the Pna-17 accession, collected from the same location as Pna-10, has no such deletion. Further analysis of 135 lines collected from the same location as Pna-10 and Pna-17 revealed that four more lines contain the deletion found in Pna-10 accession, suggesting that either the deletion found in Pna-10 is a recent event that has not yet been eliminated through selection or that sinapoylmalate is dispensable for the growth of Arabidopsis under field conditions.