Photoperiodic regulation of CS-ACS2, CS-ACS4 and CS-ERS gene expression contributes to the femaleness of cucumber flowers through diurnal ethylene production under short-day conditions

Photoperiod and the plant hormone, ethylene, modify sex expression of flowers in cucumber (Cucumis sativus L.). In the present study, femaleness of cucumber occurred under short‐day (8 h photoperiod) conditions compared to that under long‐day (16 h photoperiod) conditions, although the effect of photoperiod was more pronounced in a monoecious than in an andromonoecious cucumber. Application of ethylene had a greater effect than photoperiod on the production of female and bisexual flowers in monoecious and andromonoecious cucumbers, respectively. Ethylene evolution and the expression of CS‐ACS2, CS‐ACS4 and CS‐ERS genes in the shoot apices of both monoecious and andromonoecious cucumber plants had a diurnal rhythm with a peak in the middle of an 8 h or a 16 h light period. Peak ethylene evolution and expression of CS‐ACS2 was greater under short‐day conditions than under long‐day conditions in a monoecious cucumber but not in an andromonoecious one. Expression of CS‐ACS4 in monoecious and andromonoecious cucumber plants did not differ, but the level was higher under short‐day conditions compared with that under long‐day conditions. Thus, CS‐ACS2 and CS‐ACS4 might be involved in the basic diurnal rhythm of ethylene evolution in cucumber. Because exogenous ethylene increased the expression of CS‐ACS2 and CS‐ERS in monoecious cucumber possessing the M locus, but not in andromonoecious cucumber in which the function of the M locus was lost (Yamasaki et al. Plant and Cell Physiology 42, 608–619, 2001), the CS‐ACS2 gene might also be involved in ethylene production by positive feedback via regulation of M locus under short‐day conditions.     

Abscisic Acid as a Stimulator for Rice Mesocotyl Growth

WHEN abscisic acid (ABA) is applied to a growing plant, it usually inhibits the growth of stem, leaf sheath and other plant parts^1–3. Here I report the possibility that ABA stimulates the growth of rice mesocotyl in darkness.     

Evidence for Naturally Occurring Inhibitors of Archegonial Differentiation in Lygodium japonicum

Archegonial differentiation in prothallia of Lygodium japonicum was inhibited when the filtrate of conditioned medium or the extracts of prothallia with organic solvents were added to the medium. By varying the timing of treatment with the methanol extract, archegonial differentiation was shown to start at least 4 days before microscopically detectable change. The inhibitory effect of methanol extract was nullified by transferring the treated plants to a fresh medium omitting the methanol extract, so that the archegonial formation became discernible 6 days after the transfer. The inhibitory activity was stable in both acidic and basic solutions at room temperature, and was partially lost by boiling at pH 3 or 11 for 30 min. The inhibitor, which could be retrieved from the filtrate and the methanol extract, was fractionated into the neutral ethyl acetate fraction, but was not found in the acidic ethyl acetate fraction and in the aqueous residue. At least two active zones were separated on thin layer chromatograms of the ethyl acetate extracts from the filtrate and the methanol extract, and the relative flow-rates of each active zone from these two sources were very similar. The evidence described above indicates that specific inhibitors of archegonial differentiation may be produced in the tissue of prothallia of Lygodium and eventually be secreted to the medium.     

Adult eclosion rhythm of the Indian meal moth Plodia interpunctella: response to various thermocycles with different means and amplitudes

In addition to photoperiod, thermoperiod (or thermocycle) might be an important Zeitgeber for entraining the circadian oscillator controlling adult eclosion rhythm in the Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae). This is confirmed by exposing larvae receiving diapause‐preventing treatments to various thermocycles with different means and amplitudes of temperature. The thermocycles investigated in the present study are TC 8 : 16 h, TC 12 : 12 h, TC 16 : 8 h and TC 20 : 4 h, where T and C represent thermophase (30 °C) and cryophase (20 °C), respectively. For all thermocycles, the peak of adult eclosion rhythm occurs at around the mid‐thermophase. This indicates that the larvae use both ‘temperature‐rise’ and ‘temperature‐fall’ signals to adjust the eclosion phase in each thermocycle. The absence (DD) or presence (LL) of light affects this time‐keeping system slightly under the given thermocycle. The rhythmic adult eclosion noted after exposure of larvae to 30 °C DD for 14 days is recorded in the thermocycles (TC 12 : 12 h, DD; mean temperature = 25 °C) with different amplitudes of 27.5/22.5 °C, 26.5/23.5 °C and 25.5/24.5 °C. The peak in adult eclosion advances in time as the amplitude of the temperature cycle decreases. In the temperature cycle of 25.5/24.5 °C, a peak occurs at the end of the cryophase, 2 h before the temperature‐rise. The adult eclosion rhythm is also observed under various thermocycles (TC 12 : 12 h, DD) consisting of different temperature levels (30 to 20 °C) with different amplitudes. It is found that the temporal position of the peak advances significantly when the amplitude of the thermocycle becomes lower.