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Global monitoring of seasonal snow water equivalent (SWE) has advanced significantly over the past decades. However, challenges remain when estimating SWE from passive and active microwave signatures, because a priori characterization of snow properties is required for SWE retrievals. Numerical experiments have shown that utilizing physical snow models to acquire snowpack characterization can potentially improve microwave‐based SWE retrievals. This study aims to identify the challenges of assimilating active and passive microwave signatures with physical snow models, and to examine solutions to those challenges. Guided by observations from a point‐based study, we designed a sensitivity experiment to quantify the effects of changes in the physically modeled SWE—and of corresponding changes to other snowpack properties—to the microwave‐based SWE retrievals. The results indicate that assimilating microwave signatures with physical snow models face some critical challenges associated with the physical relationship between SWE and snow microstructure. We demonstrate these challenges can be overcome if the microwave algorithms account for these relationships. Key Points: Simulated snow properties from SnowModel are used in microwave‐based snow water equivalent (SWE) retrievals by MEMLS3&aBiases in physically modeled SWE can induce larger biases in microwave‐based SWE retrievalsThe challenges can be mitigated when microwave algorithms account for the physical relationship of snow properties [ABSTRACT FROM AUTHOR]

Four satellite-based snow products are evaluated over the Tibetan Plateau for the 2007-2010 snow seasons. The Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua snow cover daily L3 Global 500-m grid products (MOD10A1 and MYD10A1), the National Oceanic and Atmospheric Administration Interactive Multisensor Snow and Ice Mapping System (IMS) daily Northern Hemisphere snow cover product and the Advanced Microwave Scanning Radiometer - Earth Observing System Daily Snow Water Equivalent were validated against Thematic Mapper (TM) snow cover maps of Landsat-5 and meteorological station snow depth observations. The overall accuracy of MOD10A1, MYD10A1 and IMS is higher than 91% against stations observations and than 79% against Landsat TM images. In general, the daily MODIS snow cover products show better performance than the multisensor IMS product. However, the IMS snow cover product is suitable for larger scale (~4km) analysis and applications, with the advantage over MODIS to allow for mitigation for cloud cover. The accuracy of the three products decreases with decreasing snow depth. Overestimation errors are most common over forested regions; the IMS and Advanced Microwave Scanning Radiometer - Earth Observing System Snow Water Equivalent products also show poorer performance that the MODIS products over grassland. By identifying weaknesses in the satellite products, this study provides a focus for the improvement of snow products over the Tibetan plateau. The quantitative evaluation of the products proposed here can also be used to assess their relative weight in data assimilation, against other data sources, such as modelling and in situ measurement networks. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Acceleration of flowering would be beneficial for breeding trees with a long juvenile phase; conversely, inhibition of flowering would prevent the spread of transgenes from the genetically modified trees. We have previously isolated and characterized several MADS genes from silver birch ( Betula pendula Roth). In this study, we investigated the more detailed function of one of them, BpMADS4, a member of the APETALA1/FRUITFULL group of MADS genes. The expression of BpMADS4 starts at very early stage of the male and female inflorescence development and the activity is high in the apex of the developing inflorescence. Later, some expression is detected in the bracts and in the flower initials. Ectopic expression of BpMADS4 accelerates flowering dramatically in normally flowering clones and also in the early-flowering birch clone, in which the earliest line flowered about 11 days after rooting, when the saplings were only 3 cm high. The birches transformed with the BpMADS4 antisense construct showed remarkable delay in flowering and the number of flowering individuals was reduced. Two of the transformed lines did not show any signs of flower development during our 2-year study, whereas all the control plants formed inflorescences within 107 days. Our results show that BpMADS4 has a critical role in the initiation of birch inflorescence development and that BpMADS4 seems to be involved in the transition from vegetative to reproductive development. Therefore, BpMADS4 provides a promising tool for the genetic enhancement of forest trees. [ABSTRACT FROM AUTHOR]

B-function genes determine the identity of petals and stamens in the flowers of model plants such as Arabidopsis and Antirrhinum. Here, we show that a putative B-function gene BpMADS2, a birch homolog for PISTILLATA, is expressed in stamens and carpels of birch inflorescences. We also present a novel birch gene BpMADS8, a homolog for APETALA3/ DEFICIENS, which is expressed in stamens. Promoter-GUS analysis revealed that BpMADS2 promoter is active in the receptacle of Arabidopsis flower buds while BpMADS8 promoter is highly specific in mature stamens. BpMADS2 promoter:: BARNASE construct prevented floral organ development in Arabidopsis and tobacco. In birch, inflorescences with degenerated stamens and carpels were obtained. BpMADS8::BARNASE resulted in degeneration of stamens in Arabidopsis and birch causing male sterility. In tobacco, only sepals were developed instead of normal flowers. The results show that the BpMADS2::BARNASE construct can be used to specifically disrupt floral organ development in phylogenetically distant plant species. The stamen-specific promoter of BpMADS8 is a promising tool for biotechnological applications in inducing male sterility or targeting gene expression in the late stamen development. [ABSTRACT FROM AUTHOR]

The development of flowers is regulated by a complex network of transcriptional activators and repressors, many of which belong to the MADS box gene family. In this study, we describe two MADS box genes of silver birch ( Betula pendula Roth), BpMADS1 and BpMADS6, which are similar to SEPALLATA3 and AGAMOUS in Arabidopsis thaliana, respectively. In situ hybridization showed that BpMADS1 was expressed in the inflorescence meristem at a very early stage, but not later. Both genes were expressed in developing carpels, ovules and stamens but not in tepals or scales. Ectopic expression of BpMADS1 in Arabidopsis resulted in a reduced number of floral organs or whole whorls and in petaloid or carpelloid sepals, a phenotype reminiscent of that of fil mutants. 35S::BpMADS6 caused very early flowering in Arabidopsis. In tobacco, both 35S::BpMADS1 and 35S::BpMADS6 accelerated flowering and, in addition, 35S::BpMADS6 caused changes in sepals and petals. In some transgenic birch plants, 35S::BpMADS1 antisense resulted in the development of both male and female organs in the axil of a single bract and in a change of some inflorescences into vegetative shoots. In two plants, either 35S::BpMADS6 sense or antisense constructs resulted in an increase in the number of tepals and in complete lack of stamens in some male inflorescences. These results suggest that BpMADS1 participates both in inflorescence and in flower formation and BpMADS6 participates in flower formation and that they are functional homologues to SEPALLATA3 and AGAMOUS, respectively. [ABSTRACT FROM AUTHOR]

The PISTILLATA (PI) homologue, BpMADS2, was isolated from silver birch (Betula pendula Roth) and used to study nucleotide polymorphism. Two regions (together about 2450 bp) comprising mainly untranslated sequences were sequenced from 10 individuals from each of two populations in Finland. The nucleotide polymorphism was low in the BpMADS2 locus, especially in the coding region. The synonymous site overall nucleotide diversity (π[SUBs]) was 0.0043 and the nonsynonymous nucleotide diversity (π[SUBa]) was only 0.000052. For the whole region, the π values for the two populations were 0.0039 and 0.0045, (and for the coding regions, the π values were only 0 and 0.00066 (for the corresponding coding regions of Arabidopsis thaliana PI world-wide π was 0.0021). Estimates of π or θ did not differ significantly between the two populations, and the two populations were not diverged from each other. Two classes of BpMADS2 alleles were present in both populations, suggesting that this gene exhibits allelic dimorphism. In addition to the nucleotide site variation, two microsatellites were also associated within the haplotypes. This allelic dimorphism might be the result of postglacial re-colonization partly from northwestern, partly from southeastern/eastern refugia. The sequence comparison detected five recombination events in the regions studied. The large number of microsatellites in all of the three introns studied suggests that BpMADS2 is a hotspot for microsatellite formation. [ABSTRACT FROM AUTHOR]

Despite intensive research on genetic regulation of flower development there are still only a few studies on the early phases of this process in perennial plants like trees. The aim of this study has been to identify genes that regulate early stages of inflorescence development in silver birch (Betula pendula Roth) and to follow the expression of these genes during development of the unisexual birch inflorescences. Here we describe the cloning and characterization of 3 cDNAs representing MADS-box genes designated BpMADS3, BpMADS4 and BpMADS5, all belonging to the AP1/SQUA group of plant MADS-box genes. According to RNA blot analysis, all 3 genes are active during the development of both male and female inflorescences. However, differences in patterns of expression suggest that they play different roles. BpMADS3 is most similar in sequence to AP1 and SQUA, but it seems to have the highest expression at late developmental stages. BpMADS4 is most similar in sequence to the Arabidopsis gene FRUITFULL, but is expressed, in addition to developing inflorescences, in shoots and roots. BpMADS5 is also similar to FRUITFULL; its expression seems to be inflorescence-specific and continues during fruit development. Ectopic expression of either BpMADS3, BpMADS4 or BpMADS5 with the CaMV 35S promoter in tobacco results in extremely early flowering. All of these birch genes seem to act early during the transition to reproductive phase and might be involved in the determination of the identity of the inflorescence or flower meristem. They could apparently be used to accelerate flowering in various plant species. [ABSTRACT FROM AUTHOR]

The effect of different concentrations of sucrose (0-4%) and of two growth regulators (0-50 μM 2,4-D and 0-25 μM kinetin) was tested on growth and chlorophyll content of suspension cultures of Picea abies (L.) Karst. originating from chlorophyllous embryo callus in an elevated CO2 (2%) atmosphere. A continuous chlorophyllous suspension culture was achieved on a medium containing 2% sucrose and a low level of organic nitrogen (0.25 μM arginine and 0.5 μM glutamine) supplemented with 2,4-D (0.5 μM) and kinetin (2.5 μM). The same medium with 4% sucrose gave the best growth response, but a negative correlation between chlorophylI level and growth was observed. The chlorophyllous cultures grew slowly in a medium with low (0.5%) sucrose or without any carbohydrate source, suggesting photomixotrophism. A high concentration of kinetin inhibited both growth and chlorophyll synthesis. Release of lignin into the nutrient medium was observed in several experiments, especially in slow-growing cultures supplemented with sucrose. Only a few successive passages of suspensions that produced lignin could be cultured before cell death. The cultures releasing lignin maybe unique for studies on synthesis and biodegradation of this very complex compound. [ABSTRACT FROM AUTHOR]