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Carrot is generally regarded as a biennial plant with an obligatory vernalization requirement. Early spring cultivation makes plants vulnerable to premature bolting, which results in a loss of commercial value. However, our knowledge of flowering time genes and flowering mechanisms in carrot remain limited. Bolting behavior of D. carota ssp. carota 'Songzi', a wild species sensitive to flower induction by vernalization and photoperiod, and orange cultivar 'Amsterdam forcing', and their offspring were investigated in different growing conditions. We performed RNA-seq to identify the flowering time genes, and digital gene expression (DGE) analysis to examine their expression levels. The circadian patterns of related genes were identified by qPCR. The results showed bolting behavior of carrot was influenced by low temperature, illumination intensity and photoperiod. A total of 45 flowering time-related unigenes were identified, which were classified into five categories including photoperiod, vernalization, autonomous and gibberellin pathway, and floral integrators. Homologs of LATE ELONGATED HYPOCOTYL (LHY) and CONSTANS-LIKE 2 (COL2) were more highly expressed under short day condition than under long day condition. Homologs of COL2, CONSTANS-LIKE 5 (COL5), SUPPRESSION OF OVEREXPRESSION OF CONSTANS 1 (SOC1), FLOWERING LOCUS C (FLC) and GIBBERELLIC ACID INSENSITIVE (GAI) were differentially expressed between 'Songzi' and 'Amsterdam forcing'. The homolog of COL2 (Dct43207) was repressed by light, but that of COL5 (Dct20940) was induced. A preliminary model of genetic network controlling flowering time was constructed by associating the results of DGE analysis with correlation coefficients between genes. This study provides useful information for further investigating the genetic mechanism of flowering in carrot.

To understand the relative importance of density-dependent and density-independent factors on plant fitness, we examined the effects of local densities and surrounding ground surface conditions on the reproductive output of a monocarpic biennial plant, Lysimachia mauritiana var. rubida in a natural population. Observations were conducted during five successive years in open dry habitats on rocky coastal cliffs of the subtropical Bonin (Ogasawara) Islands, Japan. Local density and ground surface conditions, categorized by gravel size, were remarkably heterogeneous in the study population. Therefore, we hypothesized that number of flowers per plant was affected by local density, ground surface condition, and their interaction. During 3 of 5 years, the number of flowers per individual L. mauritiana var. rubida plant was only negatively affected by the local density around the plant. The interaction effects of local density and ground surface conditions were observed in two years. Taken together with the results of previous studies, these results suggest that density effects are dominated survival in the early growing season and reproduction, while the effects of ground conditions are important for seedling recruitment and survival in the late growing season. Thus, interactive effects between density-dependent and density-independent factors on the life cycle from germination to reproduction regulate populations of L. mauritiana var. rubida in spatially heterogeneous habitats.

Fusarium yellows, caused by the soil-borne fungus Fusarium oxysporum f. sp. betae (Fob), can lead to significant yield losses in sugar beet. This fungus is variable in pathogenicity, morphology, host range and symptom production, and is not a well characterized pathogen on sugar beet. From 1998 to 2003, 86 isolates of F. oxysporum and 20 other Fusarium species from sugar beet, along with four F. oxysporum isolates from dry bean and five from spinach, were obtained from diseased plants and characterized for pathogenicity to sugar beet. A group of sugar beet Fusarium isolates from different geographic areas (including nonpathogenic and pathogenic F. oxysporum, F. solani, F. proliferatum and F. avenaceum), F. oxysporum from dry bean and spinach, and Fusarium DNA from Europe were chosen for phylogenetic analysis. Sequence data from b- tubulin, EF1a and ITS DNA were used to examine whetherFusarium diversity is related to geographic origin and pathogenicity. Parsimony and Bayesian MCMC analyses of individual and combined datasets revealed no clades based on geographic origin and a single clade consisting exclusively of pathogens. The presence of FOB and nonpathogenic isolates in clades predominately made up of Fusarium species from sugar beet and other hosts indicates that F. oxysporum f. sp. betae is not monophyletic.

The main objective of this study was to analyze whether plant material transfer is a suitable approach for establishing plant populations with spatial patterns and population structures resembling those of remnant populations. We studied pattern formation and population characteristics in three remnant and two restored populations of the biennial plant species Arabis nemorensis in the upper Rhine valley in southwestern Germany over a period of 2 years. We investigated spatial patterns of seedlings, juveniles, and adults as well as the small-scale horizontal and vertical distribution of seeds in the soil, followed the fate of individual plants and recorded structural habitat parameters such as vegetation and litter cover. Population dynamics differed between the study sites, but there was no pronounced difference between restored and remnant sites. Seedlings, juveniles, and adults as well as seeds in the seed bank showed aggregated spatial patterns on all study sites, with positive autocorrelation on a scale of 20-60 cm. Within sites, patterns remained approximately stable through time. Restored sites experienced rapid seed bank formation as a result of the restoration measures. Our results suggest that the restoration measures were not only successful in transferring the target species but also triggered rapid formation of spatially structured populations that, years after restoration, closely resembled those of remnant sites.

In Central Europe, fungicides to control leaf spot disease in sugar beet caused by Cercospora beticola are applied based on thresholds of disease incidence (DI, per cent of infected plants). As variety-specific fungicide application was not analyzed to date, the epidemiology of C. beticola and its effect on white sugar yield (WSY) in varieties with different susceptibility were investigated at seven sites in Germany and Austria in 2004 and 2005. All varieties reached the summary thresholds 5 ⁄ 15 ⁄ 45% DI in all environments. Fitting a logistic growth curve to DI revealed significant differences among varieties. At high disease pressure, susceptible varieties reached a considerably higher disease severity (DS, per cent of infected leaf area) at harvest and a larger area under disease progress curve (AUDPC) than resistant varieties. Fitting a logistic growth curve to DS showed an increasing differentiation among varieties with time. The growth rate estimated based on the logistic growth curve was the only variable that performed equally well in differentiating varieties under low and high disease pressure. With increasing disease pressure, varieties differed considerably in WSY, but differences between susceptible and resistant varieties were significant only in some environments. The disease-loss relation between AUDPC and relative WSY was varietyspecific. Resistant varieties had an approximately identical WSY with and without infection and compensated for negative infection effects even at higher AUDPC. Therefore, at high disease pressure, resistant varieties had a higher relative yield compared to susceptible ones. However, our results indicate that there is no need to develop variety-specific thresholds, but resistant varieties reach the established thresholds later than susceptible ones. Consequently, the time of fungicide application can be delayed in resistant varieties. This will help to reduce the use of fungicides to the bare essentials as requested for the integrated crop protection management.

Selective absorption (SA) of K over Na (i.e. the preferential absorption of K over Na) has been proposed as a Na tolerance mechanism but genotypic variation for this trait has not been assessed with sugar beet in the field. Thus, the aim of this study was to explore the variation of SA in 14 sugar beet cultivars and to relate SA with yield and root quality in two sites of central Greece (Amfithea and Pyrgetos). Genotypic variation for SA was significant and the SA values were higher in Pyrgetos, the site with the lower soil K and Na concentrations. In Pyrgetos, a favourable environment for sugar beet growth, cultivars yielded more and root quality was better. In that site, a negative relationship between SA and yield (fresh root weight, sugar yield) was found indicating that strong Na exclusion from root is a disadvantage for high yielding. Negative SA-yield relationships were evident in Amfithea when five cultivars with very low SA values (

Functions of sodium (Na + ) and potassium (K + ) are closely associated. In some crops, Na + is able to prevent or reduce considerably the occurrence of K + deficiency. Sugar beet (Beta vulgaris L.) is a natrophilic crop, and positive effects of Na + applications on yield were observed when K + was sufficiently supplied. However, it is not known which specific function of K + can limit the growth of sugar beet when K + is substituted by an equivalent amount of Na + . Therefore, K + substitution by Na + was investigated for sugar beet in hydroponics. Surprisingly, no K + -deficiency symptoms were observed. However, calcium (Ca 2+ ) concentrations in the leaves were significantly decreased. Moreover, Ca 2+ uptake and translocation through xylem sap were reduced in Na + -treated plants. It is concluded that Ca 2+ uptake by roots and its translocation via xylem sap primarily limit the possibility of K + substitution by Na + in sugar beet nutrition.

Sugar beet (Beta vulgaris ssp. vulgaris L.) has a relatively narrow genetic base and several programmes have sought to evaluate the potential for introducing novel traits from wild and cultivated Beta germplasm into the crop. In particular, resistance to important sugar beet diseases has been identified within individual Beta accessions. We report here the successful transfer of resistance to Beet mild yellowing virus (BMYV) from garden beet, fodder beet and leaf beet accessions to progeny populations in initial crosses with sugar beet. Twelve plant populations derived from different Beta accessions were inoculated with viruliferous aphids carrying BMYV and the virus content of individual plants subsequently quantified by an ELISA test. Seven populations were significantly more resistant than a control sugar beet cultivar (P ≤ 0.05). BMYV resistance was successfully inherited in BC 1 and BC 2 generations, suggesting that resistance could potentially be introgressed from these sources into elite sugar beet lines.

Two sugar beet (Beta vulgaris sp.) varieties, which were supposed to differ in drought tolerance, were exposed to drought stress in a growth chamber and a container experiment in field. The aim was to test for (i) differences between the varieties in water use efficiency (WUE), biomass production and distribution and (ii) the relationship between WUE and carbon isotope discrimination (A). and between biomass production and A. Significant differences in WUE were detected between plants of well-watered and drought treatments in both experiments, but not between the varieties. Production losses due to drought were large for both varieties in both experiments. Losses in the growth chamber were up to 50 % of plant dry weight and the corresponding value in the field was 24 %, when plants were given 60 and 30 %, respectively, of the full-watered treatments. Significant negative correlations between WUE and A were found, but not between biomass production and A, when both varieties were included. Negative correlations between WUE and A were also found for each variety separately. The results suggest that A estimates from leaf tissue of sugar beet may provide a useful tool for genetic selection of drought-tolerant sugar beet varieties.

Summary 1 Monocarpy in facultative biennials can be favoured by selection when there is a more than proportional increase in fitness with size. The possible contributions of larger reproductive output and higher offspring quality to such an increase were investigated in the facultative biennial plant Digitalis purpurea. Straw mass (rosette leaves and flowering stem excluding fruits and seeds) was determined for 100 individuals of varying size and correlated with the number of flowers and seeds per flower to examine whether sex-allocation is size dependent. 2 To determine whether maternal size influences offspring growth, and whether this effect is more pronounced in the presence of competition, seeds from 32 maternal plants were grown alone, and with one, two or four competitors. 3 Total seed number increased proportionally with size. Seed quality, measured as seed size, germination percentage and speed also increased with maternal size. The combined fitness measures of total seed mass (seed number × seed size), number of seedlings (seed number × germination percentage) and total female fitness (seed number × germination percentage × mean offspring dry mass after 14 weeks) all increased disproportionally with size. 4 Sex-allocation was size dependent, with large plants emphasizing the female function. 5 Offspring dry mass after both 8 and 14 weeks of growth was strongly influenced by competition, whereas the effect of maternal size was significant only at the first harvest date. Competition did not accentuate the effects of maternal size. 6 The results support that monocarpy exists in D. purpurea because of increased offspring quality rather than a disproportionate advantage in seed output of large individuals.

Summary 1 Seven populations of Beta vulgaris ssp. maritima (wild beet) situated along a latitudinal cline were studied for their vernalization requirement and its consequences for fitness. 2 Various cold regimes were applied in glasshouses and experimental gardens with plants of different ages. Three additional experimental sites (on the French Mediterranean, Atlantic and North Sea coasts) situated near three of the sampled populations, and thus including a reciprocal transplant design, were used to evaluate the influence of latitude under natural conditions. Survival and plant size were measured over 3 years. 3 The vernalization requirement was greater in plants from more northern origins. The level of cold required to allow flowering overcompensated for the colder springs, so that northern plants in northern sites flowered less than southern plants in southern sites. 4 Young seedlings were more difficult to vernalize than plants that had already developed vegetative rosettes. 5 Differences in vernalization requirement seem to be an adaptive response to spring temperatures and season length in a particular latitude. A whole winter vernalization almost always led to flowering in the subsequent year whatever the latitude or geographical origin. 6 Plants from the Atlantic and Channel coasts showed the highest lifetime reproductive success at all sites. Southern populations were better adapted to disturbed habitats as shown by their higher first-year reproductive success. The North Sea population had a lower reproductive success than the Atlantic populations, even in its native environment.

Two mycotrophic species (Lactuca sativa and Abutilon theophrasti) and one nonmycotrophic species (Beta vulgaris) were grown in a P-deficient soil, and the effects of mycorrhizal inoculation on three variables that determine growth rate were assessed for each. The phosphorus-use efficiency (PUE, dW/dP) is the ratio of d. wt increase to P content increase. Plant P is the amount of P (the limiting resource) controlled by the plant, which can be allocated to various purposes. The phosphorus efficiency index (PEI, dP/Pdt) is the efficiency with which plant P is used to acquire P from the soil. Inoculated and control plants of a given species initially contained the same amount of P because all plants were grown from seed. Mycorrhizal colonization significantly increased the PEI of Lactuca and Abutilon (by 23 and 32%, respectively). As expected, mycorrhizal inoculation did not significantly increase the PEI of Beta. As a result, mycorrhizal inoculation significantly increased the P content of Lactuca and Abutilon, but not Beta. Mycorrhizal colonization decreased the PUE of lettuce, but did not significantly affect that of Abutilon or Beta. Mycorrhizal inoculation therefore slightly increased the growth rate of Lactuca, greatly increased the growth rate of Abutilon, and ultimately had no significant effect on the growth rate of Beta.

We investigated plant reproduction in relation to genetic structure, population size, and habitat quality in 13 populations of the rare biennial plant Pedicularis palustris with 3-28500 flowering individuals. We used AFLP (amplified fragment length polymorphism) profiles to analyze genetic similarities among 129 individuals (3-15 per population). In a cluster analysis of genetic similarities most individuals (67%) were arranged in population-specific clusters. Analysis of molecular variance indicated significant genetic differentiation among populations and among and within subpopulations (P < 0.001). Gene flow (N(e) m) was low (0.298). On average, plants produced 55 capsules, 17 seeds per fruit, and 42 seedlings in the following growing season. The number of seeds per capsule was independent of population size and of genetic variability. In contrast, the number of capsules per plant (P < 0.05) and the number of seedlings per plant (P < 0.05) were positively correlated with population size. The relation between population size and the number of seeds per plant was not significant (P = 0.075). The number of capsules and of seeds and seedlings per plant (P < 0.01) were positively correlated with genetic variability. Genetic variability was independent of actual population size, suggesting that historical population processes have to be taken into account, too. Stepwise multiple regressions revealed additional significant relationships of habitat parameters (soil pH, C:N ratio), vegetation composition, and standing crop on reproductive components. We conclude that populations of P. palustris are genetically isolated and that reproductive success most likely is influenced by population size, genetic variability, and habitat quality. Management strategies such as moderate grazing, mowing, and artificial gene flow should endeavor to increase population size as well as genetic variation.

A pot experiment was conducted under greenhouse conditions with two subspecies of beet, fodderbeet (Beta vulgaris cv. Majoral) and seabeet (Beta maritima), under saline conditions. Growth and physiological parameters (dry weight, leaf area, water relations and net photosynthesis) were recorded. The two subspecies responded differently in terms of growth parameters. Plant growth was significantly reduced at 400 m m NaCl, while no significant growth reduction occurred at 200 m m NaCl. Fairly high values of relative growth rate were associated with the leaf area of the cultivars. The water content of the shoot decreased with plant age. The fodderbeet cultivar Majoral showed a significant increase in dry matter at 200 m m NaCl after 5 weeks. This growth improvement may be related to the better adaptation of the plants under saline conditions.

Although it is widely recognised that chemical composition controls the patterns of decomposition and N mineralisation of crop residue materials, there has been little agreement as to the nature of the most important chemical fractions. We investigated whether this could be attributed to differences in methodologies employed for chemical characterisation of the lignin and cellulose fractions of plant materials. The cellulose and lignin contents of cauliflower, potato, red beet, Brussels sprouts and wheat crop residues were analysed by a number of contrasting methods. These were forage fibre and forest products analyses, which utilise KMnO4 and H2SO4 respectively to separate the two fractions, and a third method, which employs NaClO2. For all the materials, the forage fibre method gave substantially lower amounts of both lignin and cellulose than the other methods. There was correlation between lignin determined by the different methods. Low recovery of lignin by the forage fibre method was found to arise partly from incomplete delignification by KMnO4. The cellulose contents given by the different methods were highly correlated. However, it was apparent that the forage fibre method underestimated cellulose, since only alpha-cellulose was measured.

Studies in the 1970s showed that sugar beet partitioned into root, crown and scalp had large concentrations of impurities in the scalp, the root portion had the best processing quality and the crown was intermediate. Since then the processing quality of beet has improved. This paper reports similar studies on today's varieties, in an experiment at IACR-Broom's Barn over the three years 1993–1995, and extended in 1996 to the most important soil types used for sugar beet production in England. The crown is now a smaller proportion of the total beet weight (70 compared to 130 g kg−1) but the distribution of the concentrations of the quality parameters (sugar and the impurities potassium, sodium, amino nitrogen, raffinose, betaine and invert sugars) between the beet portions has not changed. This distribution was not significantly affected by year, variety or beet size but was affected by soil type. Nitrogen-rich soils produced beet with heavier crowns and a smaller differential in impurity concentration between the root and the crown. The scalp material had a variable sugar concentration, but it always contained large concentrations of impurities, especially invert sugar. The equation of Pollach et al (Zucker industrie116: 689–700 (1991)) which includes invert sugar as a variable, was applied to the data. It indicated that including all the crowns in the factory process with the roots would increase white sugar yield by approximately 6%. The increase due to inclusion of the scalp was much smaller (2%), and would probably be expensive to achieve. © 1999 Society of Chemical Industry

The possible involvement of acid invertase (sucrose hydrolysis) as a prerequisite for sucrose mobilization from the vacuole of storage cells was investigated. Sugarcane (Saccharum officinarum) stalks, carrot (Daucus carota) roots and red beet (Beta vulgaris) hypocotyls were planted under greenhouse conditions and allowed to growth. The plants, however, were not permitted to become photosynthetically autotrophic by removing the new expanded leaves. Sucrose levels declined significantly in all three tissues without the development of acid invertase (EC 3.2.1.26) during the 21-day experimental period. Acid invertase and thus sucrose hydrolysis within the vacuole was, therefore, not required for sucrose mobilization.

Previously, we reported that phosphate (P i ) starvation of suspension cells or seedlings of Brassica nigra results in a large elevation in the activity of pyrophosphate-dependent phosphofructokinase (EC 2.7.1.90) (PFP). However, other researchers have found that P i deprivation either causes a significant reduction or no change in extractable PFP activity of Catharanthus roseus suspension cells, or roots of Nicotiana tabacum and Phaseolis vulgaris seedlings. The present study was undertaken to examine the prevalence of P i starvation-inducible PFP in seedlings, root cultures, or suspension cells of a variety of plant species differing in phylogenetic relatedness to B. nigra. In all species examined. fresh weights were decreased and acid phosphatase (EC 3.1.3.2) activities were increased by P i limitation. Brassica napus suspension cells, Arabidopsis thaliana seedlings, and roots of B. napus, B. carinata, B. oleracea, Beta vulgaris, Fagopyrum esculentum, Sinapis alba, and S. arvensis seedlings grown with P i -limited media contained 170-510% greater PFP activity than did nutrient-sufficient controls. In five of these species the induction of PFP activity by P i limitation was based in part upon an increased susceptibility of the enzyme to its allostcric activator, fructose-2,6-bisphosphate By contrast, the PFP activity in P i -deprived Lycopersicon esculentum root cultures and Nicotiana silvestris suspension cells decreased by 45-65% relative to P i -sufficient controls. Immunoblotting of extracts from A. thaliana seedlings, S. arvensis, F. esculentum and B. oleracea roots, and B. napus suspension cells probed with potato tuber PFP antibodies indicated that the upregulation of PFP activity by P i stress in these species was not correlated with an alteration in the amount or subunit composition of PFP. Our findings suggest that induction of PFP during long-term P i starvation may be characteristic of members of the Cruciferae. Chenopodiaceae and Polygonaceae families whose roots do not form symbiotic associations with mycorrhizal fungi.

A fully habituated (auxin- and cytokinin-independent) nonorganogenic (HNO) sugarbeet (Beta vulgaris) callus produces very little ethylene as compared with a normal (N) hormone-requiring callus of the same strain. Both callus types react by growth changes to application of inhibitors of ethylene biosynthesis and ethylene action, of 1-aminocyclopropane-1-carboxylic acid (ACC) as the immediate precursor of ethylene, to transfer from light to darkness, and also to application of exogenous ethylene or an ethylene trapper. This indicates their growth dependency upon their endogenously biosynthesized ethylene and also their sensitivity to exogenous gas. However, the sensitivity was generally higher for the HNO callus producing naturally less ethylene. The weaker reaction of the HNO callus to the exogenous ethylene was attributed to its hyperhydric status (a water layer surrounding the cells). Because low ethylene production appears as a general characteristic of habituated cell lines, the causal and/or consequential relationships of this low ethylene production with other characteristics of habituated tissues (absence of exogenous hormones in the culture media, deficiency of cell differentiation, accumulation of polyamines in neoplastic tissues) are discussed.

For organisms with indeterminate growth, life history theory predicts that in environments where organisms experience high survival rates or gain fecundity with age or size, natural selection favors delayed maturity. In semelparous perennial plants the onset of reproduction is regulated by a threshold size for flowering. We tested this prediction by comparing sand dune populations of the facultative biennial herb Cynoglossum officinale. We collected data on flowering probability, survival, and growth rate in relation to plant size in two habitat types, open areas and poplar thickets, in Meijendel, The Netherlands, and in Holkham, England. Survival of established rosettes was highest in Holkham and lowest in open areas in Meijendel. Relative growth rates in Holkham were about three times as high as those in Meijendel. These findings agreed with the differences in threshold sizes found among the sites: the Holkham field population harbored higher threshold sizes than the Meijendel sites. We used the field data to compare optimal threshold sizes for flowering predicted by three existing models. All three models gave the same rank order for threshold sizes as found in the field: Meijendel open < Meijendel poplar thicket < Holkham. One model, which maximized population growth rate λ, predicted optimal threshold sizes that agreed very well with threshold sizes found in the field. The predictions of the two other models, both maximizing R0, were consistently lower than the threshold sizes observed in Meijendel, while their predictions for Holkham were too high.

SUMMARY Cell walls were isolated and purified from Ri T-DNA-transformed carrot roots to determine whether arbuscular mycorrhizal (AM) fungi need a signal from the host root in order to form appressoria. Large cell-wall pieces were generated by the Parr nitrogen bomb technique. Purified cell walls were sterilized and inoculated with single spores of Gigaspora gigantea (Nicol. & Gerd.) Gerdemann & Trappe and Gigaspora margarita Becker & Hall using an in vitro culture technique. Appressoria only formed on epidermal cell walls isolated from host roots (Daucus carota L.) but did not form on epidermal cell walls isolated from non-host roots (Beta vulgaris L.). Although appressoria formed on host-cell walls, penetration hyphae did not fully develop. The results of this study indicate that appressorium formation by these AM fungi is a contact recognition event that does not require a signal secreted from the host root or the presence of intact host cells.

Colchicine uptake into ovules of sugar beet after 7 days of culture and its chromosome-doubling effect on ovule-derived plants were studied with high colchicine concentrations (0.4–6.0%) and short treatment duration (0–5 h). The best result of 4.2 diploid plants per 100 ovules was produced by treatment with 0.4% colchicine for 2.5 h. Both colchicine concentration and treatment time of ovules showed toxic effects on embryo formation, but it was stabilized at a low level with short exposure. The chromosome-doubling effect, by contrast, was unchanged with the colchicine concentrations used, but highly affected by the duration of exposure studied. A maximum percentage of 60% diploid plants was obtained after 3–5 h of uptake, which corresponds to only 31–39% of the total capacity for colchicine uptake in the ovules. Further uptake of the drug produced mainly toxic effects. Flow-cytometric measurements of the ploidy level in plantlets in vitro and of the same plants before flowering in soil were similar in about 80% of cases. Thus, flow-cytometric selection of diploid plants in vitro may be an efficient tool.

Although leaf photosynthesis and plant growth are initially stimulated by elevated CO 2 concentrations, increasing insensitivity to CO 2 (acclimation) is a frequent occurrence. In order to examine the acclimation process, we studied photosynthesis and whole plant development in swiss chard (Beta vulgaris L. Koch ssp. ciela) and sugarbeet (Beta vulgaris L. ssp. vulgaris) grown at either ambient or twice ambient concentrations of CO 2 . In an initial controlled environment study, photosynthetic acclimation to elevated CO 2 levels was observed in both subspecies 24 days after sowing (DAS) but was not observed at 42 and 49 DAS for sugarbeet or at 49 DAS for swiss chard. Although sugarbeet and swiss chard differed in root size and morphology, this was not a factor in the onset of photosynthetic acclimation. The reversal of photosynthetic acclimation that was observed in older plants grown at elevated CO 2 concentrations was associated with a rapid increase in root development (i.e. increased root : shoot [R/S] ratio), increased sucrose levels in sinks (roots) and no differences in total soluble leaf protein of either subspecies relative to the ambient CO 2 condition. In a second set of experiments, swiss chard and sugarbeet were grown in outdoor Plexiglass chambers at different times of the year (i.e. summer and early fall). Average 24-h temperature was 30.7 and 19.4°C for the summer and fall plantings, respectively. In agreement with the controlled environment study, lack of photosynthetic acclimation, determined from the response of photosynthesic rate to intemal CO 2 concentration, was correlated with increased root biomass and sucrose concentration relative to the ambient condition. However, photosynthetic acclimation was observed depending on the season, i.e. summer (swiss chard) or fall (sugarbeet), suggesting that acclimation was affected by environmental factors, such as temperature. Data from both experiments suggest that continued long-term photosynthetic stimulation may be dependent upon the ability of increased CO 2 to stimulate new sink development which would allow full utilization of the additional carbon made available in a high CO 2 environment.

Biogenic emissions of halomethanes (CH 3 Cl, CH 3 Br and CH 3 I) and methanethiol (CH 3 SH) are of major significance to atmospheric chemistry, but there is little information on such emissions from higher plants. We present evidence that plants can produce all these gases through an identical methyltransferase reaction. A survey of 118 herbaceous species, based on CH 3 I production by leaf discs supplied with KI, detected the presence of in vivo halide methyltransferase activity in 87 species. The activities ranged over nearly 4 orders of magnitude. Plants generally considered salt tolerant had relatively low activities, and salinization of three such species did not increase the activity. The highest activities were found in the family Brassicaceae. Leaf extracts of Brassica oleracea catalysed the S-adenosyl-L-methionine-dependent methylation of the halides I - , Br - and Cl - to the respective halomethanes. In addition, the extract similarly methylated HS - (bisulphide) to CH 3 SH. These two types of enzyme activity (halide and bisulphide methyltransferase) were also present in all of the 20 species comprising a subsample that represented the range of CH 3 I emissions observed in the initial survey of in vivo CH 3 I production ability, and in a marine red alga Endocladia muricata. Moreover, the two activities occurred in approximately the same ratio in all the higher plants tested. These findings highlight the potential of higher plants to contribute to the atmospheric budget of halomethanes and methanethiol. The halide and bisulphide methyltransferase activities may also provide a mechanism for the elimination of halide and HS - ions, both of which are known to be phytotoxic.

Mesophyll protoplasts from two of five sugar beet lines tested were regenerated into plants. Mesophyll protoplasts of all lines showed high plating efficiencies up to 4.0% developed hard compact callus, and two of the lines also developed white, soft and friable callus consisting of starch grain-containing cells. Whereas the compact callus never regenerated into plants, the white friable ones frequently developed globular structures, which became green in the light and formed adventitious shoots after cytokinin (BAP or thidiazuron) treatment. Genetic analysis by PCR-fingerprinting and flow cytometry showed uniformity and unchanged ploidy levels in 15 independently regenerated plantlets in line NF, but altered ploidy level (from diploid to triploid) in a regenerated plantlet of clone VRB.

In breeding for resistance to rhizomania, breeding material was routinely examined for resistance to the rhizomania virus over several years. This study was performed in order to investigate the value of virological examination of sugarbeet breeding material in breeding for resistance to the rhizomania virus. Tests were conducted with varieties susceptible or partially resistant to rhizomania, as well as with several new and more-resistant hybrids. A test on young plants showed that all genotypes contained beet necrotic yellow-vein virus (BNYVV), but that the virus content differed widely. Plants of two commercially used partially resistant varieties had, on average, only half the virus content of susceptible varieties in their roots, and plants of eight new hybrids still in the process of registration contained less than one third of that amount. There was a significant negative correlation between the quantity of BNYVV in young plant roots and final yield under disease conditions in the field. Opportunities for further improvement in the level of the resistance to BNYVV in sugarbeet by means of conventional breeding programmes are discussed.

Summary Variable fluorescence and carbon dioxide exchange rate (CER) were measured in intact leaves of glyphosate-treated sugarbeet plants, to investigate rapid effects on photosynthesis. In one experiment, a significant effect on variable fluorescence and CER was found within 8 h after herbicide application. The effect on stomatal conductance was not significant. In a second experiment, the effects of light or dark conditions during herbicide application and 24 h later were evaluated. Under light conditions glyphosate significantly reduced variable fluorescence after 4 h. However under initial conditions of 24 h darkness, followed by alternating 8 h light/8 h dark, the effect was not significant until 44 h after treatment, by which time the plants had received several hours of light. The eflect on variable fluorescence 8 h after herbidde application correlated positively with plant survival 7 days later.

The cost of nitrogen storage to current growth was examined in relation to N availability in the biennial Cirsium vulgare. Plants were grown outdoors, in sand culture, with continuous diel drip irrigation of fertilization medium containing one of five different N concentrations. Plants grown at the highest N concentration stored twice as much N in their tap roots as did plants grown at the lowest N concentration. In high-N-grown plants, the storage of N reserves occurred during the period of maximum growth, at the same time as tap-root production. At the time of maximum biomass, stored N was also at a maximum. During the period following maximum biomass, no additional storage of N occurred. This pattern was observed despite frequent late-season leaf senescence which resulted in a large pool of potentially mobile N which could have been stored at no cost to growth. In low-N-grown plants, the production of tap-root storage tissue and the filling of that tissue with stored N were staggered. Tap-root production and growth occurred during the period of maximum growth, as in the high-N-grown plants. However, filling of the storage tissue with N occurred late in the growing season, when the pool of mobile N from senescent leaves was large. The utilization of this late-season N source occurred with little or no cost to growth, and this N is labelled, according to previous definitions, as ‘accumulated’. The costs of storing N in plants of the different N treatments were calculated using two models based on different growth constraints. In one model, the cost of N storage was represented as lost growth due to allocation of N to storage, rather than to the photosynthetic shoot (i.e. growth was assumed to be limited by carbon acquisition). In the second model, the storage cost was calculated as lost growth due to allocation of N to storage, rather than to the nitrogen-acquiring fine-root system (i.e. growth was assumed to be limited by nitrogen acquisition). In both models, the total cost of N storage was predicted to decrease as N availability decreased due to smaller storage pool sizes in plants of the low-N treatments. The cost of filling the tap root with stored N as a percentage of the total storage cost was also reduced as N availability decreased due to the occurrence of late-season accumulation. By relying, at least in part, on late-season accumulation, plants grown at the lowest three levels of N availability reduced total storage costs by 15 to 22%. The results demonstrate that plants are capable of adjusting their storage patterns in response to low nitrogen availability such that the costs of storage are reduced.

Inefficiency in N use by plants contributes to environmental degradation. We examined the use of Ca 2+ as a means of increasing NH 4 + absorption in beet (Beta vulgaris cv. Detroit dark red). Ammonium absorption was measured in greenhouse and field studies. In the greenhouse, beet plants received full-strength nutrient solutions with Ca 2+ : NH 4 + molar ratios (MR) of 0, 0.25, 0.5 and 1.0 (Ca 2+ :NH 4 + ) and a NO 3 − check. Absorption of 15 NH 4 + was monitored over a 30-h period. The field production trials occurred over 3 yr on a calcareous Saneli silty clay loam (clayey over sandy or sandy-skeletal, montmorillonitic (calcareous), thermic Vertic Torrifluvent]. The 15 NH 4 + absorption study showed the greatest plant weight at the molar ratio (MR) of 1.0 in tops (except in seedlings) and at 0.5 in bulbs

Pea (Pisum sativum L. cv. Fenomen) and sugar beet (Beta vulgaris L. cv. Monohill) were cultivated in nutrient media without or with 10 μM CdCl2. Leaves of the same size and stage of development, detached or still attached to the intact plants, were submerged into redistilled water containing 1 to 250 μM CdCl2. The uptake experiments were run for 1 to 8 h at pH 3.6 and 5.1. Cuticular transpiration rate, density of leaf and density of stomata were also measured. Percentage of open stomata was studied at different pH. Foliar uptake of Cd into the leaf is evident since Cd is transported from the exposed part of the pea leaves, through the petioles and into the stipules, and since the Cd concentration of the leaves increases with time and external Cd concentration. The foliar uptake depends on the permeability of the cuticular membrane, which is increased by a high intrinsic Cd level, which in turn enhances the foliar uptake of Cd in sugar beet. Higher cuticular permeability in pea than in sugar beet is shown by a 2.5 times higher cuticular transpiration rate and a 4 times lower density of leaf for pea, which causes a 7 times higher foliar uptake in pea than in sugar beet. Low pH decreases the net uptake of Cd, probably by an exchange reaction in the cutin and pectin of the cuticular membrane. Stomata are not directly involved in the Cd uptake, and the differences in the sum total of stomatal aperture area per unit leaf area is not related to differences in foliar uptake of Cd. Percentage of open stomata, calculated as average of both sides of the leaves, was not affected by changes in pH: but especially at high pH. proportionally more stomata were open on the adaxial than on the abaxial side.

With a reduced stratospheric ozone concentration, the generation of UV-tolerant plants may be of particular importance. Among different crop plants there is large variation in sensitivity to UV-B radiation. This study was undertaken to investigate the possibilities of using somaclonal variation and selection in vitro for improving UV-B tolerance in sugar beet (Beta vulgaris L.). Sugar beet callus was exposed to UV radiation (280–320 nm, 0.863–5.28 kJ m-2 day-1, unweighted) and resultant shoots were selected from surviving cells. After establishment of the plants, they were grown under either visible radiation (114 μmol m-2 s-1 PAR) or with the addition of UV radiation (6.3 kJ m-2 day-1 biologically effective UV-B). Screening of regenerants in vivo for tolerance to UV radiation was undertaken 10 months after termination of the UV selection pressure. Screening was done visually and by using a number of physiological parameters, including chlorophyll fluorescence induction, ultraweak luminescence, pigment analysis and total content of UV-screening pigments. A clear difference between the unselected and the UV-selected somaclones was observed when visually studying the UV damage and other leaf injury. The observations were supported by the ultraweak luminescence measurements. Unselected plants showed significantly greater damage when subjected to subsequent UV radiation as compared to the selected plants. The clones subjected to UV selection pressure displayed a significantly higher concentration of UV-screening pigments under subsequent UV radiation. The unselected plants under subsequent UV treatment showed a lower carotenoid concentration when compared to selected plants. However, no significant difference between treatments was found for chlorophyll a/b, or F/Fmax, a measure of photosynthetic quantum yield.

SUMMARY Extinction of local populations of plants of many biennial plant species has been frequently reported. Survival of these species on the meta-population level implies a balance between extinction and regeneration, either through seed dispersal or from the seedbank. We distinguish between three types of biennials (transient, fugitive and persistent) and review the relation between dynamics of local populations and habitat characteristics, such as disturbance. Some species are safe-site limited whereas other species demonstrate a combination of safe-site and seed limitation. Meta-population dynamics are illustrated with two examples (Senecio jacobaea and Cynoglossum officinale). We distinguish between patch dynamics (loss and genesis of sites that are suitable for population development) and meta-population dynamics of biennials (population behaviour within and between sites, and dispersal). A hypothesis is developed on the regulation of patch dynamics. Finally we discuss the question: what makes biennials suited for exploiting temporary habitats?

A study was conducted on the germination traits and seed-bank dynamics ofOenothera glazioviana (=O. erythrosepala), which sets seed in August in sand-dune systems in Japan. More than 90% of freshly matured seeds germinated over a wide range of temperature in light, but less than 10% did so in continuous darkness. Stratification (chilling under moist conditions) was ineffective in diminishing the light-requirement for germination. When fresh seeds were imbibed for 24 h including a 12-h light period, followed by 7-day air-drying, 94% of them became germinable in the dark at 25°C, but remained dormant at less than 15°C. of seeds collected in March from capsules of dead plants, 58% germinated in the dark at 25°C. After four cycles of alternatc 1-day wetting followed by 2-day drying or 1.5-day wetting followed by 1.5-day drying under a 12-h photoperiod, the fraction of viable seeds declined from 76% to 40% and 22%, respectively, due to germination during the wet periods. Seed-bag experiments were conducted in the field, using seeds given and not given a light-stimulus. Forty percent of the light-stimulated seeds germinated in the soil, whereas the seeds without a light-stimulus remained dormant throughout the experiment. When seeds were placed on the soil surface or at a depth of 0.5-1 cm, the proportion of germinable seeds declined during late spring and autumn, but not during winter and early spring. The seed-bank size of a natural population just prior to current seed dispersal was 2–3% of the seed production in the previous year, suggesting a high turnover rate of the seed-bank.

Oenothera glazioviana (= O. Erythrosepala) behaves as a facultative biennial in an infertile sand-dune system in Japan. In the field, seedlings emerge mainly in autumn following seed ripening in late summer with an additional small peak in spring. The effects of emergence time on subsequent survival and fecundity, and the ultimate numbers of seeds produced per emerging seedling (Fs) were examined by a demographic model. The model showed that seedlings emerging either in March or in September–October will attain higherFs than those emerging in other months. If mortality in the seed bank is taken into account, autumn seems to be the best season for emergence to maximize the number of seedlings in the next generation.

A requirement for developing cover crop systems is to find cover crop species and cultivars that are both suitable and adapted in such systems, including sufficient frost resistance, for the local climate. The objective of this study was to detect the freezing resistance of different winter annual and biennial legumes, and to clarify whether the freezing resistance is correlated to the developmental stages of the plants. The study included a growth chamber experiment with nine species-cultivars, including white clover (Trifolium repens L., cv. Milkanova) as a control plant, and three developmental stages. At different developmental stages the test plants were exposed to five different freezing temperatures. The best freezing resistance, independent of sowing time, was shown by hairy vetch (Vicia villosa Roth. cv.Welta). Crimson clover (T. incarnatum L. cv. Heusers Ostsaat) and yellow sweet-clover [Melilotus officinalis (L.) Pall, cv. Nordgold Yellow] also showed good freezing resistance. Black medic (Medicago lupulina Gaertn. cv.Virgo Pajberg) showed medium freezing resistance, a little better than subclover (T. subterraneum L. cv. Denmark). Poorest freezing resistance was exhibited by barrel medic (M. trunculata Gaertn. cv. Parabinga) and snail medic [M. scuttelata (L.) Mill, cv. Kelson]. In hairy vetch, especially cv. AU EarlyCover, negative correlation between freezing resistance and age of the plants was detected. Generally, this was also true for crimson clover, subclover, barrel, and snail medic. In contrast, yellow sweetclover and white clover showed tendencies to positive correlation between freezing resistance and age of the plants. The results revealed the importance of developmental stage, at least in some species-cultivars, in the determination of freezing resistance.

Summary Reproduction was examined in one summer annual (Euphrasia pseudokerneri) and two biennials (Linum catharticum and Gentianella amarella) in chalk grassland, and three dune winter annuals (Erophila verna, Cerastium semidecandrum and Myosotis ramosissima). Gentianella was examined in 1979 to 1981 and all other species in 1980 and 1981, making a total of 13 separate datasets. Plants with one or two fruits had fewer seeds per fruit in all 13 cases. As plant size increased to six to ten fruits, seed number gradually increased. The relationship was similar in 1980 and 1981 for all six species. A ‘depauperate’ plant was therefore denned as one which produces significantly fewer seeds per fruit than large plants. Field populations of all species averaged less than nine fruits per plant, so that the relationship between seed number and fruit number was important in determining seeds produced per plant. Although this relationship has only been noted in three other species, I interpret five recent papers as suggesting the existence of a similar relationship between fruit number and seed number. I interpret the effect as analogous to the abortion of fruits in plants with many fruits.

SUMMARY The frequency of annuals, monocarpic perennials and polycarpic perennials among the dicotyledonous, herbaceous representatives of the European plant families are compared and related to various characteristics of plant architecture. It is suggested that the evolution of life-history may be governed by plant architecture. A comparison between annual and biennial Centaurium species suggests that the selective advantage of bienniality could relate to the production of a large stem within a short period. The typical architecture of a monocarpic perennial does not automatically imply an allometric relation between seed production and plant size. Size-dependent seed allocation, when present, is due to disproportionality between the plant's size and the amount of resources available for reproductive allocation, and not to the size constraints imposed by the plant's architecture. The evolution of monocarpic perenniality is therefore not a simple allometric step. Interpopulation differences in seed allocation may arise from differences in the nature or the availability of that particular resource that limits the reproductive allocation of biomass, and do not necessarily reflect differences in partitioning strategies.

SUMMARY A model is developed to calculate the population growth rate of different lineages within a biennial species, in a density-independent situation. The types differ in the minimum size they require for flowering. The environment is stochastic in the sense that each year a value for combined seed and early seedling survival was drawn from a probability distribution. Other probabilities of survival and growth were entered into the model as fixed rates, which are only dependent on the size of the plant. From demographic data on the delayed biennials Cirsium vulgare and Cynoglossum officinale, the model predicts that for both species (1) there exists a unique, optimal value of minimum size or weight w* for flowering, i.e. delayed flowering is profitable, (2) there is weak selection against flowering at sizes larger than optimal w* but strong selection against flowering at sizes smaller than optimal w*, and (3) that optimal w* is 2 g or more. In the field the size requirement was between 1 and 2 g for both species. The optimal value of w* is mostly determined by the fact that delayed flowering results in an increase in the expected number of seeds and less by delayed flowering resulting in averaging of variable recruitment over the years.

Three critical phenomena of flowering can be recognized in nature: critical age, critical initial size and critical switchover size. In order to understand the ecological significance of these flowering phenomena from the viewpoint of matter production, a simple model of flowering phenomean (critical-production model) was studied, assuming that plant flowering is controlled by the productive capacity of the plant (critical-production model, under the condition that plants forecast environmental conditions affecting matter production. Thus, we concluded that all three critical phenomena are various manifestation of the same critical-production principle. Then, using the model simulation, the reliability of each critical phenomenon for securing a given critical production was investigated in relation to the photosynthetic productivity of the habitat. The main predictions obtained from the simulation were as follows: 1) Only annual and biennial plants will show critical age phenomena, and most biennials will be facultative. 2) Among perennials, the critical initial size phenomenon will appear in low productive habitats, whereas in high productive habitats the critical switchover size phenomenon will be observed.

In order to gain understanding of the relationship of life history characteristics to coloniza- tion success, species cohabitation, and species replacement, a known number of seeds (fruits, achenes) of teasel, a "biennial" plant species, Dipsacus sylvestris Huds. were experimentally intro- duced into 52 permanent plots within each of 8 contiguous abandoned fields of various vegetation types in Michigan, USA. The nearest naturally occurring teasel population was 11.2 km from the study site; no teasel seeds or plants were present in the fields except where controlled introductions were made for this study. Permanently marked teasel and control plots were monitored over a 5-yr period for colonization success of teasel, species composition, and species net annual primary production. Results fall into three categories, the first of which has implications for studies of plant strategies and the last 2 have implications for studies of community structure and succession. 1) Life history characteristics of teasel and initial colonization success: A cohort of teasel seeds spreads its germination over more than one growing season; the length of time in the rosette stage may extend to 4 yr or more. Teasel did not successfully colonize the field that had thick quackgrass litter due to low germination of seed and high mortality of seedlings. In other fields, teasel rosettes grew at various mean rates, depending upon the presence of grass, other herbaceous dicots, and shading shrubs. Critical size for flowering was reached in either 2, 3, or 4 yr in six of the eight fields and these populations produced -7x more seeds than was originally introduced. 2) A mechanism for recolonization on a site: A teasel rosette creates an opening in vegetation that is colonized by teasel seedlings, or if teasel seeds are unavailable, by short-lived winter annuals, spe- cially Barbarea vulgaris L. The number of species in a field (excluding teasel) increased with teasel colonization, probably due to the creation of these openings by teasel rosettes. 3) Cohabitation with teasel: Grass growing with teasel was not reduced in productivity (compared to that in Control plots), despite the significant production by teasel. However, the herbaceous di- cotyledonous plants were slowly reduced over 4 yr as teasel increased in biomass. Roots of flowering teasel plants do not occupy the same soil layer as roots of the shallow grasses in this study, but probably do compete with those of the morphologically similar herbaceous dicots. Studies of commu- nity succession have often recorded changes in the number of species and in site productivity; such changes can here be directly attributed to colonization of the sites by a new species.

Seeds of 4 annual cultivars of celery (Apium graveolens L. No. 15, 16, 17 and 143) were able to germinate in the dark, under high temperature, in relatively high concentrations of NaCl solutions and in the presence of relatively high concentrations of the inhibitors of the biosynthesis of gibberellin, paclobutrazol and ancymidol. Seeds of two biennial cultivars [Florida and Earlibell (EB)] showed very low germinability, or failed to germinate under the same conditions. These results are discussed in terms of endogenous gibberellin levels, which may be higher in the seeds of annual cultivars as compared to biennial ones.

This paper compares two contrasting biennial plant species of the sand dunes of Holkham, North Norfolk. A survey of distribution, in relation to various habitat factors, showed that Lactuca virosa L. is characteristic of the tall, Ammophila-dominated grassland on the younger dunes. It is favoured by gaps in the vegetation cover such as those produced by local wind erosion, but it is very sensitive to rabbit grazing. Cynoglossum officinale L. is a plant of older dune grassland and is not normally grazed by rabbits. It can exploit the bare ground around rabbit warrens, benefiting from the higher nitrogen levels resulting from rabbit excreta. Studies on seed production and germination showed that Lactuca can produce large numbers

The "biennial" plant species Verbascum thapsus, Oenothera biennis, Daucus carota, and Tragopogon dubius are all found in abandoned agricultural fields, but they differ in their time of first appearance, peak abundance, and length of time populations persist. In experimental field studies these species showed differences in their abilities to colonize various types of ground cover. Seedling emergence, survival, and growth were highest for all four species in patches of bare ground. The small-seeded species, Verbascum and Oenothera, survived only in bare ground. In contrast, the large-seeded species, Daucus and Tragopogon, survived in several ground cover types. Relative coverage of three ground cover types and differences in seedling performance in these cover types were compared in a 1-yr and 15-yr old field. Verbascum and Oenothera became estab- lished only in the 1-yr old field where bare ground was abundant and not in the 15-yr old field where these patches were rare ( 1-2 yr and are not often present in a newly disturbed area. Once dispersed to and established in an area, they can persist for several generations because their seedlings can survive in several types of ground cover, including those with thick vegetation.

Although the biennial variety of MAelilotus alba has been known in the United States for a long time, the annual variety has been found only within recent years (28). The annual may be distinguished from the biennial variety in that the food and energy in the annual are used to form a main central vertical stem with smaller lateral branches, whereas in the biennial, although they form a central vertical shoot, greater emphasis is placed upon the production of numerous lateral branches. From buds on the crown of the biennial plant, lateral branches arise during the second season and produce numerous flowers. In view of the fact that the two varieties are functionally different, the present investigation was undertaken to ascertain whether any cytological differences exist between them.