Crop traits and the tolerance of wheat and barley to foliar disease

The relationship between yield loss and disease severity can differ widely between crops. This has given rise to the concept of disease tolerance, with some crops exhibiting a smaller yield loss under a given severity of disease than others. Genetic improvement to minimise yield loss under disease is an attractive goal, as it exerts little or no selection pressure on pathogen populations, and could form a useful component of durable disease management programmes. However, progress towards this end requires a thorough understanding of the phenotypic traits that influence the response of yield to disease, their genetic control and the possible trade-offs involved with other desirable agronomic characteristics. This paper examines the candidate crop traits that may confer tolerance of foliar disease in wheat and barley and reviews evidence of genetic variation in their expression. In wheat grown under the relatively low light conditions of North-West Europe, post-anthesis source (assimilate supply) and grain sink capacity (capacity for dry matter accumulation) appear to be closely balanced. Traits associated with maintaining post-anthesis radiation interception and radiation use efficiency in spite of disease may confer tolerance. The most promising traits include a larger flag leaf and compensatory increases in photosynthetic rate in non-infected parts of leaves. In barley, yield is often more strongly sink limited, and early-season disease management is required to protect the formation of potential grain sites. A wider range of potential traits may influence tolerance including compensatory adjustments in leaf growth and morphology, and differences in the sensitivity of tiller and spikelet mortality to photoassimilate supply. Different methods for quantifying tolerance are suggested depending on the trait of interest.     

The regulation of xanthophyll cycle activity and of non-photochemical fluorescence quenching by two alternative electron flows in the diatoms Phaeodactylum tricornutum and Cyclotella meneghiniana

Intact cells of diatoms are characterized by a rapid diatoxanthin epoxidation during low light periods following high light illumination while epoxidation is severely restricted in phases of complete darkness. The present study shows that rapid diatoxanthin epoxidation is dependent on the availability of the cofactor of diatoxanthin epoxidase, NADPH, which cannot be generated in darkness due to the inactivity of PSI. In the diatom Phaeodactylum tricornutum, NADPH production during low light is dependent on PSII activity, and addition of DCMU consequently abolishes diatoxanthin epoxidation. In contrast to P. tricornutum, DCMU does not affect diatoxanthin epoxidation in Cyclotella meneghiniana, which shows the same rapid epoxidation in low light both in the absence or presence of DCMU. Measurements of the reduction state of the PQ pool and PSI activity indicate that, in the presence of DCMU, NADPH production in C. meneghiniana occurs via alternative electron transport, which includes electron donation from the chloroplast stroma to the PQ pool and, in a second step, from PQ to PSI. Similar electron flow to PQ is also observed during high light illumination of DCMU-treated P. tricornutum cells. In contrast to C. meneghiniana, the electrons are not directed to PSI, but most likely to a plastoquinone oxidase. This chlororespiratory electron transport leads to the establishment of an uncoupler-sensitive proton gradient in the presence of DCMU, which induces diadinoxanthin de-epoxidation and NPQ. In C. meneghiniana, electron flow to the plastoquinone oxidase is restricted, and consequently, diadinoxanthin de-epoxidation and NPQ is not observed after addition of DCMU.     

Formation of chromosome aberrations in androgenetic rainbow trout Oncorhynchus mykiss

Residues of maternal nuclear DNA in the form of chromosome fragments were observed in the healthy and morphologically normal androgenetic rainbow trout Oncorhynchus mykiss. A hypothetical model for formation of chromosome re‐arrangements caused by the incomplete maternal nuclear DNA inactivation in the androgenetic rainbow trout was proposed in the present paper.     

Recovery from a near-lethal exposure to ultraviolet-C radiation in a scleractinian coral

Hermatypic (reef building) corals live in an environment characterized by high ambient levels of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR). Photoadaptive mechanisms have evolved to protect the sensitive cell structures of the host coral and their photosynthetic, endosymbiotic zooxanthellae. Environmental stressors may destabilize the coral-zooxanthellae system resulting in the expulsion of zooxanthellae and/or loss of photosynthetic pigment within zooxanthellae, causing a condition known as bleaching. It is estimated that 1% of the world’s coral population is lost yearly, partly due to bleaching. Despite intensive research efforts, a single unified mechanism cannot explain this phenomenon. Although UVA and UVB cellular damage is well documented, UVC damage is rarely reported due to its almost complete absorption in the stratosphere. A small scale coral propagation system at the University of Maine was accidentally exposed to 15.5 h of UVC radiation (253.7 nm) from a G15T8 germicidal lamp, resulting in a cumulative surface irradiance of 8.39 × 10⁴ J m⁻². An experiment was designed to monitor the progression of UVC induced damage. Branch sections from affected scleractinian corals, Acropora yongei and Acropora formosa were submitted to histopathology to provide an historical record of tissue response. The death of gastrodermal cells and necrosis resulted in the release of intracellular zooxanthellae into the gastrovascular canals. Zooxanthellae were also injured as evidenced by pale coloration, increased vacuolization and loss of membrane integrity. The recovery of damaged coral tissue likely proceeds by re-epithelialization and zooxanthellae repopulation of gastrodermal cells by adjacent healthy tissue.     

Protective Effect of Rare Earth Against Oxidative Stress Under Ultraviolet-B Radiation

The effects of lanthanum (III) (La(III)) in protecting soybean leaves against oxidative stress induced by ultraviolet-B (UV-B) radiation were investigated. The increase in contents of hydrogen peroxide (H₂O₂) and superoxide () due to UV-B radiation suggested oxidative stress. The increase in the content of malondialdehyde (MDA) and the decrease in the index of unsaturated fatty acid (IUFA) indicated oxidative damage on cell membrane induced by UV-B radiation. La(III) partially reversed UV-B-radiation-induced damage of plant growth. The reduction in the contents of H₂O₂, , and MDA and increase in the content of IUFA, compared with UV-B treatment, also indicated that La(III) alleviated the oxidative damage induced by UV-B radiation. The increase in the activities of superoxide dismutase and peroxidase and the contents of ascorbate, carotinoids, and flavonoids were observed in soybean leaves with La(III) + UV-B treatment, compared with UV-B treatment. Our data suggested that La(III) could protect soybean plants from UV-B-radiation-induced oxidative stress by reacting with reactive oxygen species directly or by improving the defense system of plants.     

Differential response of leaf gas exchange to enhanced ultraviolet-B (UV-B) radiation in three species of herbaceous climbingplants

We measured diurnal changes in photosynthetic rate, transpiration rate, stomatal conductance and water use efficiency in three species of herbaceous climbing plants (Luffa cylindrica, Trichosanthes kirilowii and Dioscorea opposita) exposed to two intensities of UV-B radiation: 3.0 μw cm^?2 (R1) and 8.0 μw cm^?2 UV-B (R2) radiation under ambient growth conditions. Responses differed per species and per treatment. In Luffa all values increased compared to the Control in both treatments, except for stomatal conductance in R2. In Trichosanthes photosynthetic rates and water use efficiency increased, while the transpiration rates decreased under both treatments, and stomatal conductance was lower in R1. In Dioscorea photosynthetic rates and water use efficiency decreased under both treatments, while the transpiration rates and stomatal conductance increased. The results suggested that to some extent increased UV-B radiation was beneficial to the growth of L. cylindrica and T. kirilowii, but detrimental to D. opposita.     

小珊瑚藻对赤潮异弯藻的克生效应及其 对UV-B辐射增强的响应

通过共培养方法,以细胞密度为主要测定指标,研究了小珊瑚藻对赤潮异弯藻的克生效应及其对UV-B辐射增强的响应.结果表明：小珊瑚藻的新鲜组织和水溶性抽提液对赤潮异弯藻的生长表现出显著的抑制作用(P＜0.05),说明小珊瑚藻对赤潮异弯藻具有克生效应;而小珊瑚藻干粉末和培养水过滤液对赤潮异弯藻生长则无明显影响(P>0.05).将小珊瑚藻用不同剂量的UV-B辐射预处理后,再与赤潮异弯藻共培养,除培养水过滤液外,其新鲜组织、干粉末和水溶性抽提液对赤潮异弯藻生长的作用效果均有所改变,高剂量(3.0 J·m^-2)UV-B辐射使小珊瑚藻对赤潮异弯藻的抑制作用减弱(P＜0.05),而低剂量(0.9 J·m^-2) UV-B辐射则使抑制作用增强(P＜0.05).     

大豆异黄酮对电离辐射小鼠淋巴细胞的防护作用

目的研究大豆异黄酮(SI)对小鼠淋巴细胞的辐射防护作用。方法24只雄性昆明小鼠,随机分为正常对照组、辐射对照组和辐射补充0.5%SI组,喂养2周后,4.0Gy照射。照射后24 h处死小鼠,取血、胸腺和脾脏分离淋巴细胞,进行血淋巴细胞计数、观察DNA损伤情况;培养胸腺和脾脏淋巴细胞,检测3H-dT掺入量,观察淋巴细胞的增殖能力,计算淋巴细胞的增殖指数。结果辐射使小鼠胸腺和脾脏淋巴细胞数明显减少、胸腺淋巴细胞增殖能力和脾脏淋巴细胞转化指数降低、血淋巴细胞DNA损伤增加,这些变化均具有统计学意义;补充SI可降低胸腺和脾脏淋巴细胞数的减少幅度,降低胸腺淋巴细胞增殖能力和脾脏淋巴细胞转化指数下降幅度,减少辐射对血淋巴细胞DNA损伤程度,其中SI对胸腺淋巴细胞增殖能力和对血淋巴细胞DNA损伤程度的防护作用与辐射对照组相比有统计学意义。结论大豆异黄酮可对小鼠的血、胸腺和脾脏淋巴细胞有一定的辐射防护作用。     

~(60)Co诱变大豆后代农艺性状的研究

用60Co对晋豆24号进行辐射处理,对诱变后代M4、M5代16个主要农艺性状进行主成分分析,将与产量密切相关的各项指标转化成"单株产量构成"因子、"株型和粒型"因子和"粒重"因子等三大主成分.以M5代春播群体为代表进行的聚类分析将后代分为高产、中产和低产三类,确定"单株产量构成"因子(第一主成分)为影响大豆产量的主导因素.