彩叶草对模拟干旱胁迫的生理响应

Physiological responses of Coleus blumei to simulated drought stress

关键词:  模拟干旱  彩叶草  生长  渗透调节  抗氧化酶

Key words:  simulated drought stress  Coleus blumei  growth  osmotic adjustment  antioxidant enzyme

摘要:

采用盆栽试验,对彩叶草进行PEG-6000浓度为0(对照)、5%、10%、15%、20%(W/V)模拟干旱胁迫,研究在干旱胁迫下彩叶草的生长、渗透调节能力及抗氧化酶活性的变化。结果表明:与对照相比,随着PEG-6000浓度的增加,鲜质量、干质量、含水量、水势、根系脱氢酶活性、无机离子含量包括K⁺、Na⁺、Ca²⁺、Mg²⁺等均呈下降趋势; NO^-₃含量呈先下降后上升趋势; 硝酸还原酶活性、可溶性蛋白含量、可溶性糖含量、超氧化物歧化酶活性均呈先上升后下降趋势; 脯氨酸含量、游离氨基酸含量、过氧化物酶活性、过氧化氢酶活性、超氧阴离子(O^-₂·)产生速率、质膜透性则呈上升趋势。因此,模拟干旱胁迫对彩叶草生长有抑制作用,且随着PEG-6000浓度增加,其生长受抑制和水分胁迫程度加重; 模拟干旱胁迫下,彩叶草不积累K⁺、Na⁺、Ca²⁺、Mg²⁺和NO^-₃等无机离子进行渗透调节,而积累脯氨酸、可溶性蛋白、可溶性糖、游离氨基酸等有机小分子物质进行渗透调节,但这4种小分子物质增加幅度不尽相同; 轻度模拟干旱胁迫虽增强彩叶草抗氧化酶活性,但仍表现轻度的氧化伤害; 重度模拟干旱胁迫加重彩叶草氧化伤害。研究结果可为彩叶草耐旱生理机制的研究积累资料,也为其节水型栽植和养护提供依据。

Abstract:

In the present study,Coleus blumei seedlings were treated with PEG-6000 at the concentrations of 5%,10%,15%,or 20% as the simulated drought stress,and without PEG-6000 treatment as control to investigate the changes of the growth,osmotic adjustment ability and the antioxidant enzyme activities of C. blumei. The results demonstrated that,comparing with the control,the fresh and dry biomass,water content and potential,root dehydrogenase activity and the contents of inorganic ion(K⁺,Na⁺,Ca²⁺,Mg²⁺)declined gradually as the increase of PEG-6000 concentrations. The content of NO^-₃ decreased at first and then increased,but lower than that of the control; On the contrary,nitrate reductase(NR)activity,soluble protein content and soluble sugar content increased at first and then decreased,and the contents of the latter two parameters were higher than that of the controls; in addition,proline and free amino acid content elevated in a PEG-6000-dose dependant manner. We noticed that the superoxide dismutase(SOD)activities also initially increased and then decreased,and reached the peak under 10% PEG-6000 treatment. However,peroxidase(POD)activities,catalase(CAT)activities,O^-₂· production rates and membrane permeability were greatly improved as the increase of PEG-6000 concentrations. Comprehensive analysis showed that moderate simulated drought stress(5%-10% PEG-6000)resulted in the decreased absorption of inorganic ion and water in C. blumei root,but enhanced ability of NO^-₃ reduction,suggesting that the inhibition on growth and the degree of water deficit were not detrimental,and thus ornamental values were hardly impaired. However,severe simulated drought stress(15%-20% PEG-6000),caused significant loss of inorganic ion absorption and deficit of water as well as the decrease of NO^-₃ assimilation,which further aggravated the inhibitory effect on growth and osmotic srtess,and finally destroyed its ornamental value. We observed that C. blumei seedlings did not accumulate inorganic ion,such as K⁺,Na⁺,Ca²⁺,Mg²⁺ and NO^-₃; however,it indeed accumulated organic small molecules,such as proline,soluble protein,soluble sugar and free amino acid,to maintain the osmotic balance in spite of the increasing rate of these molecules were not parallel. Although moderate simulated drought stress could enhance the antioxidant enzyme activities(SOD,POD and CAT)of C. blumei seedlings,slight oxidative injuries were observed. As the increase of PEG-6000 concentration,the notable elevation of O^-₂·generation rate might result from the decreasing activity of SOD,a key enzyme for scavenging O^-₂·; although POD and CAT,another two important antioxidant enzymes,could be significantly induced when suffering from the drought stress. As a result of imbalance of these antioxidant enzymes,the injury of membrane lipid peroxidation was inevitable. These findings will provide some useful experimental basis for elucidating the physiological mechanisms of C. blumei drought tolerance,and also contribute to water-saving planting and maintaining of C. blumei in practice.