Glucose‐ and mannose‐induced stomatal closure is mediated by ROS production,Ca2+ and water channel in Vicia faba

Sugars act as vital signaling molecules that regulate plant growth, development and stress responses. However, the effects of sugars on stomatal movement have been unclear. In our study, we explored the effects of monosaccharides such as glucose and mannose on stomatal aperture. Here, we demonstrate that glucose and mannose trigger stomatal closure in a dose‐ and time‐dependent manner in epidermal peels of broad bean (Vicia faba). Pharmacological studies revealed that glucose‐ and mannose‐induced stomatal closure was almost completely inhibited by two reactive oxygen species (ROS) scavengers, catalase (CAT) and reduced glutathione (GSH), was significantly abolished by an NADPH oxidase inhibitor, diphenylene iodonium chloride (DPI), whereas they were hardly affected by a peroxidase inhibitor, salicylhydroxamic acid (SHAM). Furthermore, glucose‐ and mannose‐induced stomatal closure was strongly inhibited by a Ca²⁺ channel blocker, LaCl₃, a Ca²⁺ chelator, ethyleneglycol‐bis(beta‐aminoethylether)‐N,N'‐tetraacetic acid (EGTA) and two water channel blockers, HgCl₂ and dimethyl sulfoxide (DMSO); whereas the inhibitory effects of the water channel blockers were essentially abolished by the reversing agent β‐mercaptoethanol (β‐ME). These results suggest that ROS production mainly via NADPH oxidases, Ca²⁺ and water channels are involved in glucose‐ and mannose‐induced stomatal closure.     

HAWAIIAN SKIRT regulates the quiescent center‐independent meristem activity in Arabidopsis roots

Root apical meristem (RAM) drives post‐embryonic root growth by constantly supplying cells through mitosis. It is composed of stem cells and their derivatives, the transit‐amplifying (TA) cells. Stem cell organization and its maintenance in the RAM are well characterized, however, their relationships with TA cells remain unclear. SHORTROOT (SHR) is critical for root development. It patterns cell types and promotes the post‐embryonic root growth. Defective root growth in the shr has been ascribed to the lack of quiescent center (QC), which maintains the surrounding stem cells. However, our recent investigation indicated that SHR maintains TA cells independently of QC by modulating PHABULOSA (PHB) through miRNA165/6. PHB controls TA cell activity by modulating cytokinin levels and type B Arabidopsis Response Regulator activity, in a dosage‐dependent manner. To further understand TA cell regulation, we conducted a shr suppressor screen. With an extensive mutagenesis screen followed by genome sequencing of a pooled F₂ population, we discovered two suppressor alleles with mutations in HAWAIIAN SKIRT (HWS). HWS, encoding an F‐box protein with kelch domain, is expressed, partly depending on SHR, in the root cap and in the pericycle of the differentiation zone. Interestingly, root growth in the shr hws was more active than the wild‐type roots for the first 7 days after germination, without recovering QC. Contrary to shr phb, shr hws did not show a recovery of cytokinin signaling. These indicate that HWS affects QC‐independent TA cell activities through a pathway distinctive from PHB.     

Identification and characterization of a novel antioxidant peptide from feather keratin hydrolysate

Objectives

To improve the potential value of feather, which is a valuable protein resource, we have separated and identified antioxidant peptide(s) from feather hydrolysate.

Results

Feather hydrolysate was prepared by fermentation with Bacillus subtilis S1–4. Antioxidative peptides were separated by sequential acid precipitation, cation exchange, and reversed-phase fast performance liquid chromatography. Finally, a peptide with antioxidative activity was identified as Ser-Asn-Leu-Cys-Arg-Pro-Cys-Gly by MALDI time-of-flight (TOF)/TOF analysis, and determined to represent a portion of feather keratin near its N-terminal. A synthesized peptide with the same sequence was used to characterize its antioxidative properties, including scavenging free radicals, reducing power, and Fe²⁺ chelation. In terms of the peptide’s amino acid composition, the antioxidative activity might be mainly attributed to Cys and other amino acid residues.

Conclusion

Feather keratin is a good source for the quantitative preparation of antioxidative peptides.

     

Calcium regulates glutamate dehydrogenase and poly-γ-glutamic acid synthesis in <Emphasis Type="Italic">Bacillus natto</Emphasis>

Objective

To study the effect of Ca²⁺ on glutamate dehydrogenase (GDH) and its role in poly-γ-glutamic acid (γ-PGA) synthesis in Bacillus natto HSF 1410.

Results

When the concentration of Ca²⁺ varied from 0 to 0.1 g/l in the growth medium of B. natto HSF 1410, γ-PGA production increased from 6.8 to 9.7 g/l, while GDH specific activity and NH₄Cl consumption improved from 183 to 295 U/mg and from 0.65 to 0.77 g/l, respectively. GDH with α-ketoglutarate as substrate primarily used NADPH as coenzyme with a K _m of 0.08 mM. GDH was responsible for the synthesis of endogenous glutamate. The specific activity of GDH remained essentially unchanged in the presence of CaCl₂ (0.05–0.2 g/l) in vitro. However, the specific activity of GDH and its expression was significantly increased by CaCl₂ in vivo. Therefore, the regulation of GDH and PGA synthesis by Ca²⁺ is an intracellular process.

Conclusion

Calcium regulation may be an effective approach for producing γ-PGA on an industrial scale.