Abstract:

The possible physiological mechanism of enhancement of cold tolerance by salicylic acid (SA) in banana seedlings (Musa acuminata cv. Williams 8188) was explored. Measurements of leakage electrolyte after 2 d of recovery at 30/22 ℃ (day/night) following 3 d of cold stress at 7 ℃ showed that pretreatment with hydroponic solution containing SA 0.3－0.9 mmol/L as foliar spray under normal growth conditions (30/22 ℃) could significantly enhance cold tolerance of banana plants. The highest enhancing effect of SA occurred at 0.5 mmol/L and it showed the lowest leakage rate of electrolyte or smaller leaf wilting area after 2 d of recovery at normal temperature from 3 d of 7 ℃ or 5 ℃ cold stress. Higher concentrations (≥2.5 mmol/L) of SA, however, caused more electrolyte leakage, indicating that they aggravated chilling damage. Enhanced cold tolerance by SA could be related to H2O2 metabolism. Compared with water-treated seedlings (control), SA 0.5 mmol/L treatment inhibited activities of catalase (CAT) and ascorbate peroxidase (APX), increased peroxidase (POX) activity, but did not affect the activity of superoxide dismutase (SOD) under normal growth conditions, and these changes might lead to an accumulation of H2O2, whereas SA pretreatment enhanced the activities of CAT and APX, and reduced the increase in productions of H2O2 and thiobarbituric acid-reaction substances (TBARS) during subsequent 7 ℃ cold stress and recovery periods. Exogenous H2O2 treatments (1.5－2.5 mmol/L) also increased cold tolerance of banana seedlings. Furthermore, pretreatment of banana seedlings with dimethylthiourea (a trap for H2O2) significantly inhibited cold tolerance induced by SA. These results suggested that endogenous H2O2 may be required for SA-enhanced cold tolerance. The significance of the interaction of SA, H2O2 and H2O2-metabolizing enzymes during cold stress has been discussed.

水杨酸提高香蕉幼苗的抗冷性与H₂O₂代谢有关
康国章 王正询  孙谷畴

（1. 中国科学院华南植物研究所，广州510650；2.  广州大学生物系，广州510405）

探讨了水杨酸(salicylic acid，SA)提高香蕉幼苗抗冷性的可能机理。在常温下(30／22℃)用不同浓度(0—3．5mmol／L)的SA水溶液喷洒叶片1d，置于7℃低温下冷胁迫3d，随后于常温下恢复2d后测定电解质泄漏率，结果表明：SA0．3～0．9mmol／L能显著提高香蕉幼苗的抗冷性，以0．5mmol／L效果最佳。若把冷胁迫温度降到5℃，SA0．5mmol／L预处理可显著减少幼苗叶片的萎蔫面积。但当SA浓度高于1．5mmol／L时，恢复期间的电解质泄漏甚至高于对照(蒸馏水处理)，表明它们加剧了冷害。SA提高香蕉幼苗的抗冷性可能需要H₂O₂的参与：1)SA0．5mmol／L常温处理诱导了H₂O₂的积累和活性氧造成的膜脂过氧化——三氯乙酸反应物质(TBARS)的增加，这可能与H₂O₂的清除酶——过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性的受抑和H₂O₂的产生酶—超氧化物歧化酶(SOD)活性几乎不受影响有关；2)外源H₂O₂(1．5—2．5mmoL／L)也能显著降低低温胁迫期间的电解质泄漏，表明也能提高抗冷性；3)而用H₂O₂的捕捉剂——二甲基硫脲(DMTU)可明显抑制SA诱导的抗冷性；4)在低温胁迫与恢复期间，SA预处理明显提高了CAT和APX的活性，抑制了H₂O₂与TBARS的快速上升。