Tse Seng Chuah

Indole-3-acetic acid (IAA) induced changes in oil content, fatty acid profiles and expression of four fatty acid biosynthetic genes in Chlorella vulgaris at early stationary growth phase.

Microalgae lipids and oils are potential candidates for renewable biodiesel. Many microalgae species accumulate a substantial amount of lipids and oils under environmental stresses. However, low growth rate under these adverse conditions account for the decrease in overall biomass productivity which directly influence the oil yield. This study was undertaken to investigate the effect of exogenously added auxin (indole-3-acetic acid; IAA) on the oil content, fatty acid compositions, and the expression of fatty acid biosynthetic genes in Chlorella vulgaris (UMT-M1). Auxin has been shown to regulate growth and metabolite production of several microalgae. Results showed that oil accumulation was highest on days after treatment (DAT)-2 with enriched levels of palmitic (C16:0) and stearic (C18:0) acids, while the linoleic (C18:2) and α-linolenic (C18:3n3) acids levels were markedly reduced by IAA. The elevated levels of saturated fatty acids (C16:0 and C18:0) were consistent with high expression of the β-ketoacyl ACP synthase I (KAS I) gene, while low expression of omega-6 fatty acid desaturase (ω-6 FAD) gene was consistent with low production of C18:2. However, the increment of stearoyl-ACP desaturase (SAD) gene expression upon IAA induction did not coincide with oleic acid (C18:1) production. The expression of omega-3 fatty acid desaturase (ω-3 FAD) gene showed a positive correlation with the synthesis of PUFA and C18:3n3.

Effects of Soil Types on Phytotoxic Activity of Pretilachlor in Combination with Sunflower Leaf Extracts on Barnyardgrass (Echinochloa crus-galli)

Abstract The increasing use of synthetic chemicals for pest control in rice has become an overwhelming economical border, and more important, it could pose a serious threat of the environment. In addition, the extensive use of synthetic herbicides has been the cause for the evolution of herbicide-resistant barnyardgrass worldwide. This weed species is the most competitive weed in rice after the red rice. Thus, this study was conducted to examine the combination effects of aqueous sunflower leaf extracts with lower rate of pretilachlor on barnyardgrass emergence and growth in Marang (sandy loam) and Seberang (silt loamy) soil series under glasshouse conditions. Interestingly, the ED95 values (rate that causes 95% inhibition) of pretilachlor for emergence and shoot fresh weight (SFW) of barnyardgrass were reduced by 79 and 82%, respectively, when being mixed with sunflower leaf extracts in Marang series. In contrast, the addition of sunflower leaf extracts increased ED95 value of pretilachlor in Seberang series. Rice seedlings at 4 and 8 d after sowing (DAS) were found to be tolerant to this mixture treatment. However, root growth of rice seedlings were inhibited at 0 and 2 DAS. These results suggest that sunflower leaf extracts have potential to reduce rate of pretilachlor for inhibiting emergence and growth of barnyardgrass without injuring rice seedlings in rice fields depending on soil types and growth stage of rice. Nomenclature: Pretilachlor, 2-chloro-N-(2,6-diethylphenyl)-N-(2-propoxyethyl)acetamide; barnyardgrass, Echinochloa crus-galli (L.) Beauv., ECHCG; rice and red rice biotype, Oryza sativa L.; sunflower, Helianthus annuus L.

Molecular basis for resistance to ACCase-inhibiting fluazifop in Eleusine indica from Malaysia

Eleusine indica (goosegrass) populations resistant to fluazifop, an acetyl-CoA carboxylase (ACCase: EC6.4.1.2)-inhibiting herbicide, were found in several states in Malaysia. Dose-response assay indicated a resistance factor of 87.5, 62.5 and 150 for biotypes P2, P3 and P4, respectively. DNA sequencing and allele-specific PCR revealed that both biotypes P2 and P3 exhibit a single non-synonymous point mutation from TGG to TGC that leads to a well known Trp-2027-Cys mutation. Interestingly, the highly resistant biotype, P4, did not contain any of the known mutation except the newly discovered target point Asn-2097-Asp, which resulted from a nucleotide change in the codon AAT to GAT. ACCase gene expression was found differentially regulated in the susceptible biotype (P1) and highly resistant biotype P4 from 24 to 72h after treatment (HAT) when being treated with the recommended field rate (198gha(-1)) of fluazifop. However, the small and erratic differences of ACCase gene expression between biotype P1 and P4 does not support the 150-fold resistance in biotype P4. Therefore, the involvement of the target point Asn-2097-Asp and other non-target-site-based resistance mechanisms in the biotype P4 could not be ruled out.

Identification and characterization of RAPD–SCAR markers linked to glyphosate-susceptible and -resistant biotypes of Eleusine indica (L.) Gaertn

Eleusine indica is one of the most common weed species found in agricultural land worldwide. Although herbicide-glyphosate provides good control of the weed, its frequent uses has led to abundant reported cases of resistance. Hence, the development of genetic markers for quick detection of glyphosate-resistance in E. indica population is imperative for the control and management of the weed. In this study, a total of 14 specific random amplified polymorphic DNA (RAPD) markers were identified and two of the markers, namely S4R727 and S26R6976 were further sequence characterized. Sequence alignment revealed that marker S4R727 showing a 12-bp nucleotides deletion in resistant biotypes, while marker S26R6976 contained a 167-bp nucleotides insertion in the resistant biotypes. Based on these sequence differences, three pairs of new sequence characterized amplified region (SCAR) primers were developed. The specificity of these primer pairs were further validated with genomic DNA extracted from ten individual plants of one glyphosate-susceptible and five glyphosate-resistant (R2, R4, R6, R8 and R11) populations. The resulting RAPD–SCAR markers provided the basis for assessing genetic diversity between glyphosate-susceptible and -resistant E. indica biotypes, as well for the identification of genetic locus link to glyphosate-resistance event in the species.