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 paclobutra zol (P) and ancymidol (A) at 50 and 25 mg 1(-1) respectively and air d ried. Seedlings were germinated and grown in a controlled environment cabinet with a day/night temperature of 23/18 degrees C and a photoper iod of 16 h with a PPFD of 150 mu E m(-2) s(-1). Ten-day-old seedlings were stressed by exposing them either to a high temperature of 51 deg rees C for 8 h or a low temperature of 3 degrees C and a photoperiod o f 16 h with a PPFD of 640 mu E m(-2) s(-1) for 48 h. Both stresses, de creased 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 symp toms 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 evidenc e from previous studies with triazoles, we suggest that the stress pro tection conferred by P + A may be mediated to some extent by an enhanc ed activity of free-radical scavenging systems.