Translocation and Metabolism of Endosperm-Applied [2-C] Indoleacetic Acid in Etiolated Avena sativa L. Seedlings

The role of free indole-3-acetic acid (IAA) in the endosperm of Avena sativa L. seedlings was investigated to determine its contribution to free IAA in the shoot. [2-¹⁴C]IAA was injected into the endosperm of darkgrown seedlings and the transport and metabolism of the [¹⁴C]-labeled compounds determined. It was concluded that translocation of free IAA directly from the endosperm is probably not a significant source of free IAA in the shoot, mainly because even small amounts of [¹⁴C]IAA introduced into the endosperm were rapidly metabolized. This suggested that, in Avena, free IAA does not normally exist in the liquid endosperm.     

Changes in lipoxygenase properties and activity related to postgerminative growth and senescence in oat (Avena sativa L cv. Victory 1 )

Lipoxygenase (LOX), one of the main oxidative catalysts in plants, is involved in the regulation of growth and senescence. We investigated changes in LOX activity or its properties as they related to the development of oat plants at four stages (germination, growth, natural senescence, and dark-incubated senescence). LOX activity was high during early growth and at senescence. At pH 4.5, activity showed an abrupt surge compared with a normal enzyme reaction pattern at pH 6.5. The optimum reaction temperature was 25°C; LOX and peroxidase exhibited similar activity patterns. Polyacrylamide gel electrophoresis revealed that the purified LOX consisted of three isoenzymes in germinating seeds, two in growing seedlings, and three during both natural and dark-induced senescence. As determined by isoelectric focusing, the isoelectric points (pl) of LOX ranged from 3.6 to 6.5 throughout the four developmental stages; for natural or dark-induced senescence, the pl was 9.0.     

黄芩干物质累积和氮磷钾吸收、分配规律研究

为了探讨黄芩干物质累积和氮、磷、钾吸收与分配的特点及两者间的相互关系,通过田间试验和采样分析,研究了黄芩不同生育期植株的干物质和氮、磷、钾累积量.结果表明,黄芩干物质的累积量随生育进程不断地增加,出苗后52～85 d干物质累积量占总累积量的61.62％.在整个生育期,黄芩对K2O的吸收累积量最大,N次之,P2O5最小,N、P2O5、K2O吸收比例约为2.8∶1.0∶2.9,并且黄芩地上部氮磷钾的累积量大于根部,不同生育期,根部N、P2O5、K2O的累积比例呈现增加—降低—增加的趋势.黄芩对氮磷钾的积累量与干物质积累量呈极显著正相关关系.在供试的土壤和施肥条件下,每生产100 kg的黄芩根需要从土壤和肥料中吸收6.34 kg的N,2.60 kg的P2O5,7.02 kg的K2O.     

Changes in the Distribution of Magnesium, Potassium, Calcium and Phosphorus during Growth of Cucurbita Seedlings

Ockenden, I. and Lott, J. N. A. 1988. Changes in the distributionof magnesium, potassium, calcium and phosphorus during growthof Cucurbita seedlings—J. exp. Bot. 39: 973–980. Etiolated seedlings of Cucurbita maxima cv. Warted Hubbard andCucurbita andreana, grown in distilled water, showed considerablegrowth. However, only a small percentage of the minerals storedin the large cotyledons was mobilized to the root-shoot axisof the etiolated seedlings. The proportion of minerals removedfrom the cotyledons to the root-shoot axis was about two-timeshigher in C. andreana than in C. maxima. When the seedlingswere grown in distilled water in the presence of light, thepercentage of cotyledon mineral content that was mobilized waslower than the amount mobilized during growth in the dark. Cotyledonsof light-grown seedlings that were given adequate nutrients,took up minerals from the medium. These fully-expanded and photosyntheticcotyledons had slightly more P and Mg than did the cotyledonsof the dry embryos but had increased their K content 5-foldand their Ca content 50-fold. Key words: Cucurbita, minerals, seeds, seedings, NAA     

Uridine and the Control of Phototropism in Oat (Avena sativa L.) Coleoptiles

The short-term growth response of oat (Avena sativa L.) coleoptiles to exogenously applied uridine was studied both in excised apical segments and in the intact seedlings. In both cases growth of coleoptile tissue was inhibited by uridine. The inhibition of coleoptile growth consistently occurred 20–30 min after uridine treatment, which is within the lag period of their phototropic response. Asymmetric application of uridine to coleoptiles in the intact seedlings resulted in their bending toward the direction to which uridine was applied in the absence of light stimulus. These findings suggest that uridine or its metabolites, plays an important role in the phototropism of oat coleoptiles and provide support to the Bruinsma–Hasegawa theory as an alternative to the Cholodny–Went theory for explaining phototropism.     

Glycosyltransferases from Oat (Avena) Implicated in the Acylation of Avenacins

Plants produce a huge array of specialized metabolites that have important functions in defense against biotic and abiotic stresses. Many of these compounds are glycosylated by family 1 glycosyltransferases (GTs). Oats (Avena spp.) make root-derived antimicrobial triterpenes (avenacins) that provide protection against soil-borne diseases. The ability to synthesize avenacins has evolved since the divergence of oats from other cereals and grasses. The major avenacin, A-1, is acylated with N-methylanthranilic acid. Previously, we have cloned and characterized three genes for avenacin synthesis (for the triterpene synthase SAD1, a triterpene-modifying cytochrome P450 SAD2, and the serine carboxypeptidase-like acyl transferase SAD7), which form part of a biosynthetic gene cluster. Here, we identify a fourth member of this gene cluster encoding a GT belonging to clade L of family 1 (UGT74H5), and show that this enzyme is an N-methylanthranilic acid O-glucosyltransferase implicated in the synthesis of avenacin A-1. Two other closely related family 1 GTs (UGT74H6 and UGT74H7) are also expressed in oat roots. One of these (UGT74H6) is able to glucosylate both N-methylanthranilic acid and benzoic acid, whereas the function of the other (UGT74H7) remains unknown. Our investigations indicate that UGT74H5 is likely to be key for the generation of the activated acyl donor used by SAD7 in the synthesis of the major avenacin, A-1, whereas UGT74H6 may contribute to the synthesis of other forms of avenacin that are acylated with benzoic acid.     

Induction of Flavonoid Synthesizing Enzymes by Light in Etiolated Pea (Pisum sativum cv. Midfreezer) Seedlings

Etiolated pea (Pisum sativum cv. Midfreezer) seedlings respond to illumination with white light by changes in the activity of phenylpropanoid and flavonoid synthesizing enzymes. Unlike in cell cultures, changes in enzyme activity in pea seedlings are not concerted. Phenylalanine ammonia-lyase (EC 4.3.1.5) activity peaked approximately 18 hours after onset of illumination. The phenylacetate path did not interfere with the measurement of phenylalanine ammonia-lyase activity. Activity of cinnamic acid 4-hydroxylase (EC 1.14.13.11) showed an early peak after 8 hours illumination, declined thereafter sharply, then gradually increased during the remainder of the experiment. Activities of chalcone synthase and UDP glucose:flavonol 3-O-glucosyltransferase (EC 2.4.1.91) increased steadily and reached a plateau after approximately 70 hours illumination time. Activity of 4-hydroxycinnamate:coenzyme A ligase (EC 6.2.1.12) remained relatively unchanged, whereas that of chalcone isomerase (EC 5.5.1.6) declined steadily during the course of the experiment. The relative in vitro enzyme activities suggest that the rate-limiting step for the phenylpropanoid path is the cinnamic acid 4-hydroxylase, that of the flavonoid pathway is the chalcone synthase. Integration of enzyme activity curves, however, show that only the curve deriving from phenylanine ammonia-lyase activity matches closely the production of the flavonol glycosides.     

Regulation of Growth in Avena (Oat) Stem Segments by Gibberellic Acid and Abscisic Acid

The purpose of this study was to analyze the nature of the interaction between gibberellic acid (GA₃) and abscisic acid (ABA) in the regulation of growth in excised Avena (oat) stem segments. Growth, compared to sucrose controls, was inhibited by ABA in the range of 10^?4 to 10^?6M. GA₃-promoted growth was also inhibited by ABA in the same concentration range. A Lineweaver-Burk analysis of the interaction between GA₃ and ABA indicated that ABA acts in a non-competitive fashion with GA₃. This same result was obtained previously with GA₃-indoleacetic acid (IAA) and GA₃-kinetin interactions with Avena stem sections. Our results indicate that ABA can inhibit GA₃-promoted growth within physiological concentrations, and that it is probably acting at a different physiological site from that for GA₃.     

Gene Cloning,Expression, and Antifungal Activities of Permatin from Naked Oat (Avena nuda)

Probiotics and Antimicrobial Proteins - Thaumatin-like proteins (TLPs) are the products of a large, highly complex gene family involved in host defense. TLPs also belong to the pathogenesis-related...     

A possible mechanism of high temperature dormancy regulation in seeds of Avena sativa L. (cv. Moyencourt)

Embryos of Avena sativa L. (cv. Moyencourt) show no high temperature dormancy. The dormancy is induced by the presence of endosperm-aleurone part of the seed. Germination of isolated embryos at 30°C can be prevented by ABA and the inhibition is reversed by GA. Inhibitors of GA synthesis also inhibit embryo germination. The embryos of dormant and non-dormant seeds vary greatly in their sensitivity to exogenous ABA. High temperature dormancy of the entire seeds can be relieved by low concentrations of ethanol. On the basis of these facts a hypothetic model is proposed showing how interaction between endogenous GA and ABA-like inhibitory substance, may regulate the high temperature dormancy of the seeds.     

Combined effect of Nitrogen,Phosphorus and Potassium fertilizers on the contents of glucosinolates in rocket salad (Eruca sativa Mill.)

Nitrogen (N), phosphorous (P) and potassium (K) are the most limiting factors in crop production. N often affects the amino acid composition of protein and in turn its nutritional quality. In Brassica plants, abundant supply of N fertilizer decreases the relative proportion of glucosinolates (GSLs), thus reducing the biological and medical values of the vegetables. Hence effort was made to evaluate the influence of different proportions of nutrient solutions containing N–P–K on the GSL profiles of rocket salad (Eruca sativa Mill.). Fifteen desulpho-(DS) GSLs were isolated and identified using liquid chromatography–mass spectrometry (LC/MS) analysis. Rocket salad plants supplied with lesser amount of N, P or higher concentrations of K showed a typical improvement in total GSL contents. In contrast, total GSL levels were less at higher N supply. Furthermore, with N concentrations above 5 mM and K concentrations less than 2.5 mM, the GSL amounts were on average 13.51 and 13.75 μmol/g dry weight (DW), respectively. Aliphatic GSLs predominated in all concentrations of NPK while indolyl GSLs made up marginally less amount of the total compositions. Five and 2 mM N and P possessed much higher levels of several types of aliphatic GSLs than other concentrations, including glucoerucin, glucoraphanin and dimeric 4-mercaptobutyl GSL. From this perspective, it is contended that supply of less N results in enhancing the metabolic pathway for the synthesis of GSLs in rocket salad.     

Isolation and structure of peptides from oat (Avena sativa) seedlings

The level of proteolytic activity in tissues of oat seedlings was characterized under acidic conditions, and the number and content of the main components in low-molecular-mass fractions of the extract were determined. The structures of the majority of predominant peptide components isolated from the extract were studied. The use of a database of protein structures helped suggest possible structures of protein precursors of the peptides isolated. Detailed information on a plant peptidome was obtained for the first time.     

Isolation, purification, and characterization of glutathione S-transferase from oat (Avena sativa) seedlings

Glutathione S-transferase (GST) from oat seedlings was purified by ammonium sulfate precipitation and glutathione (GSH) affinity chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the presence of two major protein subunits with molecular masses of 29 and 31 kDa, respectively. Isoelectric focusing revealed a major band with pI of 3.43 and a minor band with pI of 7.42. Kinetic analysis with respect to 1-chloro-2,4-dinitrobenzene (CDNB) as substrate revealed a K _m of 1.18 mM and V _max of 0.94 mol/min and a specific activity of 17.96 mol/min/mg. Inhibition studies indicated that oat GST is strongly inhibited by chlorophyllin, hemin, and anthocyanin and only weakly by bilirubin and biliverdin.     

Inhibition of the Coleoptile Growth in Avena sativa by Endosperm Removal--Changes in Auxin, Osmotica and Cell Wall

Removal of the endosperm from 84-h-old etiolated oat seedlingsstrongly retarded the subsequent growth of coleoptiles. Thecontribution of the endosperm to coleoptile growth was studied.Endosperm removal was found to: (1) decrease the endogenouslevel of indole-3-acetic acid (IAA) in the coleoptile tip. IAAapplied to the coleoptile tip stimulated coleoptile growth inseedlings with and without the endosperm. The sensitivity ofthe coleoptile to a suboptimal concentration of IAA was higherin seedlings without the endosperm than in intact ones. At theoptimal concentration of IAA, however, the final length of thecoleoptile was larger in intact seedlings than in those withoutthe endosperm. (2) decrease the concentration of the solublesugars and amino acids in the cell sap. (3) retard the increasein the amount of polysaccharides in the cell wall of the coleoptile,particularly noncellulosic ones. (4) make the cell wall mechanicallyrigid according to stress-relaxation analysis of the cell wall.(5) induce an increase in the osmotic potential of the coleoptilecell sap. From these results, it was concluded that the endosperm suppliesthe coleoptile with IAA, sugars and amino acids, thus promotingcoleoptile growth. (Received September 24, 1987; Accepted February 3, 1988)     

Nitrogen, Phosphorus, and Potassium Nutrition of the Edaphic Ecotypes in Cynodon dactylon (L.) Pers.

A differential response to nitrogen, phosphorus, and potassiumwas observed for the three edaphic ecotypes in Cynodon dactylon(L.) Pers. naturally occurring at Malla, Shiwalik, and Chandigarh.The soils of these sites differ markedly with respect to availablenutrients. The better growth of the Malla population comparedto the Chandigarh population in low potassium and low nitrogenmedia could be related to the low availability of these nutrientsin the calcareous Malla soil. The Shiwalik population tendedto show an intermediate behaviour. Whilst the Malla populationwas susceptible to ‘phosphate toxicity’, the growthyield of the Shiwalik and the Chandigarh populations improvedwith increase in phosphorus in the medium. The three populationsalso differed from each other with respect to the uptake ofvarious nutrients. These results could be correlated with thenatural habitat conditions in which the three ecotypes occur.It was concluded that besides calcium which was shown to bepartly responsible for the restriction of the three ecotypesto their respective habitats, the availability of nitrogen,potassium, and also phosphorus may play an important role.     

Isolation and elucidation of structure of peptides from oat (Avena sativa) seedlings

The level of proteolytic activity in tissues of oat seedlings was characterized under acidic conditions, and the number and content of the main components in low-molecular-mass fractions of the extract were determined. The structures of the majority of predominant peptide components isolated from the extract were studied. The use of a database of protein structures helped suggest possible structures of protein precursors of the peptides isolated. Detailed information on a plant peptidome was obtained for the first time.     

Changes in Endogenous Gibberellins and the Metabolism of [H]GA(4) after Geostimulation in Shoots of the Oat Plant (Avena sativa)

The recovery from “lodging,” or bending over, by shoots of 42-day-old Avena sativa plants is controlled primarily by a negatively geotropic differential growth of the lower halves of the p-1 node-pulvinus and the base of the p-1 internode, relative to the upper halves. Although geostimulation causes a significant reduction in p-1 internode length, dry matter accumulation in the p-1 node-pulvinus is increased, apparently at the expense of the sheath. Recovery to an angle of 30° is associated with changes in endogenous gibberellin-like substances (GAs), and in differential metabolism of applied [³H]GA₄ (1.4 Curie per millimole). Although geostimulation depressed total GAs (relative to upright plant parts) to 0.40 and 0.13 for node-pulvini and sheaths, respectively, it increased them 2-fold for internodes. Within the plant part geostimulation increased GAs (relative to upper halves) 29- and 7-fold in lower halves of node-pulvini and internodes, respectively, but reduced GAs to 0.3 in lower halves of sheaths. At age 42 days a GA_4/7-like (nonpolar) substance predominates, with lesser amounts of a GA₃-like (polar) substance. Native GAs of Avena include GA₃, GA₄, and GA₇. Geostimulation enhanced the ratio of nonpolar to polar GAs for both halves of internodes, but tended to depress it for sheaths and nodepulvini.     

Potassium induces positive changes in nitrogen metabolism and antioxidant system of oat (Avena sativa L cultivar Kent)

Potassium is actively involved in many functions such as enzyme activation, osmotic adjustment and uptake of deleterious ions like Na. Present report analyses the effectivity of different potassium salts on growth and certain components of nitrogen metabolism and antioxidant system in oat and their possible role in amelioration of water stress. Potassium induced enhancement in the activities of nitrate reductase and aminotransferases was evident indicating a positive role of potassium in nitrogen metabolism. Potassium supplementation enhanced activities of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase) and contents of total phenols and tannins, probably strengthening both the enzymatic as well as non enzymatic antioxidant system. Free amino acids, proline and free sugars also exhibited the same trend in treated plants ensuring better plant growth.     

Cloning and expression of a lipase gene from rice (Oryza sativa cv. Dongjin)

Lipases are useful enzymes that are primarily responsible for the hydrolysis of acylglycerides during lipid processing. We have cloned a lipase gene from a rice seed coat cDNA library (Oryza sativa cv. Dongjin). The cDNA was 1,445 bp in length and encoded 361 amino acid residues (GenBank accession No. AY580163). The deduced amino acid sequence had 82 and 56% identity to Oryza sativa (cv. Chuchung) and Arabidopsis thaliana lipase genes, respectively, and there was a GxSxG consensus motif near the catalytic triad at the active serine site. The deduced sequence had little homology to mammalian and microbial lipases. When the Oryza sativa lipase gene was expressed in Escherichia coli with the pET expression system, activity was found mainly in the pellet fraction. The purified product had lipolytic activity towards tributyrin and was about 40 kDa in size.