Effect of l-Canavanine on Nitrate Reductase in Corn Roots

Modification of the endogenous NO level influences apple embryos dormancy by alterations of nitrated and biotinylated protein patterns

NO donors and Arg remove dormancy of apple embryos and stimulate germination. Compounds lowering NO level (cPTIO, L -NAME, CAN) strengthen dormancy. Embryo transition from dormancy state to germination is linked to increased nitric oxide synthase (NOS)-like activity. Germination of embryos is associated with declined level of biotin containing proteins and nitrated proteins in soluble protein fraction of root axis. Pattern of nitrated proteins suggest that storage proteins are putative targets of nitration. Nitric oxide (NO) acts as a key regulatory factor in removal of seed dormancy and is a signal necessary for seed transition from dormant state into germination. Modulation of NO concentration in apple (Malus domestica Borkh.) embryos by NO fumigation, treatment with NO donor (S-nitroso-N-acetyl-D,L-penicillamine, SNAP), application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), N ω-nitro-L-arginine methyl ester (L-NAME), canavanine (CAN) or arginine (Arg) allowed us to investigate the NO impact on seed dormancy status. Arg analogs and NO scavenger strengthened embryo dormancy by lowering reactive nitrogen species level in embryonic axes. This effect was accompanied by strong inhibition of NOS-like activity, without significant influence on tissue NO2 (-) concentration. Germination sensu stricto of apple embryos initiated by dormancy breakage via short term NO treatment or Arg supplementation were linked to a reduced level of biotinylated proteins in root axis. Decrease of total soluble nitrated proteins was observed at the termination of germination sensu stricto. Also modulation of NO tissue status leads to modification in nitrated protein pattern. Among protein bands that correspond to molecular mass of approximately 95 kDa, storage proteins (legumin A-like and seed biotin-containing protein) were identified, and can be considered as good markers for seed dormancy status. Moreover, pattern of nitrated proteins suggest that biotin containing proteins are also targets of nitration.

Differential effects of amino acid analogs on growth and heterocyst differentiation in two nitrogen-fixing blue-green algae

Effects of a few amino acid analogs on growth and heterocyst differentiation have been studied in two nitrogen-fixing species ofAnabaena. All the analogs except α-methyl-DL-aspartic acid inhibited growth. Exposure ofAnabaena doliolum, toDL-5-fluorotryptophan andDL-p-fluorophenylalanine caused pronounced fragmentation of filaments into single cells. At low concentrations (0.01 mM), α-methyl-DL-aspartic acid stimulated growth of the strain ofA. doliolum as well as the strain of the second (unidentified)Anabaena species. Ethionine,DL-p-fluorophenylalanine,DL-5-fluorotryptophan, and canavanine blocked heterocyst differentiation, whereas α-methyl-DL-aspartic acid, α-methyl-DL-methionine,N-o-nitrophenylsulfenyl-L-tryptophan, norleucine, andS-2-aminoethyl-L-cysteine did not show any significant effect. Treatment with 7-azatryptophan,DL-β-hydroxynorvaline,L-methionine-DL-sulfoximine,L-methionine sulfone, and β-2-thienyl-DL-alanine led to a twofold increase in heterocyst frequency. Possible modes of action of the analogs in growth inhibition and changes in heterocyst frequency are discussed.