Effect Of Magnesium On Different Genotypes Of Watermelon In Some Physiological And Biochemical Metabolism

Watermelon cultivars 'Rishengxintianling','Xinhongbao' and 'Heimeiren' grown in pots contained sand were used to study for the growth,carbon and nitrogen metabolism,photosynthetic system,antioxidant systems,membrane function and fruit quality under Mg concentration of Omg/L,24mg/L,48mg/L,96mg/L,192mg/L.The main results were as follows:(1)The optimum Mg levels for‘Rishengxintianling','Xinhongbao' and 'Heimeiren'growing were 48mg/L,less than 24 mg/L or more than 96 mg/L would affect the growth of watermelon.Less than 24 mg/L was low magnesium levels and much than 96mg/L was high levels of magnesium.The symptoms of Mg stress began to appear from the old leaves on lower part of the plant,The height of Mg efficiency of three watermelon was'Rishengxintianling'>'Heimeiren'>'Xinhongbao'.(2)Mg deficiency,low and high Mg levelsdecreased the biological yield,plant height,root length,root activity of watermelon.Mg deficiency,low Mg levels had agreater effect on agronomy indexes than that of high Mg stress of three watermelon,the symptoms of Mg deficiency and low Mg levels appearedearlier and was severier than that of high Mg levels stress.(3)Mg deficiency,low and high Mg levels decreased the chlorophyll content and NR activity of watermelon.It made the soluble protein and soluble sugar content of watermelon decreased,obstructedcarbon and nitrogen metabolism.Applied the right amount of Mg could increase the capacity of carbon and nitrogen metabolism.(4)Mg deficiency,low and high Mg levels reduced the photosynthetic pigment of watermelon leaves,and the number of PS ? reaction center decreased,most PS ? reaction center was closed and QA was accumulated,and PS ? reaction center activity weakened.At the same time the oxygen evolving complex OEC of PS ? donor side of watermelon leaves was hurt,H2O cleavage was inhibited,while the rate of QA restored in PS ? receptor side was accelerated,and the energy required was reduced,the electron transfer of PS ? reaction center was obstructed.(5)Mg deficiency,low and high Mg levelsenhanced energy absorption capacity of each unit area of leaf PS ? reaction center and the single unit of PS II reaction center,but PS ? reaction center captured energy that could be used to transfer electronic was reduced and blades enhanced heat dissipation,electron transfer was blocked,and caused the rate of photosynthetic declined.(6)Mg deficiency,low and high Mg levels madeSOD?POD?CAT?DHAR activity of watermelon leaf decreased at each growing time.Weaken the ability of watermelon to clear superoxide and hydrogen peroxide,and it also accelerated plant senescence.(7)Mg deficiency,low and high Mg levelsincreased APX?MDAR?GR activity of watermelon leaf at each growing time,In order to ensur that the plant antioxidant system can operate normally.(8)Mg deficiency,low and high Mg levels decreased the proportion of ASA/DASA and GSH/GSSG of watermelon leaf at each growing time.Obstructed the AsA-GSH cycle and increased accumulation of reactive oxygen,Indirectly affected the dark reaction of photosynthesis.(9)Mg deficiency,low and high Mg levels increased the content of MDA and cell membrane in leaves of watermelon at each growing time.The membrane structure was destroyed and it affected membrane function,suggested that watermelon was hurt by the stress.It also caused the blade free proline accumulation in order to relieve stress injury and protected leaves.(10)Under 48mg/L Mg levelthe soluble solids content of soluble sugar,soluble protein,vitamin Cwere the highest among all the 5 Mg treatments.Mg deficiency,low and high Mg levels would reduce the quality of watermelon fruits.