Cyclical DNA Methyltransferase 3a Expression Is a Seasonal and Estrus Timer in Reproductive Tissues

It is becoming clear that epigenetic modifications such as DNA methylation can be dynamic and, in many cases, reversible. Here we investigated the photoperiod and hormone regulation of DNA methylation in testes, ovaries, and uterine tissue across multiple time scales. We hypothesized that DNA methyltransferase 3a (dnmt3a) is driven by photoperiodic treatment and exhibits natural variation across the female reproductive cycle and that melatonin increases whereas estrogen reduces DNA methylation. We used Siberian hamsters (Phodopus sungorus) due to their robust changes in reproductive physiology across seasonal and estrus time scales. Our findings indicate that short-day (SD) winter-like conditions significantly increased global DNA methylation and dnmt3a expression in the testes. Using immunohistochemistry, we confirm that increased dnmt3a expression was primarily localized to spermatogonium. Conversely, the ovaries did not exhibit variation in DNA methylation or dnmt3a/3b expression. However, exposure to SD significantly increased uterine dnmt3a expression. We then determined that dnmt3a was significantly decreased during the estrus stage. Next, we ovariectomized females and subsequently identified that a single estrogen+progesterone injection was sufficient to rapidly inhibit dnmt3a and dnmt3b expression. Finally, we demonstrate that treatment of human embryonic kidney-293 cells with melatonin significantly increased both dnmt3a and dnmt3b expression, suggesting that long-duration nocturnal signaling in SD may be involved in the regulation of DNA methylation in both sexes. Overall, our data indicate that dnmt3a shows marked photoperiod and estrus plasticity that likely has broad downstream effects on the timing of the genomic control of reproductive function.

Effect of gibberellic acid on total antioxidant activity during Chenopodium rubrum L. ontogenesis invitro

Total antioxidant activity (TAA) represents the combined ability of diverse antioxidants present in a sample of plant material to scavenge free radicals. Chenopodium rubrum L. sel. 184 is a qualitatively short-day plant; as an early-flowering species, it is a suitable object for studying ontogenesis in vitro. We investigated the effect of GA3 (5 mg/l) on TAA during C. rubrum ontogenesis under two different inductive photoperiodic regimes in vitro. Total antioxidant activ?ity does not change in different phases of C. rubrum ontogenesis under the same photoperiodic treatment. Exposure to continuous irradiation caused an increase of TAA in both C. rubrum plants and collected matured seeds. Gibberellic acid stimulated stem elongation, but did not affect leaf development or the number of matured seeds per plant, regardless of photoperiodic treatment; it induced a decrease of TAA in C. rubrum plants regardless of photoperiodic treatment or the phase of development, while it had no effect on TAA of matured seeds.

Daylength affects both free and conjugated indole-3-acetic acid levels in leaves and flowering in Doritis pulcherrima (orchid)

Total indole-3-acetic acid (IAA) levels (free IAA plus IAA conjugates) in Doritis pulcherrima (Doritis pulcherrima Lindley, cv. S 84-335-2) leaves were threefold lower in plants exposed to 30 d of short-day (SD) conditions than in plants exposed to 30 d of long-day (LD) conditions. Free IAA levels were also significantly lower in SD-treated leaves than those in 0 day of photoperiodic treatment and 30 d of LD. Results indicate that plants exposed to 30 d of SD contained significantly higher levels of ester-IAA and reduced amide-IAA concentrations compared to those grown under LD conditions. A high level of ester-IAA and a reduction of amide-IAA in leaves may be related to increased SD floral initiation ability in D. pulcherrima. Key words: Doritis pulcherrima, floral initiation, indole-3-acetic acid, photoperiod

391 THE INFLUENCE OF COLD DURING SEEDLING STAGE AND PHOTOPERIOD ON FORCING PERENNIALS FOR POT PLANTS

The influence of cooling, photoperiod and chemical branching on early spring flowering of perennial species was studied. Cooling was provided while plants were in plugs (128 plugs per tray) and dikegulac-sodium, a compound found to induce breaks in other species, was applied prior to, during and after cooling. Plants were cooled in insulated lighted coolers for 4, 8 or 12 weeks at 4C, and brought to a greenhouse with night temperatures between 8-12C. Long and short days were provided in the greenhouse after plants came out of the coolers. Little response to dikegulac occurred, however, Campanula, Sedum, Leontopodium, Catananche, Aubrietia, Arabis, Gypsophila, Anchusa and Aquilegia responded to cooling and photoperiodic treatment. Flowering and vegetative characteristics such as internode elongation and plant height responded to photoperiod and cooling but not all genera responded similarly. Anchusa, Campanula, Aquilegia and Gypsophila flowered significantly earlier under LD compared to SD. Twelve weeks of cooling resulted in flowering of all genera, however, some genera were equally responsive to shorter cooling times.

Relationships between secretory patterns of growth hormone, prolactin and body reserves and milk yield in dairy ewes under different photoperiod and feeding conditions

ABSTRACTDairy ewes (Prealpes breed) were subjected to differential photoperiod treatments: either long (15·5 light (L): 8·5 dark (D) or short (8·5 L: 15·5 D). Treatments started 15 days before lambing and continued until the 5th week of lactation. After lambing the 22 ewes of each photoperiodic treatment were divided in two groups and fed on either a high or low plane (19 v. 10·5 MJ/day and 370 v. 237 g crude protein per day). Milk yield was not affected by photoperiod but significantly modified by feeding levels (1154 v. 789 ml/day). Protein content of the milk was reduced under long days (—4·9 g/1) compared with short days, while no effect was observed for fat content. Body chemical composition changes, estimated by the deuterium oxide (heavy water) dilution technique between weeks 1 and 4, were affected by both treatments, with a significant interaction between photoperiod and diet for body protein changes: under short days lipid and protein changes were closely related while under long days they were independent.Blood samples were taken on day 23 of lactation from six ewes per group, every 30 min from 07.30 to 15.30 h for growth hormone (GH) and prolactin (PRL) measurements. The timing of GH and PRL pulses were different, but there was evidence that secretory patterns of each hormone were synchronized across ewes within the four treatments. Long photoperiod increased plasma PRL baseline rather than pulse amplitude, with no effect of diet. Undernutrition mainly increased GH pulse amplitude rather than baseline concentration, with no significant effects of photoperiod.High spontaneous concentrations of GH were associated with body lipid mobilization (R2 = 0·51) and were also involved in the control of protein changes (R2 = 0·71). These results indicate that GH (and PRL) are involved in nutrient partitioning in the lactating ewe.

Vegetative Activity of the Main Stem Terminal Bud Under Photoperiod and Flower Removal Treatments in Soybean

Effects of photoperiod and flower removal on vegetative activity of the main stem apical bud were examined for an indeterminate ('Williams') and a determinate ('Bragg') soybean cultivar. Plants grew under long day conditions until the V2 stage. Then, they were subjected to three photoperiodic treatments: (1) short days of 9 h of solar radiation during all the experiment (SD); (2) 10 short days followed by long days until the end of the experiment (SD + LD); and (3) long days during all the experiment (LD). From the moment anthesis was reached, half of the plants of each photoperiodic treatment were periodically deflowered. Flower removal induced an additional but limited vegetative growth of the main stem apex, due to the elongation of the youngest internodes. This effect was only seen under SD because long day applications (SD+LD and LD) induced a high flower abortion. On the contrary, long days stimulated internode elongation, leaf expansion and, under LD, delayed anthesis which resulted in enhanced vegetative activity of apical buds and a greater production of nodes and branches. Thus, a close but inverse relation was observed between flower induction and vegetative structure differentiation by apical buds. As in Bragg, Williams may stop vegetative activity of buds by their simple transition to a terminal raceme hence, only posterior differentiated internode elongation will be either limited or stimulated depending on SD or LD conditions, respectively.