Single Short Day Research Articles

Acute downregulation of Type II and Type III iodothyronine deiodinases by photoperiod in peripubertal male and female Siberian hamsters

Availability of the thyroid hormone triiodothyronine (T3) in the mediobasal hypothalamus plays a central role in seasonal reproductive responses to photoperiod. Across many vertebrates, Type 2 iodothyronine deiodinase (DIO2) is elevated under reproductively stimulatory long days (LD) and synthesizes the conversion of thyroxine to T3; Type 3 iodothyronine deiodinase (DIO3) reduces T3 production and signaling, and is upregulated under reproductively-inhibitory short days (SD). In Siberian hamsters, regulation of hypothalamic T3 is dominated by dio3 expression, whereas dio2 expression is less-consistently affected by photoperiod. In adult hamsters, changes in deiodinase mRNA expression typically require several weeks to manifest, but it is not known whether or how quickly these mechanisms are engaged during the rapid responses to photoperiod observed in young, peri-pubertal hamsters. This experiment tested the hypotheses that (1) deiodinase responses to photoperiod are accelerated in juvenile hamsters and (2) photoperiodic downregulation of deiodinase expression occurs more rapidly than upregulation. Hypothalamic dio2 and dio3 mRNA expression was quantified in male and female Siberian hamsters that were weaned on postnatal day 18 (PND 18) into SD or remained in their natal LD, and on PND 31 were exposed to a single long or short day. In SD males and females, a single long day inhibited dio3 mRNA expression, but did not increase dio2 mRNA. In LD males, a single short day rapidly inhibited dio2 mRNA expression, but did not stimulate expression of dio3 mRNA. Downregulation of dio2 and dio3 mRNAs precedes gonadotrophin responses to day length. Rapid photoperiodic inhibition of deiodinase mRNAs may initiate changes in thyroid hormone signaling in advance of longer-term, melatonin-dependent, responses.

Effects of 9,10-ketol-octadecadienoic acid (KODA) application on single and marginal short-day induction of flowering in Pharbitis nil cv. Violet

Seedlings of the Japanese morning glory (Pharbitis nil, formerly Ipomoea nil) cv. Violet are induced to flower by a single short day treatment, and endogenous levels of 9,10-ketol-octadecadienoic acid (KODA) in cotyledons were found to correlate with this mode of short-day induction. When 100 μM KODA solution was sprayed on 7-day-old seedlings before and after a marginal short-day induction, the seedlings bore approximately 4 flower buds, a one-bud increase compared with control seedlings. In treated seedlings, the second node most commonly bore the first flower bud, one node lower than in the control seedlings. We then used RT-PCR to determine expression levels of 10 genes related to photoperiodic induction of flowering. In the cotyledons, no differences were observed in expression of any genes, including P. nil FLOWERING TIME LOCUS T (PnFT1 and PnFT2), between the KODA-treated and the control seedlings. In the apical buds, P. nil APETALA1 (PnAP1) was expressed earlier in the KODA-treated seedlings than in the control seedlings. A decrease in the expression of P. nil TERMINAL FLOWER1b (PnTFL1b) was also observed in the KODA-treated seedlings. These results suggest that KODA acts as a weak enhancer of flower bud formation.

Environmental control of ovarian dormancy in natural populations of Drosophila melanogaster

Drosophila melanogaster from Australia, Europe and North America enter an adult ovarian dormancy in response to short days and low temperatures. The independent effects of temperature and day length in the determination of dormancy have been examined only in one long-established laboratory line (Canton-S). In all other studies of natural or laboratory populations, dormancy has been assessed at either a single short day or a single moderately low temperature. Herein, we determine the relative roles of temperature, photoperiod, and their interaction in the control of ovarian dormancy in D. melanogaster from two natural populations representing latitudinal extremes in eastern North America (Florida at 27 degrees N and Maine at 44 degrees N). In both natural populations, temperature is the main determinant of dormancy, alone explaining 67% of the total variation among replicate isofemale lines, whereas photoperiod has no significant effect. We conclude that ovarian dormancy in D. melanogaster is a temperature-initiated syndrome of winter-tolerant traits that represents an adaptive phenotypic plasticity in temperate seasonal environments.

Photoperiodic regulation of the diapause of the progeny in Trichogramma embryophagum Htg. (Hymenoptera, Trichogrammatidae): Dynamics of sensitivity to photoperiod at the immature stages of maternal females

Photoperiodic regulation of T. embryophagum progeny prepupal diapause was investigated under laboratory conditions. Maternal females developed at 20°C, the position of the photosensitive period was detected by transferring immature stages between the diapause-inducing “short” day (L:D = 12:12) and the diapause-averting “long” day (L:D = 20:4). Progeny generation developed at L:D = 12:12 under the near-threshold temperature of 13°, 14°, or 15°C. Experiments showed that, at least under the used photo-thermal regimens, only the pupal stage was sensitive to the photoperiod influence. The highest photosensitivity was recorded during the last two days before the adult emergence. In this critical period, even a single short day cycle induced diapause in most of individuals. However, the reaction to the long day was weaker: at least two long light days immediately preceding the maternal adult emergence were necessary to avert the diapause. If a short day was preceded by a long day by more than 2–3 days before the adult emergence, the stepwise photoperiodic response caused an increase in the tendency to diapause. The results of this study could be used in pest biocontrol practice for elaboration of optimal methods for Trichogramma mass rearing and storage and also for prediction of its seasonal cycles under natural conditions.

Partial floral evocation by high irradiance in the long‐day plant Sinapis alba

Previous work has shown that increased irradiance promotes flower initiation in the long‐day plant Sinapis alba when given during the first half of a single, suboptimal long day. It is without flower‐promoting effect, however, when given during a single short day. In the present work it is shown that, in the apex of plants exposed to a single short day at high irradiance, some changes occur that are normally observed during the transition to flowering (full evocation), e.g., elevated soluble sugar and starch levels, increased numbers of mitochondria and changed nucleolus structure. These changes are of similar magnitude and follow the same sequence as the corresponding changes during full evocation. Other changes, normally associated with full evocation, e.g., increased mitotic activity, are not caused by one short day at high irradiance. This treatment thus produces only what we call “partial evocation”.

RNA Synthesis in the Apex ofSinapis albain Transition to Flowering

RNA synthesis in the 1-5 mm apex during floral evocation of Sinapis alba (a long-day plant) was measured using a double-labelling technique to compare precursor incorporation in evoked and vegetative apices, followed by analysis by gel electrophoresis and oligo(dT)-cellulose chromatography. In plants induced to flower by exposure to a single long day, higher levels of RNA synthesis showed a two-phase pattern, the first increase starting very early in evocation, from 10 h after the start of the long day. This early extra synthesis is of rRNA, and then also sRNA.2 Subsequently higher levels of RNA synthesis, especially rRNA and 5S RNA, are shown from 36 h. At no time was such additional synthesis of the RNA fraction retained on oligo(dT)-cellulose detected. The experiment was repeated with plants subjected to a single displaced short day, a treatment which also induces flowering, and similar higher RNA synthesis found in evoked apices. These results were compared with those obtained in two non-inductive treatments which result in some features of floral evocation: a single short day at high intensity light, and a single treatment with benzyladenine. Neither gave rise to additional RNA synthesis, and thus the observed high levels of synthesis of rRNA and sRNA seem to be associated with other features of floral evocation.

Changes in the carbohydrate content of the leaf and the apical bud of Sinapis during transition to flowering

Vegetative plants of Sinapis alba L. were induced to flower by a single long day of 20 h or by a single short day of 8 h starting at an unusual time of the 24-h cycle ("displaced short day"). The soluble sugar and starch contents of the just-expanded leaf and the apical bud were measured at various times after the start of each of these two photoinductive treatments. Associated with the induction of flowering there were temporary increases in the soluble sugar and starch contents of the leaf and of the bud. These increases were apparent 14 h after the start of the long day and 12 h after the start of the displaced short day. The starch content of the bud increased later. These results indicate that an increase of the soluble sugar content of the bud is required for its transition from the vegetative to the reproductive condition.

Flowering response oflemna paucicostata in japan

Twenty-two strains ofLemna paucicostata collected from various districts in Japan are classified into 4 types having different morphological features and photoperiodic behaviors. (I) The “N-1” type, widely distributed in north and middle Japan, consists of many short-day strains with similar morphological characteristics. The strain of northern origin, however, has a shorter critical dark period than that of southern origin, and most of the strains flower in response to a single short day though some from middle Japan require 2 short days. (2) The “N-2” type, found in a limited area of northern Japan, is also a short-day type, but has very long critical dark periods and requires 3–5 short-day cycles for flowering. (3) The “S” type, distributed in southern Japan, never flowered in any photoperiod or culture conditions tested. (4) The “K” type, strain 351, collected at the experimental farm of Kyoto University, is a day-neutral type and flowers independently of photoperiod. Application of some SH inhibitors, tungstate or EDTA, or exposure to blue, far-red or low-intensity light caused daylength-independent flowering in short-day strain 6746 (California origin), but none of these treatments caused flowering in any short-day strain collected in Japan.

LX.— Note on the Feldspars of Canisp

Every visitor to Loch Inver in Sutherland is familiar with the red porphyry of Canisp. Ice-borne blocks are to be seen all along the shore of the loch, in the bed of the Canisp Burn, and built into nearly every wall, where their bright red colour and large embedded crystals must attract the attention of the least observant. These crystals have been very fully described by Professor Heddle; and it is with some diffidence that I communicate this note of a single short day’s gleaning in a field where he has harvested. The two feldspars present in this rock are Orthoclase, and a plagioclase that may fairly be classed as Albite, although it contains a small proportion of lime. Owing probably to the presence of this constituent, the Albite weathers with markedly greater ease than the accompanying Orthoclase. With still greater ease the paste in which the feldspars are embedded decomposes into a red clay, from which the crystals can readily be extracted. The Orthoclase of Canisp occurs in distinct and well developed crystals up to about 20 mm. in length. The predominant forms are b, c, m , with o and y always present, but always subordinate. Dr Heddle says that the form z , truncating the edge b/m , occurs only occasionally. It is often difficult, because of the rounding of the edges of the crystals, to determine with certainty the presence of narrow faces such as these, but this form seems to be shown by about 20 per cent. of