摘要
【目的】了解外源5-氨基乙酰丙酸(5-aminolevulinic acid,ALA)预处理对桃树幼叶低温胁迫的影响。【方法】以春季桃树幼叶为试材,用50 mg·L^(-1)ALA溶液喷施叶片,然后于处理后3、6、9和12 d采集幼叶,置于-6℃低温冰柜中处理0、2、4和6 h,测定不同处理的叶片叶绿素快速荧光曲线,分析PSⅡ和PSⅠ反应中心最大光化学效率及其电子传递速率。选取ALA预处理6 d的叶片,测定相对电导率、渗透调节物质含量、抗氧化酶活性及丙二醛(MDA)含量,分析PSⅡ反应中心蛋白编码基因和脯氨酸代谢关键基因的相对表达量。【结果】与对照相比,ALA预处理6~12 d,可以显著抑制低温胁迫导致的桃树叶片叶绿素快速荧光诱导动力学曲线早期荧光上升和晚期荧光下降。方差分析表明,ALA预处理6 d时显著提高PSⅡ和PSⅠ反应中心最大光化学效率(分别为φP_(o)和φR_(o))、PSⅠ反应中心被氧化的最大速率(V_(PSI))以及PSⅡ传递电子还原PSI反应中心的最大速率(V_(PSII-PSI))。生理生化分析表明,低温胁迫导致桃树叶片相对电导率上升,而ALA预处理显著抑制其上升幅度。ALA预处理提高了低温胁迫下的桃叶SOD、CAT和POD酶活性,提高了可溶性蛋白质、可溶性糖和脯氨酸含量,降低了MDA含量。qRT-PCR分析表明,ALA预处理上调了PSⅡ反应中心关键基因PsbB、Psb28、PsbO、PsbR和PsbY以及脯氨酸合成关键基因P5CS1和P5CR的表达,下调了脯氨酸降解基因PDH的表达。【结论】外源ALA预处理可以缓解低温胁迫对桃树幼叶PSⅡ和PSⅠ反应中心的伤害,维持PSⅡ反应中心重要蛋白相关基因表达水平,提高抗氧化酶活性,增加渗透溶质含量。
【Objective】Peach(Prunus persica L.)is an important temperate deciduous fruit crop in China as well as the rest of the world.It is well-liked for its delicious and juicy fruit.However,peach trees are often vulnerable to be injured from the late frost due to its flowering in early spring,which will seriously affect the fruit yield and quality.Therefore,it is meaningful to study how to improve the trees’ability to defend against cold temperature in early spring.5-Aminolevulinic acid(ALA)is one of naturalδ-amino acids,but not involved in the biosynthesis of proteins.It is an essential biosynthetic precursor of all tetrapyrrole compounds like chlorophyll and heme.Therefore,it plays an important role in photosynthesis and respiration of plants.ALA has also been suggested as a new plant growth regulator,which can be used to improve plant stress tolerance including cold resistance.However,it has never been reported before whether ALA can improve cold tolerance of peach in early spring.To understand the effect of ALA on improving peach cold tolerance,we artificially exerted low temperature stress at different days after spraying an exogenous ALA solution.【Methods】The young leaves of peach at bud break stage were sprayed with 50 mg·L^(-1)ALA solution,then harvested at 3,6,9,and 12 d,and put in a freezer at-6℃for 0,2,4,and 6 h.After then,the chlorophyll fast fluorescence was measured with a multiple plant efficiency analyzer(M-PEA),and the maximum photochemical efficiency and the electron transfer rate of the photosystemⅡ(PSⅡ)and the photosystemⅠ(PSⅠ)reaction centers were analyzed.Additionally,the leaves pretreated with ALA for 6 d were used to determine the relative electrical conductivity,the content of osmotic solutes(including soluble sugars,free proline and soluble proteins),antioxidant enzyme(including SOD,CAT and POD)activities and MDA content.And finally,the relative expressions of genes coding the proteins in PSII reaction center and the key genes in proline metabolism were detected by qRT-PCR.【Results】It was shown that 2-hour chilling at-6℃did not significantly affect the chlorophyll fast fluorescence curves of young leaves,and 3 d pretreatment of ALA did not show enough protective potency against chilling stress.It was found that 4 or 6 hours chilling greatly increased the early rise and the late decrease in the kinetic curves,suggesting that the chlorophyll fluorescence properties were impaired by chilling stress,while ALA pretreatment for 6-12 d significantly inhibited the changes.The variance analysis of the maximum photochemical efficiency of PSⅡ(φP_(o))and PSⅠ(φR_(o))reaction center of peach leaves showed that longer-term stress caused significant decreases ofφP_(o)andφR_(o)in the control whereas that in the pretreated situation for 6-12 d by ALA kept rather high level,suggesting that ALA pretreatment at least for 6 d significantly improved chilling tolerance for PSⅡand PSⅠreaction center.PSⅡreaction center seemed to be more sensitive to chilling stress than PSⅠ.Similarly,the maximum oxidation rate of PSⅠreaction center(V_(PSI))and the maximum reduction rate of PSⅠreaction center by the electrons transferred from PSⅡreaction center(V_(PSII-PSI))were significantly improved by ALA pretreatment.Once again,V_(PSII-PSI)in the young leaves was more sensitive to chilling stress than V_(PSI),and the protective effect of ALA pretreatment was also greater on the inter-system electron transfer.Physiological and biochemical analyses showed that chilling stress resulted in dramatic increases of the relative electrical conductivity of peach leaves,while ALA pretreatment significantly prevented the rise amplitude.ALA pretreatment significantly improved the soluble sugar content in the young leaves compared with the control,implying a result of ALA improving leaf photosynthesis and thus accumulating more carbohydrate,which is crucial to enhance leaf chilling tolerance.Furthermore,ALA pretreatment improved the soluble proteins and free proline content in young leaves,which was more significant after chilling stress.2 h chilling stress stimulated the activities of antioxidant enzymes including SOD and POD,which then decreased after longer time.The activity that ALA pretreatment stimulated increased more and kept higher for longer time.The activity of CAT in peach leaves did not increase during chilling stress.In fact,it depressed with chilling stress.However,ALA pretreatment caused the enzyme activity higher than the control after 4-6 h chilling.Therefore,the content of lipid peroxidation product MDA in the control increased significantly after 2 h chilling while that in the ALA pretreated leaves kept unchanged.The qRT-PCR analysis showed that the relative expression of PsbB under low-temperature stress was significantly higher than the control,and that of Psb28,PsbO,PsbR and PsbY in the ALA pretreatment was also higher than that of the control,especially under longer chilling stress.However,the PsbA gene expression in peach leaves was sensitive to chilling stress,whether with ALA pretreatment or not.On the other hand,the relative expressions of P5CS1 and P5CR,two key genes in proline biosynthetic route,were significantly higher in ALA pretreated leaves than that of the control,while the expression of PDH,an important gene for proline catabolism was down-regulated by ALA pretreatment,suggesting that ALA pretreatment promoted proline biosynthesis and blocked its catabolism during chilling stress.【Conclusion】Spraying peach leaves with ALA solution at least 6 d before chilling stress can improve the resistance to low temperature stress at-6℃for 6 h.Exogenous ALA pretreatment can relieve the damage to PSII and PSI,maintain important protein gene expression of PSII reaction center,improve antioxidant enzyme activity,increase osmotic solute content,and enhance its ability to resist the harm of the late frost in early spring.
作者
张建婷
魏欣
张海雯
梁若琳
安玉艳
汪良驹
ZHANG Jianting;WEI Xin;ZHANG Haiwen;LIANG Ruolin;AN Yuyan;WANG Liangju(College of Horticulture,Nanjing Agricultural University,Nanjing 210095,Jiangsu,China)
出处
《果树学报》
CAS
CSCD
北大核心
2022年第8期1407-1421,共15页
Journal of Fruit Science
基金
江苏省农业科技自主创新资金项目[CX(20)2023]。
关键词
桃
叶片
低温胁迫
ALA
叶绿素荧光
抗氧化酶活性
渗透溶质
Peach
Leaves
Low-temperature stress
ALA
Chlorophyll fluorescence
Antioxidant enzyme activity
Osmotic solutes
