使用灭活疫苗低致病性禽流感

在一个国家或地区广泛使用优质的H9N2灭活疫苗,可明显减少该地区禽流感的暴发次数,降低由禽流感给养禽业带来的经济损失。     

The effect of nitrogen fertilization and shading on the incidence of “colour spots” in sweet pepper (Capsicum annuum) fruit

SUMMARY

“Colour spots” (CS) in pepper fruit is a physiological disorder characteristic of some sweet pepper cultivars. The symptoms are yellowish spots on the outer surface of affected fruits. We investigated the effects of shading and nitrogen supply on the susceptibility of three sweet pepper cvs (Maor, Lady Bell and 899) to CS. The most susceptible was ‘Maor’. The incidence of CS was promoted by high N and shading. The fruits of all cultivars had lower nitrogen concentrations than the leaves but there were no significant differences in fruit N content between Maor and the CS-insensitive cultivars. The CS-affected areas of the pericarp tissue had higher calcium concentrations than unaffected tissue. Differences in magnesium or potassium concentrations in these spots were less pronounced. Scanning electron microscopy revealed that the affected pericarp cells contained crystals, presumably of calcium oxalate. Only in ‘Maor’ fruits was the oxalate concentration elevated by approximately nine-fold when the nitrogen supply to shaded plants was increased. We suggest that in the fruits of the sensitive cultivar, oxalic acid production is enhanced under high-nitrogen + shading conditions and causes the CS damage, possibly be chelating intracellular calcium.     

Methylene blue increases the tolerance of tomato plants to abiotic stresses

Summary

Environmental stresses such as high temperature and high salinity are known to cause oxidative stress in plants by enhancing the generation of reactive oxygen species (ROS), which have a strong impact on plant development. Mitochondria constitute one of the major sources of ROS in roots. Recently, it has been shown in mammalian systems that methylene blue (MB) at very low concentrations can attenuate mitochondrial ageing by scavenging ROS. In the present study, we tested whether MB could be used to protect tomato (Lycopersicon esculentum L.) seedlings against the harmful effects of high salinity and high root temperature. Tomato seedlings were grown hydroponically and were subjected to two abiotic stresses: high salinity (150 mM NaCl) in the nutrient medium, or high root temperature (35ºC) for 14 d. These stress treatments were applied with or without the addition of 10^–8 M MB. The results showed that, under normal conditions, MB enhanced root and shoot growth, increased root respiration, decreased root H₂O₂ and malonyldialdehyde (MDA) concentrations, and enhanced root superoxide dismutase (SOD) activity. Both high salinity and high root temperature stress impaired root and shoot growth, and caused an enhancement of root oxidative stress. MB had a significant protective effect against both abiotic stresses and restored the levels of oxidative stress-related components (i.e., H₂O₂ and MDA) in root and leaf tissues almost to normal levels. It is hypothesised that MB could confer its protective effect not only through interactions with root mitochondria, but also via additional cellular targets in the root.     

Effect of heat stress on the growth,root sugars,acid invertase and protein profile of pepper seedlings following transplanting

The development of pepper transplants is sensitive to the prevailing temperature in the field. High temperatures immediately after transplanting pepper seedlings delay their development in the field. During nine days of post-transplanting heat stress (30/25°C or 35/25°C, day/night temperature regimes), root and shoot growth were inhibited compared to the control transplants (25/18°C) with a significant decline in total protein and soluble acid invertase activity in the roots of the heat stressed plants. Acid invertase activity was less sensitive to the heat stress in the leaves than in the roots. A significant reduction in the root invertase activity occurred as early as two days after the beginning of the stress. Transplanting caused a 72% inhibition in the carbon allocation to the roots, compared with the non-transplanted seedlings. Exposure to heat after transplanting did not further reduce carbon allocation to the roots. The protein profile on SDS-PAGE from leaves shows that during the heat stress, some heat related proteins were synthesized concomitant with the reduction in the synthesis of constitutive proteins. In the roots, the synthesis of heat related proteins was barely detectable with no visible changes in the protein profile. The results suggest that roots are more sensitive to heat stress than leaves, possibly because they are less able to synthesize heat related proteins. The causal relationship between protein synthesis during heat stress and the performance of the transplants is not well understood.     

The susceptibility of pepper (Capsicum annuum) to heat induced flower abscission: Possible involvement of ethylene

SUMMARY

Heat stress causes abscission of flowers in pepper plants and thus reduces yield. In the present study, we investigated the involvement of ethylene in heat-stress related flower abscission, by comparing the response of flowers of bell pepper, cv. Maor, known to be sensitive to flower abscission, and flowers of paprika, cv. Lehava, a resistant cultivar of Capsicum annuum. Their differing susceptibilities to high temperatures depend on light. Under high-temperature, high-light conditions, bell pepper was less susceptible than paprika, but, under high-temperature low-light, bell pepper was more susceptible. At high temperatures, flower explant abscission was much higher with bell pepper than paprika. Ethylene production (EP) by bell pepper explants reached a maximum at 34°C and decreased at higher temperatures (42 and 48 C), while in paprika EP rates were lower and reached the maximum at 42°C. Explants of bell pepper flowers were more susceptible to exogenous ethephon than paprika flowers. The sensitivity of a collection of pepper cul-tivars to heat induced flower abscission was more closely correlated with their flower sensitivity to ethephon than with the flower EP rate. We suggest that the differential susceptibility of bell pepper and paprika to heat stress is a result of both different ethylene production by their flowers and their differing sensitivities to ethylene produced under high-temperature stress. However, the sensitivity of the flower to ethylene may be more important in inducing their abscission.     

Interaction with salinity of GA3-induced leaf elongation,petiole pithiness and bolting in celery

GA₃ sprayed on celery plants, which received a continuous supply of 0, 0.2, 0.4, 0.6 or 1.0% NaCl solutions to the roots, caused a pronounced increase in leaf elongation.Along with enhanced elongation, GA₃ increased breakdown of parenchymatous tissue in the petiole, but this effect was drastically suppressed in the salt-treated plants. In a similar fashion, the effect of GA₃ on the elongation of the flowering-stem (bolting) was significantly diminished in salt-treated plants. In no case did the salinity treatment totally abolish the bolting-process induced by GA₃.Changing the temperature of the lower part of the root system altered the magnitude of GA₃ effect on bolting. As the temperature was lowered from 30 to 6° C, the ability of GA₃ to cause bolting was greatly reduced.The results are discussed in view of the possible interaction between salinity and the GA₃ effect on petiole elongation, cellular breakdown and bolting.     

Variation in flower abscission of peppers under stress shading conditions

Summary Seedlings from 77 accessions including inbreds, F₁ hybrids and seven F₂ populations were exposed to approximately 60% shading for 35 days following transplanting into the field.Most of the lines did not set fruit under the shading due to heavy abscission of flowers. A few exceptional lines, hybrids and F₂ segregants showed resistance to abscission and set normal fruits under the shading regime. This procedure is suggested for screening against stress-induced flower abscission. An association is suggested between resistance to shading and to high temperatures and its genetic control.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel No. 1209-E, 1993 series.     

Cuticular cracking in pepper fruit. I. Effects of night temperature and humidity

Summary

The objective of the present study was to characterize some of the anatomical and physiological characteristics of fruit cracking in bell pepper (Capsicum annuum L.). Scanning-electron micrographs show that initiation of fruit cracking in bell pepper is by formation of mini-cracks on the cuticle layer; these then enlarge into cracks and traverse the epidermal cells. Pepper cultivars differ in their sensitivity to cracking, partly because of differences in fruit pericarp thickness. Limitation of night transpiration by high humidity or low temperature increased the turgor potential of the fruit pericarp and enhanced cracking. Likewise, leaf pruning suppressed night transpiration and concomitantly increased cracking. Fruit cuticle transpiration was found to be low in the early stages of fruit development and to increase as the fruit became susceptible to cracking. Environmental conditions which enhanced cracking also increased cuticle transpiration in a sensitive pepper cultivar but not in a less sensitive one. We suggest that fruit cracking in bell pepper occurs because reduction in night transpiration causes high turgor pressure in the fruit. As the cuticle becomes permeable to water, the inner turgor pressure causes the cuticle to crack. Differences in cultivar sensitivity may be partly due to differences in pericarp thickness and cuticle properties, but additional factors may be involved.     

Effects of an evaporative cooling system on greenhouse climate,fruit disorders and yield in bell pepper (Capsicum annuum L.)

Summary

The main goal of this research was to investigate the effects of a wet pad-and-fan evaporative cooling system (ECS) on the incidence of blossom-end rot (BER) and fruit cracking in greenhouse-grown bell pepper (Capsicum annuum L.). The specific objectives were: (i) to study the efficiency of the wet pad-and-fan ECS in improving plant water status and reducing transpiration; and (ii) to explore the impact of these conditions on fruit yield, fruit Ca content and the incidence of BER and fruit cracking. For 3 years, peppers were grown in the Lachish Region, Israel, in a greenhouse divided into two compartments, one with and one without (control) a pad-and-fan ECS. The results showed that the ECS increased total fruit yield and the incidence of cracked fruits, but reduced the incidence of BER. The efficiency of the ECS in reducing temperature and vapour pressure deficit (VPD) decreased as the distance from the wet pad increased. Consequently, the incidence of cracked fruits decreased with distance from the wet pad, whereas the incidence of BER increased.     

Packing C60 in boron nitride nanotubes

We have created insulated C60 nanowire by packing C60 molecules into the interior of insulating boron nitride nanotubes (BNNTs). For small-diameter BNNTs, the wire consists of a linear chain of C60 molecules.With increasing BNNT inner diameter, unusual C60 stacking configurations are obtained (including helical, hollow core, and incommensurate) that are unknown for bulk or thin-film forms of C60.C60 in BNNTs thus presents a model system for studying the properties of dimensionally constrained "silo" crystal structures. For the linear-chain case, we have fused the C60 molecules to form a single-walled carbon nanotube inside the insulating BNNT.