More than meets the eye: subretinal aspirate from an acutely blind dog

A 14-year-old, spayed female Cocker Spaniel was presented to the Boren Veterinary Medical Teaching Hospital at Oklahoma State University with acute loss of vision in the right eye and a history of intermittent bloody diarrhea of unknown duration. Small, white, plaque-like lesions in the retina and subretina were visualized by direct ophthalmic examination, and aspirated with ultrasound-guidance. A direct smear of the subretinal fluid was highly cellular and contained large numbers of pleomorphic organisms consistent with Prototheca sp. The structures were round, oval, or elongated, 4-6 microm width and 8-16 microm in length and surrounded by a thin, clear cell wall. Small, central, pink to purple nuclei were observed in some organisms, but in most, the nuclei were obscured by a deeply basophilic, granular cytoplasm. Some organisms contained endospores. Negatively-stained structures of similar size and shape were considered to be empty casings (theca) of ruptured sporulating and nonsporulating forms of the organism. Protothecosis usually is a disseminated, fatal disease in dogs. The Prototheca organisms observed in this case showed characteristic morphology, illustrating the ability to diagnose protothecosis in cytologic samples.     

大葱根系分泌物对黄瓜种子萌芽和枯萎病病原菌的化感作用及其GC–MS 分析

 采用连续根系分泌物收集系统（CRETS）收集大葱根系分泌物,研究其对黄瓜种子萌芽及其枯萎病病原菌的化感作用,并利用气相色谱—质谱技术（GC–MS）分析其化学组成。结果表明：大葱根系分泌物对黄瓜种子萌发和芽苗生长均表现低浓度促进、高浓度抑制的作用,‘元藏大葱’比‘章丘大葱’的化感作用更强;随着根系分泌物浓度升高,对病原菌菌丝生长和孢子萌发的抑制作用逐渐增强,‘元藏大葱’根系分泌物的抑制程度大于‘章丘大葱’。大葱根系分泌物中含有杂环化合物、酯类、酰胺类、酸类、烃类、醛酮类、酚类、醇醚类以及萘类等物质,其中,前三者所占的比例较大。邻苯二甲酸酯类和苯并噻唑类物质相对含量较高,2,2’–亚甲基双（4–甲基–6–叔丁基苯酚）、苯甲酸苄酯、苯甲酸–4–甲基苯酯、2–甲硫基异硫氰酸苯酯相对含量较低,同一物质‘元藏大葱’根系分泌物中相对含量高于‘章丘大葱’。     

缺钾胁迫对连作草莓生长和土传病害的影响

 以草莓‘红颜’品种为试材,设缺K（K+ 48.75 mg · L^-1,缺量水平）、1/2K（K+ 415.58 mg · L^-1, 半量水平）和全量K（K+ 782.41 mg · L^-1,正常水平）营养液处理,对缺钾胁迫与草莓连作障碍的关系进 行了探讨。结果表明,缺钾处理显著抑制二茬草莓植株地下部分和地上部分的生长,其中缺K 的长势最 弱,1/2K 比全量K 的长势强;缺K 二茬植株根系分泌物对草莓组培苗生长有显著影响,表现为低浓度（1%、 2%）根系分泌物促进幼苗侧根和茎叶生长,高浓度（4%）则抑制根系生长。不同浓度钾营养液处理的三 茬植株分别接种尖孢镰刀菌和大丽轮枝菌后,在不同时期比未经过连作的基质对照发病都严重。缺K 三 茬植株发病最重,接菌后10 d 时病情指数就高达75,全量K 三茬植株发病次之,1/2K 三茬植株发病相 对较轻。因此,缺K 环境会加重草莓的连作障碍,适宜的K 量对草莓连作障碍的防治有重要意义。     

三种湿地植物在高负荷养猪废水脱氮过程中的根际效应

为了探究不同湿地植物在处理高负荷养猪废水时的根际效应,本研究通过野外小区控制试验,以3种常见的挺水植物美人蕉(Canna indica)、梭鱼草(Pontederia cordata)、黄菖蒲(Iris pseudacorus)为研究对象构建表流人工湿地,研究人工湿地植物根系分泌物与根际氮循环微生物之间的关系。结果显示,梭鱼草对养猪废水的处理效果最好,氨氮、硝氮和总氮的去除率分别为78.3%、93.4%和81.2%。与试验前相比,梭鱼草和黄菖蒲根系可溶性有机碳(DOC)分泌速率在试验后分别增加了44.9%和13.5%;根系总有机酸(TOA)分泌速率分别增加了125.1%和147.5%。在处理养猪废水后,3种植物根际硝化过程氨氧化细菌(AOB)占主导地位,AOB-amoA基因丰度在黄菖蒲根际土中最高,为2.6×10⁸ copies·g^-1;反硝化过程nirK基因占主导地位,nirK基因丰度在梭鱼草根际土中最高,为4.3×10⁸ copies·g^-1。同时,3种植物根际均存在较明显的厌氧氨氧化过程,hz...     

凋落物输入对根系分泌物碳输入及土壤氮的影响

以马尾松人工林及林下灌木短柱茶为研究对象,采用根系分泌物原位收集法,分析凋落物处理[对照(保持原状凋落物不变,CK)、去除凋落物(LR)、添加凋落物(LA)]对两树种根系分泌物碳输入速率、根际土壤氮含量和氮转化相关酶活性的影响,并分析其相关关系。结果表明:凋落物输入量变化对马尾松和短柱茶根系分泌物碳输入速率无显著影响。同一凋落物处理下,马尾松和短柱茶根系分泌物碳输入速率无显著差异。凋落物输入量变化不显著影响根际土壤氮含量及马尾松根际土壤脲酶、羟胺还原酶、硝酸还原酶和亚硝酸还原酶活性,短柱茶根际土壤硝酸还原酶活性表现为去除凋落物处理显著大于对照,其余氮转化相关酶活性未表现出显著差异。可能是凋落物处理时间较短,凋落物未完全分解或者是林分年龄较大有关。相关关系结果表明,单位根长根系分泌物碳输入速率与根际土壤全氮(TN)含量呈显著负相关关系,单位根表面积根系分泌物碳输入速率与根际土壤硝态氮含量(NO-3-N)含量呈显著负相关关系。表明根系分泌物碳输入与根际土壤氮素相互影响。     

Purification and characterization of phytase induced in tomato roots under phosphorus-deficient conditions

Phytase (myo-inositol hexakisphosphate phosphohydrolase; EC 3.1.3.8) was purified from roots of tomato plants grown under phosphorus-deficient conditions using five purification schemes. The phytase was successfully separated from the major acid phosphatase to an electrophoretic homogeneity. The native molecular weight of this enzyme was estimated to be about 164 kD by Bio-Gel P-200 gel filtration. The molecular weight of the subunit on SDS-PAGE was approximately 82 kD, indicating that the native form of the enzyme was a homodimer. The isoelectric point of tomato phytase was about 5.5. The enzyme exhibited a high affinity for phytic acid (K _m = 38 μM), and was strongly inhibited by phosphate, molybdate and fluoride. Among other characteristics of tomato phytase, the pH and temperature optima were 4.3 and 45°C, respectively. Tomato phytase contained a fairly high concentration of aspartic, glutamic acid and glycine residues.     

Excretion of dibutyl phthalate by sorghum roots under Fe‐stress: Evidence of its action on chlorosis recovery

Sorghum (Sorghum bicolor L. Moench) cv. CSH‐7, an Fe‐efficient hybrid was grown and subjected to Fe‐deficiency stress. The nutrient medium was extracted for isolation of reductant chemicals. By means of thin layer chromatography, I.R. spectrum and HPLC analysis, dibutyl phthalate was identified as the principal component. This chemical was not found in the nutrient medium extracted before the onset of chlorosis or in that after the plants recovered from chlorosis. Furthermore, synthetic dibutyl phthalate and that obtained from the exudate when supplied to the nutrient medium caused greening of chlorotic sorghum in 24 hours. Evidence that the root medium of the Fe‐efficient sorghum can induce recovery of an Fe‐inefficient sorghum grown together, has also been obtained. It is concluded that dibutyl phthalate released by the Fe‐efficient sorghum subjected to stress, is responsible for making Fe available for utilisation. The mechanism of action of dibutyl phthalate on chlorosis recovery is still an open question.     

Diurnal variations in uptake,transport and assimilation of NO3 ‐and efflux of OH‐ in maize plants

Maize plants, grown for 7 and 21 days on a nutrient solution with NO₃ ^‐ as the sole nitrogen source showed a clear diurnal pattern with respect to the in vivo NRA. Especially in roots dark/light fluctuations of the enzyme activity were high. Also in NO₃ ^‐ uptake, OH^‐ efflux and endogenous content of water soluble carbohydrates a diurnal variation was found. The plant age did not significantly affect the daily rhythm.

Because day/night changes of the in vivo root NRA and nitrate uptake were proportional, the relative content of reduced N in the xylem sap of the plants was constant during a day/night interval. At both day 7 and day 21 about 40–50% of the N was transported via the xylem as amino N. As a result of non‐synchronous variation of the specific root and shoot NRA, root reduction capacity showed a great within‐day variation. It varied between 20 and 40% of the whole plant reduction capacity. Since the ratio N‐organic to N‐total in the xylem sap was about 0.5, cycling of organic nitrogen was very likely in these maize plants.     

Effect of root exudates of different resistant varieties of cucumber on fusarium wilt and preliminary studies on their resistance mechanism

This study investigated the effect of root exudates of cucumber varieties, Jinyan 4 (susceptible variety), Jinchun 4 (resistant variety) and Yinnan Black seed squash on fusarium wilt. The results showed that fusarium wilt occurrence of plants treated with the root exudate of Jinyan 4 was earlier. The infection rate was significantly higher 15 days after inoculation, but similar to the control 20 days after inoculation. In contrast, the infection rate of plants treated with the root exudate of Jinchun 4 was significantly lower than that of the control. The plant height and fresh weight of Jinyan 4 treated with its own root exudate were lower than those of the control, and the root vigor decreased but the conductance increased. There was no significant effect of the root exudates from Jinchun 4 and Black seed squash on plant height and fresh mass of Jinyan 4. We found that the root exudate of susceptible cucumber variety stimulated the growth of Fusarium oxysporum pathogen, in contrast, that of resistance variety and Black seed squash suppressed the growth. __________ Translated from Chinese Journal of Applied Ecology, 2007, 18(3): 559–563 [译自: 应用生态学报]     

Physiological and Cytological Studies on the Inhibition of Striga Seed Germination by the Plant Growth-promoting Bacterium Azospirillum brasilense

Striga hermonthica (Del.) Benth. is an obligate parasitic weed of tropical cereals whose rhizosphere can also be colonised by bacteria of the genus Azospirillum. A previous study demonstrated that the two organisms (Azospirillum and striga) interacted during cerealroot colonisation. Two strains of A. brasilense isolated from an African sorghum rhizosphere prevented the germination of striga seeds although they were stimulated to germinate by the presence of sorghum roots. Azospirillum cells suspended in a synthetic germination stimulant (GR24) did not inhibit striga seed germination, but did block radicle elongation. Those radicles had an abnormal morphology, and contained no vacuolated cells in the root elongation zone. Lipophilic compounds extracted from the medium of bacteria in the log and stationary growth phases prevented the germination of striga seeds.