Jatropha curcas L. (Euphorbiaceae) modulates stomatal traits in response to leaf-to-air vapor pressure deficit

Cultivation of Jatropha curcas in arid and semiarid non-cultivated areas could be a sustainable strategy for stimulating biofuel production without competing with food crops for land and water resources. J. curcas is considered a drought-tolerant species; however, the mechanisms that provide tolerance are unknown. Few efforts have been made to understand the connections between stomatal development and environment conditions. Here, we compared changes in stomatal density (SD) and stomatal index (SI) and their influence on gas exchange in J. curcas. Plants were cultivated in both rainy and dry regions. We describe a distinctive distribution of stomata under the adaxial and abaxial leaf epidermises, where higher SD may have caused the increase in stomatal conductance (g_s) with positive effects on net photosynthetic rate (P_N). However, when rain was excluded, the variation in g_s was strongly related to vapour pressures deficit (VPD), and VPD was strongly related to the P_N. Thus, our results suggest that J. curcas may also contribute mitigating the effect of CO₂ deposition in the atmosphere, given that a remarkable change in SD and other leaf traits was observed in response to seasonal variations. Moreover, multivariate analysis highlights the high sensitivity of J. curcas plants to VPD which in turn induces rapid stomatal closure and consequent reduction of P_N for long periods of time which reflect into a change in the pattern of development resulting in higher SI. These results can help us to understand the relationship between stomatal features and gas exchange in response to environment changes.     

Distribution of Salmonella typhimurium in romaine lettuce leaves

Leafy greens are occasionally involved in outbreaks of enteric pathogens. In order to control the plant contamination it is necessary to understand the factors that influence enteric pathogen-plant interactions. Attachment of Salmonella enterica serovar typhimurium to lettuce leaves has been demonstrated before; however, only limited information is available regarding the localization and distribution of immigrant Salmonella on the leaf surface. To extend our knowledge regarding initial pathogen-leaf interactions, the distribution of green-fluorescent protein-labeled Salmonella typhimurium on artificially contaminated romaine lettuce leaves was analyzed. We demonstrate that attachment of Salmonella to different leaf regions is highly variable; yet a higher attachment level was observed on leaf regions localized close to the petiole (7.7 log CFU g⁻¹) compared to surfaces at the far-end region of the leaf blade (6.2 log CFU g⁻¹). Attachment to surfaces located at a central leaf region demonstrated intermediate attachment level (7.0 log CFU g⁻¹). Salmonella displayed higher affinity toward the abaxial side compared to the adaxial side of the same leaf region. Rarely, Salmonella cells were also visualized underneath stomata within the parenchymal tissue, supporting the notion that this pathogen can also internalize romaine lettuce leaves. Comparison of attachment to leaves of different ages showed that Salmonella displayed higher affinity to older compared to younger leaves (1.5 log). Scanning electron microscopy revealed a more complex topography on the surface of older leaves, as well as on the abaxial side of the examined leaf tissue supporting the notion that a higher attachment level might be correlated with a more composite leaf landscape. Our findings indicate that initial attachment of Salmonella to romaine lettuce leaf depends on multiple plant factors pertaining to the specific localization on the leaf tissue and to the developmental stage of the leaf.     

优化炼胶工艺改善胎面气孔率

Φ250冷喂料螺杆挤出机,挤出的工艺优点是胎面更换规格、尺寸比较容易,劳动生产率高。由于胎面规格种类多,在挤出过程中经常出现半成品表面不平滑、尺寸和质量波动较大的问题,特别是胶部件内部气孔较多,气孔率有时达到7%以上,导致挤出半成品无法使用,返回率较高,影响正常生产。气孔的存在会影响成品轮胎的耐磨性能,且易出现崩花、掉块和花纹沟裂等质量问题。本文通过增加胎面胶的混炼段数以提高炭黑分散度,来改善胎面胶的气孔率。     

Erratum to "Structural and physiological responses to ozone in Manna ash (Fraxinus ornus L.) leaves of seedlings and mature trees under controlled and ambient conditions"

Leaf-level microscopical symptom structure and physiological responses were investigated in seedlings experimentally exposed to ozone (O₃) in indoor chambers (150 ppb, 8 h d^− 1 per 7 weeks), and field trees of Manna ash (Fraxinus ornus) exposed to ambient O₃ (max 93 ppb per one growing season). Ozone-induced leaf injury, including leaf reddening and stippling, was observed in both seedlings and mature trees, but the morphology of injury in the stipples differed, being hypersensitive-like (HR-like) in the chamber seedlings and accelerated cell senescence (ACS) in the field trees. In both exposure conditions, the main structural impact of O₃ was on the mesophyll and especially the upper assimilating cell layers. The main physiological impact was on carbon assimilation and on stomatal sluggishness. These effects were not due to stomatal structural injury and were more severe in juvenile compared to mature trees because of environmental (water availability, light) and constitutional (gas exchange capacity) factors and differences in the cell physiology processes (HR-like vs. ACS) triggered by ozone stress. Given the plasticity of plant responses to ozone stress, dose/response relationships for tree seedlings in the indoor chambers cannot be extrapolated to mature trees unless ambient conditions are closely simulated.     

Effects of CeCl3 and LaCl3 on callus and root induction and the physical response of tobacco tissue culture

La³⁺ and Ce³⁺ have positive effects on plant growth and production. Although it is well known that rare earth elements promote cell growth, the biological effects of La³⁺ and Ce³⁺ on callus, shoot and root induction in tobacco are still unclear. The relationships among callus induction, rooting, enzyme activities and stomatal characteristics in tobacco are unknown. The objectives of this study were to identify the relationships between the induction of calluses, shoots, roots, stomata and enzyme activities. The induction percentages of calluses, buds, roots were recorded at 5, 10, 15, 20 and 25 days after La³⁺ and Ce³⁺ treatments. Peroxidase isoenzyme activity was determined by electrophoresis. The characteristics of the stomata were observed under an optical microscope. Our results show that low concentrations of Ce³⁺ (<15 mg/L) result in increases in the induction percentages of calluses, buds and roots, but La³⁺ (>5 mg/L) inhibits the induction of calluses, buds and roots. There are more peroxidase isoenzyme bands in Ce³⁺ treatments than in La³⁺ treatments. This is consistent with the induction percentages of calluses, buds and roots in Ce³⁺ and La³⁺ treatments. High enzyme activities may promote the induction of calluses, buds and roots. The stomata area and stomata number of leaves are significantly different between La³⁺ treatments and Ce³⁺ treatments. La³⁺ improves the stomata area and number. Based on these results, we speculate that La³⁺ may promote the development of the photosynthetic system. Ce³⁺ may promote tobacco growth and rooting by improving enzyme activities.     

Structural and physiological responses to ozone in Manna ash (Fraxinus ornus L.) leaves of seedlings and mature trees under controlled and ambient conditions

Leaf-level microscopical symptom structure and physiological responses were investigated in seedlings experimentally exposed to ozone (O₃) in indoor chambers (150 ppb, 8 h d^− 1/7 weeks), and field trees of Manna ash (Fraxinus ornus) exposed to ambient O₃ (max 93 ppb/one growing season). Ozone-induced leaf injury, including leaf reddening and stippling, was observed in both seedlings and mature trees, but the morphology of injury in the stipples differed, being hypersensitive-like (HR-like) in the chamber seedlings and accelerated cell senescence (ACS) in the field trees. In both exposure conditions, the main structural impact of O₃ was on the mesophyll and especially the upper assimilating cell layers. The main physiological impact was on carbon assimilation and on stomatal sluggishness. These effects were not due to stomatal structural injury and were more severe in juvenile compared to mature trees because of environmental (water availability, light) and constitutional (gas exchange capacity) factors and differences in the cell physiology processes (HR-like vs. ACS) triggered by ozone stress. Given the plasticity of plant responses to ozone stress, dose/response relationships for tree seedlings in the indoor chambers cannot be extrapolated to mature trees unless ambient conditions are closely simulated.     

Salmonella Typhimurium internalization is variable in leafy vegetables and fresh herbs

Despite washing and decontamination, outbreaks linked to consumption of fresh or minimally-processed leafy greens have been increasingly reported in recent years. In order to assure the safety of produce it is necessary to gain knowledge regarding the exact routes of contamination. Leaf internalization through stomata was previously reported as a potential route of contamination, which renders food-borne pathogens protected from washing and disinfection by sanitizers. In the present study we have examined the incidence (percentage of microscopic fields harboring ≥ 1 GFP-tagged bacteria) of Salmonella Typhimurium on the surface and underneath the epidermis in detached leaves of seven vegetables and fresh herbs. The incidence of internalized Salmonella varied considerably among the different plants. The highest incidence was observed in iceberg lettuce (81 ± 16%) and arugula leaves (88 ± 16%), while romaine (16 ± 16%) and red-lettuce (20 ± 15%), showed significantly lower incidence (P < 0.05). Internalization incidence in fresh basil was 46 ± 12%, while parsley and tomato leaves demonstrated only marginal internalization (1.9 ± 3.3% and 0.56 ± 1.36%, respectively). Internalization of Salmonella in iceberg lettuce largely varied (0-100%) through a 2 year survey, with a higher incidence occurring mainly in the summer. These results imply that Salmonella internalization occurs in several leafy vegetables and fresh herbs, other than iceberg lettuce, yet the level of internalization largely varies among plants and within the same crop. Since internalized bacteria may evade disinfection, it is of great interest to identify plants which are more susceptible to bacterial internalization, as well as plant and environmental factors that affect internalization.