氮、钾、甜菜碱对水分胁迫下夏玉米叶片膜脂过氧化和保护酶活性的影响

采用盆栽试验研究了水分胁迫和适量供水条件下,氮、钾和甜菜碱对2种不同基因型夏玉米陕单9号（抗旱品种）和陕单911（不抗旱品种）各生育期叶片膜脂过氧化和保护酶活性的影响,旨在揭示这些因子通过提高上述酶活性而增强作物抗旱性的生理功能。结果表明,水分胁迫下夏玉米超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）活性显著降低,不抗旱品种更甚;而丙二醛(MDA)含量有不同程度升高,抗旱品种的MDA含量和变幅小于不抗旱品种。苗期2个品种对水分胁迫响应较弱,SOD、POD、CAT和MDA均较低;拔节和抽雄期响应强烈,酶活性增高。SOD和POD达到最大值的时间比CAT晚,MDA在全生育期中呈现“升—降—升”的变化规律。施用氮、钾肥和甜菜碱能不同程度地提高夏玉米SOD、POD和CAT活性,降低MDA含量,减缓水分胁迫下膜脂过氧化作用。不抗旱品种施用氮肥增强了水分胁迫条件下叶片SOD、POD、CAT活性,降低了MDA含量,氮肥用量的影响有显著差异;抗旱品种施用低氮效果显著,施用高氮则降低了生育前期酶活性,增加了MDA含量,但生育后期氮肥用量的影响间无显著区别。钾肥和甜菜碱对受水分胁迫的夏玉米表现出比氮肥更突出的效果。而对适量供水条件下的夏玉米,氮、钾肥的作用明显下降,甜菜碱的效果甚至消失。说明施用氮、钾肥和甜菜碱对改善水分胁迫下玉米叶片膜脂过氧化作用和提高保护酶活性有重要贡献。     

干旱胁迫对不同生态型大豆生理生化特征的影响

为了研究干旱胁迫对大豆生理生化特征和产量的影响,选用22份不同生态型大豆品种为研究材料,用盆栽称重法与大田试验结合的方法,研究花期不同生态型大豆抗旱生理生化特征。结果表明：干旱胁迫下,不同生态型大豆品种的叶片相对含水量、过氧化物酶(POD)、超氧化物歧化酶(SOD)活性、叶绿素a含量、总叶绿素含量和净光合速率都有一定程度的降低,与大豆品种的抗旱性均呈正相关,表现为抗旱性强的品种下降幅度较小,而抗旱性弱的品种下降幅度较大;而丙二醛含量、相对电导率和可溶性糖都有一定程度的增加,与抗旱性均呈极显著负相关,表现为抗旱性强的品种增加的幅度较小,而抗旱性弱的品种则相反;脯氨酸含量与抗旱性呈极显著正相关,表现为抗旱能力强的品种脯氨酸含量增加幅度大。这一结果说明,在干旱胁迫环境下,水分亏缺降低了大豆叶片相对含水量,膜脂过氧化伤害加重,引起丙二醛的累积,相对电导率升高,游离脯氨酸及可溶性糖含量升高,而丙二醛含量的升高导致保护酶活性降低,同时水分亏缺导致叶绿素含量降低,净光合速率下降,最终导致产量下降。     

脱落酸与水分胁迫下棉花幼苗水分关系及保护酶活性的影响

以晋棉21和抗虫棉99B为材料,研究了脱落酸处理的棉花幼苗,在聚乙二醇(PEG)6000不同渗透胁迫(0.5MPa,0.8MPa,1.1MPa)下,叶片相对含水量、渗透势、质膜透性以及超氧歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)变化。结果表明,脱落酸能减缓水分胁迫时期棉花叶片含水量的降低,提高叶片渗透势;两个品种的SOD、POD、CAT的活性都比未处理的高;且品种之间表现出明显的差异,晋棉21比抗虫棉99B膜脂过氧化程度低,减少了膜脂过氧化产物丙二醛(MDA)在叶片中的积累。表明脱落酸能增加棉花体内保护酶活性,降低膜脂过氧化作用,保护膜结构的完整性,减少水分胁迫的伤害,且晋棉21比抗虫棉抗水分胁迫能力强;同时表明抗虫棉与抗旱性没有相同的生理基础。     

甘薯膜脂过氧化作用和膜保护系统的变化与品种抗旱性的关系

张明生等对水分胁迫下甘薯叶片膜脂过氧化作用和膜保护系统变化进行了研究。结果表明，水分胁迫下不同甘薯品种叶片中Q2产生速率、丙二醛含量、超氧化物歧化酶和过氧化物酶活性、维C含量比对照均有明显增加；除少数抗旱性较强的品种外，其余品种过氧化氢酶活性比对照均有不同程度下降，但品种抗旱性愈强，其过氧化氢酶活性下降幅度愈小。Q2和丙二醛的相对值（占对照％）与品种抗旱性均呈极显著负相关，而超氧化物歧化酶、过氧化物酶、过氧化氢酶及维C的相对值与品种抗旱性均呈极显著正相。因此，这些指标可用于甘薯不同品种抗旱性的评定。     

稀土对水分胁迫下棉花幼苗膜脂过氧化作用的影响

稀二元素能明显增加聚已二醇(PEG)水分协迫下棉花叶片的相对含水量，减少水分的丢失，提高其保水能力。稀土处理的棉花叶片，超氧物歧化酶、过氧化物酶及过氧化氢酶活性增加，其中超氧物歧化酶活性与稀土浓度呈正相关。膜脂的过氧化声物丙二醛含量减少，质膜透性降低，提高了棉花的抗旱性。     

白刺对干旱胁迫的生理生化反应

研究白刺幼苗抗旱特性的生理学机制,期望为干旱农业生产提供理论依据。实验采用盆栽,用控制浇水的方法对不同强度的干旱胁迫梯度上对白刺幼苗叶片相对含水量、丙二醛、脯氨酸、可溶性蛋白质、叶绿素含量、超氧离子自由基产生速率和抗氧化酶活性的变化特点进行了研究。试验结果表明：在干旱胁迫下,白刺叶片相对含水量降低、脯氨酸含量呈增加趋势;可溶性蛋白质、叶绿素含量在轻度和中度干旱胁迫时上升,在重度干旱胁迫时显著下降;随着干旱胁迫的加剧,膜透性上升,丙二醛含量和超氧离子自由基产生速率增加。抗氧化系统酶活性测定结果表明,SOD、POD、CAT 3个酶能配合协同作用,降低膜脂过氧化程度,减少水分胁迫造成的伤害。     

低温对玉米光合作用、超氧物歧化酶活性和籽粒产量的影响

玉米在孕穗期和灌浆期,尤其是在孕穗期遇低温逆境会导致光合速率下降,光合有效叶面积降低,叶片和雌穗(或籽粒)超氧物歧化酶(SOD)活性下降、丙二醛含量剧增和相对电导率提高,造成低温冷害。孕穗期低温处理主要抑制了雌穗分化和发育,减少了穗粒数,灌浆期低温逆境主要影响了籽粒灌浆,致使百粒重下降,引起产量降低。     

施氮对干旱条件下晚稻产量与生理的影响

为探究干旱条件下氮素运筹对双季超级稻晚稻的影响。选用超级杂交晚稻品种五丰优T025,于幼穗分化期正常和干旱条件下,进行氮素蘖肥(干旱前)与氮素穗肥(干旱后)重施处理,考查产量及有关生理生态指标,结果表明:干旱将导致水稻产量显著下降,幼穗分化期是晚稻水分亏缺敏感期;2种水分条件下,氮素蘖肥重施产量均显著高于穗肥重施处理,分蘖期是晚稻需氮关键期;干旱条件下氮素蘖肥重施处理的单株有效穗数和结实率高于穗肥重施处理,差异均达显著水平;干旱条件下相对于氮素蘖肥重施处理,氮素穗肥重施处理抽穗期和开花期的光合速率(Pn)、蒸腾速率(Tr)等光合指标不同程度提高,但茎、叶部位氮素及干物质转运率低,滞留严重,转运至穗部的氮素相对较低,叶片渗透调节物质含量下降,丙二醛(MDA)含量生育后期提高,同时硝酸还原酶(NR)与谷丙转氨酶(GPT)等氮代谢酶活性在旱后短期内呈现增高趋势。因此,水稻上存在一定的"以氮调水"效应,适当提高氮素蘖肥可在一定程度上减轻晚稻穗分化期干旱胁迫造成的产量损失。     

甘蔗叶片衰老与膜脂过氧化

对甘蔗叶片衰老与膜脂过氧化关系进行的研究表明,在甘蔗叶片衰老过程中,伴随着膜脂过氧化产物丙二醛(MDA)含量的急剧上升,质膜透性迅速增大;膜脂过氧化防御酶超氧物歧化酶(SOD)活性和抗氧化物质抗坏血酸、还原型谷胱甘肽(GSH)等含量显著下降;组织自动氧化速率明显增大。可以认为,膜脂过氧化是甘蔗叶片衰老的重要原因之一。     

孕穗期干旱胁迫对超级稻剑叶部分生理指标及产量的影响

本研究以6个超级稻品种(组合)及1个耐旱常规稻品种为材料,在防雨棚内进行盆栽试验,研究了孕穗期干旱胁迫对超级稻剑叶部分生理指标及产量的影响。结果表明:孕穗期干旱胁迫处理使超级稻剑叶含糖量、脯氨酸及丙二醛含量均有显著或极显著增加,过氧化物酶、超氧化物歧化酶活性均极显著提高;有效穗及穗实粒数下降,千粒重提高;生物产量及经济产量均有不同程度的下降;Y两优2号、新两优6号、丰两优4号在正常灌溉及干旱处理条件下经济产量均位居前三位,且较其他品种产量提高均达极显著水平。建议,在安徽江淮丘陵区可以推广种植Y两优2号、新两优6号、丰两优4号。     

A note on the origin of Kalanchoë x vadensis Boom & Zeilinga (Crassulaceae)

Summary K x vadensis is a hybrid of K. blossfeldiana and K. marmorata obtained after doubling the number of chromosomes.     

Mechanisms and diversity of resistance to sorghum shoot fly,Atherigona soccata

Sorghum shoot fly, Atherigona soccata, is one of the important pests of postrainy season sorghums. Of the 90 sorghum genotypes evaluated for resistance to this pest, RHRB 12, ICSV 713, 25026, 93046 and 25027, IS 33844‐5, Giddi Maldandi and RVRT 3 exhibited resistance in postrainy season, while ICSB 463, Phule Anuradha, RHRB 19, Parbhani Moti, ICSV 705, PS 35805, IS 5480, 5622, 17726, 18368 and 34722, RVRT 1, ICSR 93031 and Dagidi Solapur showed resistance in rainy season, suggesting season‐specific expression of resistance to A. soccata. ICSB 461, ICSB 463, Phule Yasodha, M 35‐1, ICSV 700, 711, 25010, 25019 and 93089, IS 18662, Phule Vasudha, IS 18551 and 33844‐5 and Barsizoot had fewer deadhearts than plants with eggs across seasons, suggesting antibiosis as one of the resistance mechanism. Five genotypes exhibited resistance with high grain yield across seasons. Correlation, path and stepwise regression analyses indicated that leaf glossiness, seedling vigour, trichome density, oviposition and leaf sheath pigmentation were associated with the expression of resistance/susceptibility to shoot fly, and these can be used as marker traits to select and develop shoot fly‐resistant sorghums.     

Reaction of tritordeum to Fusarium culmorum and Septoria nodorum

Summary Hordeum chilense is a wild barley extensively used in wide crosses in the Triticeae. It could be a valuable source of resistance to Fusarium culmorum and Septoria nodorum. Some H. chilense x Triticum spp. amphiploids, named tritordeums, were more resistant than the parental wheat line to these diseases, others were not. Average contents of ergosterol and deoxynivalenol (DON) suggested that resistance to colonization by Fusarium was the highest for Hordeum chilense, followed by tritordeum and wheat in decreasing order. In particular, the H. chilense genotypes H7 and H17 enhanced the wheat resistance to F. culmorum in its tritordeum offsprings. Resistance to S. nodorum in tritordeum was not associated with tall plant height. There is sufficient genetic variation for resistance to F. culmorum and S. nodorum among tritordeum to allow the breeding of lines combining short straw and resistance to both diseases.     

Avoidance of leaf rust fungi in wild relatives of cultivated cereals

Summary Avoidance of rust fungi that was based on poor appressorium induction was previously found in Hordeum chilense. In the present study 95 accessions of Triticeae were screened for avoidance of Puccinia hordei. The percentage of appressorium formation per germinated spore ranged from 6 to 90%. On none of the 41 accessions of Aegilops, Agropyron, Elymus, Secale, Thinopyrum or Triticum studied was the rate of appressorium formation lower than 25%. Lower rates of appressorium formation were, however, found on accessions of wild barley species Hordeum brachyantherum, H. marinum, H. parodii and H. secalinum. Its implications in cereal breeding are discussed.     

Disease resistance in protected crops and mushrooms

Summary Cultivars of tomatoes, cucumbers, lettuce and peppers have been bred for resistance to one or more pathogens. Some tomato and cucumber cultivars have resistance to a wide range of diseases. Resistance has been transient in many cases and a succession of cultivars with new genes or new combinations of resistance genes has been necessary to maintain control. There has been a number of notable exceptions and these have included durable resistance to such pathogens asFulvia fulva and tomato mosaic virus. With lettuce the resistance situation is complicated by the occurrence of fungicide resistant pathotypes. There are no strains ofAgaricus bisporus purposely bred for disease resistance.In protected flower crops only resistance to Fusarium wilt in carnations has been purposely bred but differences in disease resistance are apparent in cultivars of many ornamental crops. This is particularly so in chrysanthemums where there are cultivars with resistance to many of the major pathogens. Similar situations occur with other flower crops and pot plants. Cultivars of some species have not been systematically investigated for resistance.The need for genetic resistance will increase with the further reduction, in the limits on pesticide use and an increasing public awareness and importance of pesticide pollution.ADAS is an executive agency of the Ministry of Agiculture, Fisheries and Food and the Welsh Office.     

Genetic constitution and diversity in four narrow endemic redwoods from the family Cupressaceae

The genetic constitution and diversity of four relictual redwoods are discussed in this review. These include monotypic genera of the family Cupressaceae: coast redwood (Sequoia sempervirens), giant sequoia (Sequoiadendron giganteum), dawn redwood (Metasequoia glyptostroboides), and alerce (Fitzroya cupressoides). All four species are narrow endemics, share a number of common phenotypic traits, including red wood, and are threatened species. Fossil history suggests that the ancestors of redwoods probably originated during the Cretaceous and Tertiary periods and flourished thereafter for millions of years. Towards the end of the Tertiary period began their decline and struggle for existence that continued during the subsequent geologic upheavals and climate changes, until the survival of the present-day redwoods in the current restricted locations in the world (USA, China, and South America). Although two species, Sequoiadendron and Metasequoia, are diploids (2n = 22), and the other two are polyploids: Fitzroya a tetraploid (2n = 4x = 44), and Sequoia a hexaploid (2n = 6x = 66); they all share the same basic chromosome number x = 11. The genome size in the hexaploid Sequoia is one of the largest (31,500 MB) in the conifers, while the genome sizes of diploid Metasequoia and Sequoiadendron are about one-third (~10,000 MB) of Sequoia. Genetic diversity in the redwoods is lower than most other gymnosperms, except in Sequoia, which seems to rank near the upper quarter of the coniferous forest trees. Genomic research is sparse in the redwoods, and should be pursued for a better understanding of their genome structure, function, and adaptive genetic diversity.     

Distribution,ecology and reproductive biology of wild tomatoes and related nightshades from the Atacama Desert region of northern Chile

Over the past 20 years, several expeditions were made to northern Chile to collect populations of wild tomatoes (Solanum chilense, S. peruvianum) and allied nightshades (S. lycopersicoides, S. sitiens), and obtain information about their geographic distribution, ecology and reproductive biology. Restricted mainly to drainages of the Andean and the coastal cordillera, populations are geographically fragmented. The two nightshade species are rare and threatened by human activities. Adaptation to extreme aridity and soil salinity are evident in S. chilense and S. sitiens (the latter exhibits several xerophytic traits not seen in the tomatoes) and to low temperatures in S. lycopersicoides and S. chilense. All tested accessions are self-incompatible, with the exception of one S. peruvianum population collected at the southern limit of its distribution. Several distinguishing reproductive traits—anther color, attachment, and dehiscence, pollen size, and flower scent—suggest S. sitiens and S. lycopersicoides attract different pollinators than S. chilense and S. peruvianum. The four Solanum spp. native or endemic to Chile provide a variety of novel traits which, through hybridization and introgression with cultivated tomato, could facilitate development of improved varieties, as well as research on a variety of basic topics, including plant-pollinator interactions, abiotic stress responses, and evolution of reproductive barriers.     

The induction in vitro of adventitious shoots in Rosa

Summary Adventitious shoots were formed on excised leaves, roots and callus of Rosa persica x xanthina and on excised leaves of R. laevigata and R. wichuraiana on culture media that included BAP and NAA as growth regulators. Shoots formed freely on freshly cultured callus of R. persica x xanthina but their production declined in successive cultures and ceased after twelve weeks. Transplantation to soil was improved by rooting plantlets in cellulose plugs in vitro and transferring plantlets to soil while still in the plugs.     

The exploration of genetic resources of Portuguese cabbage and kale for resistance to several Brassica diseases

Summary Twenty three accessions of nine Portuguese cabbage and kale land races from different geographic origins were tested at the seedling stage for resistance to several important brassica diseases. Resistance to downy mildew (Peronospora parasitica), expressed as necrosis of the cotyledon mesophyll, was found in all the accessions. Type A resistance to cabbage yellows (Fusarium oxysporum f. sp. conglutinans race 1) was present in most of the landraces. Resistance to clubroot (Plasmodiophora brassicae race 6) was found in one accession of the Portuguese tree kale. High resistance to blackleg (Leptosphaeria maculans) and white rust (Albuco candida) was not detected, although several accessions showed 20 to 30% of plants with intermediate expression of resistance. All Portuguese cole accessions were susceptible to blackrot (Xanthomonas campestris pv. campestris).     

Production and characterization of intergeneric diploid cybrids derived from symmetric fusion between Microcitrus papuana Swingle and sour orange (Citrus aurantium)

Plants were regenerated from intergeneric somatic hybridization between embryogenic protoplasts of Microcitrus papuana Swingle and leaf-derived protoplasts of sour orange (Citrus aurantium L.) via electrofusion. The regenerated plants were morphologically similar to the leaf parent in growth vigor, leaf and branch structure. FCM analysis showed that they were diploids. Simple-sequence-repeat (SSR) and cleaved-amplified-polymorphic-sequence(CAPS) were employed for hybridity characterization. SSR banding patterns of the regenerated plants were identical to the leaf parent, sour orange, indicating that they possessed nuclear component derived from sour orange. DNA amplification with chloroplast and mitochondrial universal primers, followed by restriction endonuclease digestion, revealed polymorphism between the fusion parents. Therefore, this method was used to determine the cytoplasmic compositions of the regenerated plants. Banding patterns for all the polymorphic primer/enzyme combinations of the regenerated plants were similar to those of the embryogenic parent, M. papuana, suggesting that only the cytoplasmic components derived from the embryogenic parent were present in the regenerated plants. FCM, SSR and CAPS demonstrated that intergeneric diploid cybrids have been successfully obtained by symmetric fusion. Related results concerning nuclear and cytoplasmic composition of previous diploid somatic hybrids and potential mechanism for regeneration of such kind of plants are discussed herein. This revised version was published online in July 2006 with corrections to the Cover Date.