Partial rootzone drying increases water-use efficiency of lemon Fino 49 trees independently of root-to-shoot ABA signalling.

To determine whether irrigation strategy altered the sensitivity of Citrus leaf gas exchange to soil, plant and atmospheric variables, mature (16-year-old) Fino 49 lemon trees (Citrus limon (L.) Burm. fil. grafted on Citrus macrophylla Wester) were exposed to three irrigation treatments: control (irrigated with 100% of crop potential evapotranspiration, ETc), deficit irrigation (DI) and partial rootzone drying (PRD) treatments,which received 75% ETc during the period of highest evaporative demand and 50% ETc otherwise. Furthermore, to assess the physiological significance of root-to-shoot ABA signalling, the seasonal dynamics of leaf xylem ABA concentration ([X-ABA]leaf) were evaluated over two soil wetting-drying cycles during a 2-week period in summer. Although stomatal conductance (gs) declined with increased leaf-to-air vapour pressure deficit (LAVPD), lower leaf water potential and soil water availability, [X-ABA]leaf was only related to stomatal closure in well irrigated trees under moderate (<2.5kPa) atmospheric vapour pressure deficit (VPD). Differences in [X-ABA]leaf were not detected between treatments either before or immediately after (<12h) rewatering the dry side of PRD trees. Leaf water potential was higher in control trees, but decreased similarly in all irrigation treatments as daily LAVPD increased. In contrast, DI and PRD trees showed lower stomatal sensitivity to LAVPD than control trees. Although DI and PRD decreased stomatal conductance and photosynthesis, these treatments did not significantly decrease yield, but PRD increased crop water use efficiency (WUE) by 83% compared with control trees. Thus PRD-induced enhancement of crop WUE in a semiarid environment seems to involve physiological mechanisms other than increased [X-ABA]leaf.

Validation of high-performance liquid chromatography methods for determination of zidovudine, stavudine, lamivudine and indinavir in human plasma

Objetivo: Fueron descritos y validados m¨¦todos anal¨ªticos simplespara la determinaci¨®n de zidovudina (AZT), estavudina (d4T),lamivudina (3TC), e indinavir (INV) en plasma humano por cromatograf¨ªal¨ªquida de alta resoluci¨®n (HPLC) con detecci¨®n UV.M¨¦todo: Se aplic¨® la extracci¨®n en fase s¨®lida para la preparaci¨®nde las muestras previo al an¨¢lisis. La corrida cromatogr¨¢ficase realiz¨® en una columna anal¨ªtica C-18 y el tiempo de retenci¨®nse movi¨® en un rango de 6,8-11,9 min para d4T, 7,5-9,0para 3TC y 11,2-11,9 para AZT e INV. Se validaron 4 m¨¦todosen cuanto a especificidad, precisi¨®n y exactitud entre d¨ªas y en eld¨ªa, as¨ª como recobrado y estabilidad.Resultados: Los rangos de concentraciones de las curvasanal¨ªticas eran de 10-1600 ng/ml para d4T, 50-3200 ng/ml para3TC, 0,05-5,0 ¦Ìg/ml para AZT y 0,1-10,0 ¦Ìg/ml para INV. Sedemostr¨® la estabilidad del analito durante el procesamiento de lasmuestras y el almacenamiento. Para las 4 formulaciones los resultadosdel por ciento de recobrado fue superior al 89%.Conclusiones: Estos m¨¦todos demostraron ser simples, exactos,precisos y son los utilizados actualmente en nuestro laboratoriopara el an¨¢lisis cuantitativo de productos antirretrovirales enplasma, as¨ª como para posteriores estudios de farmacocin¨¦tica ybioequivalencia(AU)

Objective: Simple methods for the determination of zidovudine(AZT), stavudine (d4T), lamivudine (3TC) and indinavir (INV)in human plasma by reversed-phase liquid chromatography(HPLC) with UV detection were described and validated.Method: Solid-liquid extraction procedures were applied tothe samples prior to analysis. Chromatography was performed ona C-18 analytical columns and the retention time ranged from 6.8to 8.0 min for stavudine, 7.5 to 9.0 min for lamivudine, 11.2 to11.9 min for zidovudine and indinavir. Four methods were validatedfor specificity, inter-and intra-assay precision and accuracy,absolute recovery and stability.Results: Analytical curve ranged from 10-1600 ng/ml forstavudine, 50-3200 ng/ml for lamivudine, 0.05-5.0 ¦Ìg/ml forzidovudine and 0.1-10.0 ¦Ìg/ml for indinavir. Analytes stabilityduring sampling processing and storage were established. Extractionrecoveries are higher than 89% for all formulations.Conclusions: These methods proved to be simples, accurateand precise, and are currently in use in our laboratory for thequantitative analysis of antiretrovirals products in plasma, and forfurther pharmacokinetics and bioequivalence studies(AU)