Diurnal changes in phosphoenolpyruvate carboxylase and pyruvate, orthophosphate dikinase properties in the natural environment: interplay of light and temperature in a C4 thermophile

Activities of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) were measured in leaf extracts of field grown Amaranthus paniculatus L. (C₄) during a natural diurnal irradiance and temperature pattern. Enzyme assays were run at both fixed (30°C) and the corresponding leaf temperature at the time of harvest. Light activation of PEP carboxylase (PEPCase) at fixed assay temperatures was expressed as a decrease in S_0–5 (PEP) after a threshold (> 330 μmol m^–2 s^–1) photon fluence rate was surpassed at noon. Earlier in the morning, increase in apparent enzyme affinity for PEP was observed when the assay was run at leaf temperature, indicating a physiologically meaningfull effect of temperature on S^0.5 (PEP). The 3.3-fold increase in PEPCase activity at low PEP and fixed assay temperature between the minimal and maximal irradiance and temperature hours of the day, became 12.8-, 11.5- and 7.4-fold when assays were run at the corresponding leaf temperature during three diurnal cycles with respective temperature differences (max minus min) of 9.0, 8.3 and 7.4°C. The extent of malate inhibition was the same for both day and night forms of PEPCase assayed at 35°C, but increased considerably with night enzyme at 25°C. The results indicate that light increases the apparent affinity of PEPCase for PEP and that at lower temperatures malate becomes more inhibitory. Pyruvate orthophosphate dikinase activity started to increase immediately after sunrise and the 10-fold increase at fixed temperature became 14.8-, 14.2- and 13.1-fold when assays were run at the above leaf temperatures. This indicates that the light effect predominates with pyruvate, orthophosphate dikinase, while with phosphoenolpyravate carboxylase, light and temperature co-operate to increase the day enzyme activities.     

玉米根微粒体ABA结合蛋白的性质及逆境胁迫的影响

以玉米根微粒体为材料进行的微量放射配体结合（ＭＲＬＢ）实验表明玉米根微粒体膜上存在着ＡＢＡ结合位点,ＡＢＡ与ＡＢＡ结合蛋白（ＡＢＡ－ＢＰ）结合的最适ｐＨ为６．５,结合反应对温度（０℃和２５℃）不太敏感,ＡＢＡ与ＡＢＡ－ＢＰ的结合反应是一个动态平衡过程,５ｍｉｎ即可达最大结合（Ｂｍａｘ）的５０％,３０ｍｉｎ达到最大结合,１ｈ内基本保持不变。胰蛋白酶处理表明此结合位点为蛋白质,冻融实验则表明此蛋白与ＡＢＡ的结合不仅要求其自身具有特定构象而且需要有一定的膜脂环境,ＤＴＴ处理实验结果显示ＡＢＡ－ＢＰ中可能存在着二硫键。逆境处理可以提高玉米根微粒体膜对ＡＢＡ的结合活性,盐胁迫、渗透胁迫、干旱胁迫和热冲激处理分别使结合活性上升３４．９％、１７．８％、２３．１％和１３．３％。     

面向21世纪的中国生态学

面向２１世纪的中国生态学陈涛（中国科学院沈阳应用生态研究所,１１００１５）ＥｃｏｌｏｇｙＴｏｗａｒｄｓ２１ｓｔＣｅｎｔｕｒｙｉｎＣｈｉｎａ．ＣｈｅｎＴａｏ（ＩｎｓｔｉｔｕｔｅｏｆＡｐｐｌｉｅｄＥｃｏｌｏｇｙ,ＣｈｉｎｅｓｅＡｃａｄｅｍｙｏｆＳｃｉｅｎ...     

Choice of selection environment for improving crop yields in saline areas

Spatial variability in salt-affected fields is normally very high. Thus, most salinity affected lands are actually comprised of many micro-environments, ranging from low to high salinity in the same field. The evidence on testing genotypes across a broad range of salinity levels shows that the genotype-by-salinity level interaction is commonly large. Thus, breeding for saline areas can be compared to what has been known as breeding for wide adaptation. The target environments both for breeding for saline soils or for wide adaptation are actually a population of many possible environments, for which there exists a significant component of genotype-by-environment(G x E) interaction. Thus it is possible to study the merit of potential strategies for breeding for salinity tolerance using the tools that have been developed for the study of breeding for wide adaptation. The evidence from selection and breeding experiments for wide adaptation seems to favour testing on a representative subset of environments, including stress and non-stress locations; but the choice of these locations is complicated by the multidimensional nature of G x E. However, in the case of salt stress, the crop-yield response functions to salinity are well known. This paper presents an attempt to systematise the choice of the optimum environment(s) to select for improved yield under saline soil conditions, based on the three-piece linear equation presented by Maas and Hoffman (1977) and the theory of direct and indirect responses to selection. It is proposed that three saline levels should be enough to make a valid estimation of the suitability of a number of selection strategies. A worked example with data from a set of grain sorghum inbred lines tested on ten saline levels shows that the same selection strategies would be chosen using the information from the ten saline levels as that obtained using the two extremes and one intermediate level.     

A comparison of rooting environments in containers of different sizes

Experiments on plants are often carried out in growth chambers or greenhouses which necessitate the use of an artificial rooting environment, though this is seldom characterized in detail. Measurements were made to compare the rooting environment in large boxes (0.25 m³) with that in small pots (0.19, 0.55 and 1.90 dm³) in naturally lit chambers. Diurnal temperature fluctuations of 14.6, 11.6 and 7.7°C occurred in the post compared with only 1.9°C in the boxes. Soil drying to a matric potential of-50 kPa was approximately 25 times faster in the pots. The mean heights of 2 year old Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings grown throughout their second growing season in the three sizes of pots were 38, 62 and 92% of the mean height of those grown in the boxes. Soil solution nutrient concentrations in the boxes were considerably increased by soil drying, an aspect which seems to have received little attention in experiments involving artificially imposed drought. An alternative system of constraining the roots of individual plants within nylon fabric bags, embedded in larger volumes of soil, to facilitate harvesting of complete root systems is described. The importance of the rooting environment in determining the outcome of physiological experiments is also briefly discussed.     

Changes in spatial distribution during the life history of a tropical tree,Scaphium macropodum (Sterculiaceae) in borneo

We studied the spatial distribution of fruits and plants, mortality and growth rates ofScaphium macropodum (Sterculiaceae) in four 1-ha plots in a tropical rain forest in West Kalimantan, Indonesia. The species is a large deciduous tree and produces wind-dispersed fruits on defoliated twigs. The density of dispersed fruits on the ground decreased with increasing distance from a parent tree. The area under the parent's crown had the highest density of the fruits and the highest mortality of the seedlings immediately after germination. Consequently, the density of the established seedlings peaked 14 m from the tree which is outside its crown. Thick litter mainly from the parent tree seemed to physically prevent the seedlings' root from reaching the soil surface and caused the high mortality. Juvenile and mature trees distributed exclusively, suggesting that regeneration is the most successful outside of the crown of mature trees. Saplings under canopy shade did not grow well.Scaphium macropodum is hypothesized to require a gap for seedling growth and successful regeneration, whereas it can germinate and last under closed canopies as suppressed seedlings or saplings.     

Defenses against oxidative stress in the Antarctic scallop Adamussium colbecki and effects of acute exposure to metals

Since a general pathway of toxicity induced bypollutants is the enhancement of reactive oxygenspecies, biochemical responses associated withvariations in the antioxidant cellular system havebeen often proposed as biomarkers ofpollutant-mediated toxicity associated with oxidativestress. Antarctic organisms live in an extremeenvironment characterized by low water temperature,high level of dissolved oxygen, presence of ice andstrong seasonal changes in light intensity andavailability of food, conditions which could influenceboth the formation of reactive oxygen species and themechanisms for their removal. In this respect andconsidering the utility of this as a key species formonitoring marine Antarctic environment it was ofinterest to investigate the antioxidant defense systemof the scallop Adamussium colbecki.The parameters examined in the digestive gland of thescallop were the concentration of glutathione and theactivity of several glutathione dependent andantioxidant enzymes (glyoxalase I and II, glutathioneS-transferases, glutathione peroxidases, glutathionereductase, catalase, superoxide dismutase). Very highlevels of catalase suggest a possible adaptation toAntarctic extreme conditions, while the highactivities of glutathione S-transferases are moreprobably related to the feeding behavior of Pectinids.Enzymes from Adamussium colbecki generallyappeared to be active at low temperatures but, with afew exceptions, their activities increased with risingtemperature. Exposure of A. colbecki tosublethal concentrations of Cu or Hg resulted in asignificant reduction in the levels of totalglutathione and in the activity of catalase andglutathione S-transferases. Antioxidant responses ofA. colbecki could represent a useful tool inassessing the biological impact of environmentalpollutants in the Antarctic ecosystems.     

洪湖生态环境的化学结构

本文探讨了化学元素在洪湖水、植物、沉积物中的分布,在此基础上分析了水生植物对元素的吸收特征及元素在生态系统中的贮存和迁移规律。指出湖水中Ｃａ￣（２＋）和是主要的阳离子和阴离子,湖水酸容纳能力在１．２×１０￣（－３）－２．０×１０￣（－３）ｍｏｌ／ｌＨ￣＋之间,水化学的稳定性受到碳酸盐地球化学平衡过程的控制;湖中水生植物具有富集Ｃ、Ｎ、Ｋ、Ｃａ和Ｃｄ的性质,并导致这些元素在沉积物表层集累;系统中Ｃ多存在于植物体中,Ｎ、Ｐ、Ｋ、Ｃａ和Ｍｇ多存在于沉积物中,沉积物分室是营养元素主要的贮存库。