干旱预处理对抗旱性不同的2个草地早熟禾品种耐热性能的影响

为探讨干旱预处理诱导草地早熟禾耐热性效应和生理机制及不同品种对干旱预处理的差异响应,对抗旱性不同的2个草地早熟禾品种,“Midnight”(抗)和“Brilliant”(敏感)分别进行充足浇水(对照)和两轮干旱预处理,然后置入35℃/30℃(昼/夜)高温中胁迫25 d。在胁迫的0,5,10,15,20,25 d分别测定草坪外观质量及相应生理反应的动态变化。在胁迫期间,预处理“Brilliant”的草坪质量(TQ)显著(P<0.05)高于未经预处理材料;在胁迫5 d后,经预处理的“Brilliant”渗透势(OP)不断下降,而对照材料基本维持不变,在10和15 d时,预处理Brilliant的相对含水量(RWC)显著(P<0.05)高于对照;在胁迫的10～20 d,经预处理“Brilliant”的超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性显著(P<0.05)高于未经预处理材料,而电解质渗透率(EL)值则相反;15 d时,经预处理的棕榈酸(16∶0)和硬脂酸(18∶0)含量显著(P<0.05)低于未经预处理材料,而亚麻酸(18∶3)含量正好相反,与之相对应,预处理“Brilliant”的双键系数(DBI)显著(P<0.05)高于对照。“Midnight”两处理的各测定指标变化趋势相近,无明显差异。结果表明,干旱预处理未能进一步提高抗旱性品种“Midnight”的耐热性,而有效提高了干旱敏感品种“Brilliant”的耐热性。“Brilliant”耐热性的获得与干旱预处理诱导其渗透调节能力的提高,激活抗氧化酶(SOD、CAT)活性从而保护膜脂中不饱和脂肪酸(18∶3)免受活性氧伤害而急剧下降密切相关,从而有效阻止叶片失水,稳定膜结构,延缓植株衰老。

Effects of drought preconditioning on physiological responses to heat stress in two Kentucky bluegrasses

The effect of improved heat tolerance through drought preconditioning on responses to drought preconditioning under heat stress was studied in two Kentucky bluegrasses. Plants of Kentucky bluegrass (Poa pratensis) cultivars “Midnight” (drought resistant) and “Brilliant” (drought sensitive) were well watered (non-preconditioned control) or exposed to two cycles of drought stress without irrigation (drought preconditioning) and then exposed to heat stress (35℃/30℃, day/night) for 25 days in growth chambers. Turf quality and other physiological parameters in leaves were determined at 0 (end of drought preconditioning and beginning of heat treatment), 5, 10, 15, 20, and 25 days of heat treatment. During the period of heat stress, drought-preconditioning of cv. “Brilliant” resulted in significantly (P＜0.05) higher turf quality compared with the non-preconditioned “Brilliant”. After 5 days of heat stress, osmotic potential gradually declined in drought-preconditioned “Brilliant”, but there was little change in the non-preconditionied “Brilliant”. Plants of drought-preconditioned “Brilliant” maintained significantly (P＜0.05) higher relative water content than those of non-preconditioned plants at 10 and 15 days of heat stress. The activities of superoxide dismutase and catalase were significantly (P＜0.05) higher in drought-preconditioned “Brilliant” than in non-preconditioned “Brilliant” at 10 and 20 days of heat stress, but electrolyte leakage was the reverse. There was significantly (P＜0.05) higher fatty acid (16∶0 and 18∶0) content in drought-preconditioned “Brilliant” than in non-preconditioned “Brilliant” after 15 days of heat stress, although the content of 18∶3 was the opposite. Drought-preconditioned “Midnight” had a higher double bond index (DBI) than non-preconditioned “Brilliant”. The physiological parameters were not significantly different in the two treatments in “Midnight” under heat stress. In conclusion, drought preconditioning improved heat tolerance in the drought sensitive cv. “Brilliant” but failed to improve heat tolerance in the drought resistant cv. “Midnight'. Improved heat tolerance through drought preconditioning in “Brilliant” was associated with increased osmoregulatory ability and the promotion of antioxidant activities which can protect unsaturated fatty acids from damage. These changes may play an important role in improving leaf relative water content, protecting membrane systems and delaying leaf senescence.