Bernd Kastenholz

Temperature responses of roots: impact on growth, root system architecture and implications for phenotyping

Root phenotyping is a challenging task, mainly because of the hidden nature of this organ. Only recently, imaging technologies have become available that allow us to elucidate the dynamic establishment of root structure and function in the soil. In root tips, optical analysis of the relative elemental growth rates in root expansion zones of hydroponically-grown plants revealed that it is the maximum intensity of cellular growth processes rather than the length of the root growth zone that control the acclimation to dynamic changes in temperature. Acclimation of entire root systems was studied at high throughput in agar-filled Petri dishes. In the present study, optical analysis of root system architecture showed that low temperature induced smaller branching angles between primary and lateral roots, which caused a reduction in the volume that roots access at lower temperature. Simulation of temperature gradients similar to natural soil conditions led to differential responses in basal and apical parts of the root system, and significantly affected the entire root system. These results were supported by first data on the response of root structure and carbon transport to different root zone temperatures. These data were acquired by combined magnetic resonance imaging (MRI) and positron emission tomography (PET). They indicate acclimation of root structure and geometry to temperature and preferential accumulation of carbon near the root tip at low root zone temperatures. Overall, this study demonstrated the value of combining different phenotyping technologies that analyse processes at different spatial and temporal scales. Only such an integrated approach allows us to connect differences between genotypes obtained in artificial high throughput conditions with specific characteristics relevant for field performance. Thus, novel routes may be opened up for improved plant breeding as well as for mechanistic understanding of root structure and function.

Effects of altered α‐ and β‐branch carotenoid biosynthesis on photoprotection and whole‐plant acclimation of Arabidopsis to photo‐oxidative stress

Functions of α- and β-branch carotenoids in whole-plant acclimation to photo-oxidative stress were studied in Arabidopsis thaliana wild-type (wt) and carotenoid mutants, lutein deficient (lut2, lut5), non-photochemical quenching1 (npq1) and suppressor of zeaxanthin-less1 (szl1) npq1 double mutant. Photo-oxidative stress was applied by exposing plants to sunflecks. The sunflecks caused reduction of chlorophyll content in all plants, but more severely in those having high α- to β-branch carotenoid composition (α/β-ratio) (lut5, szl1npq1). While this did not alter carotenoid composition in wt or lut2, which accumulates only β-branch carotenoids, increased xanthophyll levels were found in the mutants with high α/β-ratios (lut5, szl1npq1) or without xanthophyll-cycle operation (npq1, szl1npq1). The PsbS protein content increased in all sunfleck plants but lut2. These changes were accompanied by no change (npq1, szl1npq1) or enhanced capacity (wt, lut5) of NPQ. Leaf mass per area increased in lut2, but decreased in wt and lut5 that showed increased NPQ. The sunflecks decelerated primary root growth in wt and npq1 having normal α/β-ratios, but suppressed lateral root formation in lut5 and szl1npq1 having high α/β-ratios. The results highlight the importance of proper regulation of the α- and β-branch carotenoid pathways for whole-plant acclimation, not only leaf photoprotection, under photo-oxidative stress.

Medicinal Plants: A Natural Chaperones Source for Treating Neurological Disorders

Currently, no pharmaceuticals for the etiological treatment of neurodegenerative protein-misfolding diseases (e.g., ALS, Alzheimers or prion diseases) are available. In this brief communication the development of chaperone-based medications from medicinal plants (e.g., Ginkgo biloba) are reviewed as referred to specific protein-protein interactions of plant metallochaperones and human enzymes. It is indicated that bioactive copper chaperones for superoxide dismutase isolated from medicinal plants may be lead molecules for drug development in several diseases concerning metal ion metabolisms of man and animals.

Important contributions of a new quantitative preparative native continuous polyacrylamide gel electrophoresis (QPNC-PAGE) procedure for elucidating metal cofactor metabolisms in protein-misfolding diseases--a theory.

The quantitative analysis of metallochaperone proteins in biofluids (e.g. blood, liquor) may be a major prerequisite for clinical investigations concerning the structure-function relationships of biologically-active metal cofactor-containing chaperones in protein-misfolding diseases (e.g. Alzheimers or related diseases). For these purposes, a new state-of-the-art gel electrophoresis [quantitative preparative native continuous polyacrylamide gel electrophoresis procedure (QPNC-PAGE)] combined with biological mass and NMR spectrometries might essentially contribute to provide fundamental insights into the metabolisms of important metal cofactors in biological systems and the proper folding of metallochaperones in conformational diseases.

Plant metal chaperones: a novel perspective in dementia therapy

Dys-homeostasis of copper metabolism and oxidative stress are major hallmarks in the brains of Alzheimer patients. Therefore, metal bioavailability and mechanisms of copper ion homeostasis throughout the body are crucial and potential targets for therapeutic agents. Many of the medications used or suggested, respectively, at present time, may either be toxic, reveal a lack of specificity or have unknown mechanisms of action in vivo. Metal chaperones from medicinal plants are proposed as medications that are relatively free from these disadvantages. Furthermore, these agents are a promising class of molecules for studies aimed at developing innovative and etiological treatments for protein-misfolding diseases, especially Alzheimers disease.

Phenotype of Arabidopsis thaliana semi-dwarfs with deep roots and high growth rates under water-limiting conditions is independent of the GA5 loss-of-function alleles

Background and Aims The occurrence of Arabidopsis thaliana semi-dwarf accessions carrying inactive alleles at the gibberellin (GA) biosynthesis GA5 locus has raised the question whether there are pleiotropic effects on other traits at the root level, such as rooting depth. In addition, it is unknown whether semi-dwarfism in arabidopsis confers a growth advantage under water-limiting conditions compared with wild-type plants. The aim of this research was therefore to investigate whether semi-dwarfism has a pleiotropic effect in the root system and also whether semi-dwarfs might be more tolerant of water-limiting conditions. Methods The root systems of different arabidopsis semi-dwarfs and GA biosynthesis mutants were phenotyped in vitro using the GROWSCREEN-ROOT image-based software. Semi-dwarfs were phenotyped together with tall, near-related accessions. In addition, root phenotypes were investigated in soil-filled rhizotrons. Rosette growth trajectories were analysed with the GROWSCREEN-FLUORO setup based on non-invasive imaging. Key Results Mutations in the early steps of the GA biosynthesis pathway led to a reduction in shoot as well as root size. Depending on the genetic background, mutations at the GA5 locus yielded phenotypes characterized by decreased root length in comparison with related wild-type ones. The semi-dwarf accession Pak-3 showed the deepest root system both in vitro and in soil cultivation experiments; this comparatively deep root system, however, was independent of the ga5 loss-of-function allele, as shown by co-segregation analysis. When the accessions were grown under water-limiting conditions, semi-dwarf accessions with high growth rates were identified. Conclusions The observed diversity in root system growth and architecture occurs independently of semi-dwarf phenotypes, and is probably linked to a genetic background effect. The results show that there are no clear advantages of semi-dwarfism at low water availability in arabidopsis.

Novel detection system for plant protein production of pharmaceuticals and impact on conformational diseases.

tate-of-the-art biochemistry methods in combination with an automated phenotyping method demonstrate the high potential of transgenic tobacco plants in producing properly-folded therapeutic proteins for the treatment of protein-misfolding diseases (e.g., Alzheimers disease). This molecular farming approach led to highest protein production of hydroponically-grown tobacco compared to other growth substrates generally used in plant cultivation.

Herbal Drugs in Mirror of Alzheimer’s Disease

Oxidative stresses and dys-homeostasis of metal metabolism, especially Cu and Zn, in association with intracellular protein-misfolding processes of amyloid beta (Aβ) peptides, are major hallmarks in the brains of Alzheimer patients. 1 Currently, no medications for etiological treatments of Alzheimer’s disease (AD), implying the recovery and modulation of metal ion homeostasis inside the cell, are so far available. Several therapeutic strategies and nearly all medications used or suggested, aim at the treatment of AD symptoms only and are not focused on the origin of this cureless chronically progressive neurodegenerative disease. 1