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Maintenance of photosynthesis at low leaf water potential in wheat : role of potassium status and irrigation history 总被引:2,自引:2,他引:0
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The interaction of low water potential effects on photosynthesis, and leaf K+ levels in wheat (Triticum aestivum L.) plants was studied. Plants were grown at three K+ fertilization levels; 0.2, 2, and 6 millimolar. With well watered plants, 2 millimolar K+ supported maximal photosynthetic rates; 0.2 millimolar K+ was inhibitory, and 6 millimolar K+ was superoptimal (i.e. rates were no greater than at 2 millimolar K+). Photosynthesis was monitored at high (930 parts per million) and low (330 parts per million) external CO2 throughout a series of water stress cycles. Plants subjected to one stress cycle were considered nonacclimated; plants subjected to two successive cycles were considered acclimated during the second cycle. Sensitivity of photosynthesis to declining leaf water potential was affected by K+ status; 6 millimolar K+ plants were less sensitive, and 0.2 millimolar K+ plants were more sensitive than 2 millimolar K+ plants to declining water potential. This occurred with nonacclimated and acclimated plants at both high and low assay CO2. It was concluded that the K+ effect on photosynthesis under stress was not mediated by treatment effects on stomatal resistance. Differences between the K+ treatments were much less pronounced, however, when photosynthesis of nonacclimated and acclimated plants was plotted at a function of declining relative water content during the stress cycles. These results suggest that K+ effects on the relationship between relative water content and water potential in stressed plants was primarily responsible for the bulk of the K+-protective effect on photosynthesis in stressed plants. In vitro experiments with chloroplasts and protoplasts isolated from 2 millimolar K+ and 6 millimolar K+ plants indicated that upon dehydration, K+ efflux from the chloroplast stroma into the cytoplasm is less pronounced in 6 millimolar K+ protoplasts. 相似文献
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Cyclopiazonic acid (CPA) and aflatoxin are known sometimes to coexist in nature but little is known of possible biological interaction in mammals that consume mixtures of these two mycotoxins. Guinea pigs were dosed orally with CPA (2.2 mg/kg) or aflatoxin (0.045 mg B1/kg) singly or in combination. Effects of toxin consumption were determined on clinical health, body weight gain, pathological change, and several immunologically related parameters including delayed cutaneous hypersensitivity, antibody response, complement hemolytic titer, intracutaneous mitogen (PHA) and in vitro lymphocyte blastogenesis. In contrast to an earlier study by others, significant synergy between these two toxins was demonstrated in reduced rate of body weight gain, lethality and histologic changes (vacuolization) in hepatocytes. Reductions in complement titer, intradermal PHA, delayed cutaneous hypersensitivity response and in vitro lymphocyte blastogenesis were related to aflatoxin activity. No effects on antibody formation to Brucella abortus were observed with either toxin or the combination of toxins. Cyclopiazonic acid appeared to restore the suppressive effects of aflatoxin in delayed cutaneous hypersensitivity response and in vitro lymphocyte blastogenesis. 相似文献
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In a new case of interstitial del(2q), measurements of ribulose 5-phosphate 3-epimerase activity suggested that the locus for this enzyme might be localized to the subregion 2q32q33.3. 相似文献
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Daniele Arobba Andrea Quaglia Paolo Panagia Paolo Minuti Sergio Innocenti Pier Luigi Odda 《Aerobiologia》1988,4(1-2):38-46
Riassunto Sono state rilevate durante un monitoraggio aerobiologico effettuato a Pietra Ligure (Savona) nel corso del 1987 le concentrazioni
polliniche di 50 taxa ed è stata valutata l'influenza relativa dei fattori meteorologici. Le osservazioni palinologiche sono
state rapportate alle concentrazioni sieriche delle IgE specifiche, alla reattività bronchiale specifica ed aspecifica valutate
in 101 pazienti allergici (rinitici ed asmatici), sensibilizzati a Graminaceae ed Urticaceae (Parietaria) al fine di riconoscere
correlazioni tra le caratteristiche aerobiologiche di questi allergeni edi meccanismi patogenetici che sostengono la reattività
bronchiale.
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