Primary Analysis of Components in Different Soybean Nodulating Mutants and their Effects on Nitrate Reductase Activity and Nodulation

The water extracts of leaves and roots from supernodulating soybean (Glycine max (L.) Merr. ) nts 382 and nonnodulating soybean Nod 49 have been chromatographed using filtering method through the column (25 cm × 2 cm) Sephadex G25 and 4 fractions, namly, nts 382 (Nod 49) F1, nts 382 (Nod 49) F2, nts 382 (Nod 49) F3, and nts 382 (Nod 49) F4 could be distinguished according to nitrate reductase (NR) activities inhibited by the eluate. The inhibition of NR activity by the noninoculated nts 382 F2 and the nts 382 F4 in vitro were much stronger than that by the inoculated nts 382 F2 and nts 382 F4. On the contrary, the obvious inhibition of NR activity in vitro by the noninoculated Nod 49 F2 and Nod 49 F4 were substantialy strengthed again by the innoculated Nod 49 F2 and Nod 49 F4. The facts indicated that the quantity of NR inhibitors in the leaf cells of soybean nts 382 reduced after the inoculation but was that in the inoculated Nod 49 leaf cells further more accumulated. Both nodulations assays, the nodulation of soybean "Bragg " injected with inoculated nts 382 Fl, nts 382 F2, nts 382 F3 and nts 382 F4 from leaves and roots and the nodulation of soybean nts 382 injected with inoculated Nod 49 F2, Nod 49 F3 and Nod 49 F4 from leaves only showed that nts 382 Fl and nts 382 F2 increased nodules of soybean "Bragg" by 1 to 3 times but nts 382 F3 and nts 382 F4 did not. Inhibition of soybeannts 382 nodulation by inoculated Nod 49 F2 Nod 49 F3 and Nod 49 F4 expressed that the Nod 49 F4 only inhibited the nodulation strongly by one time in the experiments with nts 382 plants with leaves, and by 15 times in the experiments with nts 382 plants without leaves at 10 d of inoculation and injection and this inhibition was nonreversible even after stopping injection from the 11th day to the 15th day after inoculation.     

Soybean Seedling Extracts Inhibit Supernodulation

When soybean (Glycine max ) nodulation mutant nts 382 was inoculated with Bradyrhizobium japonicum, these plants nodulated significantly more than the parental type Bragg. Nts 382 seedlings displayed wild-type nodulation pattern when aqueous extracts of young Bragg shoots were applied to the cultural medium together with nutrient solution. Application of young nts 382 shoot extracts to Bragg seedlings did not result in any apparent increase in nodule number. In graft experiments, young shoots from mutant nts 382 induced supernodulation on Bragg root stocks, while no supernodulation was observed when Bragg seedlings were used as scion and grafted onto nts 382 root stocks. Further, the effectiveness of Bragg plant extracts to suppress supernodulation on nts 382 seedlings was found to depend on the age of the plant material used, being very ineffective with extracts from 60-day-old plants. The age effect was not observed in graft experiments. These findings suggest that soybean supernodulation phenomenon may be controlled by one or a few unknown chemicals or plant hormones.     

寄主大豆对根结瘤的控制

我国９个大豆（ＧｌｙｃｉｎｅｍａｘＬ．Ｍｅｒｒ．）品种感染根瘤菌ＵＳＤＡ１１０后,产生不同的结瘤数,低者在２０个以下．高者在６０个以上。赤豆、绿赤豆也可被感染结瘤,而豇豆、扁豆则不能。超结瘤大豆ｎｔｓ３８２作为接穗时能诱导我国大豆原结瘤数有４５个的开育１０号、原结瘤数有１２个的大黄分别发生高结瘤。ｎｔｓ３８２作为砧木时,则不能表现超结瘤．表明超结瘤因子能传给我国大豆,反之存在于我国大豆中的限制超结瘤的因子也能传给ｎｔｓ３８２。ｎｔｓ３８２于ＮＯ３－环境中仍表现超结瘤的特点也能导入开育１０号、大黄及赤豆根部,并使之在ＮＯ３－环境中结瘤。在ＮＯ３－环境中不能结瘤的开育１０号作为接穗,ｎｔｓ３８２作为砧木的嫁接植株,于子叶生长阶段接受ＮＯ３－时,仍能结瘤,于真对生长时接受ＮＯ３－时．则不能结瘤,表明限制结瘤因子于真叶细胞中被诱导形成。     

Lack of Systemic Suppression of Nodulation in Split Root Systems of Supernodulating Soybean (Glycine max [L.] Merr.) Mutants

Wild-type soybean (Glycine max [L] Merr. cv Bragg) and a nitrate-tolerant supernodulating mutant (nts382) were grown in split root systems to investigate the involvement of the autoregulation response and the effect of timing of inoculation on nodule suppression. In Bragg, nodulation of the root portion receiving the delayed inoculation was suppressed nearly 100% by a 7-day prior inoculation of the other root portion with Bradyrhizobium japonicum strain USDA 110. Significant suppression was also observed after a 24-hour delay in inoculation. Mutant nts382 in the presence of a low nitrate level (0.5 millimolar) showed little, if any, systemic suppression. Root fresh weights of individual root portions were similar for both wild type and nts382 mutant. When nts382 was grown in the absence of nitrate, a 7-day delay in inoculation resulted in only 30% suppression of nodulation and a significant difference in root fresh weight between the two sides, with the delayed inoculated side always being smaller. Nodulation tests on split roots of nts382, nts1116, and wild-type cultivars Bragg, Williams 82, and Clark demonstrated a difference in their systemic suppression ability. These observations indicate that (a) autoregulation deficiencies in mutant nts382 result in a reduction of systemic suppression of nodulation, (b) some suppression is detectable after 24 hours with a delayed inoculation, (c) the presence of low nitrate affects the degree of suppression and the root growth, and (d) soybean genotypes differ in their ability to express this systemic suppression.     

Growth comparisons of a supernodulating soybean (Glycine max) mutant and its wild-type parent

The growth of a supernodulating, nitrate-tolerant soybean [ Glycine max (L.) Merr.] mutant nts 382 (nitrate-tolerant symbiosis) was compared to that of its wild-type parent, cv. Bragg, over the first 50 days after sowing. Plants were grown either inoculated in the absence of an external nitrogen source or uninoculated in the presence of 5 m M KNO₃. For both treatments, nts 382 growth up to 13 days after planting was faster than that of cv. Bragg. Thereafter, supernodulation of inoculated nts 382 occurred and growth of cv. Bragg was faster; shoot and root dry weight increments and leaf area were greater in cv. Bragg, but the N content of nts 382 was higher. Relative growth and net assimilation rates were lower in nts 382, which had faster shoot and root respiration rates. Shoot growth of uninoculated plants was similar for both mutant and wild-type but roots of nts 382 were slightly smaller than those of cv. Bragg. Total plant N content was similar in uninoculated cv. Bragg and nts 382 but the latter had a higher leaf N content. Early lateral root formation (prior to nodule emergence) was greater in nts 382 regardless of whether rhizobia or KJNO₃ were present. We conclude that nts 382 has some inherent differences from its parent but that supernodulation significantly retards plant growth.     

Effects of Doubled CO2 on Contents of Photosynthetic and on Kinetic Parameters of Fluorescence Induction in Different Genotypes of Soybean

Effects of doubled C02 on photosynthetic characteristics of soybean ( Glycine max L. ) Bragg (wild type) and its different monogene mutation strains--Nts 382 (supemodulation mutant) and Nod 49 (non-nodulation mutant) were studied. The experimental results showed that the contents of chlorophyll and carotenoid of Bragg, Nts 382 and Nod 49 were increased under doubled CO2, respectively, although to different extent. The determination results of fluorescence induction kinetic parameters showed that PS Ⅱ activity, the efficiency of primary conversion of light energy of PS Ⅱ and the efficiency of potential photosynthetic quantum conversion of a leaf from Bragg and its mutants were raised in doubled CO2. Fluorescence photochemical quenching coefficient and the overall photochemical quantum yield of PS Ⅱ were raised and non-photochemical quenching coefficient was reduced with CO2 enrichment; such changes were bigger in Nts 382 than those in Bragg and Ned 49. It might be that atmospheric N2 was more effectively utilized by Nts 382 than by Bragg and Ned 49.     

Nitrogenase activity and ureide levels in a supernodulating soybean mutant: Effects of inoculum dose and nitrate treatment

The effects of nitrate on nitrogenase (EC 1.18.2.1) activity of soybean ( Glycine max [L.] Merr) cv. Bragg and its supernodulating mutant derivative, nts382, were compared. A short-term nitrate treatment was used to allow effects on nitrogenase activity to be studied in the absence of effects on nodule growth and a low inoculum dose, which prevented supernodulation of nts382, was employed to test for any interaction between supernodulation and the magnitude of the effect of nitrate on nitrogenase activity. At the usual inoculum dose, nitrogenase activity, per g nocule, of nts382 was lower than that of Bragg and was proportionally less affected by nitrate. Decreasing the inoculum dose increased nitrogenase activity of nts382 and also the proportional decline in response to nitrate. The decline in the ureide conentration in xylem exudate in response to nitrate was proportionally similar to the decline in nitrogenase activity per plant. However, although nitrogenase activity per plant of nts382 was several-fold less than that of Bragg, the ureide flux rate (ureide concentration x xylem sap exudation rate), was not different. At the usual inodulum dose, the ureide content of the nocules, stems plus petioles and leaves of nts382 was greater than that of Bragg. Decreasing the inoculum dose reduced the ureide content of the nodules of nts382 but not of Bragg. Ureide degradative capacity of the leaves was the same for Bragg and nts382. Low activities of 5-phosphoribosyl pyrophosphate amidotransferase (EC 2.4.2.14) and glutamine synthetase (EC 6.3.1.2) in the nodules reflected the low nitrogenase activity of nts382.     

Development ofBradyrhizobium infections in supernodulating and non-nodulating mutants of soybean (Glycine max [L.] Merrill)

Summary The early events in the development of nodules induced byBradyrhizobium japonicum were studied in serial sections of a wild type (cv. Bragg), a supernodulating mutant (nts 382) and four non-nodulating mutants (nod49, nod139, nod772, andrj ₁) of soybean (Glycine max [L.] Merrill). Cultivar Bragg responded to inoculation in a similar manner to that described previously for cv. Williams; centres of sub-epidermal cell divisions were observed both with and without associated infection threads and most infection events were blocked before the formation of a nodule meristem. The non-nodulating mutants (nod49, nod772, andrj ₁) had, at most, a few centres of sub-epidermal cell divisions. In general, these were devoid of infection threads and did not develop beyond the very early stages of nodule ontogeny. Sub-epidermal cell divisions or infection threads were never observed on mutant nodl39. This mutant is not allelic to the other non-nodulating mutants and represents a defect in a separate complementation group or gene that is required for nodulation. The supernodulating mutant nts382, which is defective in autoregulation of nodulation, had a similar number of sub-epidermal cell divisions as the wild-type Bragg, but a much greater proportion of these developed to an advanced stage of nodule ontogeny. Mutant nts382, like Bragg, possessed other infection events that were arrested at an early stage of development. The results are discussed in the context of the progression of events in nodule formation and autoregulation of nodulation in soybean.Abbreviations nts nitrate tolerant symbiosis - RT root tip (i.e., position of the tap root tip at the time of inoculation) - SERH shortest emerging root hair (i.e., position of the shortest emerging root hair on the tap root at the time of inoculation) - SCD subepidermal cell divisions     

ALLELOPATHIC GROWTH INHIBITION OF NODULATED AND UNNODULATED ALNUS CRISPA SEEDLINGS BY POPULUS BALSAMIFERA

Water extracts of fresh leaves, buds, and leaf litter of Populus balsamifera (balsam poplar) were tested at different dilutions for allelopathic effects on nodulation, nitrogenase activity and growth of nodulated green alder (Alnus crispa) seedlings, and on growth of unnodulated green alder seedlings. All extracts inhibited height growth, root elongation and dry weight increment of nodulated and unnodulated green alder seedlings to some degree during a 2-month experiment. Foliar nitrogen content of both nodulated and unnodulated seedlings was significantly lower in extract treated plants than in controls. Growth inhibition was about 25% less in nodulated than in unnodulated seedlings. The number of nodules per plant in seedlings treated with any balsam poplar extract was only 51% that of control plants. Acetylene reduction by seedlings treated with bud and leaf litter extracts indicated a decrease of 62% compared to controls. Growth inhibition was not mediated by pH or osmotic effects of the extracts. The possible ecological significance is discussed.     

Roles for redox regulation in leaf senescence of pea plants grown on different sources of nitrogen nutrition

Leaf senescence and associated changes in redox components were monitored in commercial pea (Pisum sativum L. cv. Phoenix) plants grown under different nitrogen regimes for 12 weeks until both nodules and leaves had fully senesced. One group of plants was inoculated with Rhizobium leguminosarum and grown with nutrient solution without nitrogen. A second group was not inoculated and these were grown on complete nutrient solution containing nitrogen. Leaf senescence was evident at 11 weeks in both sets of plants as determined by decreases in leaf chlorophyll and protein. However, a marked decrease in photosynthesis was observed in nodulated plants at 9 weeks. Losses in the leaf ascorbate pool preceded leaf senescence, but leaf glutathione decreased only during the senescence phase. Large decreases in dehydroascorbate reductase and catalase activities were observed after 9 weeks, but the activities of other antioxidant enzymes remained high even at 11 weeks. The extent of lipid peroxidation, the number of protein carbonyl groups and the level of H(2)O(2) in the leaves of both nitrate-fed and nodulated plants were highest at the later stages of senescence. At 12 weeks, the leaves of nodulated plants had more protein carbonyl groups and greater lipid peroxidation than the nitrate-fed controls. These results demonstrate that the leaves of nodulated plants undergo an earlier inhibition of photosynthesis and suffer enhanced oxidation during the senescence phase than those from nitrate-fed plants.     

Properties of nitrate reductase from seedling leaves of selected barley genotypes

Crude extracts from leaves of 6-day barley seedlings of parental genotypes (cv. Aramir and primitive line R567) and selected doubled haploid (DH) lines were not found to have significant differences in the NADH:NR activity, while considerable differences between these genotypes were shown by the NAD(P)H:NR activity. The cv. Aramir and DH lines did not differ by nitrate accumulation in the leaves. However, the primitive line R567, as compared to the remaining genotypes, was characterized by an appreciably lower ability to accumulate nitrates. In partially purified leaf extracts, significant differences in total NADH:NR activity and in distal activity dependent on methyl viologen (MV:NR) were found between the parental genotypes and selected DH lines. The studied genotypes differed also in dehydrogenase NR activity, i.e. cytochrome c reductase activity in crude extracts. In the studied genotypes, the NADH:NR activity in partially purified leaf extracts did not substantially differ by Km values for nitrates. Calculated Vmax values for NADH:NR in these genotypes were similar to total NR activity in partially purified extracts. Significant differences between the parental genotypes and selected DH lines were found in the thermal NADH:NR stability in crude and partially purified leaf extracts. From the performed studies it follows that different NR stability was one of the reasons of revealed differences in total activity and in partial NR activities in the leaf extracts between the studied genotypes of spring barley. Besides, it is suggested that varied NR gene expression in the leaves of these barley genotypes could also influence NR activity.     

Relationship between autoregulation and nitrate inhibition of nodulation in soybeans

Ten of 11 supernodulating mutants of soybean [ Glycine max (L.) Merr.] cv. Bragg, in which nodulation was far in excess of that in the wild type, showed pronounced tolerance of nodulation to applied nitrate. Mutant nts (nitrate-tolerant symbiosis) 1116 had an intermediate nodulation response and also showed some inhibition by nitrate. Mutant 1029, a revertant of nts382 (an extreme supernodulator), showed a wild-type nodulation pattern and was equally sensitive to nitrate as cv. Bragg. Grafting experiments with cv. Bragg and nts382 indicated that both supernodulation and tolerance of nodulation to nitrate were dependent on shoot factors. Total leaf nitrate reductase (EC 1.6.6.1 and EC 1.6.6.2) activity of the supernodulating mutants was similar to that in cv. Bragg. We conclude from these results that the inhibitory effect of nitrate on nodule initiation and development in soybean depends on an interaction between nitrate and the autoregulation singal. In the supernodulating mutants, the autoregulation signal is either altered or absent and cosequently nodulation in these mutants is not sensitive to nitrate.     

Nitrate reductase activity, distribution, and response to nitrate in two contrasting Phaseolus species inoculated with Rhizobium spp

The nitrate reductase activity distribution and response of two nodulated species of Phaseolus (Phaseolus vulgaris-common bean, and Phaseolus lunatus-lima bean) to different exogenous nitrate levels were studied during the vegetative period. These Phaseolus species showed to be very contrasting in respect to the pattern of nitrate reductase (NR) activity distribution thought the plant. The highest level of NR activity in P. vulgaris was clearly shown to occur in leaves in contrast with the lowest one detected in roots and nodules as widely seen for other tropical species of the Phaseoleae tribe. Conversely, P. lunatus had higher NR activity in the nodules, whereas its leaves exhibited a steadily decrease during the plant development. Indeed, at 32 days after emergence (pre-flowering stage), the nodulated P. vulgaris had approximately 95% of the total NR activity localized in its leaves, whereas in P. lunatus it was equally distributed in the nodules and in the leaves. Under long-term exposure to increasing exogenous level of nitrate, the leaf-NR activity of nodulated P. vulgaris presented a positive response, whereas the enzyme activity was very low and unresponsive in P. lunatus. In contrast, the nodule-NR activity showed a reverse response to the increasing NO(3)(-) level. The nodule-NR activity of P. lunatus significantly increased whereas in the P. vulgaris nodules it was very low and unresponsive. This present study suggests that P. lunatus inoculated with Rhizobium tropici presents a singular pattern of nitrate reduction distribution among leaves and nodules during the vegetative development. It is speculated that the nodulated Phaseolus lunatus may have different NR isoforms in their leaves (at least a constitutive type) and an inducible form in their nodules, responsive to long-term exposure to nitrate.     

Differential belowground allelopathic effects of leaf and root of Mikania micrantha

This study evaluates the relative contributions of leaves and roots to the belowground allelopathic effects of Mikania micrantha. The hypothesis that leaves contribute more to the allelopathic effect than roots was experimentally tested. We assessed the allelopathic effects of aqueous extracts from Mikania leaves and roots on the seed germination and seedling growth of two co-occurring woody plants in southern China, Lagerstroemia indica L. and Robinia pseudoacacia L. The results showed that the aqueous extracts from Mikania leaves and roots had inhibitory effects on the woody species. Allelopathic activity depended on the concentration of the extracts, target species, and the extract sources (i.e., leaves vs. roots of Mikania). Leaf extract showed stronger allelopathic effects than root extract on germination percentage, initial germination time, speed of germination, and shoot height; while root extract had greater allelopathic effects on roots than leaf extract. The latter phenomenon might greatly promote the invasion success of Mikania due to more direct and effective allelopathy of root. Our results suggest that allelopathy of root extract on belowground biomass might be greater than that of leaf extract for some species in contrast allelopathy of leaf extract on belowground biomass might also be greater than that of root extract for other species, at least for their effects on root growth of the target species.     

小桐子提取物除草活性的生物测定

为全面了解小桐子(Jatropha curcas L. )提取物的除草活性,以萝卜(Raphanus sativus L. )、苋(Amaranthus tricolor L. )、苏丹草[Sorghum sudanense (Piper) Stapf]和黑麦草(Lolium perenne L. )为实验材料,对小桐子果壳和枝叶的水、乙醇(体积分数95%)、正丁醇、乙酸乙酯、氯仿和石油醚粗提物的除草活性进行了生物测定,并从中筛选出抑制作用最强的水粗提物进行进一步的活性组分分离及其除草活性的生物测定.测定结果显示,小桐子果壳和枝叶的6种溶剂提取物(10 g·L~(-1))对供试的4种植物幼苗的根长和茎高均有不同程度的抑制作用,其中水粗提物和乙醇(体积分数95%)粗提物的抑制作用较强,且水粗提物对供试的4种植物幼苗的根长和茎高的抑制作用均在75%以上,显著高于其他溶剂粗提物(P<0.05);石油醚粗提物的抑制作用最小,均在10%以下.小桐子果壳和枝叶水粗提物的石油醚、氯仿、乙酸乙酯、正丁醇和水萃取物(10 g·L~(-1))对萝卜和苏丹草幼苗的根长和茎高均有不同程度的抑制作用,其中水、正丁醇和乙酸乙酯萃取物的抑制作用显著高于氯仿和石油醚萃取物,抑制率均在70%以上;水萃取物的抑制作用最强,抑制率均在80%以上;石油醚萃取物的抑制作用最小,抑制率均在10%以下.研究结果表明,小桐子果壳和枝叶的水粗提物具有一定的除草活性,其有效成分为极性较大的组分.     

Regulation of nitric oxide (NO) production by plant nitrate reductase in vivo and in vitro.

NO (nitric oxide) production from sunflower plants (Helianthus annuus L.), detached spinach leaves (Spinacia oleracea L.), desalted spinach leaf extracts or commercial maize (Zea mays L.) leaf nitrate reductase (NR, EC 1.6.6.1) was continuously followed as NO emission into the gas phase by chemiluminescence detection, and its response to post-translational NR modulation was examined in vitro and in vivo. NR (purified or in crude extracts) in vitro produced NO at saturating NADH and nitrite concentrations at about 1% of its nitrate reduction capacity. The K(m) for nitrite was relatively high (100 microM) compared to nitrite concentrations in illuminated leaves (10 microM). NO production was competitively inhibited by physiological nitrate concentrations (K(i)=50 microM). Importantly, inactivation of NR in crude extracts by protein phosphorylation with MgATP in the presence of a protein phosphatase inhibitor also inhibited NO production. Nitrate-fertilized plants or leaves emitted NO into purified air. The NO emission was lower in the dark than in the light, but was generally only a small fraction of the total NR activity in the tissue (about 0.01-0.1%). In order to check for a modulation of NO production in vivo, NR was artificially activated by treatments such as anoxia, feeding uncouplers or AICAR (a cell permeant 5'-AMP analogue). Under all these conditions, leaves were accumulating nitrite to concentrations exceeding those in normal illuminated leaves up to 100-fold, and NO production was drastically increased especially in the dark. NO production by leaf extracts or intact leaves was unaffected by nitric oxide synthase inhibitors. It is concluded that in non-elicited leaves NO is produced in variable quantities by NR depending on the total NR activity, the NR activation state and the cytosolic nitrite and nitrate concentration.     

内蒙古产柽柳和多枝柽柳α-葡萄糖苷酶抑制活性

首次利用体外α-葡萄糖苷酶抑制模型以96微孔板法,对内蒙古产2种柽柳属植物不同溶剂提取物进行活性评价,并与阳性对照Acarbose比较,发现6种提取物均有较好的α-葡萄糖苷酶抑制作用,远远强于阳性对照Acarbose(IC50=1103.01μg·mL-1)的抑制活性。结果显示,同一植物不同溶剂提取物相比较,两者石油醚提取物α-葡萄糖苷酶抑制活性不及乙酸乙酯和正丁醇提取物;不同植物同一溶剂的提取物抑制活性也不同,6种提取物中,多枝柽柳的正丁醇和柽柳的乙酸乙酯提取物抑制活性最高(IC50=13.36和17.35μg·mL-1)。所有提取物对α-葡萄糖苷酶活性的抑制效果均很好,且多枝柽柳抑制活性整体上较柽柳好,具有良好的潜在开发价值。     

红薯水提物对外来入侵植物喜旱莲子草生长的化感影响

从植物化感作用的角度,探索利用具有较高经济价值的本地植物或伴生的本地物种对入侵植物进行抑制和清除,是一种控制外来入侵植物行之有效的方法。本研究以本地作物红薯和入侵植物喜旱莲子草为试验对象,探究红薯不同部位(根、茎、叶)3个浓度(0.025、0.05、0.1 g·mL^-1)的水提物对喜旱莲子草的化感作用。以形态学指标(无性系小株个数、节数、叶片数、叶面积、株高、总干重和根数)、化感响应指数、性状比值(肉质化程度、根冠比、比叶面积、叶生物量比、茎生物量比、根生物量比)、新生叶片中过氧化氢酶(CAT)、过氧化物酶(POD)、丙二醛(MDA)、超氧化物歧化酶(SOD)等作为衡量红薯对喜旱莲子草根状茎生长影响程度的参数。结果表明: 1)不同浓度不同部位红薯水提物对喜旱莲子草生长有不同影响。0.1 g·mL^-1根水提物显著抑制所有形态学指标,除总干重和根数外,其他形态学指标均随不同部位水提物浓度的升高而显著降低。2)所有处理的综合化感响应指数均为负值,说明红薯水提物对喜旱莲子草各指标具有负效应,抑制其正常生长。在所有处理中,0.1 g·mL^-1根水提物的化感抑制作用最强,化感响应指数为-0.73,其次为0.1 g·mL^-1茎水提物和0.05 g·mL^-1根水提物,化感响应指数均为-0.44。3)从性状比值可以看出,红薯水提物对肉质化程度、根冠比、比叶面积和叶生物量比有显著抑制作用,而对茎生物量比和根生物量比无显著性影响。4)红薯水提物显著增加新生叶片中丙二醛含量,显著降低超氧化物歧化酶含量,但对过氧化氢酶和过氧化物酶无显著影响。表明红薯水提物对喜旱莲子草根状茎生长有显著抑制作用。     

Rapid modulation of nitrate reductase in leaves and roots: Indirect evidence for the involvement of protein phosphorylation/dephosphorylation

Nitrate reductase activity (NRA; NADH-nitrate reductase, E. C. 1.6.6.1) has been measured in extracts from leaves of spinach ( Spinacia oleracea L.) in response to rapid changes in illumination, or supply of CO₂ or oxygen. Measured in buffers containing magnesium, NRA from leaves decreased in the dark and increased again upon illumination. It decreased also, when CO₂ was removed in continuous light, and was reactivated when CO₂ was added. Nitrate reductase (NR) from roots of pea ( Pisum sativum L.) was also rapidly modulated in vivo. It increased under anaerobiosis and decreased in air or pure oxygen. The half time for inactivation or reactivation in roots and leaves was 5 to 30 min.
When spinach leaves were harvested during a normal day/night cycle, extractable NRA was low during the night, and high during daytime. However, at any point of the diurnal cycle, NR could be brought to a similar maximum activity by preincubation of the desalted leaf extract with AMP and/or EDTA. Thus, the observed diurnal changes appeared to be mainly a consequence of enzyme modulation, not of protein turnover. In vivo, the reactivation of the inactivated enzyme from both leaves and roots was prevented by okadaic acid, and inhibitor of certain protein phosphatases. Artificial lowering of the ATP-levels in leaf or root tissues by anaerobiosis (dark), mannose or the uncoupler carbonyl cyanide m -chlorophenyl hydrazon (CCCP), always brought about full activation of NR.
By preincubating crude leaf or root extracts with MgATP, NR was inactivated in vitro. Partial purification from spinach leaves of two enzymes with molecular masses in the 67 kD and 100 kD range, respectively, is reported. Both participate in the ATP-dependent inactivation of NR.
Alltogether these data indicate that NR can be rapidly modulated by reversible protein phosphorylation/dephosphorylation, both in shoots and in roots.     

Foliar and fine root nitrate reductase activity in seedlings of four forest tree species in relation to nitrogen availability

Summary Seedlings of red maple, white pine, pitch pine and red pine were fertilized with nutrient solutions containing 4 levels of nitrate or ammonium additions. These levels corresponded to approximately 0.5, 1, 2 and 4 times normal availability of nitrogen in northeastern forests. Nitrate reductase (NR) activity was assayed in roots and leaves. Red maples treated with nitrate showed much higher leaf activities and higher ratios of leaf NR activity to root NR activity than any other species. Ammonium additions to red maple and white pine appeared to inhibit NR activity in leaves. With high nitrate additions, NR activity was induced in roots and leaves of pine species, but activity in roots remained much higher than in leaves.