Maize ( Zea mays L.) is highly sensitive to drought stress, resulting in large losses in yield; therefore, strategies aimed at enhancing drought tolerance are essential. Melatonin improves stress tolerance in plants; however, its mechanism in maize seedlings under drought stress remains unknown. Therefore, we investigated the effects of foliar-sprayed melatonin (100 umol L −1 ) on the antioxidant system, photosynthetic gas exchange parameters, stomatal behavior, endogenous melatonin and abscisic acid (ABA)-related gene expression in maize seedling leaves under 20% polyethylene glycol (PEG)-induced drought stress. PEG treatment resulted in oxidative stress and stomatal closure, resulting in chlorophyll degradation and inhibition of photosynthesis; thereby, reducing seedling biomass. Melatonin pretreatment significantly improved the relative water content, photosynthetic gas exchange parameters and stomatal behavior; thereby, maintaining chlorophyll contents and photosynthesis. Melatonin also stimulated the antioxidant system, enhancing the clearance of reactive-oxygen species, preventing severe damage under PEG-induced drought. Pre-treatment also increased endogenous melatonin and inhibited up-regulation of NCED1 , an ABA synthesis-related gene, as well as selectively up-regulating ABA catabolic genes ABA8ox1 and ABA8ox3 , reducing ABA accumulation and inducing stomatal reopening. Overall, these findings suggest that melatonin pre-treatment alleviated the inhibitory effects of drought stress on photosynthesis, enhancing tolerance in maize seedlings.

To explain the underlying mechanism of melatonin-mediated drought stress responses in maize, maize pre-treated with or without melatonin was subjected to 20% PEG nutrient solution to induce drought stress. We found that exogenous melatonin significantly improved drought tolerance, demonstrated by improved photosynthesis, reduced ROS accumulation, enhanced activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and increased content of glutathione (GSH). Comparative iTRAQ proteomic analyses revealed a higher abundance of differentially expressed proteins (DEPs) in melatonin-treated maize under drought stress for carbon fixation in photosynthetic organisms, photosynthesis, biosynthesis of amino acids, and biosynthesis of secondary metabolites, compared to untreated plants. Changes in the above molecular mechanisms could explain the melatonin-induced physiological effects associated with drought tolerance. In summary, this study provides a more integrated picture about the effects of melatonin on the physiological and molecular mechanisms in maize seedlings responding to drought stress.

To determine the role of melatonin in aging maize seeds (Zea mays L.), we investigated the physiological characteristics and performance analysis of the transcriptome after applying melatonin to maize seeds as a response to aging. In this study, we demonstrated that applying exogenous melatonin alleviated aging-induced oxidative damage, improved the activity of aging seeds, promoted growth of the germ and radicle, enhanced antioxidant enzyme activity, and reduced membrane lipid peroxidation. In addition, transcriptome sequencing revealed that various metabolic processes were induced by exogenous melatonin application in aging maize seeds, including hormone signal transduction, cellular processes, carbohydrate metabolism, secondary metabolites, and amino acid metabolism. In summary, the findings provide a more comprehensive understanding for analysing the protective effect of melatonin in aging maize seeds.

The compound 5-aminolevulinic acid (ALA) is an essential precursor for the biosynthesis of porphyrins, including chlorophyll, heme, and cytochromes. The protective effects of ALA on photosynthesis and the expression of photosynthetic genes in wheat under drought stress are not well understood. Two wheat cultivars, drought-tolerant Aikang-58 and drought-sensitive Chinese Spring, were exposed to drought stress induced by 20% polyethylene glycol (PEG-6000) after foliar pretreatment with ALA for 3 days. The results showed that exogenous application of ALA protected the drought-stressed wheat seedlings by significantly inhibiting the decrease in relative water and chlorophyll contents. The ALA-mediated alleviation of stress was similar between the drought-tolerant and drought-sensitive wheat cultivars. Meanwhile, compared to seedlings under drought treatment alone, the ALA-pre-treated wheat seedlings under drought stress maintained higher photosystem II (PSII) functional indexes. The ALA pretreatment reduced the drought-driven accumulation of both H2O2 and ABA and increased the stomatal conductance. Real-time PCR analysis showed that the psbA and psbD gene transcripts were both upregulated under drought stress following ALA pretreatment. The present study suggests that the exogenous foliar application of ALA alleviates the drought stress on wheat seedlings, which is associated with the enhancement of PSII function by inducing chlorophyll synthesis and psbA and psbD transcription. Moreover, the protective effect of ALA pretreatment was not related to the decline in stomatal conductance caused by ABA or H2O2 accumulation.

We examined the effects of 2,4-epibrassinolide (EBR) application on photosynthesis, antioxidant enzyme activity, and Rubisco activase (RCA) gene expression in wheat ( Triticum aestivum L.) seedlings under a combination of drought and heat stress. The net photosynthetic rates (P n ) of wheat seedlings decreased significantly, the photosynthetic capability was inhibited, and the activities of superoxide (SOD), peroxidase (POD), catalase (CAT), and RCA as well as the initial and total activity of Rubisco declined under the combined stress. These decreases and inhibitory effects were significantly ameliorated by exogenous EBR application. Three subunits (45–46, 41–42, and 38–39 kDa) of RCA were observed in wheat seedlings. The abundances of the 38–39 kDa and 41–42 kDa subunits were significantly lower in plants subjected to stressful conditions than in unstressed plants. Interestingly, a marked increase in 45–46 kDa RCA was observed under heat or heat combined with drought stress. The abundance of 38–39 kDa RCA in seedlings exposed to heat, drought, or their combination was significantly enhanced by EBR pretreatment, which paralleled the changes in initial Rubisco activity and P n , but was not consistent with observed mRNA abundance. These results indicated that the larger subunit of RCA (45–46 kDa), which is more thermostable and increased in response to moderate heat stress, and the smaller isoform (38–39 kDa) of RCA may play important roles in maintaining the photosynthetic capability by EBR under stress conditions.

This experiment was conducted to test the effects of foliar application of progesterone on the photochemical efficiency of photosystem II (PSII) and photosynthetic rate in wheat flag leaves subjected to cross-stress of heat and high light during grain-filling stage. The results showed that progesterone pretreatment increased the activities of superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase, and the contents of ascorbic acid and glutathione under the cross-stress. Meanwhile, the rate of O2 − production, hydrogen peroxide (H2O2) and malondialdehyde contents in progesterone pretreated leaves were significantly lower under heat and high light stress. In parallel with the alleviation of oxidative stress, higher content of D1 protein in PSII reactive center was observed in progesterone pretreated leaves, resulting in a significant increase in the potential (Fv/Fm) and actual (ΦPS II) photochemical efficiency of PSII, and the net photosynthetic rate. In summary, this study suggested that foliar application of progesterone might protect the PSII complex from heat and high light stress-induced damage through enhancing antioxidant defense system and further facilitating D1 protein stability in the wheat leaves.

microRNA是一种非编码蛋白质的小分子RNA,参与了植物生长发育及环境胁迫响应的调控,主要通过对靶基因的负调控去影响生物学过程.基于前人对拟南芥全基因组microRNAs及其靶基因的预测,我们找到了靶向15个缺铁响应基因的22个microRNAs(miR158a、miR164c、miR172a、miR1887、miR2111ab、miR3933、miR395ade、miR414、miR828、miR831、miR837-3P、miR837-5P、miR854abcd、miR857、miR861-5P、miR864-5P).对这些microRNAs的启动子进行分析,发现分别有17、10和4个microRNAs启动子中包含缺铁响应元件IDE1、生长素响应元件和乙烯响应元件.进一步通过Poly(T) adaptor RT-PCR方法对这22个microRNAs在缺铁条件下的表达变化做了检测,结果显示,除miR158a和miR837-5P外的20个microRNAs在缺铁条件下的表达变化都有显著差异,且具有时间依赖性.这20个microRNAs可作为缺铁响应的候选microRNAs.

In this study, we investigated the effects of foliar applied salicylic acid (SA) on protecting wheat (Triticum aestivum) from heat and high light stress during the grain filling stage. Specifically, the Photosystem II (PSII) photochemistry of wheat flag leaves under the treatment of SA was studied as indicators for stress response. Our results indicated that under stress, SA-supplemented wheat plants maintained higher chlorophyll content, photochemical activity of PSII, and net photosynthetic rate in comparison to non-SA treated plants, and, in addition, the SA-supplemented plants recovered more rapidly from photoinhibition when the stress was removed. SA-treated plants inhibited the decrease of the psbA gene transcription that is caused by stress and then recovered to the original control level after the stress was removed. In addition, foliar supplementation of SA could maintain or elevate the activities of antioxidative enzymes, including superoxide dismutase, ascorbate peroxidase, and catalase, which are known to provide protection against oxidative stress for wheat crops. Taken together, our results suggest that foliar application of SA can protect the PSII complex from photo-damage through enhanced transcription of the psbA gene (encoding D1 protein), as well as through mitigating photo-oxidation enabled by a high level of anti-oxidative enzyme activities, which allows for faster functional recovery of PSII from heat and high light stress.

以小麦（Triticum aestivum）矮抗58为材料,采用0.1mmol/L的外源水杨酸（SA）处理小麦叶片,以清水为对照,通过Western blotting蛋白质印记技术和叶绿素荧光分析,研究了高温强光胁迫（38℃和1600μmol m-2s-1）对小麦叶绿体Deg5蛋白酶、D1蛋白和叶绿素荧光参数的影响及SA的调节作用。结果表明,高温强光胁迫导致小麦叶绿体Deg5蛋白酶、D1蛋白含量和PSⅡ最大光能转化效率（Fv/Fm）降低,原初荧光（Fo）升高。和对照相比,外源SA处理可维持较高的Deg5蛋白酶、D1蛋白、Fv/Fm水平和较低的Fo。说明外源水杨酸可减轻高温强光对Deg5蛋白酶和D1蛋白的损伤,维持较强的PSⅡ功能。

Escherichia coli and Shigella spp. are two major bacterial contaminants in raw milk. Effective screening of the two microbes before starting the production process is a critical step for the quality and safety guarantee of the resulting dairy products. This study reported a rapid and simple realtime PCR assay using a ubiquitous primer and probe set targeting the tuf gene for the detection of E. coli and Shigella spp. An internal amplification control (IAC) was also comprised to indicate false-negative results. The duplex realtime PCR assay showed a high efficiency above 96 % and a detection limit <10 cfu per PCR. When artificially contaminated raw milk samples were further evaluated, the assay performed equally as well as the traditionally cultural-based method, and facilitated quantitative detection of the two microbes in the range from ~102 to ~106 cfu mL−1 raw milk. The detection limit was ~102 cfu mL−1 raw milk for either or a mixture of the two strains without pre-enrichment step, and could be <10 cfu per 10 mL of raw milk if a pre-enrichment step was added. Considering the detection effectiveness, time-consumption saving, and economical efficiency, the present duplex realtime PCR assay has a great potential in the application in raw milk for assessing their microbiological quality and safety in relation to E. coli and Shigella spp.

Abscisic acid (ABA) regulates many aspects of plant development, including somatic embryo (SE) initiation. However, mechanisms of ABA functions on SE initiation have remained to be investigated. In this study, we examined the endogenous ABA contents of calli in Arabidopsis during the SE inductive process. We further found that the capacity for SE initiation was strongly impaired by treatment of fluridone, a potent inhibitor of ABA biosynthesis, as well as by mutation of ABA biosynthetic gene ABA2, suggesting that ABA is required for SE initiation. Furthermore, treatment of fluridone inhibited local auxin biosynthesis and auxin polar transport in the embryonic calli, resulting in the disturbance of auxin response pattern and the decreased regeneration frequency of SEs. However, application of exogenous ABA in the medium almost recovered patterns of auxin response and SE initiation. Thus, the results suggest that ABA functions on SE initiation through mediating both auxin biosynthesis and polar transport for establishment of auxin response pattern in callus. Our study provides new information for understanding mechanisms of SE initiation.

Plant somatic cells have the capability to switch their cell fates from differentiated to undifferentiated status under proper culture conditions, which is designated as totipotency. As a result, plant cells can easily regenerate new tissues or organs from a wide variety of explants. However, the mechanism by which plant cells have such remarkable regeneration ability is still largely unknown. In this study, we used a set of meristem-specific marker genes to analyze the patterns of stem cell differentiation in the processes of somatic embryogenesis as well as shoot or root organogenesis in vitro . Our studies furnish preliminary and important information on the patterns of the de novo stem cell differentiation during various types of in vitro organogenesis.