Aluminum-Induced Genes (Induction by Toxic Metals, Low Calcium, and Wounding and Pattern of Expression in Root Tips)

Abstract

We have investigated the response of four AI-induced genes (walil, -3, -4, and -5) from wheat (Triticum aestivum L.) to other stresses. The relative transcript levels of walil (encoding a plant metallothionein-like protein), wali3 and wali5 (putative BowmanBirk proteinase inhibitors), and wali4 (phenylalanine ammoniaiyase) increased in root tips of wheat after 2-d treatments with toxic levels of ali other metals tested (Cd, Fe, Zn, Cu, Ca, In, and La). l h e expression levels of walil, -3, -4, and -5 also increased in the root tips of plants grown in the presence of low levels of Ca (10 PM). The transcript levels of walil, -3, and -5 increased in wounded leaf and root tissue, whereas the transcript levels of wali4 increased only in wounded leaves. The site of expression of walil, -3, and -5 in root tips was identified using in situ hybridization. walil was expressed predominantly in the meristematic tissue of the root tip, whereas wali3 and wali5 were expressed predominantly in the cortical tissue of the root. Some changes in the site of expression of these genes were evident in the roots of AI-treated plants.A1 in soils becomes soluble under acidic conditions (below pH 51, causing an inhibition of root elongation and subsequently of plant growth (Clarkson, 1965). The mitotic activity of root tip cells decreases (Clarkson, 1965) and the root tip thickens, primarily due to an increase in the size of the cortical cells (Bennet et al., 1985). To further our understanding of how plants respond to Al, genes whose expression is affected by A1 toxicity have been identified.Previously we isolated seven cDNA clones (walil-wali7) whose transcripts accumulate with A1 treatment in wheat (Triticum aestivum L.) (Snowden and Gardner, 1993;Richards et al., 1994). Six of these genes show an Alinduced increase in transcript levels in two different wheat cultivars: Warigal (Al-sensitive) and Waalt (Al-tolerant). In contrast, A1 induction of the seventh gene, wali2, by A1 stress occurred only in Warigal.walil encodes a plant metallothionein-like protein, homologous to genes isolated from a number of other plant '

Purification and Immunological Identification of Metallothioneins 1 and 2 from Arabidopsis thaliana

“…We subsequently found that root growth was a more sensitive indicator of copper tolerance than fresh weight increase (Murphy and Taiz, 1996). These results are consistent with the finding that the walil MT homolog RNA message in wheat is localized in root tips (Snowden et al, 1995) and suggest that the root tip is an important site of MT2/ copper binding. Although MTs are clearly not abundant proteins, the recovery of MT1 and MT2 from copper-treated plants was 22 times higher in root tips than in basal root tissues and 6 times higher than in leaves (see Table I).…”

Al-Induced, 51-Kilodalton, Membrane-Bound Proteins Are Associated with Resistance to Al in a Segregating Population of Wheat

“…At this point, it may be premature to speculate whether any of the wali genes might encode our 51-kD proteins; however, the fact that the wali genes are expressed in both resistant and sensitive genotypes argues against this point. Snowden et al (1995) also demonstrated that transcript levels of walil, wali3, wali4, and wali5 increased in root tips after treatment with excess Cd, Fe, Zn, Cu, Ga, In, and La. Low levels of Ca and wounding also increased transcript levels of wali3, wali4, and wali5.…”

“…Low levels of Ca and wounding also increased transcript levels of wali3, wali4, and wali5. Thus, Snowden et al (1995) envisioned that the wali genes might encode a series of general stress response genes. We previously reported that excess Cd and Ni were mildly effective in increasing levels of our 51-kD proteins; however, excess Cu, Mn, and Zn, along with heat shock and cold stress, were ineffective elicitors (Basu et al, 1994a).…”

Aluminum Induces Oxidative Stress Genes in Arabidopsis thaliana1

“…After three washes with water, seeds (5000 per bottle) were added to 1-L Schott bottles containing 400 mL of low-ionic-strength Ruakura medium (pH 4.3;Snowden et al, 1995). The bottles were aerated in a growth chamber under conditions of 16 h of light (190 mol m Ϫ2 s Ϫ1 ) at 22°C and 8 h of dark at 18°C.…”

“…The most highly induced genes included a metallothionein-like protein and two Bowman-Birk protease inhibitors. These genes were also induced by toxic levels of all other metals tested and by physical wounding of roots (Snowden et al, 1995). An acidic PR protein, PR-2, was found to be induced in wheat by Al, as well as by a wide range of other stresses (Cruz-Ortega and Ownby, 1993).…”