Effects of Day and Night Temperatures on Hypocotyl Elongation and Endogenous Levels of Indole-3-acetic and Abscisic Acids in Radish (Raphaus sativus L.)

Abstract

The effect of the difference between day and night temperatures (DIF), under a 12-hr photoperiod on hypocotyl elongation (HE) of radish (Raphanus sativus L.) and the roles of endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) on this growth process were investigated. At 10 DIF, HE was rapid enhanced during the day (DP) but slow at night (NP). Hence, the elongation pattern showed a stepped curve. At 0 DIF, HE during DP was only slightly shorter than that during NP so that the slope of the growth curve changed gradually. At -10 DIF, HE was enhanced at NP, whereas it nearly stopped during DP, so that the stepped curve became exaggerated. In all DIF treatments, changes in IAA content paralleled those of HE ; the highest level of IAA was found at 10 DIF at night. Contrarily, a rapid increase and the highest level in ABA occurred after 36 hr after treatment started at -10 DIF during which HE was retarded. These data indicate that DIF regulates HE in radish by controlling endogenous IAA and ABA synthesis.