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The usage of the word interaction by physiologists has led to a consensus that gibberellin and abscisin interact in affecting plant responses. However, no such consensus is admissible if one uses the statisticians' definition which is more physiologically sound than that used by physiologists.
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The present study was undertaken to determine in vivo and in vitro effects of some plant growth regulators on rat erythrocyte carbonic anhydrase (CA) and glucose-6-phosphate dehydrogenase (G6PD) activities. Both in vivo and in vitro, spermidine and kinetin did not affect enzymatic activities of CA and G6PD, whereas putrescine decreased these activities, and abscisic acid increased them. Since plants use such growth regulators, their effects should be considered on mammals consuming them since they may possess important biological effects.
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Indole-3-acetic acid is the major auxin in most plants. In Cruciferae, including Brassicaceae, indole-3-acetic acid is synthesized from indole-3-acetonitrile by nitrilase, after indole-3-acetonitrile is formed from tryptophan via indole-3-acetaldoxime or indole glycosinolates as the intermediate. We cloned and sequenced the gene for nitrilase (EC 3.5.5.1), which catalyzes the hydrolysis of indole-3-acetonitrile to indole-3-acetic acid, from Alcaligenes faecalis JM3. The amino acid sequence deduced from the nucleotide sequence of the nitrilase gene shows 34.7% identity with that of Klebsiella ozaenae nitrilase. A DNA clone containing the nitrilase gene expressed the active enzyme in Escherichia coli with excellent yield. Among five cysteine residues (Cys-40, Cys-115, Cys-162, Cys-163, and Cys-218) in the Alcaligenes nitrilase, only Cys-163 was conserved at the corresponding position in the Klebsiella nitrilase. Two mutant enzymes, in which Cys-162 and Cys-163 were replaced with Asn and Ala, respectively, were constructed by site-directed mutagenesis. A 35% increase of the specific activity and a large reduction of the Km for thiophene-2-acetonitrile (which was used as a standard substrate for the nitrilase) were observed in the Cys-162-->Asn mutant enzyme. The Cys-163-->Ala mutation resulted in complete loss of nitrilase activity, clearly indicating that Cys-163 is crucial for the activity and Cys-162 could not provide the catalytic function of Cys-163.
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Casein kinases are critical in cell division and differentiation across species. A rice cDNA fragment encoding a putative casein kinase I (CKI) was identified via cDNA macroarray under brassinosteroid (BR) treatment, and a 1939-bp full-length cDNA, OsCKI1, was isolated and found to encode a putative 463-aa protein. RT-PCR and Northern blot analysis indicated that OsCKI1 was constitutively expressed in various rice tissues and upregulated by treatments with BR and abscisic acid (ABA). Enzymatic assay of recombinant OsCKI1 proteins expressed in Escherichia coli showed that the protein was capable of phosphorylating casein. The physiological roles of OsCKI1 were studied through antisense transgenic approaches, and homozygous transgenic plants showed abnormal root development, including fewer lateral and adventitious roots, and shortened primary roots as a result of reduced cell elongation. Treatment of wild-type plants with CKI-7, a specific inhibitor of CKI, also confirmed these functions of OsCKI1. Interestingly, in transgenic and CKI-7-treated plants, exogenously supplied IAA could restore normal root development, and measurement of free IAA content in CKI-deficient primary and adventitious roots revealed altered auxin content, indicating that OsCKI1 is involved in auxin metabolism or that it may affect auxin levels. Transgenic plants were less sensitive than control plants to ABA or BR treatment during germination, suggesting that OsCKI1 may be involved in various hormone-signaling pathways. OsCKI1-GFP fusion studies revealed the localization of OsCKI1 to the nucleus, suggesting a possible involvement in regulation of gene expression. In OsCKI1-deficient plants, differential gene expression was investigated using cDNA chip technology, and results indicated that genes related to signal transduction and hormone metabolism were indeed with altered expression.