水稻剑叶气孔性状与孕穗期耐冷性的关系研究

以人工气候室鉴定的孕穗期耐冷性不同的10个水稻品种为材料,采用扫描电子显微镜观测其剑叶的气孔密度、气孔大小和单位面积气孔周长等性状特点,以探讨水稻剑叶气孔性状与孕穗期耐冷性的关系.结果表明:耐冷性强品种'培杂软香'、'天优688'、'冈优825' 的气孔密度和单位叶面积气孔总周长较小,分别为380～410个/mm2和29.8～32.6 cm;耐冷性弱的品种'粤杂763'气孔密度和单位叶面积气孔总周长较大,分别为618个/mm~2和46.9 cm; 耐冷性中等的品种'培杂泰丰'等介于二者之间,分别为460～510个/mm~2和35.1～39.3 cm.气孔密度相近时,气孔较大的品种耐冷性较弱;单位叶面积气孔总周长相近时,气孔密度大的品种耐冷性较弱.研究发现,水稻品种剑叶的气孔密度和单位叶面积气孔总周长与其孕穗期耐冷性均呈极显著正相关,可以作为水稻孕穗期耐冷性的鉴定指标.     

In vitro screening for burrowing nematode, Radopholus citrophilus, tolerance and resistance in commercial Anthurium hybrids

Summary A reliable method to screen Anthurium for burrowing nematode resistance and tolerance in vitro was developed using 17 genetically distinct Anthurium cultivars. Based on nonparametric data analysis, tolerance and resistance were found to be independent traits to be evaluated separately. An effective parameter for tolerance evaluation was ranking of relative leaf retention, whereas an effective parameter for resistance evaluation was the ranking of nematode reproduction, log(Rf+1). A comparison of the ranking of leaf retention with ranking of nematode reproduction clustered the cultivar responses to burrowing nematode infection into four groups: intolerant and resistant, moderately tolerant but susceptible, intolerant and susceptible, and tolerant and susceptible. ‘Ozaki’ was identified as an intolerant reference, ‘Nitta’ as a susceptible reference. ‘Blushing Bride’ was the most tolerant cultivar among those screened, but it may not be an ideal tolerant reference due to its low vigor. Future screening for burrowing nematode-tolerant and-resistant cultivars in Anthurium should include ‘Ozaki’ and ‘Nitta’ as internal controls. Evaluation of resistance should be based on a resistance index obtained by log(Rf of hybrid tested +1) divided by log(Rf of ‘Nitta’ +1); tolerance should be based on ranking of relative leaf retention.     

The activity of antioxidative enzymes,contents of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and of ascorbate in tomato leaves of cultivars more or less sensitive to infection with <Emphasis Type="Italic">Botrytis cinerea</Emphasis>

The aim of the present studies was to compare H₂O₂ and ascorbate contents as well as peroxidase (PO) and catalase (CAT) activities in leaves of less susceptible cultivar Perkoz and more susceptible Corindo after B. cinerea infection. Increase in H₂O₂ contents in both Perkoz and Corindo cytosol was observed, however, it appeared earlier in the less susceptible cultivar. The increase in PO activity in the cytosol fraction was observed 48 hours after infection in both cultivars but it was greater in the less susceptible Perkoz. No significant differences between the tested cultivars were observed in ascorbate peroxidase (APX) activity and in reduced and oxidated ascorbate contents. PO activity was thoroughly analyzed in the apoplast fraction. It was measured with syringaldazine (S), tetramethylbenzidine (TMB) and ferulic acid (FA)—substrates characteristic of isoenzymes involved in lignification and stiffening of a cell wall. Increase in PO activity with these substrates was observed earlier in cultivar Perkoz than in cultivar Corindo. Similarly, increase in PO activity with NADH appeared significantly earlier in cultivar Perkoz. Apoplastic PO was separated with DEAE Sepharose and two fractions binding and non-binding were obtained. Binding PO fraction was significantly more active especially with S, TMB and NADH after B. cinerea infection. The increase in the enzyme activity was mostly observed in cultivar Perkoz. Binding PO was separated by electrophoresis on acrylamide gel and revealed six enzymatic forms from which three were much more active after infection in cultivar Perkoz. The obtained results suggest that cell wall strengthening mediated by apoplast PO is a key factor responsible for different resistance of tomato cultivars Perkoz and Corindo to B. cinerea infection.     

Investigations on Adult Plant Resistance of Barley Against Erysiphe graminis f.sp. hordei

Spring barley cultivars and lines were tested for 3 years in field studies for adult plant resistance against Erysiphe graminis f.sp. hordei. The cultivars Osiris and Asse were selected for further detailed cytological studies and compared with the susceptible cultivar Peruvian. Under controlled greenhouse conditions, the percentage of conidia that had formed a functional haustorium and secondary hyphae (infection efficiency) was reduced in fifth leaves of the adult plant resistant cultivars. On fifth and flag leaves of adult plant resistant cultivars, papillae were formed more frequently under primary germ tubes and appressoria, and fungal penetration was prevented more often than on the susceptible cultivar Peruvian. In ultrastructural studies various types of papillae were observed, but could not be strictly correlated with penetration success or failure of the fungus.     

套作大豆苗期茎秆纤维素合成代谢与抗倒性的关系

为从茎秆强度的角度研究套作大豆苗期对荫蔽胁迫的响应及耐荫抗倒机制,采用耐荫性不同的3个大豆材料,在玉米大豆套作和单作两种种植模式下,对茎秆的纤维素、可溶性糖、蔗糖、淀粉含量及蔗糖代谢中关键酶活性以及茎秆抗折力、抗倒伏指数等进行测定,研究它们与套作大豆苗期倒伏的关系.套作大豆苗期倒伏严重,茎秆抗折力、抗倒伏指数、纤维素、可溶性糖、蔗糖、淀粉含量和相关酶活性均显著低于单作.不同大豆材料受套作荫蔽影响程度不同,强耐荫性大豆南豆12茎秆抗折力降低幅度最小,在套作环境下其茎秆抗折力、抗倒伏指数大,纤维素、可溶性糖、蔗糖、淀粉含量高,酶活性强.相关分析表明： 套作大豆苗期茎秆糖含量均与抗折力呈极显著正相关,与倒伏率呈极显著负相关;蔗糖含量与蔗糖磷酸合酶(SPS)、蔗糖合酶(SS)、中性转化酶(NI)活性呈极显著正相关,与酸性转化酶(AI)活性相关性不显著;纤维素含量与SPS、SS呈极显著正相关,与NI呈显著正相关,与AI相关性不显著.套作环境下,强耐荫性大豆苗期茎秆中较高的SPS、SS活性是其维持高蔗糖和纤维素含量的酶学基础,而高纤维素含量有利于提高茎秆强度,进而增强其抗倒伏能力.本研究应用玉米大豆套作种植系统,从苗期抗倒角度,探明了光环境对不同基因型大豆茎秆纤维素代谢的影响机制,为下一步筛选耐荫抗倒大豆品种提供了理论依据.     

Development of <Emphasis Type="Italic">Colletotrichum acutatum</Emphasis> on Tolerant and Susceptible <Emphasis Type="Italic">Olea europaea</Emphasis> L. cultivars: A Microscopic Analysis

Colletotrichum acutatum is a cosmopolitan and damaging plant pathogen of temperate, subtropical, and tropical fruits and causes anthracnose on olive (Olea europaea L.). Three olive cultivars showing a variable response to infection by C. acutatum were selected to a preliminary study of pathogen development. Fruit samples, from susceptible and tolerant cultivars, were taken at 0, 24, 48, 72, and 192 h after inoculation for a microscopic and histological study of the infection and colonization process. The aim of this study was to compare the infection process: conidial germination, germ tube and appressorium formation, hyphal growth, and mesocarp colonization in susceptible and tolerant olive cultivars as a condition for further exploration of disease development, which is required to develop cultivars with improved resistance to anthracnose. The rate of mesocarp colonization differed between the susceptible and tolerant cultivars, and both intracellular hemibiotrophy and subcuticular intramural necrotrophy were observed. Hemibiotrophic infection predominated in the moderately tolerant cultivar.     

Interaction of Vesicular-Arbuscular Mycorrhizae and Cultivars of Alfalfa Susceptible and Resistant to Meloidogyne hapla

The interaction between vesicular-arbuscular mycorrhizal (VAM) fungi and the root-knot nematode (Meloidogyne hapla) was investigated using both nematode-susceptible (Grasslands Wairau) and nematode-resistant (Nevada Synthetic XX) cultivars of alfalfa (Medicago sativa) at four levels of applied phosphate. Mycorrhizal inoculation improved plant growth and reduced nematode numbers and adult development in roots in dually infected cultures of the susceptible cultivar. The tolerance of plants to nematode infection and development when preinfected with mycorrhizal fungi was no greater than when they were inoculated with nematodes and mycorrhizal fungi simultaneously. Growth of plants of the resistant cultivar was unaffected by nematode inoculation but was improved by mycorrhizal inoculation. Numbers of nematode juveniles were lower in the roots of the resistant than of the susceptible cultivar and were further reduced by mycorrhizal inoculation, although no adult nematodes developed in any resistant cultivar treatment. Inoculation of alfalfa with VAM fungi increased the tolerance and resistance of a cultivar susceptible to M. hapla and improved the resistance of a resistant cultivar.     

Enzyme Changes Associated with Host-Parasite Interactions between Pearl Millet and Downy Mildew Fungus

During the pathogenesis of pearl millet by the downy mildew (Sclerospora graminicola [Sacc.] Schroet.), the activities of peroxidase (PO) and indoleacetic acid oxidase (IAAO) and their isozyme pattern determined by isoelectric focusing on polyacrylamide gels, were observed in extracts of leaves and ears at different stages of development. The PO activity in extracts from infected plants of a susceptible cultivar was found to be higher than in healthy plants. The higher activity was most probably due to the acceleration of host senescence by the pathogen. Quantitative differences in the isozyme patterns of PO and IAAO were found. In inoculated plants of the resistant cultivar, no symptoms developed under the conditions used for infection of the susceptible cultivar and the changes in enzyme activities after inoculation were not significant. The results indicated that different proteins are synthesized in the two cultivars.     

Saccharide Content and Growth Parameters in Relation with Flooding Tolerance in Rice

Pre-submergence reserve saccharides was found adequate to substantiate the survival of tolerant cultivar under flooding. Survival percentage declined in both tolerant and susceptible cultivars with less saccharide content. However, it was more apparent in susceptible cultivar. Plant height, fresh and dry mass of shoots, leaf mass/area ratio and starch content per plant before flooding showed significant positive association with submergence tolerance. Hence, the improved seedling vigour could be used to increase submergence tolerance.     

Differences in responses to iron deficiency among various cultivars of mungbean (Vigna radiata (L.) Wilczek)

Ten mungbean cultivars were evaluated for their resistance to iron deficiency in view of chlorosis symptoms, plant growth and seed yield under field conditions on a calcareous soil in Thailand. The KPS2 cultivar was highly susceptible; the KPS1, PSU1 and Pag-asa 1 cultivars were somewhat susceptible; the VC1163B cultivar was moderately tolerant; the CN36, CN60, UT1 and CNM-I cultivars were tolerant; and the CNM8509B cultivar was very tolerant to iron deficiency. Foliar application of a solution of 5 g L^-1 ferrous sulphate was effective in correcting chlorosis that was induced by iron deficiency, and it enhanced both the growth and the yield of susceptible cultivars. Compared with the susceptible cultivar KPS2, the tolerant cultivar UT1 had a greater ability to lower the pH of the nutrient solution in response to iron deficiency. The root-associated Fe³⁺-reduction activity of UT1 that had been grown in -Fe medium was similar to that of the plants grown in +Fe medium when the acidification of the medium occurred. Acidification of the medium in response to iron deficiency might contribute to the efficient solubilization of iron from calcareous soils, and it related more closely to the resistance to iron deficiency than Fe³⁺ reduction by roots in mungbean cultivars.     

The effect of methyl jasmonate on enzyme activities in wheat genotypes infected by the crown and root rot pathogen <Emphasis Type="Italic">Fusarium culmorum</Emphasis>

The hemibiotrophic pathogen Fusarium culmorum (Fc) causes crown and root rot (CRR) in wheat. In this study, MeJA treatment was done 6 h after pathogen inoculation (hai) to focus the physiological and biochemical responses in root tissue of the susceptible wheat cv Falat, partially resistant cv Pishtaz and the tolerant cv Sumai3 at the beginning of the necrotrophic stage. The results indicate that treatment with MeJA at 6 hai significantly delayed the necrotic progress in cv Falat, whereas no significant difference was seen in other cultivars. The activities of pathogen responsive defense-related enzymes (SOD, CAT, POX, PPO, LOX and PAL), total phenols and callose contents were higher in Sumai3, while treatment with MeJA significantly increased these enzymes activities and total phenols content in Falat, signifying the most sensitive cultivar which had a weak reaction to the pathogen but a strong response to MeJA treatment. Additionally, MeJA treatment decreased the level of H₂O₂ and MDA contents particularly in cv Falat. This is the first work reporting the regulation of defense-related enzymes by MeJA treatment at particular time point of 6 hai suggests the possible role of JA in regulating basal resistance in CRR pathogen–wheat interaction. Taken together, our data add new insights into the mechanism of wheat defense including enzymatic events controlling wheat protection against Fc infection.     

Metabolic profiling of mango cultivars to identify biomarkers for resistance against Fusarium infection

Infection of mango panicles and young leaf shoots by Fusarium results in significantly lower fruit yields. Some mango cultivars are known to be tolerant to blossom malformation, while others are highly susceptible. Previous researchers linked the ability of certain cultivars to confine Fusarium infection to the production of high levels of mangiferin. This study further elucidates the role of phenolic metabolites contributing to tolerance. Phenolic profiles of mature leaf extracts from cultivars with varying degrees of resistance to Fusarium infection were obtained by ultrahigh performance liquid chromatography–time-of-flight-mass detection. Chemometric models constructed from the data revealed a clear distinction between the profiles of tolerant and susceptible cultivars and permitted the identification of biomarkers associated with susceptibility to infection. The presence of elevated levels of mangiferin, maclurin and maclurin O-galloyl-glucoside in the leaves were associated with a higher degree of tolerance. In contrast, high levels of iriflophenone glucosides were linked to increased susceptibility of the cultivars to infection. These models can serve as an important tool to investigate appropriate cultivars, prior to their introduction to areas prone to the disease.     

Effect of salicylic and abscisic acid administered through detached tillers on antioxidant system in developing wheat grains under heat stress

The mechanism imparting thermotolerance by salicylic acid (SA) and abscisic acid (ABA) is still unresolved using either spraying technique or in vitro conditions. Alternative way of studying these effects under near in vivo conditions is through the use of liquid culturing technique. Effects of SA and ABA (100 μM) on antioxidative enzymes, antioxidants and lipid peroxidation were studied in detached tillers of three wheat (Triticum aestivum L.) cultivars PBW 343, C 306 (heat tolerant) and WH 542 (heat susceptible) cultured in a liquid medium. Ears were subjected to heat shock treatment (45°C for 2 h) and then maintained at 25°C for 5 days. Heat shock treatment resulted in increased peroxidase (POD) activity, while superoxide dismutase (SOD) and catalase (CAT) activities were reduced compared to control. The decrease in CAT activity was more significant in susceptible cultivar WH 542. Concomitantly, content of α-tocopherol and lipid peroxides increased in heat-treated wheat ears, whereas contents of total ascorbate level were reduced. Following treatment with SA and ABA, activities of all three antioxidative enzymes increased in correspondence with an increase in ascorbate and α-tocopherol content. Apparently, lipid peroxide content was reduced by SA in heat tolerant cultivars (PBW 343 and C 306) whereas in susceptible cultivar it was decreased by ABA. The up-regulation of the antioxidant system by SA and ABA possibly contributes to better tolerance against heat shock-induced oxidative damage in wheat grains.     

Effects of alien cytoplasm substitution on the response of wheat cultivars to Septoria nodorum

The effects of alien cytoplasm substitution on the response of wheat to Septoria nodorum were studied, using alloplasmic series of two cultivars, Chris and Selkirk. In general, cytoplasmic substitution caused unidirectional effects on Septoria-response, alloplasmic lines of both cultivars expressing lower levels of partial resistance (in leaf and head tissue) but higher levels of yield tolerance than the corresponding euplasmic line. The reduced resistance in alloplasmics was closely associated with reduced incubation periods of Septoria infection in both leaf and head tissue. Cytoplasmic substitution resulted in increased yield tolerance to Septoria-infection in both the non-tolerant Selkirk and the relatively tolerant Chris. Unlike their effects on partial resistance, specific cytoplasms exerted similar effects on tolerance in the two parental cultivars, several cytoplasms of the D plasmatype being particularly effective in increasing Septoria-tolevance. The potential for the development of Septoria-toterant cultivars by the incorporation of alien cytoplasms is discussed, in view of the observed neutral effects of D plasmatype cytoplasms on other agronomic traits.     

Root antioxidant responses of two Pisum sativum cultivars to direct and induced Fe deficiency

The contribution of antioxidant defence systems in different tolerance to direct and bicarbonate‐induced Fe deficiency was evaluated in two pea cultivars (Kelvedon, tolerant and Lincoln, susceptible). Fe deficiency enhanced lipid peroxidation and H₂O₂ concentration in roots of both cultivars, particularly in the sensitive one grown under bicarbonate supply. The results obtained on antioxidant activities (SOD, CAT, POD) suggest that H₂O₂ accumulation could be due to an overproduction of this ROS and, at the same time, to a poor capacity to detoxify it. Moreover, under bicarbonate supply the activity of POD isoforms was reduced only in the sensitive cultivar, while in the tolerant one a new isoform was detected, suggesting that POD activity might be an important contributor to pea tolerance to Fe deficiency. The presence of bicarbonate also resulted in stimulation of GR, MDHAR and DHAR activities, part of the ASC‐GSH pathway, which was higher in the tolerant cultivar than in the sensitive one. Overall, while in the absence of Fe only slight differences were reported between the two cultivars, the adaptation of Kelvedon to the presence of bicarbonate seems to be related to its greater ability to enhance the antioxidant response at the root level.     

Distinct physiological responses of two rice cultivars subjected to iron toxicity under field conditions

Iron toxicity is recognised as the most widely distributed nutritional disorder in lowland and irrigated rice, derived from the excessive amounts of ferrous ions generated by the reduction of iron oxides in flooded soils. Rice cultivars with variable degrees of tolerance to iron toxicity have been developed, and cultural practices such as water management and fertilisation can be used to reduce its negative impact. However, because of the complex nature of iron toxicity, few physiological data concerning tolerance mechanisms to excess iron in field conditions are available. To analyse the physiological responses of rice to iron excess in field conditions, two rice cultivars with distinct tolerance to iron toxicity [BR‐IRGA 409 (susceptible) and IRGA 420 (tolerant)] were grown in two areas, with a well‐established history of iron toxicity (in Camaquã, RS, Brazil) and without iron toxicity (in Cachoeirinha, RS, Brazil). Plants from the susceptible cultivar grown in the iron‐toxic site showed lower levels of chlorophylls and soluble proteins (together with higher carbonyl levels) indicating photooxidative and oxidative damage. The toxic effects observed were because of the accumulation of high levels of iron and not because of any indirectly induced shoot deficiency of other nutrients. Higher activities of antioxidative enzymes were also observed in leaves of plants from the susceptible cultivar only in the iron‐toxic site, probably as a result of oxidative stress rather than because of specific involvement in a tolerance mechanism. There was no difference between cultivars in iron accumulation in the symplastic and apoplastic space of leaves, with both cultivars accumulating 85–90% of total leaf iron in the symplast. However, susceptible plants accumulated higher levels of iron in low‐molecular‐mass fractions than tolerant plants. The accumulation of iron in the low‐molecular‐mass fraction probably has a direct influence on iron toxicity, and the adaptive strategy of tolerant plants may rely on their capacity to buffer the iron amounts present in the low mass fraction, a new parameter to be considered when evaluating tolerance to iron excess in field‐cultivated rice plants.     

Defence‐Related Enzymes in Soybean Resistance to Target Spot

Target spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado. Information in the literature regarding the biochemical defence responses of soybean to C. cassiicola infection is rare. Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot. The activities of chitinases (CHI), β‐1‐3‐glucanases (GLU), phenylalanine ammonia‐lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin‐thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar. The target spot severity, number of lesions per cm² of leaflet and area under the disease progress curve were significantly lower for plants from cv. FUNDACEP 59 compared to plants from cv. TMG 132. The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C. cassiicola. Inoculated plants from cv. FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv. TMG 132. In conclusion, the results of this study demonstrated that the defence‐related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied. The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C. cassiicola infection were highly associated with soybean resistance to target spot.     

Aldose reductase expression contributes in sorbitol accumulation and 4-hydroxynon-2-enal detoxification in two foxtail millet (<Emphasis Type="Italic">Setaria italic</Emphasis>a L.) cultivars with different salt stress tolerance

Salt stress is a major environmental factor in arid and semi-arid regions and influences many aspects of plant development. Salinity results in generation of various free radicals that can potentially damage the cellular constituents in plants. Plants were able to effectively reduce the damage caused by these free radicals by a way of enzymatic and non enzymatic defenses for better survival. Enhanced efficacy of antioxidative enzyme systems such as superoxide dismutase, catalase and ascarbate peroxidase was well documented in several plants subjected to salinity stress. Aldose reductase, an important enzyme is also known to detoxify free toxic aldehydes like HNE (4-hydroxynon-2-enal, a hydroxyalkenal) generated during oxidative damage of cellular components. However, the role of aldose reductase to impart tolerance to the plants under salt stress has not been studied in any detail. Therefore, we were interested to study the aldose reductase activity and its expression to gain an insight into the role of aldose reductase in imparting tolerance to foxtail millet cultivars (viz., Cv. Prasad and Lepakshi) subjected to NaCl stress. We observed that subjecting foxtail millets to increasing levels of stress significantly increased aldose reductase activity and in a way that correlated positively with elevated levels of sorbitol, an osmotic solute involved in osmotic balance. This suggests the involvement of aldose reductase in sorbitol biosynthesis in foxtail millet. Additionally, we observed higher levels of 4-hydroxynon-2-enal, a major lipid peroxidation product, in the susceptible than the tolerant cultivar indicating a higher proportion of cellular damage in former than in the latter. This high content of 4-hydroxynon-2-enal in the susceptible cultivar was negatively correlated with its aldose reductase activity, indicating the involvement of aldose reductase in detoxification of 4-hydroxynon-2-enal. 4-hydroxynon-2-enal is also known to be a catalyzed by glutathione-S-transferase. Glutathione-S-transferase activity was found higher in the tolerant foxtail millet than the sensitive cultivar: the tolerant cultivar showed a low 4-hydroxynon-2-enal content compared to the susceptible cultivar, demonstrating a possible mechanism for detoxification of 4-hydroxynon-2-enal by two enzymes, glutathione-S-transferase and aldose reductase in plants under stressful conditions.     

Amelioration of lead and mercury effects on germination and rice seedling growth by antioxidants

Germination of two rice (Oryza sativa L.) cultivars (Ratna and IR 36) in the presence of 10 μM PbCl2 and 10 μM HgCl2 decreased germination percentage, germination index, shoot/root length, tolerance index and dry mass of shoots and roots. Mercury was more toxic than lead. Reduced glutathione (GSH), cysteine (Cys), ascorbic acid, and α-tocopherol alleviated the adverse effects of these metals on plants in the order GSH > Cys > ascorbic acid > α-tocopherol. The effects were more pronounced in tolerant cultivar IR 36 than in the relatively susceptible cultivar Ratna. This revised version was published online in July 2006 with corrections to the Cover Date.