Seed priming as a promising technique to improve growth, chlorophyll, photosynthesis and nutrient contents in cucumber seedlings

Seed priming is a technique to improve seed germination, seedlings growth, uniformity and yield. The, present study was designed to, investigate the physiological mechanism of seed priming with GA3 and KNO3 on cucumber seedlings growth, chlorophyll, photosynthesis and nutrients uptake. The cucumber seeds were treated as; CK; control, T1; GA3 100 ppm, T2; GA3 200 ppm, T3; KNO3 1%, T4; KNO3 5%, before seed sowing. The results showed that seed priming with GA3 and KNO3 significantly increased the plant height, fresh and dry weight and strong seedling index. Moreover, chlorophyll a, chlorophyll b, chlorophyll a+b, carotenoid contents, net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and intercellular CO2 concentration in seed priming seedlings. In addition, seed priming significantly enhanced leaf macro and micro nutrient contents. Additionally, among various treatments GA3 200 ppm and KNO3 5% are found best. These results suggested that seed priming with GA3 and KNO3 synergistically promoted the chlorophyll contents, photosynthesis and nutrients uptake in cucumber seedlings, thus leading to improve plant growth

Selection of reference genes for quantitative real-time PCR analysis in cucumber (Cucumis sativus L.), pumpkin (Cucurbita moschata Duch.) and cucumber–pumpkin grafted plants

Background Quantitative real-time PCR (qRT-PCR) is a commonly used high-throughput technique to measure mRNA transcript levels. The accuracy of this evaluation of gene expression depends on the use of optimal reference genes. Cucumber–pumpkin grafted plants, made by grafting a cucumber scion onto pumpkin rootstock, are superior to either parent plant, as grafting conveys many advantages. However, although many reliable reference genes have been identified in both cucumber and pumpkin, none have been obtained for cucumber–pumpkin grafted plants. Methods In this work, 12 candidate reference genes, including eight traditional genes and four novel genes identified from our transcriptome data, were selected to assess their expression stability. Their expression levels in 25 samples, including three cucumber and three pumpkin samples from different organs, and 19 cucumber–pumpkin grafted samples from different organs, conditions, and varieties, were analyzed by qRT-PCR, and the stability of their expression was assessed by the comparative ΔCt method, geNorm, NormFinder, BestKeeper, and RefFinder. Results The results showed that the most suitable reference gene varied dependent on the organs, conditions, and varieties. CACS and 40SRPS8 were the most stable reference genes for all samples in our research. TIP41 and CACS showed the most stable expression in different cucumber organs, TIP41 and PP2A were the optimal reference genes in pumpkin organs, and CACS and 40SRPS8 were the most stable genes in all grafted cucumber samples. However, the optimal reference gene varied under different conditions. CACS and 40SRPS8 were the best combination of genes in different organs of cucumber–pumpkin grafted plants, TUA and RPL36Aa were the most stable in the graft union under cold stress, LEA26 and ARF showed the most stable expression in the graft union during the healing process, and TIP41 and PP2A were the most stable across different varieties of cucumber–pumpkin grafted plants. The use of LEA26, ARF and LEA26+ARF as reference genes were further verified by analyzing the expression levels of csaCYCD3;1, csaRUL, cmoRUL, and cmoPIN in the graft union at different time points after grafting. Discussion This work is the first report of appropriate reference genes in grafted cucumber plants and provides useful information for the study of gene expression and molecular mechanisms in cucumber–pumpkin grafted plants

BP Network Control for Resource Allocation and QoS Ensurance in UAV Cloud

Unmanned aerial vehicle (UAV) cloud can greatly enhance the intelligence of unmanned systems by dynamically unloading the compute-intensive applications to cloud. For the uncertain nature of UAV missions and fast-changing environment, different UAV applications may have different quality of service (QoS) requirements. This paper proposes a mixed QoS ensurance and energy-balanced (MQEB) architecture for UAV cloud from a view of control theory, which can support both hard and soft QoS ensurance with the consideration of energy saving. The hard and soft QoS requirements are decoupled by being normalized into a two-level cascaded feedback loop. The former is time slot loop (TS-Loop) to enforce the absolute QoS ensurance for real-time applications, and the latter is contention window loop (CW-Loop) to enforce the plastic QoS ensurance for non-real-time applications. Finally, the back propagating (BP) neuron network is used for parameters’ self-tuning and controller design. The hardware experiments demonstrate the feasibility of MQEB. In heavy load, MQEB has greater throughput and better energy efficiency, and in light load, MQBE has lower total power consumption

Brassinosteroids are involved in response of cucumber (Cucumis sativus) to iron deficiency

BACKGROUND AND AIMS: Brassinosteroids (BR) are a class of plant polyhydroxysteroids with diverse functions in plant growth and development. However, there is little information on the role of BRs played in the response to nutrient deficiency. METHODS: To evaluate the role of BR in the response of plants to iron (Fe) deficiency, the effect of 24-epibrassinolide (EBR) on ferric reductase (FRO) activity, acidification of the rhizosphere and Fe content in cucumber (Cucumis sativus) seedlings under Fe-deficient (1 µm FeEDTA) and Fe-sufficient (50 µm FeEDTA) conditions were investigated. KEY RESULTS: There was a significant increase in FRO activity upon exposure of cucumber seedlings to an Fe-deficient medium, and the Fe deficiency-induced increase in FRO activity was substantially suppressed by EBR. In contrast, application of EBR to Fe-sufficient seedlings stimulated FRO activity. Ethylene production evoked by Fe deficiency was suppressed by EBR, while EBR induced ethylene production from Fe-sufficient seedlings. Fe contents in shoots were reduced by treatment with EBR, while Fe contents in roots were markedly increased under both Fe-deficient and Fe-sufficient conditions. The reductions in Fe contents of shoots were independent of chlorophyll (CHL) contents under Fe-sufficient conditions, but they were positively correlated with CHL contents under Fe-deficient conditions. At the transcriptional level, transcripts encoding FRO (CsFRO1) and Fe transporter (CsIRT1) were increased upon exposure to the Fe-deficient medium, and the increases in transcripts were reversed by EBR. CONCLUSIONS: The results demonstrate that BRs are likely to play a negative role in regulating Fe-deficiency-induced FRO, expressions of CsFRO1 and CsIRT1, as well as Fe translocation from roots to shoots

Dynamic Expression of miRNAs and Their Targets in the Response to Drought Stress of Grafted Cucumber Seedlings

Grafting of cucumber is widely used to improve growth and tolerance to biotic and abiotic stresses. MicroRNAs (miRNAs) regulate plant growth and development, and respond to various stresses through negative, post-transcriptional regulation of the expression of their target genes. We grafted cucumber (Cucumis sativus) scions onto pumpkin (Cucurbita moschata) rootstocks to study the molecular mechanisms of miRNA-mediated grafting-induced responses to drought stress. The relative expressions of 17 selected miRNAs and their predicted target mRNAs were detected by quantitative real-time PCR (qRT-PCR) in leaves and roots of hetero-grafted cucumber seedlings (cucumber as scion and pumpkin as rootstock) and auto-grafted cucumber seedlings (cucumber as scion and rootstock) after 24 hours of 15% PEG6000 treatment. Compared with the expression in leaves of auto-grafted cucumber seedlings, the expressions of most miRNAs in the leaves of hetero-grafted seedlings changed dynamically: induced under normal conditions, and reduced after 3 h of drought stress, and then induced after 8 h and 24 h of drought stress. Similarly, compared with the expression in roots of auto-grafted cucumber seedlings, the expressions of most miRNAs in the roots of hetero-grafted cucumber seedlings changed dynamically: reduced under normal condition, and still reduced after 1 h, but induced after 3 h and 8 h, then reduced significantly after 24 h of drought stress. These results are useful for the functional analysis of miRNAs in the mediation of grafting-dependent drought tolerance

Alterations in Ascorbic Acid Levels by Transformation of the L-galactono-1,4-lactone Dehydrogenase Gene in Solanum tuberosum

L-galactono-1, 4-lactone dehydrogenase (GLDH) is an important enzyme that catalyzes the last step of the ascorbate biosynthetic pathways in plants. A full-length cDNA clone encoding GLDH was isolated from potato (Solanum tuberosum L. ‘Favorita’) leaf and subcloned into a binary vector, pBI121, to construct sense and antisense recombinant plant expression vectors. The recombinants were introduced into potato via Agrobacterium-mediated transformation, and plants were confirmed as transgenic using PCR and quantitative real-time PCR. Two anti-sense potato lines (G1 and G2) and three sense lines (G3, G4 and G5) were obtained. The GLDH activity of G4 and G5 were increased in vivo. Moreover, the ascorbic acid (AsA) and dehydroascorbate (DHA) contents were up-regulated in both leaves and tubers. However, the shoots of G1 were suppressed and its leaves were deformed. Additionally, the AsA contents in G1 leaves and tubers decreased by 28.8% and 10.3%, respectively. The GLDH activity in leaves treated with L-galactono-1,4-lactone (L-GalL) increased in all lines, as did the AsA and DHA contents. These results indicate that GLDH activity plays an important role in regulating the AsA level as well as the growth and development of potato plants

Stair-Step Pattern of Soil Bacterial Diversity Mainly Driven by pH and Vegetation Types Along the Elevational Gradients of Gongga Mountain, China

Ecological understandings of soil bacterial community succession and assembly mechanism along elevational gradients in mountains remain not well understood. Here, by employing the high-throughput sequencing technique, we systematically examined soil bacterial diversity patterns, the driving factors, and community assembly mechanisms along the elevational gradients of 1800–4100 m on Gongga Mountain in China. Soil bacterial diversity showed an extraordinary stair-step pattern along the elevational gradients. There was an abrupt decrease of bacterial diversity between 2600 and 2800 m, while no significant change at either lower (1800–2600 m) or higher (2800–4100 m) elevations, which coincided with the variation in soil pH. In addition, the community structure differed significantly between the lower and higher elevations, which could be primarily attributed to shifts in soil pH and vegetation types. Although there was no direct effect of MAP and MAT on bacterial community structure, our partial least squares path modeling analysis indicated that bacterial communities were indirectly influenced by climate via the effect on vegetation and the derived effect on soil properties. As for bacterial community assembly mechanisms, the null model analysis suggested that environmental filtering played an overwhelming role in the assembly of bacterial communities in this region. In addition, variation partition analysis indicated that, at lower elevations, environmental attributes explained much larger fraction of the β-deviation than spatial attributes, while spatial attributes increased their contributions at higher elevations. Our results highlight the importance of environmental filtering, as well as elevation-related spatial attributes in structuring soil bacterial communities in mountain ecosystems

Climate and soil parameters are more important than denitrifier abundances in controlling potential denitrification rates in Chinese grassland soils

Denitrification is an important process that influences nitrogen (N) loss and the production of greenhouse gas in grassland soils. However, the relative contributions of abiotic and biotic factors to soil denitrification potential at the regional and sub-regional scales in grassland ecosystems remain elusive. In this study, soil samples were collected from 21 sites at three steppes of China, including the Inner Mongolia Plateau (IMP), the Xinjiang Autonomous Region (XAR) and the Tibetan Plateau (TP) grasslands. Results showed that the key factors controlling the denitrification potential were regional and scale-dependent. At the sub-regional scales, soil pH, aridity index (AI) and total organic carbon (TOC) explained the highest variances on denitrification potential in the IMP, XAR and TP steppe, respectively. At the regional scale, the mean annual precipitation (MAP) was the most important environmental driver for the denitrification potential. Partial least squares (PLS) path modeling revealed that the MAP might regulate denitrification potential directly and indirectly by its effects on the plant and soil properties. Overall, these results help to improve our understandings on the prediction of the denitrification potential under global changes and revealed that the denitrification potential at various scales could be regulated by the multiple interactions of abiotic and biotic factors. (C) 2019 Published by Elsevier B.V