Thermographic visualization of cell death in tobacco and Arabidopsis

Pending cell death was visualized by thermographic imaging in bacterio‐opsin transgenic tobacco plants. Cell death in these plants was characterized by a complex lesion phenotype. Isolated cell death lesions were preceded by a colocalized thermal effect, as previously observed at sites infected by tobacco mosaic virus (TMV) ( Chaerle et al. 1999 Nature Biotechnology 17, 813–816). However, in most cases, a coherent front of higher temperature, trailed by cell death, initiated at the leaf base and expanded over the leaf lamina. In contrast to the homogenous thermal front, cell death was first visible close to the veins, and subsequently appeared as discrete spots on the interveinal tissue, as cell death spread along the veins. Regions with visible cell death had a lower temperature because of water evaporation from damaged cells. In analogy with previous observations on the localized tobacco–TMV interaction ( Chaerle et al. 1999 ), the kinetics of thermographic and continuous gas exchange measurements indicated that stomatal closure preceded tissue collapse. Localized spontaneous cell death could also be presymptomatically visualized in the Arabidopsis lsd2 mutant.     

Subunit polypeptide composition of rubisco and the origin of allopolyploid Arabidopsis suecica (Brassicaceae)

The polypeptide composition of the large and small subunits of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) from Arabidopsis thaliana, A. suecica and Cardaminopsis arenosa have been studied by IEF (isoelectric focusing) analysis. The putative recent alopolyploid origin of A. suecica is supported. The chloroplast encoded large subunits served to identify solely A. thaliana as the maternal parent whereas the nuclear encoded small subunits indicate C. arenosa as the paternal species.     

Arabidopsis casein kinase 1-like 8 enhances NaCl tolerance,early flowering,and the expression of flowering-related genes

Members of the casein kinase 1 (CK1) family are evolutionarily conserved eukaryotic protein kinases involved in various cellular, physiological, and developmental processes in yeast. However, the biological roles of CK1 members in plants are poorly understood. Here, we report that an Arabidopsis CK1 member named casein kinase 1-like 8 (CKL8) was ubiquitously expressed in all plant organs, mainly in the stems of seedlings according to quantitative real-time PCR. Western blotting showed a remarkable expression of the AtCKL8 gene in transgenic plants induced by high salinity. A histochemical assay of AtCKL8 promoter::GUS expression revealed that the AtCKL8 promoter is very active in both seedlings and adult plants subjected to the salinity stress, while no GUS activity was detectable in all the transgenic plants grown under normal conditions. In a subcellular distribution analysis, the AtCKL8-GFP fusion protein was localized mainly in the cell membrane. AtCKL8-overexpressing transgenic plants showed an insensitivity to high salinity and an early flowering phenotype. Overall, these findings suggest that AtCKL8 plays a positive role in NaCl signaling and improves salt stress tolerance in transgenic Arabidopsis.     

Gel-permeation chromatography–enzyme-linked immunosorbent assay method for systematic mass distribution profiling of plant cell wall matrix polysaccharides

Cell walls are dynamic and multi-component materials that play important roles in many areas of plant biology. The composition and interactions of the structural elements give rise to material properties, which are modulated by the activity of wall-related enzymes. Studies of the genes and enzymes that determine wall composition and function have made great progress, but rarely take account of potential compensatory changes in wall polymers that may accompany and accommodate changes in other components, particularly for specific polysaccharides. Here, we present a method that allows the simultaneous examination of the mass distributions and quantities of specific cell wall matrix components, allowing insight into direct and indirect consequences of cell wall manipulations. The method employs gel-permeation chromatography fractionation of cell wall polymers followed by enzyme-linked immunosorbent assay to identify polymer types. We demonstrate the potential of this method using glycan-directed monoclonal antibodies to detect epitopes representing xyloglucans, heteromannans, glucuronoxylans, homogalacturonans (HGs) and methyl-esterified HGs. The method was used to explore compositional diversity in different Arabidopsis organs and to examine the impacts of changing wall composition in a number of previously characterized cell wall mutants. As demonstrated in this article, this methodology allows a much deeper understanding of wall composition, its dynamism and plasticity to be obtained, furthering our knowledge of cell wall biology.     

Heavy Metal Induction of Arabidopsis Serine Decarboxylase Gene Expression

Serine (Ser) decarboxylase (SDC) catalyzes the conversion of Ser to ethanolamine (EA) in plants, while the physiological implications of the enzyme activity remain elusive. Here, we report that SDC gene expression in Arabidopsis was greatly induced by treatments with Ni²⁺ (24-fold) and Mn²⁺ (4-fold), and discuss possible genetic engineering strategies using the SDC gene for environmental stress management.     

Current trends and future directions in flower development research

Flowers, the reproductive structures of the approximately 400 000 extant species of flowering plants, exist in a tremendous range of forms and sizes, mainly due to developmental differences involving the number, arrangement, size and form of the floral organs of which they consist. However, this tremendous diversity is underpinned by a surprisingly robust basic floral structure in which a central group of carpels forms on an axis of determinate growth, almost invariably surrounded by two successive zones containing stamens and perianth organs, respectively. Over the last 25 years, remarkable progress has been achieved in describing the molecular mechanisms that control almost all aspects of flower development, from the phase change that initiates flowering to the final production of fruits and seeds. However, this work has been performed almost exclusively in a small number of eudicot model species, chief among which is Arabidopsis thaliana. Studies of flower development must now be extended to a much wider phylogenetic range of flowering plants and, indeed, to their closest living relatives, the gymnosperms. Studies of further, more wide-ranging models should provide insights that, for various reasons, cannot be obtained by studying the major existing models alone. The use of further models should also help to explain how the first flowering plants evolved from an unknown, although presumably gymnosperm-like ancestor, and rapidly diversified to become the largest major plant group and to dominate the terrestrial flora. The benefits for society of a thorough understanding of flower development are self-evident, as human life depends to a large extent on flowering plants and on the fruits and seeds they produce. In this preface to the Special Issue, we introduce eleven articles on flower development, representing work in both established and further models, including gymnosperms. We also present some of our own views on current trends and future directions of the flower development field.     

Overexpression of Arabidopsis ATX1 retards plant growth under severe copper deficiency

In a previous study, we demonstrated that Arabidopsis Antioxidant Protein1 (ATX1) plays an essential role in copper (Cu) homeostasis, conferring tolerance to both excess and subclinically deficient Cu. The Cu-binding motif MXCXXC was required for the physiological function of ATX1. In this study, we found that overexpression of ATX1 resulted in hypersensitivity to severe Cu deficiency despite enhancing tolerance to subclinical Cu deficiency. However, overexpression of mutated ATX1, replacing the Cu-binding motif MXCXXC with MXGXXG, abolished the hypersensitivity, for no differences from the wild type under the same conditions. Thus, the expression of ATX1 must be cautiously regulated to avoid homeostatic imbalance with the over-chelation of Cu.