CO2, light and temperature influence senescence and protein degradation in wheat leaf segments

Effects of environmental conditions influencing photosynthesis and photorespiration on senescence and net protein degradation were investigated in segments from the first leaf of young wheat ( Triticum aestivum L. cv. Arina) plants. The segments were floated on H₂O at 25, 30 or 35°C in continuous light (PAR: 50 or 150 µmol m⁻² s⁻¹) in ambient air and in CO₂‐depleted air. Stromal enzymes, including phosphoglycolate phosphatase, glutamine synthetase, ferredoxin‐dependent glutamate synthase, phosphoribulokinase, and the peroxisomal enzyme, glycolate oxidase, were detected by SDS‐PAGE followed by immunoblotting with specific antibodies. In general, the net degradation of proteins and chlorophylls was delayed in CO₂‐depleted air. However, little effect of CO₂ on protein degradation was observed at 25°C under the lower level of irradiance. The senescence retardation by the removal of CO₂ was most pronounced at 30°C and at the higher irradiance. The stromal enzymes declined in a coordinated manner. Immunoreactive fragments from the degraded polypeptides were in most cases not detectable. However, an insolubilized fragment of glycolate oxidase accumulated in vivo, especially at 25°C in the presence of CO₂. Detection of this fragment was minimal after incubation at 30°C and completely absent on blots from segments kept at 35°C. In CO₂‐depleted air, the fragment was only weakly detectable after incubation at 25°C. The results from these investigations indicate that environmental conditions that influence photosynthesis may interfere with senescence and protein catabolism in wheat leaves.     

不同栽培模式对冬小麦-夏玉米轮作系统产量、氮素累积和平衡的影响

以河北山前平原区秸秆还田条件下小麦-玉米轮作体系为研究对象,设置农民习惯、高产高效、再高产和再高产高效4个模式,通过定位试验探讨各栽培模式对3个轮作周期作物产量、土壤硝态氮累积量及氮平衡的影响.结果表明: 小麦、玉米产量均以再高产模式最高,高产高效和再高产高效模式次之,均显著高于农民习惯模式;小麦季和玉米季氮肥利用效率(PFP)均以高产高效模式最高,显著高于其他模式;0～400 cm土体硝态氮累积量在 768.4～1133.3 kg·hm^-2之间,其中80%～85%累积在根下90～400 cm土层;4种模式的土壤硝态氮均有明显向下淋移现象,120～150 cm和270～330 cm处均出现了累积峰,以270～330 cm土层硝态氮累积量最大;高产高效模式的土壤硝态氮含量整体水平均低于其他模式,浓度基本维持在30 mg·kg^-1以下,在一定程度上能有效缓解环境压力;冬小麦季0～90 cm土体氮素盈余量均小于夏玉米季,并以高产高效模式的氮素表观损失量最低,显著低于其他模式.综合考虑产量、氮肥利用效率、硝态氮累积和氮平衡,以高产高效模式表现最优,但还有一定的提升空间.     

Population genetics and reproductive strategies of two Notostraca (Crustacea) species from winter ponds in Israel

Fluorescent-amplified fragment length polymorphism (FAFLP) fingerprinting assay was used to compare the genetic diversity within and between tadpole shrimps (Notostraca) populations of Lepidurus apus (n=7) and Triops cancriformis (n=2) from rain pools in Israel. Each ephemeral water body has revealed a unique fingerprint pattern with an entailed genetic drift between nearby ponds. High similarity of genotypic diversity within each geographic area led to three clusters of water bodies, north, south and center of Israel. FAFLP assays on several newly hatched individuals of T. cancriformis revealed high identity amongst kin, as compared to L. apus where newly hatched from the same maternal source showed high diversity. Results indicate that T. cancriformis populations from Israel are probably parthenogenetic as indicated by clonal structures. The higher genetic variability in the L. apus populations and in laboratory-hatched specimens indicates the existence of sexual reproduction.     

Resistance of cold-hardened winter rye leaves (Secale cereale L.) to photo-oxidative stress

Catalase and photosystem II (PSII) were strongly inactivated during exposure to 4 °C and moderate light in 22 °C-grown non-hardened leaves (NHL) of winter rye (Secale cereale L.), but highly resistant to photo-inactivation at low temperature in 4 °C-grown cold-hardened leaves (CHL). Resistance of CHL to chilling-induced photo-inactivation of catalase and PSII depended partially on more efficient de novo synthesis at 4 °C and partially on improved protection. Lower rates of chloroplast-mediated inactivation of catalase in vitro indicated that less reactive oxygen was released by chloroplasts from CHL than by chloroplasts from NHL. The contents of xanthophyll cycle carotenoids, α-tocopherol, ascorbate, glutathione, the activities of superoxide dismutase and glutathione reductase, and the tolerance against paraquat-induced photo-oxidative damage were greatly increased in CHL, relative to NHL. Zeaxanthin-related thermal energy dissipation was only of minor importance for paraquat-tolerance and protection of catalase in CHL. When CHL were transferred to a higher temperature of 22 °C the increased resistance to photo-inactivation of catalase and PSII and the increased paraquat-tolerance were largely lost within 3 d, whereas most non-enzymic and enzymic antioxidants retained higher levels than in NHL. The decline of resistance to photodamage during dehardening was not related to concomitant changes of antioxidants or antioxidative enzymes.     

The effect of increased deposition of atmospheric nitrogen on Calluna vulgaris in upland Britain

Regular (monthly) additions of NH₄NO₃ (4–12 g N m⁻² yr⁻¹) were made over a period of 8 yr (1989–98) to areas of moorland in North Wales dominated by the ericaceous shrub Calluna vulgaris . Results from the early stages of the experiment (1990–94) have shown marked and dose-related increases in shoot extension and canopy height in response to the nitrogen treatments, with significantly higher shoot nitrogen contents. The nitrogen-related stimulation in the growth of the C. vulgaris canopy over this period has resulted in large accumulations of litter on the high-nitrogen-treated plots (6.6 kg m⁻² in plots treated with 12 g N m⁻² yr⁻¹, compared with 3.8 kg m⁻² for the water controls). Litter nitrogen concentrations were also significantly increased at the higher rates of nitrogen addition, leading to a doubling of the total return of nitrogen to the litter layer over the experimental period. These changes in vegetation structure were associated with large reductions in the abundance of the bryophyte and lichen species normally present under the untreated canopy. Results since 1994, however, show little increase in shoot extension in response to the nitrogen treatments, with no clear dose response to increasing levels of addition. These findings are associated with a dose-related increase in the susceptibility of the nitrogen-treated areas of the C. vulgaris canopy to late winter injury, characterized as browning of the shoot tips in early to late spring. These results indicate that deleterious effects are now accumulating as a result of the long-term addition of nitrogen to these moorland plots.     

Short-term immobilisation and crop uptake of fertiliser nitrogen applied to winter wheat: effect of date of application in spring

Previous studies on the fate of fertiliser nitrogen applied to winter wheat in temperate climates have shown that nitrogen (N) applied early, at tillering for wheat, was less efficiently taken up than N applied later in the growth cycle. We examined the extent to which the soil microbial N immobilisation varied during the wheat spring growth cycle and how microbial immobilisation and plant uptake competed for nitrogen. We set up a pulse-15N labelled field experiment in which N was applied at eight development stages from tillering (beginning of March) to anthesis (mid-June). Each application was 50 kg N ha-1 as 15N labelled urea except for the first application which was 25 kg N ha-1. The distribution of fertiliser 15N in shoots, roots, mineral and organic soil N was examined by destructive sampling 7 and 14 days after each 15N pulse. The inorganic 15N pool was almost depleted by day 14. The N uptake efficiency increased with later applications from 45% at tillering to 65% at flowering. N immobilisation was rather constant at 13–16% of N applied, whatever the date of application. The increase in plant 15N uptake resulted in an increase in the total 15N recovery in the plant-soil system (15N in soil +15N in plant), suggesting that gaseous losses were lower at the later application dates.     

Changes of Chlorophyll Metabolism During the Albinic Stage of a Wheat Mutant

Changes of chlorophyll metabolism during the albinic stage including both degreening and regreening processes were studied. The results indicated that an decrease of Cato content was nor the cause of mutant degreening, and that the mutant belonged to the total Chl-dificient type. The changes of Chlase activity level indicated that Chi breakdown was not the main factor which led to degreen of the mutant. A greater changes of content of intermediates of Chl biosynthesis during the albinic period δ-aminolevulinic acid (ALA) and porphohilinogen (PBG) were accumulated, but uroporphyrin Ⅲ (Uro Ⅲ ), protoporphyrin IX (Proto IX ), Mg-protoporphyrin IX (Mg-Proto IX ) and protochlorophyll (ide) (Pchl (lide)) were decreased. Specialy during the degreening process Uro Ⅲ was gradually decreased, but an initiation of regreening, the Uro Ⅲ was markedly accmulated. It was proved that there was a blockage in Chi biosynthesis in the mutant, which could be somewhere in the formation of uroporphyrinogen Ⅲ (Urogen Ⅲ ).     

加拿大B.C.省中部亚北方未成熟小杆松林生态学及高生长分析

本文研究了小杆松(PinuscontortaDougl.exLoud.)高生长与生态立地质量(ecologicalsitequality)间的关系.用生物地理气候生态系统分类(biogeoclimaticecosystemclassification)方法和数量方法分析了植被、环境和林分数据,这些数据是从在B.C.省中部具有山地北方气候以及广泛的土壤水分和养分条件的72块样地中获得的.