Effects of Cr stress on growth and physiological and biochemical characteristics of'Zhongshanshan 406'seedlings
Taking the parent Taxodium distichum(Linn.)Rich.as the control,the effects of different concentrations and treatment times of Cr stress on growth,antioxidant system,and photosynthetic system of'Zhongshanshan 406'seedlings were compared by using hydroponic simulation experiments.The results show that the variation degrees of relative growth rate and relative water content,and relative conductivity,leaf chlorophyll content and malondiadehyde(MDA)content in leaves of'Zhongshanshan 406'seedings are smaller than those of T.distichum under medium concentration(5.00 μmol·L-1)and high concentration(20.00 µmol·L-1)of Cr treatment for 28 d.With the increase of Cr concentration and the extension of treatment time,the activities of superoxide dismutase(SOD)and peroxidase(POD)of leaves of'Zhongshanshan 406'seedlings show a tendency to increase in general,while the SOD and POD activities of leaves of T.distichum seedlings show a tendency to first increase and then decrease,and'Zhongshanshan 406'can maintain relatively high antioxidant enzyme activities in the later stage of treatment(28 d).Compared with the control(0.00 μmol·L-1 Cr),the variations of maximum photochemical efficiency of PS Ⅱ(Fv/Fm),effective photochemical efficiency of PS Ⅱ(Fv'/Fm'),and actual photochemical efficiency of PS Ⅱ(ΦPSⅡ)of leaves of'Zhongshanshan 406'seedlings are not great in general under the treatment of 1.25 and 5.00 μmol·L-1 Cr,while these three chlorophyll fluorescence parameters of T.distichum significantly decrease under 5.00 μmol·L-1 Cr treatment,and the decrease degree under 20.00 μmol·L-1 Cr treatment for 28 d is obviously greater than that of'Zhongshanshan 406';with the extension of treatment time,the nonphotochemical quenching coefficient(NPQ)of leaves of'Zhongshanshan 406'seedlings shows a tendency to increase in general,while that of T.distichum remains relatively unchanged since treatment for 14 d.The relative growth rate of the two plants under Cr stress has relatively high correlation degrees with both photosynthetic system indexes(chlorophyll content,Fv/Fm value,Fv'/Fm'value,and ΦpSⅡ value)and antioxidant system indexes(SOD activity,POD activity,and MDA content)of leaves,and there are also relatively strong correlations of ΦPSⅡ value and chlorophyll content with antioxidant system indexes.In conclusion,'Zhongshanshan 406'and T.distichum exhibit certain growth adaptability to low concentration(1.25 µmol·L-1)Cr stress,and'Zhongshanshan 406'shows stronger resistance to medium and high concentrations of Cr stress.Relatively strong PS Ⅱ photochemical performance,antioxidant capacity,and PS Ⅱ heat dissipation ability under Cr stress are important mechanisms for'Zhongshanshan 406'to maintain a relatively high growth rate and defend against photoinhibition and photodamage.
Cr stress'Zhongshanshan 406'Taxodium distichum(Linn.)Rich.growthantioxidant systemphotosynthetic system
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