SummaryWe have developed a novel procedure for the rapid classi®cation and identi®cation of Arabidopsis mutants with altered cell wall architecture based on Fourier-Transform Infrared (FT-IR) microspectroscopy. FT-IR transmission spectra were sampled from native 4-day-old dark-grown hypocotyls of 46 mutants and the wild type treated with various drugs. The Mahalanobis distance between mutants, calculated from the spectral information after compression with the Discriminant Variables Selection procedure, was used for a hierarchical cluster analysis. Despite the completely unsupervised nature of the classi®cation procedure, we show that all mutants with cellulose defects appeared in the same cluster. In addition, mutant alleles of similar strength for several unrelated loci were also clustered, which demonstrates the sensitivity of the method to detect a wide array of cell wall defects. Comparing the cellulose-de®cient cluster with the cluster that contained wild-type controls led to the identi®cation of wave numbers that were diagnostic for altered cellulose content in the context of an intact cell wall. The results show that FT-IR spectra can be used to identify different classes of mutants and to characterize cell wall changes at a microscopic level in unknown mutants. This procedure signi®cantly accelerates the identi®cation and classi®cation of cell wall mutants, which makes cell wall polysaccharides more accessible to functional genomics approaches.
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Reflectance measurements are used t o calculate the ordinary and extraordinary optical constants of an anisotropic MgFz crystal in the energy range 11 to 28 eV. Partially linearly polarized light is used and a method of least squares is employed to compute the results.An excitonic splitting of 0.5 eV is observed at the r point. The anisotropy of the forbidden gap is 0.2 eV while that of plasmon is 0.3 eV. A tentative interpretation is given based upon a symmetry group analysis a t the r point.Reflexionsmessungen werden zur Berechnung der ordentlichen und auBerordentlichen optischen Konstanten eines anisotropen MgF,-Kristalls im Energiebereich von 11 bis 28 eV benutet. Es wird tcilweise linear-polarisiertes Licht verwendet und eine Methode der kleinsten Quadrate zur Berechnung der Ergebnisse herangezogen. Am r -P u n k t wird eine exzitonische Aufspaltung von 0,5 eV beobachtet. Die Anisotropie der verbotenen Zone betragt 0,2 eV wahrend die des Plasmons 0,3 eV betragt. Es wird eine mogliche Erklarung angegeben, die auf einer Symmetriegruppenanalyqe am I'-Punkt beruht.
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