No abstract

A cDNA library made from mRNA of AI-treated roots of an AI-sensitive wheat (Triticum aestivum cv Victory) cultivar was screened with a degenerate oligonucleotide probe derived from the partial amino acid sequence of the AI-induced protein TAI-18. O f seven clones that initially hybridized with the probe, one encoded a nove1 1,3-P-glucanase having a calculated molecular weight of 46.3 and an isoelectric point of 6.0. Like the A6 1,3-p-glucanase gene products from Brassica napus and Arabidopsis thaliana, the predicted wheat protein had a C-terminal extension with three potential glycosylation sites. Northern analysis revealed that wheat 1,3-P-glucanase mRNA was up-regulated in AI-intoxicated roots, with highest expression after 12 h. The antibody to A6 1,3-pglucanase from B. napus cross-reacted with a 56-kD protein that was induced after 24 h. A second partial cDNA clone showed similarity to genes encoding cytoskeletal fimbrin-like (actinbundling) proteins. Although well studied in animals and fungi, fimbrins have not previously been described in plants. Fimbrin-like transcripts were up-regulated after 24 h of AI treatment in the AI-sensitive wheat cv Victory. I n the AI-tolerant cv Atlas 66, fimbrin-like mRNA was up-regulated within 12 h by AI concentrations that did not inhibit root growth. Cellular stress associated with AI toxicity therefore causes up-regulation of a defense-related gene and a gene involved i n the maintenance of cytoskeletal function.

No abstract

Hematoxylin stain is used for localization of aluminium in plant root tissue and is the basis of a rapid assay of relative Al tolerance among wheat cultivars. In the present study, mechanisms by which hematoxylin might selectively stain Al-sensitive wheat roots have been examined. The results are consistent with the idea that in Al-sensitive cuttivars. hematoxylin forms complexes with Al that precipitate with phosphate as AlPO., in intercellular spaces: (1) Al and P are co-localized in the cell wall region of the outer cortex of Al-stressed roots by using x-ray microanalysis: (2) the molybdenum blue histochemical stain for extracellular phosphate reveals areas of stain that parallel those observed with hematoxylin: (3) in vitro, the presence of phosphate in an Al-hematoxylin reaction mixture causes formation of precipitate when the P/AI ratio exceeds 1.0. I suggest that seleetive hematoxylin staining of Al-sensitive wheat eultivars is the result of direct damage by Al to root cells, leading to leakage of phosphorus into the eeii wail region. Cuitivars whose roots are damaged by Al in this way are likely to be judged Al-sensitive when other eriteria sueh as growth or crop yield are used.

In the filamentous cyanobacterium Anabaena variabiis, specialized cells called heterocysts occur in a regular pattern along the filament and are the sites of nitrogen fixation. We used two different types of DNA-excess RNA hybridization techniques to estimate the number of genes expressed in recently differentiated, mature heterocysts. In the first, RNA and DNA were incubated in a phosphate buffer at 60°C, and the hybrids were separated from the unhybridized material by hydroxylapatite chromatography. In the second, the nucleic acids were incubated at 50°C in a buffer containing 50% formamide, and the fraction of DNA in duplexes was assayed by S1 nuclease digestion. Both (2) supplemented with 3 mM NH4Cl and 1 mM NaNO3. To induce heterocyst formation, the filaments were allowed to settle for several hours, the medium was drained off, and the cells were diluted to an A650 of 0.15 to 0.20 with Allen and Arnon medium lacking nitrogen. Heterocysts were isolated from cultures 48 h after dilution.Isolation of heterocysts. The heterocyst isolation procedure of Peterson and Wolk (25) was followed with modifications..