Nutrient Deficiency Affects Root Architecture of Young Seedlings of Malus hupehensis (Pamp) Rehd. Under Conditions of Artificial Medium Cultivation

What the researchers go in for is to establish models between root architecture （RA） changes and nutrition, mold ideal root architecture of apple trees, improve the nutrient uptake efficiency, and further explore the functional mechanism of nutrient elements during the course of RA construction. The cultivation system of filter paper is utilized to research the effect of nutrient deficiency on the RA of Malus hupehensis （Pamp.） Rehd. There may be eight types of RA. In complete Hogland solution, the main type of RA is ＂lateral roots clustering in the upper and middle regions of primary root＂. With the lack of P, K or Ca, the main type of RA is ＂lateral roots clustering in the upper region primary root＂, and the ＂lateral roots clustering in the upper and middle regions of primary root＂ types of RA decrease. But with shortage of P, the type of lateral roots clustering in the upper and lower regions of primary root increases, and the type of lateral roots clustering in the middle region of primary root decreases, with the types of RA diversified. Under the condition of K deficiency, the type of no lateral root increases and types of lateral roots clustering in the middle region of primary root decrease, and the percentage of such types as ＂no lateral root＂, ＂lateral roots clustering in the upper region of primary root＂, and ＂lateral roots clustering in the upper and middle regions of primary root＂ accounts for 97.9% in all, with the types of RA simplified. With lack of Fe, Mg or Zn, the main type of RA is ＂lateral roots clustering in the upper and middle regions of primary root＂, but the type of lateral roots evenly-distributed on primary root increases. The main type of RA is ＂lateral roots evenlydistributed on primary root＂, under the condition of N deficiency, and the types of RA turn out to be diversified. There exists a close relation between nutrient deficiency and RA changes. Owing to various forms of nutrient deficiency, correspondingly different types of RA have been produced.

Effects of Cinnamon Acid on Respiratory Rate and Its Related Enzymes Activity in Roots of Seedlings of Malus hupehensis Rehd.

This paper studied the effects of cinnamon acid treatments on the respiratory rate and related enzymes activity in the seedling roots of Malus hupehensis Rehd.It would provide information for understanding the mechanisms of inhibition damage caused by continuous cultivation of apple tree.20 mL of solution containing different concentrations of cinnamon acid was added into container with the tested seedlings.After treatment,the samples were taken periodically and the respiratory rates were measured by OXY-LAB oxygen electrodes under 25°C stable temperature and then the activities of related enzymes were measured.The rates of total respiration and other 2 pathways [tricarboxylic acid cycle （TCA） and pentose phosphate pathway （PPP）] appeared initially an increasing treads and late （on the 3rd d） began to decline.However,they again appeared an increase trend at the end period,on the contrast,the respiratory rate of embden-meyer- hot-parnas （EMP） pathway appeared a stead decline tread but it had a recover on the last day.The respiratory rate of total and 3 pathways were decreased under 125 mg kg-1 （soil）.The dynamic trends of the enzymes activities of pyrophosphate-dependent phosphofructokinase （PFK）,glucose-6-phosphate dehydrogenase （G-6-PDH） and malate dehydrogenase （MDH） showed similarly.In conclusion,treatments of certain concentration of cinnamon acid would inhibit the respiratory rate and related enzymes activity of roots of M.hupehensis Rehd.And the inhibition degrees were positively related with concentration of cinnamon acid treatments.

The mitigation effects of exogenous dopamine on low nitrogen stress in Malus hupehensis

Dopamine plays numerous physiological roles in plants.We explored its role in the regulation of growth,nutrient absorption,and response to nitrogen(N)deficiency in Malus hupehensis Rehd.Under low N condition,plant growth slowed,and the net photosynthetic rates,chlorophyll contents,and maximal quantum yield of PSII(Fv/Fm)decreased significantly.However,the application of 100μmol L−1 exogenous dopamine significantly reduced the inhibition of low N stress on plant growth.In addition to modifying root system architecture under low N supply,exogenous dopamine also changed the uptake,transport,and distribution of N,P,and K.Furthermore,exogenous dopamine enhances the tolerance to low nitrogen stress by increasing the activity of enzymes(nitrate reductase,nitrite reductase,glutamic acid synthase and glutamine synthetase)involved in N metabolism.We also found that exogenous dopamine promoted the expression of ethylene signaling genes(ERF1,ERF2,EIL1,ERS2,ETR1,and EIN4)under low N stress.Therefore,we hypothesized that ethylene might be involved in dopamine response to low N stress in M.hupehensis.Our results suggest that exogenous dopamine can mitigate low N stress by regulating the absorption of mineral nutrients,possibly through the regulation of the ethylene signaling pathway.

Relationship Between Polyamines Metabolism and Cell Death in Roots of Malus hupehensis Rehd. Under Cadmium Stress

The free putrescine （Put） content, the hydrogen peroxide （H202） content and the polyamine oxidase （PAO） activity in roots of Malus hupehensis Rehd. var. pinyiensis Jiang （PYTC） were significantly increased, and reached its peak at 1, 2 and 6 h, respectively, under cadmium treatment. The free spermine （Spin） and spermidine （Spd） contents were dramatically decreased, and reached the minimum value at 4-6 h, then remained relatively stable. The change in total free polyammes （PAs） content was consistent with that of free Put. The number of root dead cells was gradually increased after treatment for 24 h, and the typical characteristics of programmed cell death （PCD） were displayed at 48 h. Throughout the Cd treatment process, changes in PAs metabolism appeared to be prior to cell death increase, and the H2O2 content was always maintained at a high level. These results indicated that polyamines could initiate cell death by generating H2O2 in roots of Malus hupehensis Rehd. under CdSO4 stress.

NO_3^-/NH_4^+ ratios affect plant growth, chlorophyll content,respiration rate, and morphological structure in Malus hupehensis seedlings

Malus hupehensis （Pamp.） Rehd. is a widely cultivated rootstock in China. We studied the effect of three NO3-/NH4＋ ratios （100/0, 50/50, and 0/100, molar basis） at total nitrogen （N） concentration of 8 mmoL L-1 in a nutrient solution on M. hupehensis seedlings. Plant biomass, NO3- and NH4＋concentrafion, chlorophyll con- tent, respiratory rate, and cellular structure were investi- gated. M. hupehensis seedlings at the NO3-/NH4＋ ratio of 50/50 had the highest level of fresh weight, dry weight, shoot length, and chlorophyll （a, b, and a ＋ b） content, but the lowest respiration rate in the leavesand roots. In addition, thickness and numbers of palisade and spongy tissue cells of the leaves were greater with this treatment than with other treatments. At the NO3-/NH4＋ ratio of 100/0, the leaves and roots had higher NO3- concentration and lower NH4＋ concentration. However, the opposite trend occurred at the NO3-/NH4＋ ratio of 0/100. Chloro- phyll （a, b, and a ＋ b） content was lowest at the NO3-/NH4＋ ratio of 100/0 than at the other ratios. At the NO3-/ NH4＋ ratio of 0/100, oxygen （02） consumption increased in the leaves and roots, and irregular epidermis and cortex cells were observed in the root apical meristematic and mature region. Our results indicated that the NO3-INH4＋ ratio at 50/50 was suitable for growth of M. hupehensis seedling to achieve the highest biomass production and efficiency.

Seasonal Variation,Microscopic and Chromatographic Analysis of Leaves in Malus hupehensis:A Protocol for Its Quality Control

Objective To establish a quality control protocol based on microscopic, TLC, and HPLC methods, and to verify the optimal harvesting time for the leaves of Malus hupehensis(LMH). Methods The LMH were pulverized into powder for microscopic identification or TLC and HPLC analysis after ultrasonic extraction with methanol. Seasonal variations of the phlorizin content and average leaf weight were determined by HPLC analysis and weighing up the leaves collected from May to October. Results Microscopic and macromorphologic characteristics have been described for the leaf identification. A qualitative TLC assay and a quantitative HPLC method have been established for the quality control of LMH. Phlorizin was selected as a reference marker, which resolved at Rf 0.53 in TLC assay and at 14.0 min in HPLC assay. The content of phlorizin decreased gradually from 17.0% in leaves collected in May to 7.5% in October. The average leaf weight reached the level of 0.6 g in August and maintained until its falling.Conclusion These methods are simple, selective, accurate, and reliable for the quality control of LMH. The period from late August to early September is suggested as the optimal harvesting time of the LMH.

Melatonin and dopamine alleviate waterlogging stress in apples by recruiting beneficial endophytes to enhance physiological resilience

Melatonin and dopamine can potentially prevent waterlogging stress in apples.The current study investigated the mechanism by which melatonin and dopamine alleviate apple waterlogging stress.This study demonstrated that melatonin and dopamine alleviated waterlogging by removing reactive oxygen species(ROS),and that the nitric oxide(NO)content and nitrate reductase(NR)activity were significantly correlated.Melatonin and dopamine were also found to recruit different candidate beneficial endophytes(melatonin:Novosphingobium,Propionivibrio,and Cellvibrio;dopamine:Hydrogenophaga,Simplicispira,Methyloversatilis,Candidatus_Kaiserbacteria,and Humicola),and these endophytes were significantly and positively correlated with plant growth.Network analyses showed that melatonin and dopamine significantly affected the endophytic bacterial and fungal communities under waterlogging stress.The metabolomic results showed that melatonin and dopamine led to waterlogging resistance by upregulating the abundance of beneficial substances such as amino acids,flavonoids,coumarins,and organic acids.In addition,melatonin and dopamine regulated the physicochemical properties of the soil,which altered the endophyte community and affected plant growth.The co-occurrence network demonstrated close and complex relationships among endophytes,metabolites,soil,and the plants.Our results demonstrate that melatonin and dopamine alleviate waterlogging stress in apples by recruiting beneficial endophytes to enhance physiological resilience.This study provides new insights into how melatonin and dopamine alleviate stress and a theoretical basis for synergistic beneficial microbial resistance to waterlogging stress.

Dopamine improves apple replant disease resistance by regulating physiological resilience and rhizosphere microbial community structure

Apple replant disease(ARD)is a complex agricultural problem caused by multiple stressors that can lead to increased reactive oxygen species(ROS)levels and limited nutrient utilization in plants.However,existing countermeasures cannot effectively address this challenge.Here,we used Malus hupehensis as a test organism to investigate whether the pleiotropic molecule dopamine can alleviate ARD using pot experiments.Exogenous application of 100μmol L-1 dopamine significantly promoted the growth of apple seedlings in the replanted soil,with a relative growth rate increase of 17.44%.Our results revealed two major pathways by which dopamine regulates ARD resistance in apple trees.First,dopamine effectively reduces the level of ROS and activates the expression of genes related to nitrogen(N)transport and metabolism.Among those genes,MdNLP5,MdNRT1.1,MdNLP2,MdNRT2.5,MdNLP3,MdNRT2.4,MdNADH-GAGOT,and MdFd-GAGOT were strongly regulated by dopamine.These regulatory effects promoted the uptake and utilization of soil N by the plants.Second,dopamine improved the physical and chemical properties,enhanced microbial community diversity,and promoted mutual cooperation between microbial communities in the soil.Furthermore,dopamine altered the microbial structure of rhizosphere soil(upregulating Clostridiales,Gaiellales,Sordariales and Mortierellales;downregulating Micrococcales,Longimicrobiales,Hypocreales and Cystobasidiales).Notably,dopamine significantly upregulated the abundances of Gaiella and Mortierella,both of which were positively correlated with soil urease activity,soil available N content,plant growth and N uptake.Dopamine also significantly downregulated the abundance of the plant pathogen Gibberella(by 11.71-fold)in replant soil.Our results provide insights into the mechanisms by which dopamine promotes ARD resistance,and can promote the sustainable development of the apple industry.

湖北海棠叶活性成分、功能特性及开发利用研究进展

湖北海棠[Malus hupehensis(Pamp.)Rehder]是药食两用植物,是湖北省西部重要的优势植物资源。近年来的研究表明,湖北海棠叶中富含黄酮类、多酚类、皂苷类等多种活性成分以及多种人体所必需的微量元素如硒、锌、铁等,具有改善认知功能、抗肿瘤、保护肝脏、雌激素样活性、降血糖、调血脂、抗氧化等功效,相关产品开发仍处于初级阶段。综述了湖北海棠叶的活性成分、功能特性及开发利用情况,以期为促进湖北海棠叶的广泛应用提供参考。

Isolation of phloridzin-degrading,IAA-producing bacterium Ochrobactrum haematophilum and its effects on the apple replant soil environment

We isolated and identified a bacterium that could produce IAA and degrade phloridzin in the rhizosphere soil of healthy replanted apple(the rootstock is M9T337 and the scion is Yanfu 3),providing a theoretical basis for reducing the obstacles associated with apple replant disease(ARD).Isolates were screened using Salkowski colorimetry and screening medium for phloridzin.The isolate of interest(W6)was identified as Ochrobactrum haematophilum based on morphological analysis,physiological and biochemical tests,and 16S rDNA sequencing.In a laboratory experiment,W6 produced auxin and promoted the growth of Arabidopsis thaliana roots,and its degradation rate of 100 mg.L^(-1 )phloridzin was 62.0%.In a pot experiment,W6 significantly reduced the phenolic acid contents of replanted soil,lowered the abundance of the harmful fungus Fusarium solani,and increased soil enzyme activities,thereby improving the micro-ecological environment of replant soil.W6 increased the root antioxidant enzyme activity and leaf photosynthetic pigment content of replanted Malus hupehensis Rehd.seedlings,effectively alleviating the decrease in net photosynthetic rate,transpiration rate and stomatal conductance caused by ARD.In a field experiment,W6 also promoted the growth of replanted apple(the rootstock is M9T337 and the scion is Yanfu 3)saplings.Therefore,W6 can promote apple growth and degrade phenolic acids,and it can be used as an effective treatment for the reduction of ARD.

The effects of crop rotation combinations on the soil quality of old apple orchard

This study investigated the effects of six crop rotation combinations on the soil quality of old apple orchard and seedling growth of Malus hupehensis Rehd.(apple rootstock) under pot conditions. The inhibitory effects of crops such as Allium fistulosum, Brassica juncea, and Triticum aestivum on four species of Fusarium were observed and compared in six treatments. These were continuous cropping(CK), fumigation with the methyl bromide(FM), rotating A. fistulosum only(R1), rotating A. fistulosum and T. aestivum(R2), rotating A. fistulosum, B. juncea, and T. aestivum(R3), and fallow(FC) in a year. The results showed that the biomass of Malus hupehensis Rehd. seedlings increased significantly. The root length increased and the root architecture was optimized. The respiration rate of the root system was increased by about 1 time after rotation. The treatments of R1, R2, R3, and FC increased bacterial count by 232.17%, 96.04%, 316.21%, and 60.02%, respectively. However, the fungi were reduced in varying degrees and bacteria/fungi ratio was increased by 5–10 times. The enzyme activities, p H, and organic matter were increased, but soil bulk density was decreased. Phenolic acids such as phloridzin was decreased significantly. The copy number of four Fusarium species declined by 85.59%, 74.94%, 69.68%, and 54.41% after rotating three different crops(R3 treatment). The root volatiles of three plants inhibited mycelial growth and spore germination of four Fusarium species.

Response of Organic Acids to Zinc Homeostasis in Zinc-Deficient and Zinc-Toxic Apple Rootstock Roots

To elucidate the mechanisms of tolerance to zinc (Zn) deficiency and Zn toxicity in the root of apple trees, the apple rootstock Malus hupehensis (Pamp.) Rehd seedlings were selected to study the responses of organic acids to Zn homeostasis in roots under low Zn (0 μmol L-1 ), adequate Zn (as control, 4 μmol L-1 ) and toxic Zn (100 μmol L-1 ) treatments. The differences of Zn concentrations and accumulations in the roots were highest, compared with those in the stems and leaves, when apple seedlings were subjected to low and toxic Zn treatments for 1 d. The concentrations and accumulations of oxalic and malic acids in the roots in the low and toxic Zn treatments increased by 20% to 60% compared with those of the control treatment. Significantly negative correlations were found between the total Zn concentrations and the concentrations of oxalic and malic acids in the roots under 1 d of low Zn treatment. However, contrary correlations were found for the toxic Zn treatment. Meanwhile, the maximum influx rates of Zn 2+ under low and toxic Zn treatments increased by 30% and 20%, respectively, compared with the rate of the control treatment. Both Zn deficiency and Zn toxicity increased the concentrations of organic acids in root after short-time Zn treatment, which could resist Zn stress through balanding Zn homeostasis in M. hupehensis Rehd.