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Growth inhibition in acid soils due to Al stress affects crop production worldwide. To understand mechanisms in sensitive crops that are affected by Al stress, a proteomic analysis of primary tomato root tissue, grown in Al-amended and non-amended liquid cultures, was performed. DIGE-SDS-MALDI-TOF-TOF analysis of these tissues resulted in the identification of 49 proteins that were differentially accumulated. Dehydroascorbate reductase, glutathione reductase, and catalase enzymes associated with antioxidant activities were induced in Al-treated roots. Induced enzyme proteins associated with detoxification were mitochondrial aldehyde dehydrogenase, catechol oxidase, quinone reductase, and lactoylglutathione lyase. The germin-like (oxalate oxidase) proteins, the malate dehydrogenase, wali7 and heavy-metal associated domain-containing proteins were suppressed. VHA-ATP that encodes for the catalytic subunit A of the vacuolar ATP synthase was induced and two ATPase subunit 1 isoforms were suppressed. Several proteins in the active methyl cycle, including SAMS, quercetin 3-O-methyltransferase and AdoHcyase, were induced by Al stress. Other induced proteins were isovaleryl-CoA dehydrogenase and the GDSL-motif lipase hydrolase family protein. NADPH-dependent flavin reductase and beta-hydroxyacyl-ACP dehydratase were suppressed.

Among many aspects of plant defence responses to pathogenic infection are changes in the composition of the exocellular matrix. To study potential defences in white lupin (Lupinus albus L.), suspension-cultured cells were treated for 24 h with one of three different elicitors : CuCl 2 , and two fungal elicitor preparations from purified cell walls of yeast and Colletotrichum lindemuthianum. Two subsets of exocellular proteins: ionicallybound wall proteins and proteins secreted into culture medium, were isolated, and their patterns compared following electrophoretic separation. Only a few proteins were observed in culture filtrates with dominating bands at 27, 33, and 42 kDa. About 30 proteins were observed in cell wall extracts. Changes in protein intensities evoked by elicitor treatments depended on the type of elicitor used, the age and composition of lupin cell culture, and concentration of applied fungal elicitor. Based on these observations, ten proteins were chosen for N-terminal sequencing, and sequences 5-30 amino acids long for nine proteins were obtained. Three of the major proteins sequenced were identified as acidic exocellular chitinase, polygalacturonase-inhibiting protein, and germin/oxalate oxidase.

The inhibitory effect exerted by water stress on acetylene reduction activity (ARA) by nodulated roots of faba beans (Vicia faba L.) was correlated with a 40% decline in the organic acid pool of nodule cytosol. Oxalate concentration was lowered (-55%) whereas a stimulation of the bacteroid oxalate oxidase concomitantly occurred. This enzyme was characterized by an optimal activity at pH 8 but, as in higher plants, exhibited a K m for oxalate of 1.4 mM and an inhibition by substrate excess. Oxalate provided to bacteroid incubations supported C 2 H 2 reduction up to 2.5 mM whereas higher concentrations were strongly inhibitory. In contrast, purified symbiosomes incubated with oxyleghaemoglobin reduced C 2 H 2 in the presence of oxalate concentrations up to 10 mM. The peribacteroid membrane (PBM), in controlling the oxalate flux to the bacteroids avoided the substrate inhibition which would limit its efficiency. Thus, oxalate present in high concentration in faba bean nodules could play a role as complementary substrate for bacteroids slowing down the nitrogen fixation decline induced by water restricted conditions.

The cDNAs encoding three germin-like proteins (PsGER1, PsGER2a, and PsGER2b) were isolated from Pisum sativum. The coding sequence of PsGER1 transiently expressed in tobacco leaves gave a protein with superoxide dismutase activity but no detectable oxalate oxidase activity according to in-gel activity stains. The transient expression of wheat germin gf-2.8 oxalate oxidase showed oxalate oxidase but no superoxide dismutase activity under the same conditions. The superoxide dismutase activity of PsGER1 was resistant to high temperature, denaturation by detergent, and high concentrations of hydrogen peroxide. In salt-stressed pea roots, a heat-resistant superoxide dismutase activity was observed with an electrophoretic mobility similar to that of the PsGER1 protein, but this activity was below the detection limit in non-stressed or H(2)O(2)-stressed pea roots. Oxalate oxidase activity was not detected in either pea roots or nodules. Following in situ hybridization in developing pea nodules, PsGER1 transcript was detected in expanding cells just proximal to the meristematic zone and also in the epidermis, but to a lesser extent. PsGER1 is the first known germin-like protein with superoxide dismutase activity to be associated with nodules. It shared protein sequence identity with the N-terminal sequence of a putative plant receptor for rhicadhesin, a bacterial attachment protein. However, its primary location in nodules suggests functional roles other than as a rhicadhesin receptor required for the first stage of bacterial attachment to root hairs.