Sucrose-Modulated Morphogenesis in Anagallis arvensis L.

Sucrose was found to have a modulating effect on the morphogenesisof Anagallis arvensis L. leaves cultured in a Murashige-Skoogmedium. Root formation and growth seem to be more independentthan other morphogenetic expressions. Roots formed without exogenoussugars at 25°C but sucrose seemed to be necessary at 32and 35°C. Sucrose at 3% improved shoot formation at 25°Cand had an inhibitory effect at 6%concentration and 35°C.Shoot growth (internode length) is inhibited by sucrose concentrationshigher than 3%. Sucrose could also replace light irradiancein regulating shoot and leaf growth. A higher sucrose concentration,than that required for roots and shoots formation, is necessaryfor flower and fruit formation, but sucrose could not replacethe photoperiod requirement for flowering in culture medium. (Received June 17, 1985; Accepted December 24, 1985)     

Expression of the Legume-Specific Nod Factor Receptor Proteins Alters Developmental and Immune Responses in Rice

Plant Molecular Biology Reporter - Legumes form symbiosis with rhizobia, which fix nitrogen for the benefit of host plant in return for carbon resources. Development of this unique symbiosis in...     

Molecular cloning, characterization and regulation of two different NADH-glutamate synthase cDNAs in bean nodules

NADH-dependent glutamate synthase (NADH-GOGAT) is a key enzyme in primary ammonia assimilation in Phaseolus vulgaris nodules. Two different types of cDNA clones of PvNADH-GOGAT were isolated from the nodule cDNA libraries. The full-length cDNA clones of PvNADH-GOGAT-I (7.4 kb) and PvNADH-GOGAT-II (7.0 kb), which displayed an 83% homology between them, were isolated using cDNA library screening, 'cDNA library walking' and RT-PCR amplification. Southern analysis employing specific 5' cDNA probes derived from PvNADH-GOGAT-I and PvNADH-GOGAT-II indicated the existence of a single copy of each gene in the bean genome. Both these proteins contain ∼100 amino acid sequences theoretically addressing each isoenzyme to different subcellular compartments. RT-PCR analysis indicated that PvNADH-GOGAT-II expression is higher than PvNADH-GOGAT-I during nodule development. Expression analysis by RT-PCR also revealed that both of these genes are differentially regulated by sucrose. On the other hand, the expression of PvNADH-GOGAT-I , but not PvNADH-GOGAT-II, was inhibited with nitrogen compounds. In situ hybridization and promoter expression analyses demonstrated that the NADH-GOGAT-I and -II genes are differentially expressed in bean root and nodule tissues. In silico analyses of the NADH-GOGAT promoters revealed the presence of potential cis elements in them that could mediate differential tissue-specific, and sugar and amino acid responsive expression of these genes.     

Glycolate-, Xanthine- and Paraquat-Mediated Inhibition of Nitrate Reductase in Detached Oat Leaves

Leaf segments of 8-day-old oat plants were incubated with 100µMglycolate or xanthine inthe dark or with 100µM paraquatin the light. These treatments were designed to enhance theinternalproduction of activated oxygen species and to allowus to study the possible role of such species in the regulationof the activity of NO₃-induced nitrate reductase (NR) in illuminatedgreen tissues. Each of the treatments inhibited NO₃-induced NR activity. HPMS(an inhibitor of glycolate oxidase) and allopurinol (an inhibitorof xanthine oxidase) protected NR from inactivation by glycolateand by xanthine. Free radical scavengers also protected NR frominactivation by xanthine and paraquat but they had no effecton the inhibition by glycolate. The activities of catalase andsuper oxide dismutase did not increase in response to the varioustreatments. Thus, while the production of active oxygen speciesappears to be stimulated under such conditions, the rates ofthe enzymatic destruction and "scavenging" of these speciesseem to remain unchanged. Hence, the endogenous levels of theseactive oxygen species can be expected to increase in the treatedleaves. We interpret our results as evidence that inhibition by glycolateof NR is caused by the H₂O₂ generated during the oxidation ofglycolate while the effects of xanthine and paraquat dependon the enhanced production of free radicals. It is concluded that activated oxygen species that are formedendogenously may play a role in the regulation of NR in greentissues. (Received August 12, 1991; Accepted February 17, 1992)     

Evidence for sugar signalling in the regulation of asparagine synthetase gene expressed in Phaseolus vulgaris roots and nodules

A cDNA clone, designated as PvNAS2, encoding asparagine amidotransferase(asparagine synthetase) was isolated from nodule tissue of commonbean (Phaseolus vulgaris cv. Negro Jamapa). Southern blot analysisindicated that asparagine synthetase in bean is encoded by asmall gene family. Northern analysis of RNAs from various plantorgans demonstrated that PvNAS2 is highly expressed in roots,followed by nodules in which it is mainly induced during theearly days of nitrogen fixation. Investigations with the PvNAS2promoter gusA fusion revealed that the expression of PvNAS2in roots is confined to vascular bundles and meristematic tissues,while in root nodules its expression is solely localized tovascular traces and outer cortical cells encompassing the centralnitrogen-fixing zone, but never detected in either infectedor non-infected cells located in the central region of the nodule.PvNAS2 is down-regulated when carbon availability is reducedin nodules, and the addition of sugars to the plants, mainlyglucose, boosted its induction, leading to the increased asparagineproduction. In contrast to PvNAS2 expression and the concomitantasparagine synthesis, glucose supplement resulted in the reductionof ureide content in nodules. Studies with glucose analoguesas well as hexokinase inhibitors suggested a role for hexokinasein the sugar-sensing mechanism that regulates PvNAS2 expressionin roots. In light of the above results, it is proposed that,in bean, low carbon availability in nodules prompts the down-regulationof the asparagine synthetase enzyme and concomitantly asparagineproduction. Thereby a favourable environment is created forthe efficient transfer of the amido group of glutamine for thesynthesis of purines, and then ureide generation. Key words: Asparagine and ureide synthesis, asparagine synthetase, nodules, Phaseolus vulgaris, sugar signalling     

Nitrogen metabolism and senescence-associated changes during growth of carnation flowers

Nitrogen metabolism including nitrate reductase (EC 1.6.6.1), glutamate dehydroge-nase (EC 1.4.1.2) and glutamate-oxalacetate aminotransferase (EC 2.6.1.1) activities were studied during growth of petals taken from carnation flowers ( Dianthus caryophyllus L. cv. Sir Arthur) together with senescence parameters (lipid hydroper-oxides, soluble amino acids and permeability). A slight decline in nitrogen percentage on a dry weight basis was found together with a sharp decrease in nitrate reduct-ase, glutamate-oxalacetate aminotransferase and glutamate dehydrogenase activities during the maximum growth phase, which was characterized by increase in respiration, dry weight, length, organic nitrogen and DNA per petal. Changes generally associated with senescence, like lipid hydroperoxide and soluble ammo nitrogen accumulation and increases in permeability began to appear already during early growth. The results indicate that permeability and proteolysis may be closely related. The possible significance of the decrease in nitrogen percentage and enzyme activities during growth of petals is discussed.