Bolting Susceptibility of Sugar Beet (Beta vulgaris) in Relation to Contents of Sulfhydryls and Disulfides and to Protein Composition of Membranes

The aim of the investigation was to correlate the sensitivity to low temperature that leads to bolting of sugar beet with a property of seedlings or seeds, analyzable without cold treatment. Populations or inbred lines were investigated, the bolting percentages of which had been determined in field trials. Sulfhydryls (—SH) and disulfide sulphur (-S-) were analyzed by amperometric titration with silver nitrate. Disulfides were broken with sulphite, and proteins were unfolded with urea. Negative correlations were found between the bolting percentage and (-SH + -S-) per leaf fresh or dry weight unit and per leaf protein nitrogen, with urea at the titrations. Positive correlations were obtained between the bolting percentage and the ratio of (-SH + -S-) titratable in the absence of urea to that titratable in the presence of urea, when leaf homogenates or leaf or seed protein precipitates were examined. Centrifugation experiments showed that membrane proteins were responsible for the correlation. By polyacrylamide gel electrophoresis of the membrane proteins it was found that the proportion between some of these proteins was correlated with the bolting percentage. From these results and such from analyses of beet plants during and after cold treatment a hypothesis was constructed: Low bolting susceptibility, i.e., low sensitivity to low temperature, is caused by a high proportion of a hydrophobic membrane protein, rich in -SH or -S-. This protein interferes with the reactivity of the plants to gibberellins resulting from low temperatures or long days.     

Genetic identification of a novel bolting locus in <Emphasis Type="Italic">Beta vulgaris</Emphasis> which promotes annuality independently of the bolting gene <Emphasis Type="Italic">B</Emphasis>

Bolting tendency in the crop species Beta vulgaris, which includes sugar beet, is a complex trait governed by various environmental cues, including prolonged periods of cold temperatures over winter (vernalization) and photoperiod, and multiple genetic factors. Two loci which promote bolting in the absence of vernalization are known in beet, the major bolting locus B on chromosome II and the B2 locus on chromosome IX. Here, genetic linkage and quantitative trait locus analyses in two populations derived from a cross between a biennial genotype, which was identified in a phenotypic screen for EMS-induced bolting mutants and requires vernalization to bolt, and an annual wild beet accession revealed the presence of a novel major bolting locus B4 which is linked to the B locus but promotes annual bolting independently of B. The genetic distance between B and B4 on chromosome II is 11 cM. A sequence-based marker was identified which co-segregates with bolting behavior and co-localizes with the B4 locus.     

EFFECT OF TEMPERATURE AND PHOTOPERIOD ON GROWTH AND DORMANCY OF BETULA PAPYRIFERA

The effects of day/night temperatures and photoperiod on the growth and dormancy of paper birch (Betula papyrifera) were studied in seedlings from different geographic origins. The response of Alaskan plants to temperature and photoperiod was distinctly different from other seed sources. Alaskan plants required very long days to prevent cessation of growth while plants from southern seed sources grew on photoperiods as short as 14 hr. Low night temperature (14 C) antagonized the promotive action of long photoperiods in Alaskan plants but had little effect in other seed sources. High day temperatures offset the inhibitory effect of the cool night to a lesser degree in Alaskan plants than in plants from other locations. Dormancy induced by short photoperiods was antagonized (relieved ?) to a lesser degree by high night temperatures in Alaskan birch than in other seed sources. Betula papyrifera var. humilis from Alaska may be an incipient species since its morphological traits are accompanied by adaptive physiological responses to its environment. These responses are as distinct as its morphological characteristics.     

Genetic and Molecular Studies for Regulation of Bolting Time of Onion (<Emphasis Type="Italic">Allium cepa</Emphasis> L.)

The control of bolting time in onion is an important approach for bulb and seed production, as onion plants which bolt do not produce marketable bulbs and seed yields are dependent on floral induction. However, genetic and molecular studies about bolting time in onion plants have not been examined yet to date. In order to understand the regulation of bolting time in onion plants, we conducted the genetic crosses between late bolting-type cultivar (MOS8) and very early bolting-type cultivar (Guikum). Segregation ratio of late to very early in F₂ populations indicated that this lateness trait was determined by a dominant locus. We also analyzed protein profiles in onion plants with different bolting time by a proteomics approach. Interestingly, a protein spot with significant similarities to chromodomains of mammalian chromo-ATPase/helicase-DNA-binding 1 or heterochromatin protein 1, which is involved in the histone modifications, was identified. Histone methyltransferase activity was also observed in onion plants. Taken together, these results suggest that a genetic pathway may be involved in the modulation of bolting time in onion plants, though there is no direct evidence that this protein spot obtained by proteomics is relevant to vernalization.     

Canola seed germination and seedling emergence from pre-hydrated and re-dried seeds subjected to salt and water stresses at low temperatures

Low soil temperatures and low water potentials reduce and delay the seed germination of canola (Brassica rapa L., B. napus L.) in western Canada. Germination is also very sensitive to the salinity effects of nitrogen fertiliser placed with the seed, especially when the seed bed is relatively dry. The effects of pre-hydration and re-drying treatment on canola (Brassica rapa L. cv. Tobin) seed germination and seedling emergence at 10°C subjected to either a water or salt stress were determined. Low water potentials, induced by polyethylene glycol (PEG 8000), low soil moisture, or high concentrations of salts, reduced both germination and seedling emergence, and increased the time to 50% germination and emergence of seeds at 10°C. At equal osmotic potentials, Na₂SO₄ was less inhibitory on low temperature germination than either NaCl or PEG, suggesting that the sulphate ion partially alleviated the inhibitory effects of low water potential. Solutions of NaCI produced more abnormal seedlings compared to Na₂SO₄, suggesting that NaCl was more toxic than Na₂SO₄ during seedling development. Pre-hydration and re-drying partially overcame the inhibitory effects of both low water potential and salts on seed germination and seedling emergence at 10°C. The seed treatment increased the germination rate in Petri dishes and seedling emergence from a sandy loam soil. Water potentials or soil water contents required to inhibit 50% germination or emergence at 10°C were lower for treated seeds compared to control seeds. Salt concentrations inhibiting 50% emergence were higher for treated seeds than control seeds. Neither treated nor control seeds produced seedlings which emerged if the soil water content was lower than 9% or when the soil was continuously irrigated with salt solutions of 100 mmol kg^-1 of NaCl or 50 mmol kg^-1 of Na₂SO₄. These results suggest that the pre-hydration and re-drying treatment did not lower the base water potentials at which seedling emergence could occur. Abnormal seedlings were observed in both treated and control seeds, particularly if the soil was watered with NaCl solutions; however, the seed treatment reduced the number of abnormal seedlings.     

A novel major quantitative trait locus controlling seed development at low temperature in soybean (Glycine max)

Low temperature is among the critical environmental factors that limit soybean production. To elucidate the genetic basis for chilling tolerance and identify useful markers, we conducted quantitative trait loci (QTL) analysis of seed-yielding ability at low temperature in soybean (Glycine max), using artificial climatic environments at usual and low temperatures and recombinant inbred lines derived from a cross between two contrasting cultivars in terms of chilling tolerance. We identified a QTL of a large effect (LOD > 15, r ² > 0.3) associated with seed-yielding ability only at low temperature. The QTL was mapped near marker Sat_162 on linkage group A2, where no QTL for chilling tolerance has previously been identified. The tolerant genotype did not increase the pod number but maintained the seed number per pod and single seed weight, namely, the efficiency of seed development at low temperature. The effect of the QTL was confirmed in a segregating population of heterogeneous inbred families, which provided near-isogenic lines. The genomic region containing the QTL also influenced the node and pod numbers regardless of temperature condition, although this effect was not primarily associated with chilling tolerance. These results suggest the presence of a new major genetic factor that controls seed development specifically at low temperature. The findings will be useful for marker-assisted selection as well as for understanding of the mechanism underlying chilling tolerance in reproductive organs.     

Effects of Temperature of Mother-plant Environment on Yield and Germination of Seeds of Lettuce (Lactuca sativa)

Experiments on the production of two separate crops of lettuceseeds, each in three different temperature environments, andsubsequent tests on the seed are described. Low production temperatures(20 °C day, 10 °C night) gave a low yield of large seeds,and high temperatures (30 °C, 20 °C) gave a higher yieldof much smaller seed; the highest yield came from medium temperatures(25 °C, 15 °C), which gave medium-sized seed. After-ripening,manifested as an increase in percentage germination at hightemperatures with increase in seed age, occurred in seed fromall three production environments of the first crop, thoughthere were differences in degree, and in that from the two higherproduction temperatures, but not the lowest, of the second crop.Measurements of the forces required to penetrate the layerssurrounding the embryo showed an inverse relationship with temperatureof the production environment for pericarps but not for endosperms,and a gradual reduction during storage for pericarps but notendosperms. Measurements of germination potential showed thatembryos from seeds produced in cool conditions were less ableto cope with high temperatures than those from warner conditions.These results are discussed in relation to the control of germinationin lettuce. Lettuce, Lactuca sativa (L.), seed production, germination, seed coverings, germination potential     

The phenology of seed‐propagated globe artichoke

The ability of globe artichoke to produce inflorescences (capitula) during the autumn when the market price is highest is lost when plants are propagated from seed, as are most F₁ hybrid cultivars. To gain an understanding of the phenology of seed‐propagated globe artichoke, both vernalised and non‐vernalised seedlings grown from open pollinated progeny of ‘Spinoso sardo’ plants were transplanted into the field at two monthly intervals covering a whole year. Final leaf number and the date of unfolding of each leaf were used to calculate the phyllochrons. The average final leaf number increased from 24 to 88 in response to increasing daylength above an approximately 11 h threshold during the first 30 days after emergence, and this variate explained about 90% of the variation in the thermal time taken to reach the bolting stage. The average phyllochron ranged from 56 to 96°Cd among the six emergence dates and was the major underlying physiological cause of the loss of early flowering shown by seed‐propagated plants. Genotypic variation for phyllochron within an emergence date was strongly associated with variation for the length of the emergence to bolting stage period. The limited effect of vernalisation on development indicated that the late flowering tendency of seed‐propagated plants cannot be attributed to an unfulfilled cold requirement.     

THE EFFECT OF MANURES ON THE BOLTING OF THE BEET PLANT

In sugar beet, the effect on bolting of additions of potash manures, of superphosphate, and of the mixture of these was not significant, whether applied at the time of sowing or previously. Dung applied in the previous autumn slightly increased the number of plants which went to seed, and when applied just before sowing it had a more marked effect. An amount of sulphate of ammonia which would have approximately the same stimulating effect as the dung gave a slightly larger amount of bolting.
On red beetroot, it was possible to compare larger and smaller dressings of various coarse organic manures, and of each of these with and without dressings of sulphate of ammonia. In all cases the sulphate of ammonia and each of the organic manures largely increased the amount of bolting, and a doubling of the organic manure dressing or the addition of sulphate of ammonia to it caused a further increase. Sewage sludge gave an abnormally large amount of bolting, but it is doubtful whether this was due to the larger amount of organic matter and nitrogen applied in this manure. In general, any manurial addition causing more vigorous growth leads to an increase in bolting. There is a very large variation in the amount of running to seed in the crop of red beetroot from different parts of the same field, but the effect of the manures on the proportion which bolted was not widely different.
The general question as to the reason why beet plants should bolt more in one season than in another is discussed, and it is suggested that a check to the plants in an early stage, whether caused by dryness or waterlogging, or by low temperature, followed by a vigorous growing period may have something to do with the matter. This would agree with the experiences recorded in the present paper.     

Critical phases in the seed development of common juniper (Juniperus communis)

Common juniper (Juniperus communis L.) populations in northwest European lowlands are currently declining in size and number. An important cause of this decline is a lack of natural regeneration. Low seed viability seems to be one of the main bottlenecks in this process. Previous research revealed a negative relation between seed viability and both temperature and nitrogen deposition. Additionally, the seeds of common juniper have a variable ripening time, which possibly influences seed viability. However, the underlying mechanisms remain unresolved. In order to elucidate this puzzle, it is important to understand in which phases of seed production the main defects are situated, together with the influence of ripening time. In this study, we compared seed viability of populations with and without successful recruitment. We examined three seed phases: (i) gamete development; (ii) fertilisation and early‐embryo development; and (iii) late‐embryo development. After the first two phases, we found no difference in the percentage viable seeds between populations with or without recruitment. After late‐embryo development, populations without recruitment showed a significantly lower percentage of viable seeds. These results suggest that late‐embryo development is a bottleneck in seed development. However, the complex interaction between seed viability and ripening time suggest that the causes should be in the second seed phase, as the accelerated development of male and female gametophytes may disturb the male–female synchrony for successful mating.     

The impact of temperature regimes on development,dormancy breaking and germination of dwarf shrub seeds from arctic,alpine and boreal sites

It has been suggested that the infrequent sexual reproduction of arctic dwarf shrubs might be related to the harsh environmental conditions in which they live. If this is the case, then increases in temperature resulting from global climate change might drastically affect regeneration of arctic species. We examined whether recruitment of Empetrum nigrum ssp. hermaphroditum and Vaccinium uliginosum (hereafter E. nigrum and V. uliginosum) was affected by temperature during three reproductive stages: seed development, dormancy breakage and germination. Seeds were collected from an arctic, an alpine (only E. nigrum) and a boreal site with different climates; stored at different winter temperatures and incubated for germination at different temperatures. Seeds of V. uliginosum developed in the boreal region had a higher percentage germination than did seeds developed in the Arctic. In contrast, seeds of E. nigrum from the arctic site had a higher or similar percentage germination than did seeds from the alpine and boreal sites. Increased winter temperatures had no significant effect on resulting germination percentage of E. nigrum. However, V. uliginosum seeds from the arctic site suffered increased fungal attack (and thus decreased germination) when they were stratified under high winter temperatures. Seeds of both species increased germination with increased incubation temperatures. Our results suggest that both species would increase their germination in response to warmer summers. Longer summers might also favour the slow-germinating E. nigrum. However, increased winter temperatures might increase mortality due to fungal attack in V. uliginosum ecotypes that are not adapted to mild winters.     

A survey of EMS-induced biennial Beta vulgaris mutants reveals a novel bolting locus which is unlinked to the bolting gene B

Beta vulgaris is a facultative perennial species which exhibits large intraspecific variation in vernalization requirement and includes cultivated biennial forms such as the sugar beet. Vernalization requirement is under the genetic control of the bolting locus B on chromosome II. Previously, ethyl methanesulfonate (EMS) mutagenesis of an annual accession had yielded several mutants which require vernalization to bolt and behave as biennials. Here, five F2 populations derived from crosses between biennial mutants and annual beets were tested for co-segregation of bolting phenotypes with genotypic markers located at the B locus. One mutant appears to be mutated at the B locus, suggesting that an EMS-induced mutation of B can be sufficient to abolish annual bolting. Co-segregation analysis in four populations indicates that the genetic control of bolting also involves previously unknown major loci not linked to B, one of which also affects bolting time and was genetically mapped to chromosome IX.     

Radicle emergence with increased temperatures following summer dispersal in Trillium camschatcense: A species with deep simple double morphophysiological dormancy in seeds

Seeds with deep simple double morphophysiological dormancy (MPD) need cold stratification during the first winter after dispersal for radicle emergence, followed by the summer for root and bud development and finally a second winter for shoot emergence. In a previous study, we demonstrated that Trillium camschatcense seeds have this type of dormancy with radicles emerging from most seeds after the first winter. However, radicles also emerged from a few seeds in autumn during the same year as dispersal. We thought that temperatures after seed dispersal played a role in radicle emergence before the first winter. To confirm our idea, we investigated germination phenology outdoors, relationships between temperatures after seed dispersal and radicle emergence in the first year outdoors, radicle emergence in the first winter under varied temperatures using incubators, and shoot emergence from seeds with an emerged radicle in the first year outdoors. Our phenology study confirmed that T. camschatcense seeds have deep simple double MPD. Over 7 years, 0.2–7.5% of radicles emerged in the first year before winter and these percentages were moderately positively correlated with temperatures, especially minimum temperatures. Increasing August and September temperatures increased radicle emergence in the laboratory. Shoots emerged from seeds with an emerged radicle in the first year after the first winter. With increased autumn temperatures in warmer regions or with global warming, we predict that germination phenology may shift: increased radicle emergence in the first year and shoot emergence following the first (and not second) winter.     

Effect of climate change on mast-seeding species: frequency of mass flowering and escape from specialist insect seed predators

Global surface temperatures are expected to increase by several degrees in the next century, with potentially large but poorly understood impacts on ecological interactions. Here we propose potential effects of increased temperatures on ecologically dominant New Zealand grasses (Chionochloa spp.) that mass flower and mast seed. Twenty-two years’ data from five masting Chionochloa species in New Zealand showed that the cue for heavy flowering was unusually high temperature in the summer of the year before flowering. Attack by predispersal insect seed predators was much reduced in mast years, apparently because predator populations were satiated. Increased temperatures would greatly decrease interannual variation in Chionochloa flowering, allowing seed predator populations to increase and potentially to devastate the seed crop annually. Similar responses are likely in masting species worldwide. This previously unrecognized effect of global warming could have widespread impacts on temperate ecosystems.     

Ecophysiology of seed dormancy and the control of germination in early spring‐flowering Galanthus nivalis and Narcissus pseudonarcissus (Amaryllidaceae)

Seed dormancy induction and alleviation in the winter‐flowering, moist temperate woodland species Galanthus nivalis and Narcissus pseudonarcissus are complex and poorly understood. Temperature, light and desiccation were investigated to elucidate their role in the germination ecophysiology of these species. The effect of different seasonal temperatures, seasonal durations, temperature fluctuations, the presence of light during different seasons and intermittent drying (during the summer period) over several ‘years’ on seed germination was investigated with outdoor and laboratory experiments. Warm summer‐like temperatures (20 °C) were necessary for germination at subsequent cooler autumn‐like temperatures (greatest at 15 °C in G. nivalis and 10 °C in N. pseudonarcissus). As the warm temperature duration increased, so did germination at subsequent cooler temperatures; further germination occurred in subsequent ‘years’ at cooler temperatures following a second, and also third, warm period. Germination was significantly greater in darkness, particularly in G. nivalis. Dormancy increased with seed maturation period in G. nivalis, because seeds extracted from green capsules germinated more readily than those from yellow capsules. Desiccation increased dormancy in an increasing proportion of N. pseudonarcissus seeds the later they were dried in ‘summer’. Seed viability was only slightly reduced by desiccation in N. pseudonarcissus, but was poor and variable in G. nivalis. Shoot formation occurred both at the temperature at which germination was greatest and also if 5 °C cooler. In summary, continuous hydration of seeds of both species during warm summer‐like temperatures results in the gradual release of seed dormancy; thereafter, darkness and cooler temperatures promote germination. Cold temperatures, increased seed maturity (G. nivalis) and desiccation (N. pseudonarcissus) increase dormancy, and light inhibits germination. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 246–262.     

Comparative <Emphasis Type="Italic">in vitro</Emphasis> germination ecology of <Emphasis Type="Italic">Calopogon tuberosus</Emphasis> var. <Emphasis Type="Italic">tuberosus</Emphasis> (Orchidaceae) across its geographic range

Seed responses to temperature are often essential to the study of germination ecology, but the ecological role of temperature in orchid seed germination remains uncertain. The response of orchid seeds to cold stratification have been studied, but the exact physiological role remains unclear. No studies exist that compare the effects of either cold stratification or temperature on germination among distant populations of the same species. In two separate experiments, the role of temperature (25, 22/11, 27/15, 29/19, 33/24°C) and chilling at 10°C on in vitro seed germination were investigated using distant populations of Calopogon tuberosus var. tuberosus. Cooler temperatures promoted germination of Michigan seeds; warmer temperatures promoted germination of South Carolina and north central Florida seeds. South Florida seed germination was highest under both warm and cool temperatures. More advanced seedling development generally occurred at higher temperatures with the exception of south Florida seedlings, in which the warmest temperature suppressed development. Fluctuating diurnal temperatures were more beneficial for germination compared to constant temperatures. Cold stratification had a positive effect on germination among all populations, but South Carolina seeds required the longest chilling treatments to obtain maximum germination. Results from the cold stratification experiment indicate that a physiological dormancy is present, but the degree of dormancy varies across the species range. The variable responses among populations may indicate ecotypic differentiation.     

MORPHOLOGICAL,ANATOMICAL, AND MOLECULAR CONSEQUENCES OF GROWTH AND DEVELOPMENT AT LOW TEMPERATURE IN SECALE CEREALE

Growth of winter cereals at low, nonfreezing temperatures is essential for the establishment of a cold-hardy state and subsequent survival of the overwintering plant. In this paper, I describe the consequences of growth and development of Secale cereale L. cv. Puma at cold-hardening temperatures with respect to leaf morphology, anatomy, and biochemistry, and with particular emphasis on their relationship to photosynthetic acclimation. Low temperature-induced structural and functional alterations at the level of ribulose bisphosphate carboxylase-oxygenase and the chloroplast thylakoid membrane are described and related to overall photosynthetic efficiency and capacity for CO₂ utilization. Growth and development at cold-hardening temperatures appear to result in changes in protein conformation and membrane organization, but not in basic composition. It is proposed that developmental temperature imparts a significant effect on the assembly of these multimeric, photosynthetic components, which leads to distinct structural and functional changes.