Reactive oxygen species (ROS) play an important role in root responses to potassium deprivation by regulating the expression of the high-affinity K(+) transporter gene AtHAK5 and other genes. Activation-tagged lines of Arabidopsis plants containing the AtHAK5 promoter driving luciferase were screened for bioluminescence under potassium-sufficient conditions. A member of the type III peroxidase family, RCI3, was isolated and when it was overexpressed by the activation tag, this led to the enhanced expression of luciferase and the endogenous AtHAK5. RCI3 was found to be up-regulated upon potassium deprivation. Plants overexpressing RCI3 (RCI3-ox) showed more ROS production and AtHAK5 expression whereas the ROS production and AtHAK5 expression were reduced in rci3-1 under K(+)-deprived conditions. These results suggested that RCI3 is involved in the production of ROS under potassium deprivation and that RCI3-mediated ROS production affects the regulation of AtHAK5 expression. This peroxidase appears to be another component of the low-potassium signal transduction pathway in Arabidopsis roots.
Manganese (Mn) is the second most prevalent transition metal in the Earth's crust but its availability is often limited due to rapid oxidation and low mobility of the oxidized forms. Acclimation to low Mn availability was studied in Arabidopsis seedlings subjected to Mn deficiency. As reported here, Mn deficiency caused a thorough change in the arrangement and characteristics of the root epidermal cells. A proportion of the extra hairs formed upon Mn deficiency were located in atrichoblast positions, indicative of a post-embryonic reprogramming of the cell fate acquired during embryogenesis. When plants were grown under a light intensity of >50 μmol m−2 s−1 in the presence of manganese root hair elongation was substantially inhibited, whereas Mn-deficient seedlings displayed stimulated root hair development. GeneChip analysis revealed several candidate genes with potential roles in the reprogramming of rhizodermal cells. None of the genes that function in epidermal cell fate specification were affected by Mn deficiency, indicating that the patterning mechanism which controls the differentiation of rhizodermal cells during embryogenesis have been bypassed under Mn-deficient conditions. This assumption is supported by the partial rescue of the hairless cpc mutant by Mn deficiency. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis revealed that, besides the anticipated reduction in Mn concentration, Mn deficiency caused an increase in iron concentration. This increase was associated with a decreased transcript level of the iron transporter IRT1, indicative of a more efficient transport of iron in the absence of Mn.
Background: Myxospermy is a process by which the external surfaces of seeds of many plant species produce mucilage-a polysaccharide-rich gel with numerous fundamental research and industrial applications. Due to its functional properties the mucilage can be difficult to remove from the seed and established methods for mucilage extraction are often incomplete, time-consuming and unnecessarily wasteful of precious seed stocks. Results: Here we tested the efficacy of several established protocols for seed mucilage extraction and then downsized and adapted the most effective elements into a rapid, small-scale extraction and analysis pipeline. Within 4 h, three chemically-and functionally-distinct mucilage fractions were obtained from myxospermous seeds. These fractions were used to study natural variation and demonstrate structure-function links, to screen for known mucilage quality markers in a field trial, and to identify research and industry-relevant lines from a large mutant population. Conclusion: The use of this pipeline allows rapid analysis of mucilage characteristics from diverse myxospermous germplasm which can contribute to fundamental research into mucilage production and properties, quality testing for industrial manufacturing, and progressing breeding efforts in myxospermous crops.
Plantago ovata Forssk. is an emerging crop yielding psyllium husk, a material comprised of hydrophilic polysaccharides that form mucilage upon wetting. Psyllium husk has important industrial uses including as a dietary fibre supplement and a textural alternative in gluten‐free bread production. Industrial applications require high‐quality and purity psyllium husk, but consistent supply of uniform quality material is often limited by climatic constraints, especially unseasonable rainfall at crop maturity. Here we compared the seed quality of four P. ovata varieties harvested before and after 26 mm of rain and validated our key findings in the following season. Colourimetry showed that the rain event caused the seeds to be darker and greener, possibly from pigment oxidation and microbial growth. Sugar profiling, water absorption assays and microscopy showed that premature hydration of the husk in rain‐damaged samples caused loss of the most soluble mucilage components and an increase in non‐mucilage contaminants, leading to a reduction in seed water absorption capacity, which is a key indicator of psyllium husk functionality. Germination was also diminished in rain‐affected seeds. In this study we show for the first time the extent that unseasonable rain at maturity has on P. ovata seed quality. We suggest that rain‐damaged seeds are unsuitable for husk production and resowing and outline potential screening methods to identify rain‐damaged seeds before purchase. Additionally, the extensive quality impacts described here may make P. ovata a suitable model or indicator species for studying acute climate effects on seed quality, especially from rain.
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