重庆市蔬菜硝酸盐、亚硝酸盐含量及其与环境的关系

在重庆市的主要蔬菜中,硝酸盐含量依次为根菜类＞叶菜类＞葱蒜类＞瓜类＞豆类＞茄果类,前３类的硝酸盐含量超标,但各种蔬菜的亚硝酸盐含量一般较低,未超过卫生标准。就同一种蔬菜的不同样品而言,硝酸盐和亚硝酸盐含量的差异很大,说明品种或环境条件可显著影响其含量。重庆市多雾少光,冬春低温,土壤含氮量和钠高子含量较高,有效钾含量较低可能是导致蔬菜大量积累硝酸盐的环境因素。蔬菜不同器官硝酸盐和亚硝酸盐含量各异,根＞茎＞叶柄＞叶片。     

INFLUENCE OF AMMONIUM AND NITRATE ON THE PROTEIN- AND FREE AMINO ACIDS IN SHOOTS OF WHEAT SEEDLINGS

Weissman , Gerard S. (Rutgers U., Camden, N. J.) Influence of ammonium and nitrate on the protein- and amino acids in shoots of wheat seedlings. Amer. Jour. Bot. 46(5): 339–346. 1959.—Total and protein nitrogen per shoot of wheat seedlings grown with endosperm attached increased at a steady rate during a 96-hr. growth period, and protein nitrogen, as a percentage of total nitrogen, remained constant at about 53%. Total and protein nitrogen concentration was greatest for 24-hr. shoots and declined as the shoots became older. Total and protein nitrogen were determined in 96-hr. shoots of seedlings grown with endosperm attached but also supplied with ammonium, nitrate, or both in the culture solution. Total nitrogen was greatest in shoots supplied with ammonium, but only 38% was in the form of protein. Maximum protein synthesis occurred in shoots grown in both ammonium and nitrate and protein nitrogen as a percentage of total nitrogen approximated that achieved in shoots lacking nitrogen in the culture solution. The protein amino acid composition of 48-, 72-, and 96-hr. shoots was very similar but differed from 24-hr. shoots which contained higher percentages of arginine and lysine and lower percentages of alanine and threonine. This may be correlated with the higher proportion of meristematic cells in 24-hr. shoots. The protein amino acids in shoots grown with ammonium resembled that of shoots lacking nitrogen in the culture solution, but nitrate shoot protein contained a higher percentage of arginine and a lower percentage of lysine. Nitrate may stimulate the formation of enzymes, possibly of a nitrate-reducing system, with high arginine- low lysine content. Free asparagine and glutamine were both at a maximum in ammonium shoots and at a minimum in nitrate shoots, but asparagine predominated in shoots supplied with ammonium while glutamine was greatest in nitrate shoots. Aspartic acid, asparagine, and glutamine appeared to have ammonia-storage functions, but glutamic acid appeared to be primarily concerned with protein synthesis. Amino acid accumulation was greatest in shoots supplied with both ammonium and nitrate. Protein synthesis in these appeared to be limited by inadequate concentrations of glutamic acid and proline. A hypothesis is proposed in explanation of the high glutamic acid concentration in shoots provided with ammonium and nitrate.     

INTERACTION OF GIBBERELLIN, KINETIN AND POTASSIUM NITRATE IN THE GERMINATION OF LIGHT-SENSITIVE TOBACCO SEEDS

1. The effects of gibberellin, kinetin, potassium nitrate, andtheir interactions in the germination of light-sensitive tobaccoseeds were studied. 2. Gibberellin was very effective in inducing the dark germinationof tobacco seeds, and a linear relation was found to exist betweenthe germination rate and the concentration of gibberellin ifa suitable temperature was chosen for germination. This linearrelation was, however, changed by illumination and by a raisedtemperature in the manner that the germination on lower concentrationsof gibberellin was increased by the former and decreased bythe latter. 3. Kinetin was effective in promoting the tobacco seed germinationonly when the seeds were irradiated. This light effect was,however, limited only to the longer wavelengths in the visibleregion. The red effect was found to be reversed by infra-redirradiation under the influence of kinetin. 4. The combination of gibberellin and kinetin was synergisticin promoting the tobacco seed germination both in the lightand in the dark, whereas the combination of potassium nitrateand gibberellin or kinetin was synergistic only in the light. (Received November 1, 1960; )     

硫和6-苄氨基腺嘌呤对水稻幼苗硝酸还原酶活性的影响

缺硫培养6天的水稻幼苗,其叶片和根中的硝酸还原酶(NR)活性明显下降。用1pPm 的6-苄氨基腺嘌呤(6-BA)处理培养了10天的水稻幼苗根系,24小时后缺硫培养的水稻幼苗叶片和根系的 NR 活性升高,加硫培养的水稻幼苗叶片和根中的 NR 活性下降。用~(35)S示踪发现,6-BA 可降低加硫幼苗对~(35)S 的吸收和转化,但促进缺硫幼苗对~(35)S 的转化。     

RELATIONSHIPS BETWEEN NITRATE REDUCTASE ACTIVITY AND RATES OF GROWTH AND NITRATE INCORPORATION UNDER STEADY-STATE LIGHT OR NITRATE LIMITATION IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1

Although activity of the enzyme nitrate reductase (NR) can potentially be used to predict the rate of nitrate incorporation in field assemblages of marine phytoplankton, application of this index has met with little success because the relationship between the two rates is not well established under steady-state conditions. To provide a basis for using NR activity measurements, the relationships among NR activity, growth rate, cell composition, and nitrate incorporation rate were examined in cultures of Thalassiosira pseudonana (Hustedt)Hasle and Heimdal, growing a) under steady-state light limitation, b) during transitions between low and high irradiance (15 or 90 μmol quanta.m^?2.s^?1), and c) under steady-state nitrate limitation. Using a modified assay for NR involving additions of bovine serum albumin to stabilize enzyme activity, NR activity in light-limited cultures was positively and quantitatively related to calculated rates of nitrate incorporation, even in cultures that were apparently starved of selenium. During transitions in irradiance, growth rates acclimated to new conditions within 1 day; through the transition, the relationship between NR activity and nitrate incorporation rate remained quantitative. In nitrate-limited chemostat cultures, NR activity was positively correlated with growth rate and with nitrate incorporation rates, but the relationship was not quantitative. NR activity exceeded nitrate incorporation rates at lower growth rates (<25% of nutrient-replete growth rates), but chemostats operating at such low dilution rates may not represent ecologically relevant conditions for marine diatoms. The strong relationship between NR activity and nitrate incorporation provides support for the idea that NR is rate-limiting for nitrate incorporation or is closely coupled to the rate-limiting step. In an effort to determine a suitable variable for scaling NR activity, relationships between different cell components and growth rate were examined. These relationships differed depending on the limiting factor. For example, under light limitation, cell volume and cell carbon content increased significantly with increased growth rate, while under nitrate limitation cell volume and carbon content decreased as growth rates increased. Despite the differences found between cell composition and growth rate under light and nitrate limitation, the relationships between NR activity scaled to different compositional variables and growth rate did not differ between the limitations. In field situations where cell numbers are not easily determined, scaling NR activity to particulate nitrogen content may be the best alternative. These results establish a strong basis for pursuing NR activity measurements as indices of nitrate incorporation in the field.     

THE ACCUMULATION OF ELECTROLYTES : XII. ACCUMULATION OF HALIDE AND NITRATE BY VALONIA IN HYPERTONIC SOLUTIONS

When cells of Valonia macrophysa were placed in hypertonic sea water, the concentration of halide and of nitrate increased, and the sum of halide + nitrate became 0.05 M greater inside than outside, which is about the same difference as is found in cells in normal sea water. In ordinary sea water the ratio of halide to nitrate is 80,000 to 1. When this was changed by substituting nitrate for halide so that the concentration of halide was 1.75 times that of nitrate the rate of entrance of halide was 1.68 times that of nitrate in 276 hours and the ratio of halide to nitrate in the sap decreased from 38 to 18.5. No halide came out in exchange for entering nitrate. The retention of chloride may well be due to the fact that even when the halide concentration of the sea water is reduced as low as 0.4 M, there is still an inwardly directed activity gradient of sodium chloride.