Regulatory Function Of Dopamine And Melatonin On Mineral Nutrient Uptake In Malus Under Drought And Nutrient Stresses

Water and mineral elements are indispensable for plant growth,development,and productivity.Mineral nutrients have electrochemical,and catalytic roles in all biological organisms,and are fundamental to hydraulic systems.Nutrient deficiencies are one of the most limiting factors and have a greater negative influence on plant growth and yield.Drought stress is one of the most limiting factors that influence many morphological,physiological,biochemical,metabolic,transcriptomic,and proteomic processes,thereby affecting plant survival,development,and yields.As one of the most economically important woody plants,apple?Malus domestica Borkh.?is widely cultivated.Northwestern China is a crucial area for apple cultivation,but arid and poor soils are common there.Drought and nutrient stress are two main serious problems that impact apple growth and productivity.In recent years,the benefits of dopamine and melatonin have been documented in studies with drought-induced and nutrient deficiency-induced stress.However,little is known about its possible role in directing the concentration,uptake,shift,partitioning,and resorption of mineral elements by plants under stress conditions.Here,we employed both hydroponics and greenhouse pot experiments to study the regulation function and mechanism of exogenous dopamine and melatonin on ionome of apple under nutrient deficiency-induced and drought-induced stress.Overexpressed TH and HIOMT transgenic apple was obtained by transgenic technology.The plants were also subjected to various adversity treatments to identify their function and mechanism under various stresses.The main results obtained are as follows:1.We investigated the role of dopamine in regulating growth,root system architecture,nutrient uptake,and responses to nutrient deficiencies in Malus hupehensis Rehd.Under a nutrient deficiency,plants showed significant reductions in growth,chlorophyll concentrations,and net photosynthesis,along with disruptions in nutrient uptake,transport,and distribution.However,pretreatment with 100?M dopamine markedly alleviated such inhibitions.Supplementation with that compound enabled plants to maintain their photosynthetic capacity and development of the root system while promoting the uptake of N,P,K,Ca,Mg,Fe,Mn,Cu,Zn,and B,altering the way in which those nutrients were partitioned throughout the plant.The addition of dopamine up-regulated genes for antioxidant enzymes involved in the ascorbate–glutathione cycle?MdcAPX,MdcGR,MdMDHAR,MdDHAR-1,and MdDHAR-2?but down-regulated genes for senescence?SAG12,PAO,and MdHXK?.These results indicate that exogenous dopamine has an important antioxidant and anti-senescence effect that might be helpful for improving nutrient uptake.Overexpression of TH in apple plants markedly enhanced their tolerance to nutrient deficency.Under low-N conditions,both relative growth rate and the concentration,uptake,and accumulation of?¹⁵N were significantly elevated in transgenic apple lines when compares with the untransformed plants?WT?.Transcript levels of NRT1;1,NRT2;4,NRT2;5,and NRT2;7 genes were greatly up-regulated in transgenic apple lines than in the WT plants.Together these results demonstrate that overexpression of TH enhances tolerance to N-deficiencies,and plays positive roles in nutrient uptake and utilization.2.We conducted greenhouse pot experiments to address how dopamine affects the drought-resistance traits of‘Naganofuji No.2'apple?Malus domestica Borkh.?trees at the physiological and molecular levels.Seedling biomass,photosynthesis rates,chlorophyll concentrations,and stomatal apertures were markedly reduced under stress,but dopamine treatment mitigated the inhibiting effects of drought on plant growth and helped maintain strong photosynthesis,chlorophyll levels,and stomatal functioning.Concentrations of most macro-,micro-,and trace elements decreased in response to drought.This stress also diminished the uptake and transport of elements in the leaves and stems,but increased the partitioning of elements in the roots.Nutrient resorption proficiency decreased while nutrient resorption efficiency increased for most analyzed elements.Exogenous dopamine significantly increased the concentrations,uptake,and transport of nutrients under drought stress,and also altered their distribution within the whole plant.However,this molecule had a negative effect on nutrient resorption.Although transcript levels of a key chlorophyll degradation gene,PAO,and SAG12 were elevated upon drought treatment,dopamine significantly suppressed the upregulation of those genes under such stress conditions.These observations indicate that dopamine has an important anti-senescence effect that might be helpful for regulating nutrient uptake,transport,and resorption,and ultimately influencing overall plant growth.Overexpression of TH in apple plants markedly enhanced their tolerance to drought stress.Under naturally drought conditions,the overexpression of TH markedly alleviated the inhibitory effects of drought on photosynthesis,stomatal apertures,chlorophyll levels,and relative water content,and it controlled the burst of relative electrolyte leakage and hydrogen peroxide.In transgenic apple plants,the concentration,uptake,utilization,and accumulation of?¹⁵N were higher than WT,these were possibly due to up-regulating N-metabolism?NR,NiR,GS,Fd-GOGAT,NADH-GOGAT?and transport?AMT1;2,AMT1;5,AMT1;6,AMT2;1,NRT1;1,NRT2;4,NRT2;5,NRT2;7?genes,and higher activity of enzymes involved in N metabolism?NR,NiR,GS,and GOGAT?.Similar results were obtained in the long drought test.Together these results demonstrate that overexpression of TH enhances tolerance to drought stress,and plays positive roles in nutrient uptake and utilization.3.We investigated the role of mealtonin in regulating growth,root system architecture,nutrient uptake,and responses to nutrient deficiencies in Malus hupehensis Rehd.Nutrient deficiency-induced stress caused a reduction in growth rates and disrupted the absorption of ionome.However,pretreatment with 0.1?M melatonin significantly alleviated such inhibitions.The addition of melatonin also upregulated genes for antioxidant enzymes involved in the ascorbate-glutathione cycle?MdcAPX,MdDHAR1,MdDHAR2,MdMDHAR,and MdcGR?and improving the expression of K transporters and genes for the CBL1-CIPK23pathway.These results indicated that melatonin can regulate the ROS signal and activate the CBL1-CIPK23 pathway to regulate the expression of a potassium channel protein gene,thereby promoting the absorption of potassium ions.4.We investigated the influence of melatonin long-term exogenous application on‘Naganofuji No.2'apple?Malus domestica Borkh.?under moderate drought conditions.Both growth and the uptake of macro-and micronutrients were generally decreased in stressed plants.However,the application of exogenous melatonin significantly mitigated this growth reduction and enabled plants to maintain uptake fluxes.This addition of melatonin also markedly alleviated the inhibitory effects of drought on photosynthesis,stomatal apertures,chlorophyll levels,and relative water content,and it controlled the burst of relative electrolyte leakage and hydrogen peroxide.Our investigation with stable isotopes further verified that exogenous melatonin was associated with significant increases in the uptake,utilization,and accumulation of?¹⁵N under drought conditions.Stress sharply reduced the activity of enzymes involved in nitrogen metabolism?NR,NiR,GS,and GOGAT?,but the application of melatonin substantially reversed that response.We also examined whether melatonin might control the expression of genes for N-metabolism and transport.Here,the transcript levels of metabolic genes?NR,NiR,GS,Fd-GOGAT,and NADH-GOGAT?and uptake genes?AMT1;2,AMT1;5,AMT1;6,AMT2;1,NRT1;1,NRT2;4,NRT2;5,and NRT2;7?were greatly up-regulated in the leaves.Exogenous melatonin treatment also significantly increased the concentration of endogenous melatonin.Overexpression of HIOMT in apple plants markedly enhanced their tolerance to drought stress.Under naturally drought conditions,the overexpression of HIOMT markedly alleviated the inhibitory effects of drought on photosynthesis,chlorophyll levels,and relative water content,and it controlled the burst of relative electrolyte leakage and hydrogen peroxide.The antioxidant capacity were significantly elevated in OE apple lines when compared with the untransformed WT under this conditions.Similar results were obtained in the long drought test.In transgenic apple plants,the concentration,uptake,utilization,and accumulation of?¹⁵N were higher than WT.Overexpression of HIOMT in apple plants markedly upregulated genes for N-metabolism?NR,NiR,GS,Fd-GOGAT,NADH-GOGAT?and transport?AMT1;2,AMT1;5,AMT1;6,AMT2;1,NRT1;1,NRT2;4,NRT2;5,NRT2;7?,and the activity of enzymes involved in N metabolism?NR,NiR,GS,and GOGAT?were significantly increased in OE apple lines when compared with the untransformed WT.Together these results demonstrate that overexpression of HIOMT enhances tolerance to drought stress.5.We investigated the influence of dopamine and melatonin long-term exogenous application on‘Fuji'apple?Malus domestica Borkh.?fruit growth and quality under moderate drought conditions.Under drought stress conditions,growth of apple fruits was significantly inhibited,but applying 100?M dopamine and melatonin noticeably alleviated this inhibition.The values of colour coordinates showed that droughts stress was unfavorable to fruit coloring.The lower color index?CI?and anthocyanin in stress fruits also indicates a slower coloring.But exogenous dopamine and melatonin increased the value of CI and content of anthocyanin significantly under drought conditions.The total soluble solids were also increased by the application of dopamine and melatonin.Stress and exogenous substances also altered the uptake fluxes of mineral nutrients in the fruits.Under drought conditions,exogenous dopamine and melatonin significantly increased the uptake fluxes of these nutrients.Our findings suggest that exogenous dopamine and melatonin could accelerate red colour development and increase pigment accumulation,soluble sugar content and nutrient uptake of apple fruit under drought stress condition.