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The present work aims to alleviate the impact of drought on flax by priming seeds in folic acid. Drought was applied in pots after 24 days from sowing, and one set of samples were collected up to the 56th day for the determination of growth parameters, malondialdehyde (MDA), H2O2, ascorbate (AsA) and glutathione (GSH), photosynthetic pigments, proteins, proline, sugars, and the activities of catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), glutathione peroxidase (GPX) and ribulose-1,5-P carboxylase/oxygenase (Rubisco). The other set was collected at seed maturity for measurements of oil yield and fatty acid composition. Drought significantly decreased growth parameters, photosynthetic pigments, proteins, AsA, GSH and the activities of CAT, APX, GR, GPX and Rubisco, but raised MDA and H2O2, soluble sugars and proline concentrations. Seed priming with folic acid alleviated the impact of drought on the tested parameters. Priming raised antioxidant level and lowered oxidative stress indices pointing to an efficient antioxidant system for scavenging of free radicles. As concerns the yield analysis, there was a reduction of the number of capsules and seeds, oil quantity and quality (fatty acid concentrations and composition). Folic acid also mitigated the decreases in the number of both capsules and seeds within capsules as well as the oil and fatty acid contents and composition. Priming resulted in a recovery in the unsaturated fatty acid level causing an improvement of the oil yield quality. The results suggest that folic acid overcame the impact of drought ameliorating the oil yield and its quality features. [ABSTRACT FROM AUTHOR]

The toxicity of rimsulfuron (Rim) on acetohydroxyacide synthase (AHAS), nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), catalase (CAT) and ascorbate peroxidase (APX) in maize was evaluated examining their kinetic parameters in vitro on second leaves of 10-day-old maize seedlings. Data showed that Rim decreased Vmax and Kcat of AHAS without changing Km; on the contrary, Vmax and Kcat of the other enzymes were unchanged while Km increased. The lowest ICSO value was found for AHAS and the highest for GOGAT. Application of Rim to 10-day-old seedlings significantly inhibited the activities of all enzymes over the next 10 days besides reducing growth, proteins, amino acids, ascorbate (ASA) and glutathione (GSH). Malondialdehyde (MDA), H2O2 and oxidized glutathione (GSSG) were instead increased. Priming of grains with branched-chain amino acids [valine, isoleucine and leucine (VIL)] or dressing with naphthalic anhydride (NA) mitigated these effects. These findings suggest that Rim caused non-competitive inhibition with AHAS due to the decreased Vmax and unchanged Km; however, the enhanced Km of the other enzymes with unchanged Vmax shows an induction of competitive inhibition. Moreover, decreases of amino acids, especially branched-chain acids, and activities of NR, NiR, GS, and GOGAT could have delayed N incorporation into proteins, thus slowing their formation. The decreases of ASA, GSH, CAT, and APX concurrent with the increase of MDA and H2O2 support the induction of oxidative stress. Application of VIL or NA can protect maize from Rim causing an attenuation of the phytotoxic effects of the herbicide and enhancing maize tolerance by compensating endogenous amino acid levels, ROS homeostasis and/or herbicide detoxification. [ABSTRACT FROM AUTHOR]

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Abstract: The recommended field dose of rimsulfuron, imazethapyr, alachlor, atrazine or fluometuron differentially reduced shoot fresh and dry weight of 10-day-old maize seedlings as well as leaf protein content during the following 12 days. These reductions seemed consistent during the whole period with fluometuron, atrazine and alachlor but appeared to be nullified by the 5th day of treatment with rimsulfuron and imazethapyr. On the other hand, all herbicides mostly provoked significant inhibitions in specific activities of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), malate dehydrogenase (MDH, EC 1.1.1.82), pyruvate phosphate dikinase (PPDK, EC 2.7.9.1) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) in leaves during the first 2 days. Thereafter, the inhibition was recovered in samples treated with rimsulfuron and imazethapyr, leveled off with alachlor but consistently augmented with atrazine and fluometuron. The kinetic characterization showed that rimsulfuron or imazethapyr unchanged V max of all enzymes in vitro, however, V max of PEPC, PPDK and Rubisco were decreased in vivo. Nevertheless, atrazine or fluometuron substantially reduced V max of all enzymes while alachlor showed a reduction in this value of PEPC, MDH and Rubisco. Thus atrazine, fluometuron and, to a lower extent, alachlor reduced concentrations of all enzymes as well as rimsulfuron and imazethapyr for only Rubisco. On the contrary, K m values of all enzymes were progressively increased by all herbicides indicating that the different herbicides altered the structural integrity of all enzymes. These findings conclude that rimsulfuron or imazethapyr competitively inhibited MDH but revealed mixed inhibition to PEPC, PPDK and Rubisco. Atrazine or fluometuron revealed mixed inhibitions to all enzymes whereas alachlor seemed to be either a competitive inhibitor to PPDK or a mixed inhibitor to PEPC, MDH and Rubisco. [Copyright &y& Elsevier]

Treatment of 14-day-old maize cultivars (Hybrid351 and Giza2) with 250 mM NaCl significantly reduced shoot fresh and dry weights and protein content during the subsequent 12 days. The magnitude of reduction was more pronounced in Giza than Hybrid. Both cultivars contained converging levels of protein for the enzymes phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH), pyruvate phosphate dikinase (PPDK) and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) under normal conditions; however, NaCl led to increase these levels in Hybrid and decrease them in Giza. Moreover, NaCl significantly inhibited the activities of PEPC, MDH and PPDK in both cultivars during the first 2 days, thereafter the inhibition nullified only in Hybrid; nonetheless, Rubisco was the least affected enzyme in both cultivars. In addition, NaCl slightly increased V (max) of PEPC, MDH and PPDK in Hybrid with no change in K (m); nevertheless V (max) dropped in Giza with an increase in K (m) of only PEPC and MDH. Also K (cat), K (cat)/K (m) and V (max)/K (m) of all enzymes were lower in treated Giza than in treated Hybrid. The increased V (max) of all enzymes in only Hybrid by NaCl confirms that they were synthesised more in Hybrid than in Giza. However, the decreased V (max) in Giza concomitant with the increased K (m) points to an interference of salinity with synthesis of enzymes and their structural integrity. This would lead to a noncompetitive inhibition for the enzymes. These findings declare that maize tolerance to NaCl was larger in Hybrid compared to Giza due to a role for C4 enzymes.