Large-scale,millennial-length temperature reconstructions from tree-rings

Over the past two decades, the dendroclimate community has produced various annually resolved, warm season temperature reconstructions for the extratropical Northern Hemisphere. Here we compare these tree-ring based reconstructions back to 831 CE and present a set of basic metrics to provide guidance for non-specialists on their interpretation and use. We specifically draw attention to (i) the imbalance between (numerous) short and (few) long site chronologies incorporated into the hemispheric means, (ii) the beneficial effects of including maximum latewood density chronologies in the recently published reconstructions, (iii) a decrease in reconstruction covariance prior to 1400 CE, and (iv) the varying amplitudes and trends of reconstructed temperatures over the past 1100 years. Whereas the reconstructions agree on several important features, such as warmth during medieval times and cooler temperatures in the 17th and 19th centuries, they still exhibit substantial differences during 13th and 14th centuries. We caution users who might consider combining the reconstructions through simple averaging that all reconstructions share some of the same underlying tree-ring data, and provide four recommendations to guide future efforts to better understand past millennium temperature variability.     

A new approach to chromosome doubling for haploid rice plants

Summary Rice nodal segments from three flowering haploids were excised and treated for different lengths of time with 0.3% or 0.4% colchicine (dissolved in 2% DMSO) in an attempt to induce fertile seeds. A combination of higher colchicine concentration and longer hours of treatment reduced the survival rate of treated segments, but more fertile plants were transformed. Pooled data showed that of the 842 segments used, 42.2% survived the treatment and sprouted, but only 31.9% were successfully established and grown to maturity. Among the 269 mature plants, 29,4% produced fertile seeds (panicles) with an average of 146.2 seeds per diploidized plant.     

Colchicine-mediated chromosome doubling during anther culture of maize (Zea mays L.)

Efficient methods of chromosome doubling are critical for the production of microspore-derived, doubled-haploid (=DH) plants, especially if, as in maize anther culture, spontaneous chromosome doubling occurs infrequently. In the present study, colchicine (5–1000 mg/l) was added to the induction medium and maize anthers were incubated in the colchicine-containing medium for different durations (1–7 days). In order to improve overall anther culture response, the culture temperature was adjusted to 14°C during the first 7 days. Colchicine applied at low concentration, i.e. 5 mg/l (7 days), or for short duration, i.e. 1–3 days (250 mg/l), showed beneficial effects on the formation of embryolike structures (=ES) and thus led to increased plant production, but was comparatively ineffective regarding chromosome doubling. Optimal doubling effects were observed when anthers had been exposed to culture medium containing 250 and 1000 mg/l of colchicine (7 days); in these treatments the doubling index (=DI), defined as the quotient of the number of DH plants and the number of totally regenerated plants in a specific treatment, rose to 0.56 and 0.53, respectively, compared to 0.20 in the untreated control. However, colchicine administered at concentrations higher than 250 mg/l seemed to be detrimental to general plant production; thus, in spite of a high DI, the overall DH plant production was even lower than in the control treatment. Maximum DH plant production for three different genotypes was accomplished with culture medium containing 250 mg/l of colchicine (7 days). With the best-responding genotype (ETH-M 36) a DH plant production of 9.9 DH plants/100 anthers was accomplished, i.e. a 7-fold increase compared to the non-treated anthers. This is the first report on efficient chromosome doubling in anther culture by subjecting anthers to colchicinecontaining induction medium during a post-plating cold treatment. Chromosome doubling as described here becomes an integral part of the maize anther culture protocol and thus represents a rapid and economical way to produce DH plants.     

Increased doubled haploid plant regeneration from rice (Oryza sativa L.) anthers cultured on colchicine-supplemented media

Plating rice anthers on a semisolid induction medium containing 250 or 500 mg/l colchicine for 24 or 48 h-incubations followed by transfer to colchicine-free medium and standard anther culture procedures resulted in overall 1.5- to 2.5- fold increases in doubled haploid green plant productions compared to control anther cultures. The addition of colchicine had no detrimental effects on the different anther culture efficiency parameters, but in some treatments led to significant enhancement of anther callusing frequency or callus green plant regenerating ability. The most efficient treatment raised doubled haploid plant recovery from 31% to 65.5%. These results suggest that post-plating colchicine treatment of anthers, since it was found to improve both anther culture efficiency and doubled haploid plant recovery frequency, could be integrated into rice doubled haploid plant production programmes.Abbreviations DH doubled haploid - NAA naphthalenacetic acid - PAS periodic acid Schiff     

Passage number of cancer cell lines: Importance,intricacies, and way-forward

Cancer cell lines play a crucial role as invaluable models in cancer research, facilitating the examination of cancer progression as well as the advancement of diagnostics and treatments. While they may not perfectly replicate the original tumor, they generally exhibit similar characteristics. Low-passage cancer cell lines are generally preferred due to their closer resemblance to the original tumor, as long-term culturing can alter the genetic and molecular profiles of a cell line thereby highlighting the importance of monitoring the passage number (PN). Variations in proliferation, migration, gene expression, and drug sensitivity can be linked to PN differences. PN can also influence DNA methylation levels, metabolic profiles, and the expression of genes/or proteins in cancer cell lines. When conducting research on cancer cell lines, it is crucial for researchers to carefully select the appropriate PN to maintain consistency and reliability of results. Moreover, to ensure dependability and replicability, scientists ought to actively track the growth, migration, and gene/or protein profiles of cancer cell lines at specific PNs. This approach enables the identification of the most suitable range of PNs for experiments, guaranteeing consistent and precise results. Additionally, such efforts serve to minimize disparities and uphold the integrity of research. In this review, we have laid out recommendations for laboratories to overcome these PN discrepancies when working with cancer cell lines.     

Induced single fertilization in maize

 Bicellular pollen with one vegetative nucleus and one diploid arrested generative cell (”monospermic” pollen) was induced by trifluralin treatment of diploid maize plants at 7–9 days before flowering. The arrested generative cell (seemingly a diploid sperm cell) fused with the central cell of diploid plants and produced shriveled endosperm resembling that of a 2n×4n cross in maize. Dual pollination experiments with a purple embryo marker revealed single fertilization events in which the union of one sperm cell with the egg occurs but there is no union of a second sperm cell with the central cell. Singly fertilized ovules survived at least 4 days. Furthermore, many viable triploid plants were obtained. This technique therefore appears to have the potential for manipulating ploidy level in crops and may become useful in investigating fertilization mechanisms of angiosperms. Received: 1 October 1996 / Revision accepted: 8 January 1997     

The effects of inbreeding on the parental values of potato dihaploids

Dihaploids obtained from a somatically chromosome-doubled dihaploid potato were crossed with Solanum phureja clones. To test the effect of inbreeding, measurements were made of their seed production and the tuber yield, tuber number and mean tuber weight of their offspring. On average, seed production of the second generation dihaploids was higher than that of the original dihaploid progenitor. Progeny tuber yield and its components were little different from those of the original dihaploid's progeny. Tuber flesh quality, as measured lack of blemishes, was better in the offspring of second generation dihaploids.
It is suggested that the negative effects of producing second generation dihaploids are minor compared with producing the first generation dihaploid from a tetraploid, because most deleterious recessives have already been unmasked. The results indicated residual variation within the original dihaploid which could be exploited for plant breeding purposes.
An indicator of inbred status, alternative to the inbreeding coefficient, is suggested which could be applied to both diploids and tetraploids.     

Plant diversity in late medieval cornfields of northern Switzerland

Weed assemblages from late medieval cornfields have been studied for the first time in northern Switzerland. Eleven samples from at least two different grain stores were investigated. The samples were collected from the carbonised remains of six wooden houses built in the late 13th century A.D. and which burnt down in the middle of the 15th century. The weed floras found in the spelt (Triticum spelta) and oats (Avena sativa) indicate a high botanical diversity in the cornfields at harvest time. Although oats are normally a summer crop and spelt a winter crop, both summer and winter crop weeds (as well as many different present-day grassland taxa) were found in each type of grain. Most of the weeds found were perennial plants, which was interpreted as an indication of both extensive tillage of the arable land and application of the three-field rotation system (Dreifelderwirtschaft). The spectra of the two palaeophytocoenoses (assemblages of ancient plant remains) studied suggest that the phytosociological method may not be reliable for classification of the late medieval remains into summer and winter crop weed communities. These findings should provide a better understanding of the development of anthropogenic plant communities, and in particular, the development of crop weed communities.     

Polyploidization in leaf callus tissue and in regenerated plants of dihaploid potato

Cytological studies on leaf callus cells and regenerated potato plants suggest that it may be possible to utilize somatic chromosome doubling to obtain tetraploids from outstanding dihaploid breeding clones. The ploidy levels found in callus-derived plants were diploid, tetraploid, and octaploid, but the proportion of these was dependent on the donor genotype. L₁ and L₃ germ layers were studied in more than 300 plants; periclinal ploidy chimerism, an undesirable feature of colchicine doubling, was not found. Leaf callus was more efficiently induced using NAA than 2, 4-D as an auxin source in the Murashige and Skoog medium. A high proportion of dividing cells in young calli were polyploid. The frequency of doubled and octaploid plants regenerated was significantly dependent on donor genotype. The extent of polyploidization was marginally higher after callus growth on a medium containing 2, 4-D than in a medium containing NAA. In some genotypes the chromosome numbers of regenerated plants were variable, being less than tetraploid (mixohypotetraploid). After tuber propagation, the original ploidy level was maintained although mixohypotetraploidy persisted. In a few somatically doubled clones, male fertility was tested and found to be satisfactory with respect to seed-setting.