Paclobutrazol and ancymidol protect corn seedlings from high and low temperature stresses

Hybrid corn (Zea mays L. cv Pioneer 3902) seeds were imbibed either in distilled water (control) or 40 mM KCl solution containing paclobutrazol (P) and ancymidol (A) at 50 and 25 mg 1^–1 respectively and air dried. Seedlings were germinated and grown in a controlled environment cabinet with a day/night temperature of 23/18°C and a photoperiod of 16 h with a PPFD of 150 E m^–2s^–1. Ten-day-old seedlings were stressed by exposing them either to a high temperature of 51°C for 8 h or a low temperature of 3°C and a photoperiod of 16 h with a PPFD of 640 E m^–2 s^–1 for 48 h. Both stresses, decreased chlorophyll and carotenoid levels. A decrease in fluorescence (Fv/Fm ratio) and increase in leakiness indicated lower photosynthetic efficiency and a loss of membrane integrity. These deteriorative symptoms in the control seedlings were ameliorated by the treatment (P+A) and the growth rates of the treated seedlings as measured by height, fresh and dry weights were greater than the control. Based on evidence from previous studies with triazoles, we suggest that the stress protection conferred by P+A may be mediated to some extent by an enhanced activity of free-radical scavenging systems.