No abstract

Transgenic plants of Artemisia annua L., a medicinal plant that produces the compound artemisinin which has an anti-malarial activity, were developed following Agrobacterium tumefaciens-mediated transformation of leaf explants. A. tumefaciens strain EHA105 carrying either pCAMBIA1301 or pCAMBIAFPS was used. Both plasmids harbored the hygromycin phosphotransferase II (hptII) gene as a selectable gene, but the latter plasmid also harbored the gene encoding for farnesyl pyrophosphate synthase (FPS), a key enzyme for artemisinin biosynthesis. Shoot regeneration was observed either directly from leaf sections or via intervening callus when explants were incubated on solidified Murashige and Skoog (MS) (1962) medium containing 0.1 mg l -1 a-naphthaleneacetic acid (NAA), 1 mg l -1 N 6 -benzyladenine (BA), 30 mg l -1 meropenem and 10 mg l -1 hygromycin. Applying vacuum infiltration dramatically increased transformation efficiency up to 7.3 and 19.7% when plasmids with and without FPS gene were used, respectively. All putative transgenic regenerants showed positive bands of hptII gene following Southern blot analysis. Expression of FPS was observed in all transgenic lines, and FPS over-expressed lines exhibited higher artemisinin content and yield, of 2.5-and 3.6-fold, respectively, than that detected in wild-type plants. A relatively high correlation (R 2 = 0.78) was observed between level of expression of FPS and artemisinin content. However, gene silencing was detected in some transgenic lines, especially for those lines containing two copies of the FPS transgene, and with some lines exhibiting reduced growth.

Soluble carbohydrates play a key role as osmolytes and significantly contribute in salt defence mechanism, especially in halophyte species. The objective of this study is to investigate the transcriptional expression of starch-related genes, sugar profile and physiological performances of two contrasting rice genotypes, Pokkali (salt tolerant) and IR29 (salt sensitive), in response to salt stress. Total soluble sugars, glucose and fructose levels in the flag leaf of salt-stressed Pokkali rice were enhanced relative to soluble starch accumulation in plants exposed to EC = 13.25 dS m(-1) (salt stress) for 3 days. In Pokkali, the net photosynthetic rate and starch metabolism may play a key role as energy resources under salt stress. In contrast, photosynthetic performance, indicated by photosynthetic pigment levels and chlorophyll fluorescence parameters, in salt-stressed IR29 was significantly reduced, leading to delayed starch biosynthesis. The reduction in photosynthetic ability and lack of defence mechanisms in IR29 caused growth inhibition and yield loss. Soluble starch and soluble sugar enrichment in Pokkali rice may function alternatively as osmotic adjustment in salt defence mechanism and strengthen carbon energy reserves, greater survival prospects under salt stress and enhanced productivity.

The aim of this research was to investigate betaine aldehyde dehydrogenase (BADH) and glycinebetaine (Glybet) biosynthesis in photoautotrophic rice seedlings. The role of Glybet on physiological and growth responses to salt stress in both salt-tolerant and salt-sensitive lines is to be investigated. The BADH activity in salt-tolerant seedlings cultured under extreme salt stress (342 mm NaCl) progressively increased during the first few hours until it peaked after 72 h. This was about 2.5 times greater than in salt-sensitive plants. Similarly, the amount of Glybet detected in salt-tolerant lines was 1.3 times more than in salt-sensitive lines at 96 h salt exposure. The BADH activities were positively related to Glybet accumulation in both salt-tolerant and salt-sensitive lines. The accumulation of Glybet in salt-tolerant lines was directly correlated with pigment stabilization. Relative water content in the salt-tolerant lines was closely related to water oxidation in photosystem II (PSII), defined by maximum quantum yield of PSII (F v /F m ). In addition, a high concentration of total chlorophyll is more efficient in capturing light energy, defined by photochemical quenching. The concentrations of chlorophyll a and total carotenoid were positively related to the quantum efficiency of PSII (U PSII ) and nonphotochemical quenching, respectively, resulting in a high net-photosynthetic rate (NPR) and the promotion of growth. The high level of Glybet in salt-tolerant lines plays a role as a salt defensive response mechanism in terms of pigment stabilization and water oxidation in PSII, resulting in high NPR and growth efficiency.