Effect of varying number of short days, gibberellic acid and ascorbic acid on the flowering of soybean

Both the cultivars of soybean, namely E.C. 2579 and Punjab I,studied were found to be qualitative short day plants. Evenone SD was sufficient to cause flower bud initiation in E.C.2579, although flower opening required 3 SDs. Pb. I did notshow flower bud initiation with less than 10 SDs. In Pb. I thenumber of flowers with 20 SDs was higher than continuous SD,indicating the favourable effect of long days prior to induction. Exogenous application of GA₃ and AA singly and in combinationsubstituted for the additional photoperiodic requirements ofincompletely induced plants of Pb. I, but were ineffective undercontinuous LDs. Treatment with these regulators of plants havingreceived 8 SDs resulted in initiation of flower buds, whichfailed to open into flowers. In plants subjected to 10 SDs flower buds were initiated withall these treatments except control. Floral buds did not openinto flowers with any treatment or combination not containingGA₃. (Received March 28, 1970; )     

Elimination of short-day melatonin signaling accelerates gonadal recrudescence but does not break refractoriness in male Turkish hamsters

Long days stimulate and short days (SDs) inhibit the reproductive axis of photoperiodic rodents. In long-day Turkish hamsters, unlike most other rodents, elimination of pineal melatonin secretion by constant light or pinealectomy initiates a cycle of gonadal involution and recrudescence outwardly similar to that induced by short days. The present study assessed whether short days and constant light induce the seasonal reproductive cycle via common or different interval timing mechanisms. Male hamsters that had undergone gonadal involution in SDs for 8 or 14 weeks were treated with LL for 14 and 8 weeks, respectively. If SDs and LL act via independent mechanisms, then gonadal quiescence of SD-regressed males, which normally lasts 10 weeks, might be extended by LL treatment; alternatively, if SDs and LL act on the same timer, or the timer cannot be retriggered, then LL will not extend the duration of reproductive quiescence. Neither of these outcomes materialized. Instead, male hamsters exposed to LL while reproductively quiescent exhibited accelerated gonadal recrudescence. Extended LL treatment did not restore responsiveness to SDs in photorefractory hamsters. In Turkish hamsters, photoperiodic history determines whether constant light inhibits or stimulates the hypothalamic-pituitary-testicular axis.     

DAY NEUTRAL FLOWERING Represses CONSTANS to Prevent Arabidopsis Flowering Early in Short Days

The photoperiodic response in Arabidopsis thaliana requires the precise regulation of CONSTANS (CO) expression in relation to the light period during the day. In short days (SDs) levels of CO expression are normally low during the light period, and this results in delayed flowering compared with long days (LDs) when CO expression rises to high levels before the end of the light period. We identified a novel flowering time gene called DAY NEUTRAL FLOWERING (DNF) that acts in the same flowering pathway as CO. DNF is a membrane-bound E3 ligase that represses CO expression and plays an important role in maintaining low levels of CO expression in SDs. The effect of DNF on the rhythm of CO expression is essential for the photoperiodic response of Arabidopsis, enabling it to have a different flowering response in LDs and SDs.     

THE ROLE OF AUXIN IN THE PHOTOPERIODIC TUBERIZATION IN BEGONIA EVANSIANA ANDR.

The formation of aerial tubers in Begonia plants, an SD response,was inhibited by IAA, NAA and IBA applied to their leaves duringthe dark periods. The effectiveness of IAA differed accordingto the time of application during the dark periods, and themost sensitive time varied with daylengths employed. In order to inhibit the tuberization under optimal photoperiods(8-hr SDs), IAA had to be applied during the first 2 days orso of the SDs. Under non-optimal photoperiods, however, IAAwas effective even when applied somewhat later. The auxin activity of leaf extracts from the plants subjectedto 8-hr SDs decreased during the first 2 or 3 days to a minimum,and then increased until finally began to decrease, again; undernon-optimal photoperiods, the minimum of auxin activity wasattained more slowly. The paper-chromatographic study suggestedthat the change in auxin activity was mainly due to the changein IAA content. The number of SDs making the auxin content minimal agreed withthe minimum number of SDs required for tuberization. On the basis of the above results, the part played by endogenousauxin in photoperiodic induction is discussed. ¹Present address: Institute for Agricultural Research, TôhokuUniversity, Sendai. ²Present address: Biological Institute, Yamaguchi University,Yamaguchi.     

Flowering in cultivars of sesame (Sesamum indicum) Differing in photoperiodic sensitivity

Studies of flowering in sesame (Sesamum indicum L.) under different photoperiods revealed that cultivars Glauca, Venezuela-52 and Oro were short day strains while a fourth cultivar, Aceitera, proved to be day length neutral. Sensitivity to varying photoperiods, then, does not seem to be a universal characteristic of all sesame cultivars. Also, no correlation was found between photoperiodic class and latitude of origin in the cultivars studied. Inheritance studies involved crosses between the day neutral cultivar and two of the short day cultivars. In all cases, the F₂ populations demonstrated continuous variation. Most of the F₂ variability was of genetic origin and heritability values ranged from 86 to 96%. Additionally, transgressive segregation was observed for both early and late flowering. It is proposed that a minimum of three loci are involved in the inheritance of photoperiodic response in the sesame cultivars studied.     

Genotype Differences in Photoperiodic Sensitivity and Vernalization Response in Wheat

The regression of final leaf number on leaf number at transferfrom an 8 h to an 18 h photoperiod was used to compare the photoperiodicresponse of eight locally-adapted lines of wheat. Comparisonsof such regressions in the vernalized and univernalized conditionsenabled detection of the presence or absence of a significantcultivar vernalization response and comparisons of differingresponses between cultivars. Prior vernalization generally did not significantly alter the‘rate’ of photoperiodic response, as the slope ofthe LNT/FLN regression, indicating a certain physiological independenceof vernalization and photoperiodic responses in wheat. Differences, both in photoperiodic and vernalization responseof the eight wheats studied have been discussed in terms ofadaptability and breeding for maturity alteration in wheat.Evidence has been produced for the possible existence of a thirdfactor influencing developmental processes associated with floweringin wheat.     

Photoperiodic and hormonal influences on fur density and regrowth in two hamster species

Temperate and boreal mammals undergo seasonal changes in pelage that facilitate thermoregulation in winter and summer. We investigated photoperiodic influences on pelage characteristics of male Siberian and Syrian hamsters. Fur density (mg fur/cm2 skin) was measured by weighing the shavings of fur patches removed from the dorsal and ventral surfaces of hamsters maintained in long days (LDs) or transferred to short days (SDs). Patches were reshaved 3 wk later to assess fur regrowth (mg regrown fur/cm2 skin). Fur density was greater in SD than in LD Siberian hamsters after 11 wk of differential phototreatment. The onset of increased fur density in SDs was accompanied by a transient increase in fur regrowth (11-14 wk on the dorsal surface and 7-10 and 11-14 wk on the ventral surface), suggestive of a seasonal molting process. Fur density, body mass, and pelage color of Siberian hamsters returned to values characteristic of LD males after a similar duration of prolonged (>27 wk) SD treatment and appear to be regulated by a similar or common interval-timing mechanism. In Syrian hamsters, dorsal fur density, fur regrowth, and hair lengths were greater in SD than in LD males. Castration increased and testosterone (T) treatment decreased dorsal and ventral fur regrowth in LD and SD hamsters, but the effects of T manipulations on fur density were limited to a decrease in dorsal fur density after T treatment. Decreased circulating T in SDs likely contributes to the seasonal molt of male hamsters by increasing the rate of fur growth during the transition to the winter pelage.     

Double loss-of-function mutation in EARLY FLOWERING 3 and CRYPTOCHROME 2 genes delays flowering under continuous light but accelerates it under long days and short days: an important role for Arabidopsis CRY2 to accelerate flowering time in continuous light

The photoperiodic response is one of the adaptation mechanisms to seasonal changes of lengths of day and night. The circadian clock plays pivotal roles in this process. In Arabidopsis, LHY, CCA1, ELF3, and other clock proteins play major roles in maintaining circadian rhythms. lhy;cca1 double mutants with severe defects in circadian rhythms showed accelerated flowering under short days (SDs), but delayed flowering under continuous light (LL). The protein level of the floral repressor SVP increased in lhy;cca1 mutants under LL, and the late-flowering phenotype of lhy;cca1 mutants was partially suppressed by svp, flc, or elf3. ELF3 interacted with both CCA1 and SVP, and elf3 suppressed the SVP accumulation in lhy;cca1 under LL. These results suggest that the unique mechanism of the inversion of the flowering response of lhy;cca1 under LL may involve both the ELF3-SVP/FLC-dependent and -independent pathways. In this work, elf3-1 seeds were mutagenized with heavy-ion beams and used to identify mutation(s) that delayed flowering under LL but not long days (LDs) or SDs even without ELF3. In this screening, seven candidate lines named suppressor of elf3 1 (self1), sel3, sel5, sel7, sel14, sel15, and sel20 were identified. Genetic analysis indicated that sel20 was a new deletion allele of a mutation in the blue light receptor, CRY2. A late-flowering phenotype and decrease of FT expression in the elf3;sel20 double mutant was obvious under LL but not under SDs or LDs. These results indicated that the late-flowering phenotype in the double mutant elf3;sel20 as well as in lhy;cca1 was affected by the presence of darkness. The results suggest that CRY2 may play more essential roles in the acceleration of flowering under LL than LDs or SDs.     

Polymorphism of DNA sequences of cryptochrome genes is not associated with the photoperiodic flowering of wild soybean along a latitudinal cline

Both cultivated soybean and its wild relative Glycine soja exhibit strong photoperiodic sensitivity at different latitudes. Recent studies have demonstrated that the blue light-absorbing cryptochrome gene, CRY1a, is involved in the photoperiodic flowering of soybeans. However, no sequence variation was found in the cDNA among cultivars at different latitudinal clines. In the present study, we examined whether positive selection due to polymorphisms in the cryptochrome genes of G. soja occurs. Partial DNA sequences, mainly exons, of cryptochrome genes CRY1a-1d and CRY2a-2c were analyzed for 18 accessions in the Japanese archipelago. The neutral evolutionary pattern of the polymorphisms for all cryptochrome genes except for CRY1a was summarized using Tajima's D test and low nucleotide diversity was shown for all genes. Although CRY1a did not show neutral evolution, balancing selection was recognized in the intron while not in the exon. No geographical pattern of polymorphisms was observed in the cryptochrome genes. These results reject the possibility of cryptochrome genes being involved in the photoperiodic flowering of wild soybeans along a latitudinal cline.     

Photoperiodic growth control in perennial trees

Plants have to cope with changing seasons and adverse environmental conditions. Being sessile, plants have developed elaborate mechanisms for their survival that allow them to sense and adapt to the environment and reproduce successfully. A major adaptive trait for the survival of trees of temperate and boreal forests is the induction of growth cessation in anticipation of winters. In the last few years enormous progress has been made to elucidate the molecular mechanisms underlying SDs induced growth cessation in model perennial tree hybrid aspen (Populus tremula × P. tremuloides). In this review we discuss the molecular mechanism underlying photoperiodic control of growth cessation and adaptive responses.     

Vegetative and Reproductive Response of Lycopersicon esculentum Mill. to Photoperiods

The photoperiodic behavior of tomato cultivars differing ingrowth habit and geographical origin was investigated. Short(8 h) and long (11 to 14 h or dark interruption) photoperiodswere obtained by using the changing seasonal daylenghs. Observationson vegetative and reproductive development indicated that thetomato cultivars responded differentially to the treatments.A highly significant interaction between photoperiod and leafposition was observed. The probable cause for the diverse andcomplex responses of the tomato species to photoperiods is discussed.     

Genetics of Heading Time in Wheat (TRITICUM AESTIVUM L.). I. the Inheritance of Photoperiodic Response

The inheritance of photoperiodic response was studied in crosses involving four spring wheats (Sonora 64, Pitic 62, Justin and Thatcher) and three winter wheats (Blackhull, Early Blackhull and Extra Early Blackhull). The parental cultivars were classified into a photoperiod-sensitive group (Justin, Thatcher, Blackhull and Early Blackhull) and a relatively photoperiod-insensitive group (Sonora 64, Pitic 62 and Extra Early Blackhull) based on their heading response when vernalized and grown under different daylength regimes.-F(1) data indicated that daylength insensitivity is not always dominant over day-length sensitivity and that the dominance relationship with respect to photoperiodic response depends on the alleles present in the parents. The heading patterns after vernalization and growth under short days of F(1), F(2), F(3) and backcross generations of a 4-parent diallel cross involving Justin, Sonora 64, Extra Early Blackhull and Blackhull could be satisfactorily explained on the basis of two major loci with three alleles at each locus. The genotype for each parent was suggested in terms of these loci. Genes with minor effects also influenced the photoperiodic response in a quantitative manner.-Diallel cross analysis of the number of days to heading (log scale) indicated significant additive and dominance genetic variances, a high average degree of dominance for earliness (photoperiod insensitivity) and a preponderance of recessive alleles in the parents acting in the direction of lateness (photoperiod sensitivity). Estimation of the genetic components of variation contained in the generation means of individual crosses (untransformed data) showed that, besides additivity and dominance, epistasis was also an important factor in the genetic control of photoperiodic response in wheat.     

Genetic control system of the differences in duration of vernalization in winter common wheat

Hypotheses of differences in genetic control on duration of vernalization for winter wheat have been considered. It has been shown that differences in this character are controlled by independent Vrd gene system. Monogenic dominant near-isogenic lines have been created. They differ in two non-allelic Vrd1 and Vrd2 genes with unequal expression. The response of created lines to photoperiodic changes and Vrd genes effects on various agronomic traits have been characterized. Vrd genotypes have been identified in a number of winter common wheat cultivars.     

Segmental duplications are hot spots of copy number variants affecting barley gene content

Copy number variants (CNVs) are pervasive in several animal and plant genomes and contribute to shaping genetic diversity. In barley, there is evidence that changes in gene copy number underlie important agronomic traits. The recently released reference sequence of barley represents a valuable genomic resource for unveiling the incidence of CNVs that affect gene content and for identifying sequence features associated with CNV formation. Using exome sequencing and read count data, we detected 16 605 deletions and duplications that affect barley gene content by surveying a diverse panel of 172 cultivars, 171 landraces, 22 wild relatives and other 32 uncategorized domesticated accessions. The quest for segmental duplications (SDs) in the reference sequence revealed many low‐copy repeats, most of which overlap predicted coding sequences. Statistical analyses revealed that the incidence of CNVs increases significantly in SD‐rich regions, indicating that these sequence elements act as hot spots for the formation of CNVs. The present study delivers a comprehensive genome‐wide study of CNVs affecting barley gene content and implicates SDs in the molecular mechanisms that lead to the formation of this class of CNVs.