Effect of silicon deficiency on secondary cell wall synthesis in rice leaf

Rice (Oryza sativa L.) is a typical Si-accumulating plant and is able to accumulate Si up to >10?% of shoot dry weight. The cell wall has been reported to become thicker under Si-deficient condition. To clarify the relationship between Si accumulation and cell wall components, the physical properties of, and macromolecular components and Si content in, the pectic, hemicellulosic, and cellulosic fractions prepared from rice seedlings grown in hydroponics with or without 1.5?mM silicic acid were analyzed. In the absence of Si (the ?Si condition), leaf blades drooped, but physical properties were enhanced. Sugar content in the cellulosic fraction and lignin content in the total cell wall increased under ?Si condition. After histochemical staining, there was an increase in cellulose deposition in short cells and the cell layer just beneath the epidermis in the ?Si condition, but no significant change in the pattern of lignin deposition. Expression of the genes involved in secondary cell wall synthesis, OsCesA4, OsCesA7, OsPAL, OsCCR1 and OsCAD6 was up-regulated under ?Si condition, but expression of OsCesA1, involved in primary cell wall synthesis, did not increase. These results suggest that an increase in secondary cell wall components occurs in rice leaves to compensate for Si deficiency.     

A novel yeast gene, RHK1, is involved in the synthesis of the cell wall receptor for the HM-1 killer toxin that inhibits β-1,3-glucan synthesis

The HM-1 killer toxin from Hansenula mrakii is known to inhibit cell wall β-1,3-glucan synthase of Saccharomyces cerevisiae and other sensitive strains of yeast. A number of mutants of Saccharomyces cerevisiae that show resistance to this toxin were isolated in order to clarify the killing mechanism of the toxin. These mutants, designated rhk (resistant to Hansenula killer), were classified into three complementation groups. A novel gene RHK1, which complements the killer-resistant phenotype of the largest complementation group rhk1, was isolated. DNA sequence analysis revealed an open reading frame that encodes a hydrophobic protein composed of 458 amino acids. Gene disruption followed by tetrad analysis showed that RHK1 is not essential and loss of RHK1 function endowed S. cerevisiae cells with complete killer resistance. A biochemical analysis suggested that RHK1 does not participate directly in the synthesis of β-1,3-glucan but is involved in the synthesis of the receptor for the HM-1 killer toxin.     

Applications of luciferin biosynthesis: Bioluminescence assays for l-cysteine and luciferase

Based on the biosynthetic pathway of firefly bioluminescence substrate d-luciferin, the concentration of l-cysteine can be quantified using a simple protocol and a conventional luminescence detector. The lower limit of quantification (signal/noise ratio [S/N] = 10) was 0.26 μM. Using our method, the total amount of free/reduced and disulfide/oxidized l-cysteine could be measured successfully in human serum. In addition, biosynthetic precursors such as 2-cyano-6-hydroxybenzothiazole and l-luciferin could replace d-luciferin in the cell-based luciferase assay. Our results suggest that the bioluminescence reaction associated with the biosynthesis of bioluminescence substrates can provide a fast and cost-effective assay method.