微生物次级代谢的调节(续)

九、次级代谢调节中的诱导作用当微生物生长达到平衡后,即“无限制的”生长期(营养期)之后,由于特定营养成份减少而停止急剧生长,进入有限的生长期——繁殖期,此时次级代谢才开始进行。因为在营养期一般不出现催化次级代谢的酶,所以可以认为在这个转换期中发生了次级代谢酶的诱导或解阻遏。下面,谈谈已经搞清楚了的诱导效应物的     

谈苹果物候期的观测和其在果园生产中的应用

一、苹果的物候期(即生物气候期) 营养生长期和相对的休眠期组成一年内苹果发育的周期,每年苹果树生长开始决定于地下部根系的开始活动及地上部芽的萌发,营养生长期结束的表现则是叶片的自然脱落,新梢组织有了不同程度的木质化,营养物质的大量积累和植株生长的停止。某些果树种类其营养生长期和相对的休眠期是颇不明显的,但苹果在相对的休眠期中,继续着的仅仅是很微弱的呼吸、蒸发、物质转化等生理作用,差不多停止了光合作用、生长作用、无机盐类的吸收等活动。由于营养期和相对的休眠期的循环,苹     

3种念珠藻多糖对自由基的清除作用

研究了地木耳（Nostoc commune）、葛仙米（N．sphaerohies）和发菜（N．flagelliforme）3种念珠藻多糖对自由基的清除作用。结果表明,3种念珠藻多糖对超氧阴离子自由基和羟自由基具有很强的清除作用,且呈量效关系,地木耳清除超氧自由基作用最强,最高清除率达72．3％,葛仙米和发菜分别为46．7％、35．5％;发菜清除羟自由基效果最强,最高清除率达74．3％,葛仙米和地木耳清除率分别为49．0％、46．7％;3种念珠藻多糖对DPPH自由基的清除作用不显著。     

青海高原地木耳中氨基酸特征与分析

地木耳在青海民间视为山珍 ,能清热解毒、凉血明目 ,是一种天然的营养保健食品。文中采用美国 6 0 0E氨基酸分析仪 ,日本岛津RF5 4 0荧光仪测定了青海高原地木耳中 1 8种氨基酸的含量 ,为科学地开发利用青海高原地木耳食物资源提供一些基础资料和科学依据     

食用蓝藻——地木耳的开发

地木耳隶属原核生物界、蓝藻门、念珠藻属,是植物界最原始的类群之一,因其形似木耳的胶质片状而得名。显微镜下的地木耳是由许多丝状体无规则地集合于一个公共胶鞘中。细胞圆形,排成一列,如念珠串的丝状体。丝状体中有一些比营养细胞略大的异形胞,将丝状体分成许多藻殖段,     

松嫩平原两个生态型羊草种群生长机制

对松嫩平原两个生态型羊草种群生长机制进行了研究.结果表明,两个生态型羊草种群分株重与密度之间关系呈幂函数变化,方程中b值（-0.098～-0.272）大于-1.两个生态型羊草种群生物量、分株重随着密度、高度的增加而逐渐增加,它们之间的关系符合幂函数或直线变化规律,达到显著或极显著相关水平.两个生态型羊草种群生物量和分株重随密度和高度的变化速率在营养生长期内均最小.灰绿生态型的变化速率b（0.7872、0.0134）在营养生长期小于黄绿生态型（0.8793、0.0222）;到果后营养期,灰绿生态型（0.8048、0.0303）逐渐超过黄绿生态型（0.7796、0.0258）.两个生态型羊草种群在研究样地环境中未达到环境容纳量,两个生态型羊草种群在整个生育期内不断生长,具有相同的生长规律,且灰绿生态型羊草种群具有更强的生长潜力.     

基于黑土农田生物多样性监测样地的地表大型节肢动物群落特征

农田生态系统是陆地生态系统的重要组成部分,是全球生态与环境研究的关键区之一.为了研究农田生物群落构建过程,探索其多样性维持机理,本研究于2015年在东北典型黑土区建立了16 hm²的农田生物多样性监测样地,按照作物生长期,于玉米生长大喇叭口期(8月初)、抽穗期(9月初)和成熟期(10月初)对陷阱法获取的地表大型节肢动物进行了统计分析.结果表明: 3次调查共获得地表大型节肢动物5284只,隶属于节肢动物门3纲12目32科47种.调查中优势类群3类,常见类群11类.节肢动物营养功能群中植食性和杂食性节肢动物所占比重较大.地表大型节肢动物物种数量和个体数量随作物生长期有显著变化.9月初节肢动物的Shannon多样性指数、Margalef丰富度指数、Pielou均匀度指数相对较高,8月初Simpson优势度指数较高.从不同物种的变异系数(CV)及群落空间插值可以看出,节肢动物群落在水平方向上存在异质性.在与土壤环境因子关系上,双变量相关分析表明,不同月份地表大型节肢动物总个体数与土壤pH值、有机质、全氮、含水量的相关性均未达到显著性水平;典范对应分析(CCA)进一步表明,优势类群和常见类群对环境因子具有较强的适应能力,在研究区内分布广泛.农田生物多样性监测样地内地表节肢动物物种组成丰富,在作物不同生长时期地表节肢动物群落组成及空间分布格局具有明显的变化过程.农田生物多样性监测样地通过大尺度、长时间对样地内土壤动物空间过程进行监测,可以为解决群落生物多样性形成和维持机制提供重要手段.     

水稻应用赤霉素的试验研究 Ⅱ.水稻营养生长期应用赤霉素的效果

水稻营养生长期喷施赤霉素可提早成熟,但增产效果不稳定。为获得早熟增产的效果,须喷施适时、浓度适宜、增加基本苗。水稻营养生长期喷施赤霉素有抑制分蘖出生,促进主茎和早出生分蘖生长的效应。正确运用这一效应,可以控制最高苗数和过剩分蘖,提高稻株的生理活性,增进优势蘖成穗,促进主茎和早出生分蘖的发育,获得穗大粒多、早熟增产的效果。     

固氮蓝细菌束毛藻生物固氮策略研究进展

固氮蓝细菌束毛藻(Tricodesmium)是海洋中丰度最高的固氮微生物,贡献了约42%的海洋生物固氮,为海洋生态系统提供了新的氮源,驱动海洋初级生产力和食物网,在海洋生物地球化学循环中发挥重要作用。作为海洋中“新氮”主要贡献者,束毛藻是一种不产生异形胞的丝状固氮蓝细菌。因为生物固氮的关键酶固氮酶对氧气十分敏感,一般固氮蓝细菌通常产生异形胞或采用夜间固氮的方式进行生物固氮,避免氧气对固氮酶的抑制作用。近年来研究发现,束毛藻具有一套独特的生物固氮体系,能够使同一藻丝在白天同时完成光合作用和生物固氮,并具有复杂的调控机制。本文综述了近年来束毛藻生物固氮策略的最新研究进展,介绍了其生物固氮和光合作用之间的精密调控机制,对拓展固氮微生物尤其是海洋蓝细菌固氮机制的认识具有借鉴意义。     

桔花蕾蛆(Contarinia pyrivora Ril.)为害与防治

柑桔花蕾蛆的成虫产卵期,据在南充、武胜的情况看来,为3月中旬至4月初旬。 柑桔花蕾自现蕾到开花可分为5期:1.花蕾绿色期,花蕾为绿色萼片包被,花蕾呈淡青色质地坚韧,成虫不在上面产卵。2.花蕾现白期,为成虫产卵最多时期。3.花蕾膨大期,成虫产卵较少。4.含苞期,花蕾     

THE ECOLOGY OF NOSTOC

Nostoc is a genus of filamentous cyanobacteria that can form macroscopic or microscopic colonies and is common in both terrestrial and aquatic habitats. Much of the success of Nostoc in terrestrial habitats is related to its ability to remain desiccated for months or years and fully recover metabolic activity within hours to days after re-hydration with liquid water . Nostoc can also withstand repeated cycles of freezing and thawing and, thus, is an important component of extreme terrestrial habitats in the Arctic and Antarctic. The ability to fix atmospheric N ₂ can provide an advantage in nitrogen-poor environments . Nostoc also has the ability to screen damaging ultraviolet light in terrestrial and shallow benthic habitats. The genus potentially could be important in paddy rice culture because it fixes nitrogen that may later be released and used by plants; it also may play a role in soil formation and may increase nitrogen input to natural aquatic and terrestrial ecosystems. The abilities to survive in terrestrial habitats and fix N ₂ are important in symbiotic interactions with fungi (lichens), liverworts, hornworts, mosses, ferns, cycads, and the angiosperm Gunnera. Nostoc is somewhat resistant to predation; this probably is related to production of large amounts of sheath material, synthesis of microcystin-like toxins by some strains, and formation of colonies that are too large for many algivores to consume. Some organisms can subsist on Nostoc, although it may not be a preferred food source. Lytic cyanophages also infect Nostoc, but little is known about population control of Nostoc in its natural environment, Late Precambrian fossils resembling Nostoc have been described, and Nostoc possibly has been an important component of many terrestrial and aquatic communities since that time .     

ROLE OF ULTRAVIOLET RADIATION IN MAINTAINING THE THREE-DIMENSIONAL STRUCTURE OF A CYANOBACTERIAL MAT COMMUNITY AND FACILITATING NITROGEN FIXATION

Cyanobacterial mat communities were collected in the mangrove forest bordering the Grand Cul de Sac Marin, Guadeloupe, French West Indies, which supports a community of nitrogen fixing cyanobacterial mats established on the trunk and branches of black mangrove ( Avicennia germinans L.). This study presents results that are focused on the mat community and the physiological and morphological adaptations to UV radiation. The dominant surface species of the mat, Nostoc cf commune Vaucher and Scytonema sp., possessed the UV-shielding pigment scytonemin. Mats grown on medium D agar without nitrogen under photosynthetically active radiation (PAR) only, rapidly became disorganized compared with those exposed to PAR + UV-A (320– 400 nm) + UV-B (280–320 nm) irradiation. Concurrent with disorganization, acetylene reduction activity (ARA = one third of N₂ reduction) was severely reduced, whereas mats irradiated with PAR + UV-A + UV-B maintained high ARA activity. Mats incubated for 27 days under PAR + UV-A + UV-B then exposed to PAR only exhibited a 68% stimulation of ARA, whereas ARA values were 33% inhibited in mats incubated with PAR only and then exposed to PAR + UV-A + UV-B. This favorable equilibrium was facilitated by the mats' three-dimensional structure in which the most UV-resistant species, N. commune , covers the surface with UV-sensitive species below this protective covering. The UV stressor was essential for the maintenance of mat structure and ARA.     

沙打旺生物量及营养物质形成规律的研究

沙打旺种群生长期地上部生物量、营养物质产量呈单峰曲线。各器官生物量及营养物质的高峰期不一致,地上部生物量在9月上旬(花期)达最大值;其中茎杆量峰值在花期以后;叶量峰值在花期以前。粗蛋白,粗脂肪产量高峰在生物量高峰前,分别为166g／m2,29g／m2;粗纤维、无氮浸出物产量高峰在生物量高峰后,达591g／m2、663g／m2。沙打旺生物量形成过程中土壤水分逐渐亏缺。从返青到生物量高峰,地上部生物量与根区3m土层贮水量呈显著负相关(r=-0.7726**)。沙打旺绝对生长速度为一单峰曲线,在7月上旬达最大值(14.9g／m2·d)：净同化率在返青后有一短暂上升期;相对生长速度持续下降。不同器官在不同生长发育阶段营养成份含量及其积累速度显著不同。     

Effects of nitrogen source on the synthesis of the UV-screening compound, scytonemin, in the cyanobacterium Nostoc punctiforme PCC 73102

The effects of nitrogen source (N(2), NO(3)(-) and NH(4)(+)) on scytonemin synthesis were investigated in the heterocystous cyanobacterium Nostoc punctiforme PCC 73102. With the required UVA radiation included, Nostoc synthesized three to seven times more scytonemin while fixing nitrogen than when utilizing nitrate or ammonium. A similar increase in scytonemin synthesis occurred when nitrate or ammonium became depleted by growth and Nostoc switched to diazotrophic metabolism with the differentiation of heterocysts. In addition, UVA-exposed cultures grown in medium with both NO(3)(-) and NH(4)(+) synthesized some scytonemin but synthesis increased when NH(4)(+) was depleted and growth had become dependent on NO(3)(-) reduction. Although the mechanism is unclear, these results suggest that the greater the restriction in nitrogen accessibility, the greater the production of scytonemin. Perhaps the entire response may be an interaction between this restriction and a resultant sensitivity to UV radiation that acts as a cue for determining the level of scytonemin synthesis. Scytonemin is a stable UVR screening compound and appears to be synthesized by cyanobacteria as a long-term solution for reducing UVR exposure and damage, but mainly or solely, when metabolic activity is absent. It is likely that during metabolic resurgence, the presence of a dense scytonemin sheath would facilitate the recovery process without the need for active defenses against UV radiation.     

PHYSIOLOGICAL ECOLOGY OF NITROGEN FIXING BLUE-GREEN ALGAL CRUSTS IN THE UPPER-SUBALPINE LIFE ZONE1

Blue-green algal (cyanobacterial) crusts composed of nitrogen fixing Nostoc commune Voucher ex Born. et Flah. and Tolypothrix conglutinata var. colorata Ghose were studied in the upper-subalpine life zone, Mission Mountain Wilderness, Montana. Rates of ethylene production were highest in the submerged shoreline crusts, lower for exposed crusts pioneering rocky shorelines and lowest in the Carex meadow. Nitrogenase activity (acetylene reduction technique) was constant between 200–285% crust moisture content (wet/dry weight) and then rapidly declined to 0 between 200–140%. Optimal temperatures for ethylene production by illuminated cells was between 20–30° C for T. conglutinata, 20° C for N. commune and about 25° C in darkness for both species. Nitrogenase activity by T. conglutinata in culture was unaffected by repeated freeze-thaw treatments whereas N. commune was severely inhibited. In contrast, N₂-ase activity of these two species in an intact crust was unaffected by repeated freeze-thaw treatments. Application of nitrogen-free growth medium to intact crusts increased nitrogenase activity by 3.7 times implying that these were mineral deficient under field conditions. Photosynthesis was light saturated at 125 μmol-m^?2.s^?1 whereas nitrogenase activity was light independent for cells with carbohydrate reserves. When carbohydrate reserves were reduced by 8 h incubation in darkness, between 1–3 h of illumination were required to restore nitrogenase activity to 80% of the maximum rate. Biochemical pathway inhibitor studies employing DCMU, MFA, and CCCP showed that oxidative metabolism was the source of reductant for acetylene reduction. Tetrazolium precipitation in heterocysts paralleled acetylene reduction activity in the inhibitor treated cells.     

Comparison of photosynthesis and productivity of Gunnera tinctoria Molina (Mirbel) with and without the phycobiont Nostoc punctiforme L.

Abstract. Marked increases in growth and nitrogen content were found with Gunnera tinctoria Molina (Mirbel) plants infected (+ Nostoc ) with the cyanobacterium Nostoc punctiforme L., in comparison to uninfected (— Nostoc ) plants and this was attributed to N₂-fixation by the phycobiont. Whilst host and symbiont can be grown separately, preliminary data indicates that the host plant is reliant on the cyanobacterium to meet its nitrogen requirements because it has little capacity to assimilate nitrate. Although the maximum light-saturated rate of photosynthesis was higher in the + Nostoc plants, there was no reduction in photosynthetic efficiency under lightlimiting conditions, despite marked differences in plant nitrogen status. Differences in photosynthetic rate were implicated as the major reason for the differences in plant productivity. Stomatal conductance was insensitive to changes in plant nitrogen status and did not parallel the variation in photosynthetic rates. The ecological significance of the largely invariant stomatal response and the consequences of differences in water and nitrogen-use efficiencies between + and — Nostoc plants is discussed.     

Molecular genetic and chemotaxonomic characterization of the terrestrial cyanobacterium Nostoc commune and its neighboring species

The phylogeny of the terrestrial cyanobacterium Nostoc commune and its neighboring Nostoc species was studied using molecular genetic and chemotaxonomic approaches. At least eight genotypes of N. commune were characterized by the differences among 16S rRNA gene sequences and the petH gene encoding ferredoxin-NADP? oxidoreductase and by random amplified polymorphic DNA analysis. The genotypes of N. commune were distributed in Japan without regional specificity. The nrtP gene encoding NrtP-type nitrate/nitrite permease was widely distributed in the genus Nostoc, suggesting that the occurrence of the nrtP gene can be one of the characteristic features that separate cyanobacteria into two groups. The wspA gene encoding a 36-kDa water stress protein was only found in N. commune and Nostoc verrucosum, suggesting that these Nostoc species that form massive colonies with extracellular polysaccharides can be exclusively characterized by the occurrence of the wspA gene. Fifteen species of Nostoc and Anabaena were investigated by comparing their carotenoid composition. Three groups with distinct patterns of carotenoids were related to the phylogenic tree constructed on the basis of 16S rRNA sequences. Nostoc commune and Nostoc punctiforme were clustered in one monophyletic group and characterized by the occurrence of nostoxanthin, canthaxanthin, and myxol glycosides.     

Ineffective utilization of nitrate by soybean during pod fill

The relative effectiveness of nitrate, allantoin, or nitrate plus allantoin as sources of nitrogen for the indeterminate soybean plant [ Glycine max (L.) Merr cv. Harper] was studied throughout vegetative and reproductive growth. All plants were provided with 3.0 m M nitrogen and were grown hydroponically in growth chambers. During vegetative and early reproductive growth, plants given nitrate or nitrate plus allantoin grew faster than plants provided allantoin only. However, during pod fill, plants provided with allantoin or allantoin plus nitrate gained weight more rapidly than plants receiving just nitrate. More importantly, at maturity plants that had been provided with allantoin or allantoin plus nitrate during pod fill were 30% heavier in total dry weight, 50% higher in nitrogen content, and 50% higher in seed yield than plants that had received just nitrate. At full bloom, all plants were inoculated with the same culture of Bradyrhizobium japonicum , and twice each week throughout pod fill each plant was assayed for nitrogen fixation (acetylene reduction). Correlation coefficients obtained by linear regression analysis show a strong positive correlation between the measured rate of nitrogen fixation and maximum plant fresh weight (r = 0.83), total plant nitrogen (r = 0.81), or seed yield (r = 0.76). The fact that nitrogen fixation during pod fill stimulates plant growth and seed yield, coupled with the facts that nitrate blocks nodulation and is not used efficiently during pod fill by the soybean plant, may explain why seed yield of field-grown soybeans usually does not respond to added fertilizer nitrogen. Thus, it is suggested that enhanced nitrogen fixation may be the key factor in improving soybean seed yield.     

光强和氮源对念珠藻胞外多糖分泌的影响

胞外多糖（EPS）是结皮蓝藻形成生物结皮的胶结剂,为了理解常球状存在的丝状蓝藻Nostoc胶结沙粒的机理,探讨了光强40、80 E/（m2s）和氮源（气态氮,硝态氮）对结皮优势种Nostoc sp.分泌EPS（包括荚膜多糖CPS和释放多糖RPS）的影响规律及其内在机理。结果发现:Nostoc sp.在气态氮和硝态氮下都有相似的快速生长,但其分泌的RPS、CPS及EPS量,在硝态氮下均随光强的增加而增加,在气态氮下却与光强没有关系。相关代谢研究发现,在硝态氮下细胞内有更高含量的可溶性糖和蔗糖。进一步的相关分析发现,在两种氮源下,蔗糖量与RPS量或CPS量间的显著正相关都只发生在80 E/（m2s）下,在气态氮中,两光强下的胞内总糖量都与CPS量显著负相关。以上结果说明,Nostoc sp.在氮源利用和光强适应方面都有明显优势,它即使在快速生长的对数期,也可同时分泌相当量的EPS,这使其在球状藻殖段形成之前胶结沙粒成为可能。由此可推知,Nostoc sp.在贫瘠沙土表面的最初生长过程中,其胞外的EPS均来自胞内的固碳产物,在高光强下,蔗糖很可能是其EPS合成的原料。