Effect of lead on nitrate reductase activity and alleviation of lead toxicity by inorganic salts and 6-benzylaminopurine

A concentration dependent decrease in root nitrate reductase (E.C.1.6.6.1) activity (NRA) by 0.1 to 2.0 mM lead acetate was noticed in three cultivars of Vigna radiata (L.) Wilczek (K851, MH8320 and ML337). Leaf NRA, on the other hand, increased significantly with increasing lead concentration which was more pronounced in cvs. MH8320 and ML337 than in cv. K851. Total nitrogen content of root and shoot was generally increased due to supply of the lead acetate, whereas the total nitrogen content of the colyledons was hardly affected in cvs. MH8320 and ML337 and decreased in cv. K851 during the early growth phase. The inhibition of root NRA could be alleviated by addition of inorganic salts (K2HPO4 and KNO3, but not CaCl2) or 6-benzylaminopurine (BAP) in the incubation medium. Lead mediated inhibition of root NRA was similar in light and dark grown seedlings, but lead induced increase in leaf NRA was more pronounced in the light than in the dark. This revised version was published online in August 2006 with corrections to the Cover Date.     

Growth and proline accumulation in mungbean seedlings as affected by sodium chloride

Mungbean (Vigna radiata L. Wilczek cv. Sujata and cv. K851) seedlings were grown in paper towelins in dark under 0, 0.5, 1, 2 and 3 % (m/v) NaCl salinity. Germination percentage, shoot and root length, fresh mass of both cultivars decreased with salinity. Total soluble saccharides and proline accumulated in the root and shoot of salt stressed seedlings. The proline accumulation in the root was four to five times higher than that of the shoot of NaCl treated etiolated mungbean seedlings.     

Role of Light in the Appearance of Glutamine Synthetase in Leaves of Pennisetum glaucum

Leaves of Pennisetum [Pennisetum glaucum (L) HHB 67] seedlings contained two isozymes of glutamine synthetase (GS, EC 6.3.1.2): cytosolic GS1 and chloroplastic GS2. Leaves of seedlings grown in light for seven days contained about twofold higher GS activity than etiolated leaves. In both light and dark grown seedlings, total GS, GS1 and GS2 activity declined with plant age with more pronounced effect in leaves of etiolated seedlings, and GS2 declined at a much faster rate than GS1. Exposure of etiolated seedlings to light markedly enhanced GS1 and GS2 activity. This increase in activity was not affected by cycloheximide, precluding light dependent de novo synthesis of the enzyme. Treatment of etiolated seedlings with photosynthetic inhibitor, dichlorophenyl dimethyl urea (DCMU) inhibited light dependent appearance of GS. Exogenous supply of sucrose to dark grown seedlings greatly increased the GS activity in dark. These results suggest that light-mediated stimulation in activity of GS in Pennisetum leaves is dependent on photosynthetic reaction.     

Distribution of diamine oxidase activity and polyamine pattern in bean and soybean seedlings at different stages of germination

Diamine oxidase (DAO, EC 1.4.3.6.) activity and polyamine content were measured in the shoot apex, leaves, epicotyl, cotyledons, hypocotyl and roots of light-grown bean ( Phaseolus vulgaris L. cv. Lingot) and soybean ( Glycine max L. cv. Sakai) seedlings at 3 different stages of germination (5, 8 and 14 days) as well as in embryos and cotyledons from soaked seeds. No DAO activity was detected in embryos and cotyledons of either plants. In bean seedlings DAO activity was only detectable in the shoot apex, primary leaves and cotyledons, while in soybean the activity was only detectable in the hypocotyl and roots. During seedling growth, in both plants, a different pattern of DAO activity was observed. In both species spermidine and spermine were the most abundant polyamines in embryos and cotyledons. Cadaverine, absent in bean, was only detected in soybean embryos. In the seedlings of both plants, increasing gradients of putrescine, spermidine and spermine from base to shoot apex were found. A high concentration of cadaverine was present in soybean hypocotyls and roots. A possible correlation between DAO activity and the endogenous content of the preferential substrate is discussed in relation to the possible involvement of the enzyme in regulating the cellular level of polyamines.     

Synthesis and degradation of barley nitrate reductase

Nitrate and light are known to modulate barley (Hordeum vulgare L.) nitrate reductase activity. The objective of this investigation was to determine whether barley nitrate reductase is regulated by enzyme synthesis and degradation or by an activation-inactivation mechanism. Barley seedling nitrate reductase protein (cross-reacting material) was determined by rocket immunoelectrophoresis and a qualitative immunochemical technique (western blot) during the induction and decay of nitrate reductase activity. Nitrate reductase cross-reacting material was not detected in root or shoot extracts from seedlings grown without nitrate. Low levels of nitrate reductase activity and cross-reacting material were observed in leaf extracts from plants grown on nitrate in the dark. Upon nitrate induction or transfer of nitrate-grown etiolated plants to the light, increases in nitrate reductase activity were positively correlated with increases in immunological cross-reactivity. Root and shoot nitrate reductase activity and cross-reacting material decreased when nitrate-induced seedlings were transferred to a nitrate-free nutrient solution or from light to darkness. These results indicate that barley nitrate reductase levels are regulated by de novo synthesis and protein degradation.     

STUDIES ON THE SOLUBLE CARBOHYDRATES AND CARBOHYDRATE PRECURSORS IN GERMINATING SOYBEAN SEED

The total soluble carbohydrate fraction of the cotyledons and embryo axis of germinating soybean seedlings declined rapidly during the first 3 days of germination. This depletion began earlier in the embryo axis than in the cotyledon. The total carbohydrate content of the cotyledons of plants grown in light and plants grown in dark was approximately the same for the first 7 days of germination. Between day 9 and 13 the total carbohydrate content of the cotyledons of soybean seedlings grown in dark was higher than that of plants grown in light. The reducing sugar content of light-grown soybean cotyledons increased approximately 5-fold during the first 9 days of germination, whereas that of dark-grown soybean cotyledons increased more slowly during this interval. Reducing sugars in the embryo increased during the early stages of germination until they approximately equalled the total carbohydrate. Between day 4 and 13, oil was depleted more rapidly in the cotyledons of seedlings grown in light than those grown in the dark. The reserve carbohydrates of soybean embryos and cotyledons consisted primarily of low molecular weight oligosaccharides, particularly sucrose, stachyose, and raffinose. These compounds decreased rapidly during germination. The isocitritase activity in the cotyledons of germinating soybean seeds increased rapidly for the first 6 days of germination and then decreased for the next 7 days. The isocitritase activity of plants grown in the dark was higher than that of the plants grown in light at all stages of development, particularly between day 7 and 11.     

Rhythmical changes in the sensitivity of cotton seedlings to herbicides

Cotton (Gossypium hirsutum L.) seedlings that were grown under a photoperiod of 12 hours darkness and 12 hours light showed oscillations in their sensitivity to the herbicides sodium 5-(2-chloro-4-trifluoromethyl)-phenoxy)-2-nitrobenzoate (acifluorfen), butyl 2-(4-((5-(trifluoromethyl)-2-pyridinyl)oxy)phenoxy)propanoate (fluazifop) and 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (bentazon). Sensitivity was expressed in appearance of necrotic areas on the cotyledons and in decreased growth of the shoot. The seedlings were least sensitive in the beginning and middle of the light period, then the sensitivity increased and reached its maximum during the beginning and middle of the dark period and then declined. Seedlings grown from germination under continuous light exhibited very small or no oscillations in sensitivity. The oscillations in sensitivity were entrained by one cycle of darkness and light. A cycle of 12 hours darkness and 12 hours light triggered the greatest oscillations while either increasing or decreasing the duration of the dark period resulted in smaller oscillations. Apparently, these oscillations in sensitivity to herbicides were endogenously controlled since after entrainment they continued irrespective of the light conditions.     

Induction and Turnover of Nitrate Reductase in Zea mays (Influence of Light)

Both light and NO3- are necessary for the appearance of nitrate reductase (NR) activity (NRA) in photosynthetic tissues. To define the light effect more precisely, we examined the response to light/dark transitions on NRA, NR protein (NRP), and NR mRNA in 6-d-old maize (Zea mays cv W64A x W182E) seedlings that had been grown in a light/dark regime for 5 d and then induced with 5 mM KNO3 for 24 h. The decay of NRA and NR mRNA in the shoot was immediate, but there were only minor changes in NRP during the initial 4 h in the dark. In root tissues, in contrast, there was a 4-h delay in the loss of NRA, NRP, and NR mRNA after transfer to the dark. When the seedlings were returned to light after a 2-h interval in the dark, shoot NRA reached 92% of the initial levels within 30 min of illumination. These results indicate that in the shoots (a) NR message production requires light and (b) the NRP that appears with light treatment and that is active is inactivated in the dark. The NRP can be reactivated when the light is turned on after short periods of darkness (2 h). Root tissues, on the other hand, probably respond to the supply of photosynthetically produced metabolites rather than to immediate products of the light reactions of photosynthesis.     

Increase in Nitrate Reductase Activity in Bean Leaves by Light Involves a Regulator Protein

Nitrate reductase activity, assayed either in vivo or in vitro was considerably higher in bean (Phaseolus vulgaris L.) leaves from 7-day-old light grown seedlings than those from dark grown, both in the absence as well as presence of nitrate. Cytochrome c reductase activity was however similar in both regimes, while peroxidase was lower in light than in dark. The light stimulated increase in nitrate reductase activity in leaf segments from dark grown seedlings was inhibited by cycloheximide, DNP, chloramphenicol, and sodium tungstate and was unaffected by lincomycin and DCMU. Under similar conditions, the increase in total chlorophyll was inhibited completely by cycloheximide and DNP, partially by chloramphenicol and lincomycin, and was unaffected by tungstate and DCMU. A supply of 1~5 mm reduced glutathione increased enzyme activity in the dark and also to some extent in light. The substrate induction of enzyme activity started after a lag of one hr in light or dark and continued for either 5 hr in the dark or 8 hr in light. Two proteinaceous inhibitors (Factors I and II) of nitrate reductase were isolated by ammonium sulfate precipitation and Sephadex gel filtration. The amount of Factor I was higher in the dark than in light. The amount and activity of Factor II was however, almost equal in light and dark. The inhibition of enzyme activity by these inhibitors increased with their concentration. It is proposed that light increases nitrate reductase activity by decreasing the amount of a nitrate reductase inhibitor.     

Die Hemmung der Isocitrat-Lyase bei Wassermelonenkeimlingen durch Weißlicht

Summary The isocitrate lyase activity (E.C. 4.1.3.1.) from watermelon cotyledons (Citrullus vulgaris Schrad.) is inhibited by white light (Fig. 5). To exclude artefacts during enzyme preparation the following experiments were performed (Table 1 and 2): 1. Mixing of raw extracts from cotyledons of light and dark grown seedlings. 2. Joint homogenization a) of cotyledons from light and dark grown seedlings, b) of purified isocitrate lyase together with cotyledons from light or dark grown seedlings. The total activity corresponded to an amount which was expected for the sum of the individual activities. The results justify the conclusion that the inhibition of the isocitrate lyase by light is real, and that the measured enzyme activities are close to the true enzyme concentrations in the plant tissue. — The relatively slow inhibition of the enzyme activity caused by light seems to be correlated with the formation of the photosynthetic apparatus.     

Developmental Effects of Sandoz 6706 on Activities of Enzymes of Phenolic and General Metabolism in Barley Shoots Grown in the Dark or under Low or High Intensity Light

The activities of three enzymes of phenolic biosynthesis and six of general metabolism were studied at 24-hour intervals between the 3rd and 8th day after planting in barley shoots treated with the chlorosis-inducing herbicide Sandoz 6706 and grown in the dark or under high or low intensity light. The herbicide had no effect on fresh weight or soluble protein (per shoot) in plants grown in the dark or under low intensity light, but slightly decreased these parameters in plants grown for more than 5 days under high intensity light. In dark-grown seedlings the herbicide had no detectable effects on plastid ultrastructure or on the activity of malate dehydrogenase, cytochrome c oxidase, NADP-cytochrome c reductase, triose phosphate isomerase, peroxidase, catalase, shikimate dehydrogenase, phenylalanine ammonia-lyase, or chalcone-flavanone isomerase. Under low intensity light, Sandoz 6706-treated plants developed plastids with single thylakoids extending across the organelle, and the activity of all enzymes examined was increased to varying degrees. When the herbicide-treated plants were grown under high intensity light, plastid lamellar organization was severely disrupted. Activities of shikimate dehydrogenase and chalcone-flavanone isomerase were markedly enhanced, phenylalanine ammonia-lyase activity slightly promoted, and catalase activity severely inhibited. The other enzymes were not appreciably affected by Sandoz 6706 under high intensity light. It is concluded that the changes in plastid ultrastructure and enzyme activities of the herbicide-treated plants are largely secondary photomorphogenetic or photooxidative responses in the carotenoid-free plants in which chlorophylls accumulate in reduced amounts (low intensity light) or are completely absent (high intensity light).     

UV-B辐射对8个大豆品种种子萌发率和 幼苗生长的影响

在生长房5种(暗处、可见光、低、中、高强度紫外线-B)处理下,研究了8个大豆品种的种子萌发率和萌发后幼苗的生长状况。结果表明,暗处种子萌发率高于自然光和UV-B辐射的种子。UV-B辐射增强对大豆种子的萌发率没有显著影响,仅使部分品种的最大萌发率降低和导致部分品种达到最大萌发率的时间延长。幼苗的生长对增强的UV-B辐射非常敏感。使大部分品种的胚根变短增粗,这可能是植物激素作用的结果。大豆的叶绿素a、叶绿素b和总叶绿素含量明显受到UV-B辐射的抑制。UV-B作用能促进类黄酮在幼苗中的积累,紫外吸收色素的增设有利于提高对UV-B的抵抗力。UV-B辐射的这种效应及大豆品种间的差异在自然情况下会产生深远的生物学和生态学意义     

The effect of indol-3-yllactic acid on maize seedling growth

D,L-indol-3-yllactie acid was applied at concentrations 0.2 – 20 mg 1^-1 (10^-6–10^-4M) to the roots of 3-d-old intact maize seedlings grown in the dark and in the light. By day 3 after application, ILA at lower concentrations (0.2–1 mg l^-1) caused slight increase in the mass of etiolated plants, mainly roots. Shoot and root length was not increased. ILA at concentrations equal to, or greater than, 2 mg 1^-1 reduced the length of the main roots and from 10 mg 1^-1 on also the length of the shoots. In contrast, root mass was decreased by higher ILA concentrations to a lesser extent than shoot mass. The response to ILA application of etiolated seedlings differed from that of the seedlings grown in the light only at 20 mg 1^-1. The inhibitory effect was more pronounced in the case of quickly growing etiolated plants.     

The role of cotyledons in the establishment of Suaeda physophora seedlings

The role of cotyledons in seedling establishment of the euhalophyte Suaeda physophora under non-saline and saline conditions (addition of 1 mM or 400 mM NaCl) was investigated. Survival and fresh and dry weights were greater for seedlings grown in the light (12-h light/12-h dark) than in the dark (24-h dark). The shading of cotyledons tended to decrease shoot height, shoot organic dry weight, number of leaves, and survival of seedlings regardless of NaCl treatment, but the effect of cotyledon shading was greater with 400 mM NaCl. Concentrations of Na⁺ were higher in cotyledons than in leaves, regardless of NaCl treatment. The K⁺/Na⁺ ratio was lower in cotyledons than in leaves for seedlings treated with 1 mM NaCl but not for seedlings treated with 400 mM NaCl. Addition of 400 mM NaCl decreased oxygen production in cotyledons but especially in leaves. These results are consistent with the hypothesis that, by generating oxygen via photosynthesis and by compartmentalizing Na⁺, cotyledons are crucial for the establishment of S. physophora seedlings in saline environments.     

Light-Dark Changes in Proline Content of Barley Leaves under Salt Stress

Proline accumulation in leaves of barley (Hordeum vulgare L. cv. Alfa) seedlings treated with 150 mM NaCl was promoted in the light and suppressed in the dark. The light/dark changes of proline content was enhanced with each 12 h light/12 h dark cycle and the proline content increased steadily. Root and shoot concentrations of Na⁺ and Cl^– in salt treated plants increased about 10 to 25 times as compared to the control. The content of these ions and the content of malondialdehyde were higher in the shoot of seedlings exposed to salt stress for 4 d in the light in comparison with the seedlings exposed to NaCl for 4 d in darkness. Light stimulated both ions and proline accumulation in the leaves and has no effect in the roots. Oxygen uptake was higher in the seedlings kept 4 d in the light which have higher endogenous free proline content. Chlorophyll fluorescence measurements showed that the photochemical activity of PS 2 slightly decreased as a result of salt stress and was not influenced by light regimes during plant growth.     

ent-Kaurene Biosynthesis in Cell-Free Extracts of Excised Parts of Tall and Dwarf Pea Seedlings

Investigations on the sites of ent-kaur-16-ene (ent-kaurene) biosynthesis were conducted with cell-free extracts from several excised parts of 10-, 13-, and 16-d-old tall and dwarf pea (Pisum sativum L.) seedlings. [¹⁴C]Mevalonic acid was incorporated into ent-kaurene in cell-free extracts from young developing leaves and elongating internodes of tall (`Alaska') and dwarf (`Progress No.9') pea seedlings at all three stages of development. ent-Kaurene biosynthesis also occurred readily in cell-free extracts from shoot tips, petioles, and stipules near the young elongating internodes. The ent-kaurene-synthesizing activity found in young developing tissues declined as tissues matured. Little or no activity was detectable in enzyme extracts from cotyledons and root tips at different stages. In light grown tall pea internodes ent-kaurene-synthesizing activity was low as they began to elongate, reached a maximum when the internodes reached about 2 cm in length and declined as they matured. Activity in extracts of dwarf shoot tips and internodes was generally lower than in equivalent tall plants, but the activity in dwarf leaves and stipules was somewhat higher than in tall plants. With the exception of root tips, there is a strong correlation between growth potential of a tissue and the rate of ent-kaurene biosynthesis in extracts from that tissue.     

Diurnal Modulation of Arginine Decarboxylase Activity of Chenopodium rubrum L. by Temperature and Light

Arginine decarboxylase (ADC), one of the key enzymes of polyaminemetabolism in plants, was investigated in Chenopodium rubrumL. seedlings under constant and alternating temperature andlighting conditions. With seedlings grown at constant temperature,ADC activity of the whole seedling increased rapidly betweenthe second and the third day after sowing. This effect was alwayshigher under continuous light than in continuous darkness. Fromthe third to the seventh day after sowing, there was a markeddecrease in ADC activity of the whole seedling almost down tothe level of the second day. Under "normal" lighting and temperatureconditions (32.5?C/10?C, light/dark) there was a marked increasein ADC activity when plants were transferred to 10?C and a rapiddecrease when they were transferred to 32.5?C. The same timecourse was observed when an "inverse" light-temperature program(32.5?C/10?C; dark/light) was applied. This means that the timecourse of ADC activity in the seedlings is slightly light-dependent,but strongly temperature-dependent. The data are discussed withrespect to the chronopathological effects of the "inverse" light-temperatureprogram. (Received March 5, 1985; Accepted October 2, 1985)     

Light regulation of protein synthesis factor EF-G in pea chloroplasts

The activity of pea chloroplast elongation factor G (EF-G), a nuclear-coded protein required for the elongation cycle of chloroplast protein synthesis, is regulated in response to light. In pea seedlings germinated and grown under continuous white or red light, EF-G specific activity reaches a maximum between days 10 to 15, and then decreases. EF-G activity is almost undetectable in extracts from dark-grown seedlings. When 13-day dark-grown pea seedlings are transferred to light, EF-G specific activity reaches a higher value after 2 to 3 days than observed in seedlings grown under continuous light. The small and large subunits of ribulose bisphosphate carboxylase continue to accumulate after EF-G specific activity has reached maximum levels. Cytoplasmically synthesized components of the chloroplast protein synthetic apparatus, such as EF-G, may help coordinate cytoplasmic and nuclear events with chloroplast gene expression during light-induced chloroplast differentiation.     

Expression of Peroxidases During Seedling Growth in <Emphasis Type="Italic">Ebenus Cretica</Emphasis> L. as Affected by Light and Temperature Treatments

Peroxidase (POD) activity and isoform patterns were investigated during seedling growth (up to 20 days) of Ebenus cretica L. Seeds germinated to approx. 100% after a 24-h imbibition. Seedling growth proceeded smoothly, in both light and dark conditions. No seedling growth was noticed at 4°C. A positive effect of light and increasing temperature (4, 10, 16, 22 and 28°C) on seedlings growth, lignin content and POD activity was observed. Lignin content was 2.5 times higher in seedlings grown under light than in seedlings grown under darkness. Seedlingsȁ9 POD activity was higher in acid pH (5.5) in comparison to neutral pH (7.0). These activities were higher in seedlings grown under darkness than in those grown under light; since additional POD isoforms were expressed in dark conditions. The increase in POD activity was accompanied with the appearance of new POD isoforms correlated with the growth of the seedlings. Four soluble anionic POD isoforms (named A₁, A₂, A₃ and A₄) and three soluble cationic POD isoforms (named C₁, C₂ and C₃) were displayed depending on the treatment and the course of growth. POD isoforms were detected in gel after PAGE. The fast migrating (A₄) isoform, which appeared in the dark-grown seedlings as well as on day 20 at 28°C in the temperature treatment, was separated by DEAE–Sepharose column chromatography. A slow migrating C₁ isoform slightly appeared in both 4 and 10°C temperature treatments and could be related to the low temperature treatments, while A₁, A₂, A₃ and C₂ to the growth stage of seedlings. The expression of seven POD isoforms during seedling growth seems to be related to different developmental events of growth and could be used as useful biochemical markers in the analysis of metabolic regulation in seedling growth of Ebenus cretica.