渗透胁迫下不同抗旱性小麦幼苗氨同化差异

在渗透胁迫下,测定了不同抗旱性小麦（抗旱性强的品种洛旱6号和抗旱性弱的品种周麦18）幼苗氨同化酶及相关参数的变化.结果表明:小麦生物量在渗透胁迫下明显降低,且抗旱性弱的周麦18降幅较大.铵态氮含量随胁迫程度的增加而增加,且周麦18增加较明显;谷氨酰胺合成酶(GS)活性在不同抗旱性品种间表现不同,抗旱性强的洛旱6号在低渗透胁迫下显著增加,在高渗透胁迫下明显降低,而周麦18随胁迫程度的增加逐渐降低;依赖还原型辅酶Ⅰ的谷氨酸脱氢酶(NADH-GDH)活性随胁迫程度的增加逐渐加大,低渗透胁迫下周麦18增加较明显,高渗透胁迫下洛旱6号增幅较大;依赖氧化型辅酶Ⅰ的谷氨酸脱氢酶(NAD^+-GDH)和依赖氧化型辅酶Ⅱ的异柠檬酸脱氢酶(NADP-ICDH)活性均随胁迫程度的增加而增加,周麦18的NAD^+-GDH活性、洛旱6号的NADP-ICDH活性增幅较大.表明小麦抗旱性的提高与铵态氮同化的增强有关,低渗透和高渗透胁迫下分别依赖GS和NADH-GDH活性的增加.     

Hydraulic redistribution: limitations for plants in saline soils

Hydraulic redistribution (HR), the movement of water from wet to dry patches in the soil via roots, occurs in different ecosystems and plant species. By extension of the principle that HR is driven by gradients in soil water potential, HR has been proposed to occur for plants in saline soils. Despite the inherent spatial patchiness and salinity gradients in these soils, the lack of direct evidence of HR in response to osmotic gradients prompted us to ask the question: are there physical or physiological constraints to HR for plants in saline environments? We propose that build‐up of ions in the root xylem sap and in the leaf apoplast, with the latter resulting in a large predawn disequilibrium of water potential in shoots compared with roots and soil, would both impede HR. We present a conceptual model that illustrates how processes in root systems in heterogeneous salinity with water potential gradients, even if equal to those in non‐saline soils, will experience a dampened magnitude of water potential gradients in the soil–plant continuum, minimizing or preventing HR. Finally, we provide an outlook for understanding the relevance of HR for plants in saline environments by addressing key research questions on plant salinity tolerance.     

产甘油假丝酵母胞浆3-磷酸甘油脱氢酶基因（CgGPD）功能分析

【目的】从高产甘油生产菌株产甘油假丝酵母（Candida glycerinogenes）基因组中克隆了NAD+依赖3-磷酸甘油脱氢酶编码基因（CgGPD）,但是该基因及其上游调控序列具体的功能还是未知的。本文研究了CgGPD基因及其上游调控序列的功能。【方法】本文以酿酒酵母（Saccharomyces cerevisiae）及其渗透压敏感型突变株为宿主,构建3种不同的酵母表达载体导入酵母细胞,研究了不同酵母转化子在渗透压胁迫条件下CgGPD基因表达对细胞的耐高渗透压胁迫应答及其细胞的甘油合成能力的影响。【结果】实验结果表明无论是以来源于S. cerevisiae 的TPI启动子还是来源于CgGPD基因的启动子,过量表达CgGPD基因的转化子均能够显著加速葡萄糖消耗速度和提高甘油合成能力,在gpd1/gpd2突变株中表达CgGPD基因能够消除细胞对外界高渗透压的敏感性,同时转化子胞内甘油大量积累。【结论】CgGPD基因在野生型酵母S. cerevisiae W303-1A表达显著提高细胞的甘油合成能力,在gpd/1gpd2突变株中能够互补GPD1基因的功能,CgGPD基因表达受渗透压诱导 调控。     

Osmotic versus toxic effects of NaCl on pepper plants

Water relations, mineral composition, growth and root morphology were studied in pepper plants (Capsicum annuum L. cv California Wonder). Two NaCl concentrations (30 and 60 mM) and two nutrient solutions in which the concentrations of macronutrients were increased were used to assess the ionic and osmotic effects of NaCl in these plants. The hydraulic conductivity (L_o), stomatal conductance (g_s), percentage of open stomata and pressure potential (Ψ_p) decreased with all treatments, in a similar way for 30 mM NaCl and for its iso-osmotic solution of macronutrients, however, the decrease was higher for 60 mM NaCl than for its iso-osmotic solution. Ion analyses also revealed that nutrient concentrations were altered greatly at 60 mM NaCl. Also, changes in morphology, such as increases in cortex cell size and in intercellular spaces, were detected. Therefore, at low salinity, the effect of NaCl was mainly osmotic, however, under higher salinity also the toxicity of Na⁺ and Cl⁻ participate.     

Seed germination and in vitro propagation of Maytenus canariensis through regeneration of adventitious shoots from axillary and apical buds

Seed germination and micropropagation protocols of the medicinal species Maytenus canariensis (Loes.) G. Kunkel & Sunding were optimized. In vitro seed germination occurred (86 to 94.7 %) only after treatment of the seeds with H₂SO₄, followed by surface sterilization and culture on solid nutrient medium without any growth regulators. Micropropagation failed when explants were taken from mature trees, and browning of the nutrient medium frequently occurred despite testing many growth media. Nonetheless, adventitious shoot regeneration was achieved employing axillary or apical buds taken from 2–2.5 months old plantlets obtained after in vitro germination of seeds, following culture on nutrient media supplemented with benzylaminopurine, kinetin and naphthalenacetic acid (NAA), attaining up to 3.9 shoots per explant, after 4–6 months. Root induction was best on a medium containing 4.0 mg dm⁻³ NAA, achieving a 100 % induction. After hardening of rooted plants, survival after transfer to soil was 71.43 %.     

短期盐胁迫下盐穗木的转录组分析

盐穗木（Halostachys caspica）是荒漠盐碱地广泛分布的盐生植物,具有极强的耐盐性。为揭示盐胁迫下盐穗木基因组层面的基因表达变化特性,通过对300和500mmol·L^-1 NaCl胁迫3h的盐穗木同化枝进行了转录组测序。有效序列组装共得到153298条平均长度为643bp的unigenes,进行GO和KEGG功能聚类,分别获得47个GO功能小类和118个KEGG通路。差异表达基因分析显示,短期低盐（300mmol·L^-1）响应基因有4432个,高盐（500mmol·L^-1）响应基因有2580个,两个胁迫的共差异基因有1245个,主要富集在细胞过程、代谢过程和响应刺激等类别中。从短期盐胁迫下盐穗木转录组筛选出渗透调节和活性氧清除的相关基因,大多为上调基因。说明盐穗木能够通过促进渗透调节和增强活性氧清除提高短期的盐胁迫适应能力。     

干旱胁迫对桢楠幼树渗透调节与活性氧代谢的影响及施氮的缓解效应

以二年生桢楠(Phoebe zhennan)幼树为研究对象, 采用盆栽控水的方法, 探讨了桢楠幼树在干旱胁迫下渗透调节和活性氧代谢的变化, 以及施氮对桢楠幼树应对干旱胁迫能力的影响。试验先将土壤含水量调整到4个梯度(田间持水量的80% (80% FC)、50% FC、30% FC和15% FC), 1周后测定受胁迫植株的相关生理指标, 之后进行3个水平的施氮处理(对照N0, 中氮MN, 高氮HN, 各施氮量分4次(即干旱梯度形成后第7、14、21和28天)分别施入)。在施氮结束后30天(即开始施肥处理后51天)再次测定各项生理指标。结果表明: 1)干旱处理7天后, 桢楠叶片中游离脯氨酸(Pro)和可溶性糖(SS)含量均随胁迫强度增大而显著增加, 重度干旱(15% FC)下的Pro含量增加尤为明显, 可溶性蛋白(SP)含量则呈先增加后降低的趋势。施氮后, 各种土壤水分状态下的Pro含量进一步增加。水分充足和轻度干旱MN水平下, SS含量也增加, 而在中度和重度干旱下的SS含量显著降低, HN水平各干旱状态下SS含量变化均不显著。施氮结束后30天时, 80% FC和50% FC下的SP含量表现为施氮组低于对照组, 而30% FC和15% FC下则相反。2)施氮前随着干旱胁迫的增强, 桢楠幼树叶片中过氧化氢(H₂O₂)含量、超氧化物歧化酶(SOD)活性、过氧化氢酶(CAT)活性显著上升, 而过氧化物酶(POD)活性呈先上升后下降的趋势。施氮后, H₂O₂含量总体上表现为减少趋势, 且MN水平下降幅度最大, HN水平反而不利于降低H₂O₂的含量。3种酶活性的变化则因干旱程度和施氮水平的不同而呈现出不同的变化趋势。3)施氮前随着干旱胁迫的增强, 叶片丙二醛(MDA)含量呈显著上升趋势, 相对电导率(REC)先显著下降后显著上升; 施氮后, 除重度干旱胁迫外, 其他各干旱处理植株的MDA含量都表现为在MN水平下有所下降, 而在HN水平下有所回升, 但在重度干旱时, 无论是MN或HN处理, MDA含量均呈上升趋势, 表明在重度干旱胁迫下, 难以通过施氮的方式缓解干旱胁迫产生的伤害。4)双因素方差分析显示, 施氮与干旱胁迫间具有极显著的交互效应。以上结果表明: 施一定量的氮肥有利于缓解桢楠幼树受到的干旱胁迫, 以年施氮量计, 施中氮(N元素质量为1.35 g·株 ^-1)对除重度干旱外的干旱胁迫具有一定的缓解作用, 但施高氮(N元素质量为2.70 g·株 ^-1)时反而会对植株造成不利影响。     

Sampling intraspecific variability in leaf functional traits: Practical suggestions to maximize collected information

The choice of the best sampling strategy to capture mean values of functional traits for a species/population, while maintaining information about traits’ variability and minimizing the sampling size and effort, is an open issue in functional trait ecology. Intraspecific variability (ITV) of functional traits strongly influences sampling size and effort. However, while adequate information is available about intraspecific variability between individuals (ITV_BI) and among populations (ITV_POP), relatively few studies have analyzed intraspecific variability within individuals (ITV_WI). Here, we provide an analysis of ITV_WI of two foliar traits, namely specific leaf area (SLA) and osmotic potential (π), in a population of Quercus ilex L. We assessed the baseline ITV_WI level of variation between the two traits and provided the minimum and optimal sampling size in order to take into account ITV_WI, comparing sampling optimization outputs with those previously proposed in the literature. Different factors accounted for different amount of variance of the two traits. SLA variance was mostly spread within individuals (43.4% of the total variance), while π variance was mainly spread between individuals (43.2%). Strategies that did not account for all the canopy strata produced mean values not representative of the sampled population. The minimum size to adequately capture the studied functional traits corresponded to 5 leaves taken randomly from 5 individuals, while the most accurate and feasible sampling size was 4 leaves taken randomly from 10 individuals. We demonstrate that the spatial structure of the canopy could significantly affect traits variability. Moreover, different strategies for different traits could be implemented during sampling surveys. We partially confirm sampling sizes previously proposed in the recent literature and encourage future analysis involving different traits.     

Osmoregulated periplasmic glucans are needed for competitive growth and biofilm formation by Salmonella enterica serovar Typhimurium in leafy-green vegetable wash waters and colonization in mice

Osmoregulated periplasmic glucans (OPGs) are major periplasmic constituents of Gram-negative bacteria. The role of OPGs has been postulated in symbiotic as well as pathogenic host–microorganism interactions. Here, we report the role of OPGs from Salmonella enterica serovar Typhimurium during growth and biofilm formation in leafy-green vegetable wash water. The opgGH mutant strain, which was defective in OPG biosynthesis, initiated the growth at a slower rate in wash waters obtained from spinach, lettuce and green collard and severely impaired biofilm formation. The lack of OPG synthesis did not influence biofilm formation by the opgGH mutant in low-nutrient low-osmolarity laboratory media. In coculture experiments initiated with equal proportions of cells, the opgGH mutant was outnumbered by the wild-type strain under the planktonic as well as the biofilm growth conditions. The opgGH mutant strain poorly colonized mouse organs when introduced orally along with the wild-type strain. This is the first report demonstrating the role of OPGs of Salmonella in competitive colonization of biofilms, planktonic cultures and mouse organs.     

Discrepancies between water potential isotherm measurements on Pinus ponderosa seedling shoots: xylem hysteresis and apoplasmic osmotic potentials *

Abstract. Sap expression, air drying and a combined technique were used to measure the water potential isotherm of Pinus ponderosa Laws, seedling shoots with the pressure chamber. Discrepancies between water relations parameters derived from these techniques can be partially explained by air entry into air drying tissues, hysteresis in the xylem water potential isotherm and dilution of apoplasmic solutes during sap expression.