Two distinct cis-acting elements are involved in light-dependent activation of the pea elip promoter

Light activation of the pea (Pisum sativum) elip gene promoter was analysed in transgenic plants and in transiently transfected plant protoplasts. A series of promoter deletions fused to the gusA reporter was tested, and the results obtained by the two experimental approaches were in good agreement. We identified two nucleotide sequence elements involved in light-regulated expression of the elip gene. One element is similar to the GT1 binding site of the rbcS-3A gene, and the other resembles a G-box-like ACGT element. The region containing both elements was able to confer light responsiveness on a heterologous basic promoter. Electrophoretic mobility shift assays demonstrated that each element is specifically recognized by DNA-binding proteins present in nuclear extracts from pea seedlings. The G-box-like ACGT element is necessary but not sufficient for light inducibility, indicating that the two elements act together in confering light responsiveness.     

Evidence that photoperiodic, dark time measurement in Pharbitis nil involves a circadian rather than a semidian rhythm

Experiments were carried out to determine whether a semidian (12 h) rhythm in flowering response operates in Pharbitis nil as the basis for photoperiodic time measurement. The effect of 5 min far-red light followed by 85 min dark (FRD) given 4, 8,14 and 22 h before the end of a 48 h photoperiod on night-break timing and critical night length was determined. When given 4 h before the end of a 48 h photoperiod, an interruption with FRD advanced the phase of the circadian rhythm in the night-break inhibition of flowering. In contrast, earlier interruptions of the photoperiod had no effect on the phase of the rhythm. The critical night length was modified by FRD given 4 h (shortened) or 8 h (lengthened) before the end of the photo-period; when given at other times FRD did not alter the critical night length. The results are discussed in relation to the basis for photoperiodic timekeeping, with particular reference to suggestions for the involvement of a semidian rhythm. A circadian model based on the concept of limit cycles is described.     

Circadian Variation in Cortisol Reactivity to an Acute Stressor

To investigate the role of the circadian pacemaker in cortisol reactivity to a cold pressor challenge, 26 diurnally subjects participated in a constant‐routine protocol and were divided into two groups. Group 1 started immediately after a monitored sleep period at 09:00 h, while group 2 started 12 h later. After 2 h of adaptation, a cold pressor test was presented every 3 h. The cortisol response was assessed by means of saliva samples that were taken before and after the test. The pretest samples were considered to be base‐rate measures and base‐rate values as subtracted from post‐test values were considered as reactivity measures. Both measures showed distinct Time‐of‐Day variations (respectively: F_7,168 = 16.92, p < 0.001, ε = 0.383; and F_7,175 = 8.01, p < 0.001, ε = 0.523). These findings are interpreted as evidence for the existence of an endogenous circadian periodicity underlying the sensitivity of the hypothalamus–pituitary–adrenal (HPA)‐axis to acute stress.     

Changes in mRNA level rhythmicity in the leaves ofSinapis alba during a lengthening of the photoperiod which induces flowering

A previous study has shown that mRNAs exhibit complex patterns of diurnal rhythms in their quantity in the leaves ofSinapis alba during an 8 h light/16 h dark short day (SD). In order to determine whether this situation is rapidly modified in plants subjected to an extended light treatment, we have usedin vitro translation and two-dimensional polyacrylamide gel electrophoresis, together with a strict gel comparison procedure giving aP=0.03 certitude level, to analyse the mRNA complement at different times during a 22 h light/2 h dark long day (LD).During this LD, complex changes affected about 10% of the mRNAs. Thirty-four different patterns were observed. Some diurnal rhythms present in SD are not modified by the lengthening of the light period, but most are affected. Moreover, we have shown that some mRNAs presenting a constant quantity under a SD regime show an increase or a decrease during the first hours of the photoperiod lengthening.InSinapis, this LD also induces flowering. All the changes in mRNA quantity detected thus parallel the photoperiodic induction of flowering in the leaves and are quantitative; no mRNA was shown to appear or to disappear.     

Induction of embryogenic callus and cell suspension culture from shoot tips excised from flower stalk buds of Phalaenopsis (Orchidaceae)

Summary Embryogenic calluses were induced from 73% of Phalaenopsis shoot-tip explants excised from flower stalk buds by culturing for 7 mo. on New Dogashima Medium (NDM) containing 0.5 μM α-naphthaleneacetic acid (NAA), 4.4 μM 6-benzylaminopurine and 29.2 mM sucrose. The sucrose concentration was increased to 58.4 mM 4 mo. after initiation of the callus culture. These calluses were successfully subcultured as cell suspension cultures in liquid NDM supplemented with 5.4μM NAA and 58.4 mM sucrose. By simply reducing the sucrose concentration to 29.2 mM, the cells grew into plantlets through a developmental process similar to that of Phalaenopsis seedlings. The occurrence of somaclonal variants was less than 10% in six out of eight genotypes examined. These results suggest that the embryogenic callus and cell suspension culture could be utilized as the materials for micropropagation and breeding of Phalaenopsis orchids.     

细胞数量与诱导作用的实现

Holtfreter最早用离体的外胚层制成“夹心面包”研究胚胎诱导问题,后来发展出浸泡法,这些方法一直沿用至今。但是,不论那种方法,外植块中含有很多细胞,它们的分化产物所表现的,除诱导物质对反应细胞的直接作用外,还包含着被诱导的细胞与细胞之间、组织与组织之间次级的相互作用。例如,外胚层