Metabolism Of Polyamines And Related Endogenous Hormones In Grape Seedlings Under Salt Stress

The objectives of this pot study were?i?to determine the tolerance of"Victoria"grape to salt injury and?ii?to compare the effects of different degrees of salt stress on polyamine and hormone metabolism.Salt stress was applied by adding NaCl to the culture media at one of four concentrations:0,1,2,and 3g/kg?referred to as CK,T1,T2 and T3,respectively?.The following variables were measured in the roots and leaves at 0,5,10,15 and 20 d after the application of salt stress:polyamine concentration,polyamine oxidase activity,polyamine synthase activity,and hormone concentrations.Plant growth,leaf photosynthesis,and leaf chlorophyll were also measured.Polyamine concentrations increased between d 0 and d 10 and then decreased.The T3 treatment had the highest polyamine concentrations,with maximum concentrations of 1 684.83 nmol/g in roots,2994.74 nmol/g in stems,and 4 592.10 nmol/g in leaves.This meant that salt stress increased polyamine accumulation.Grape leaves were more sensitive to salt stress than stems and roots.Salt stress increased putrescine concentrations more than spermine and spermidine concentrations.The activities of diamine oxidase?DAO?,arginine decarboxylase?ADC?,ornithine decarboxylase?ODC?and S-adenosine deaminase?SAMDC?increased and then decreased after salt stress ended.The activity of polyamine oxidase?PAO?in leaves increased and then leveled off.Enzyme activities were highest in leaves followed by stems and then roots.Enzyme activities also decreased in the order T3>T2>T1>CK.The PAO activity was significantly positively correlated with spermine and spermidine concentrations.The activity of ADC was greater than that of ODC and SAMDC in all plant parts.The maximum ADC activities in roots?68.74 nmol/g·h?,stems?68.98 nmol/g·h?,and leaves?69.71 nmol/g·h?were 79.67,68.80,and 90.01%greater,respectively,than those in the control treatment.These results indicated that?i?PAO plays a major role in polyamine decomposition and?ii?ADC plays a major role in polyamine synthesis.Salt stress reduced zeatin concentrations in the order CK>T1>T2>T3.The zeatin concentrations also decreased between d 0 and d 20.The T3 treatment has the lowest zeatin concentrations on d 20,with values of 0.19 ng/g in roots,0.90 ng/g in stems,and 1.39 ng/g in leaves.In contrast,abscisic acid concentrations showed the opposite trend.Specifically,abscisic acid concentrations decreased significantly in the order:T3>T2>T1>CK.In the T3 treatment,the maximum abscisic acid concentrations in roots?18.05 ng/g?,stems?14.70 ng/g?,and leaves?38.90 ng/g?were 79.67,68.80,and90.01%greater,respectively,than those in the control.These results indicate that salt stress influences endogenous hormone concentrations and their balance in plants,so that plant growth is inhibited and premature senescence occurs.Salt stress reduced plant growth.Plant height and stem diameter decreased in the order CK>T1>T2>T3.The growth rate also decreased across time.Salt stress also inhibited photosynthesis.Transpiration rate?Tr?,stomatal conductance?Gs?,and net photosynthetic rate?Pn?decreased in the order CK>T1>T2>T3.In contrast,intercellular CO₂ concentration?Ci?decreased in the order CK>T3>T1>T2.Photosynthesis,Tr,Gs,Ci,and Pn reached a maximum at 12:00 h,declined,and then rose again at 16:00 h.Chlorophyll a,chlorophyll b and carotenoid concentrations decreased in the order CK>T1>T2>T3.Chlorophyll a,chlorophyll b and carotenoid concentrations also decreased between d 0and d 20.Salt stress had the largest effect on chlorophyll a followed by chlorophyll b and then carotenoid.