Vegetative Buds Research Articles

Genotypic variation in Norway spruce correlates to fungal communities in vegetative buds.

The taxonomically diverse phyllosphere fungi inhabit leaves of plants. Thus, apart from the fungi's dispersal capacities and environmental factors, the assembly of the phyllosphere community associated with a given host plant depends on factors encoded by the host's genome. The host genetic factors and their influence on the assembly of phyllosphere communities under natural conditions are poorly understood, especially in trees. Recent work indicates that Norway spruce (Picea abies) vegetative buds harbour active fungal communities, but these are hitherto largely uncharacterized. This study combines internal transcribed spacer sequencing of the fungal communities associated with dormant vegetative buds with a genome‐wide association study (GWAS) in 478 unrelated Norway spruce trees. The aim was to detect host loci associated with variation in the fungal communities across the population, and to identify loci correlating with the presence of specific, latent, pathogens. The fungal communities were dominated by known Norway spruce phyllosphere endophytes and pathogens. We identified six quantitative trait loci (QTLs) associated with the relative abundance of the dominating taxa (i.e., top 1% most abundant taxa). Three additional QTLs associated with colonization by the spruce needle cast pathogen Lirula macrospora or the cherry spruce rust (Thekopsora areolata) in asymptomatic tissues were detected. The identification of the nine QTLs shows that the genetic variation in Norway spruce influences the fungal community in dormant buds and that mechanisms underlying the assembly of the communities and the colonization of latent pathogens in trees may be uncovered by combining molecular identification of fungi with GWAS.

Фенологические особенности начальных фаз цветения и вегетации культиваров абрикоса Дагестана

Abstract. Purpose. The study is aimed at a comparative analysis of apricot cultivars of various ecological and geographical origin of the genetic collection of the Mountain Botanical Garden by the initial phenological phases of flowering and vegetation in order to determine their degree of interconnection and determine the autochthonous varieties and forms of the Dagestan apricot. Methods. The study is based on the methods of phenological observations in accordance with generally accepted methods with their own additions. Results. It was revealed that the appearance of red bud varieties varied in a wide range (March 28 – April 21), on average, on April 6. The white bud phase was observed in the first and second decade of April from the 1st to the 25th day of the month, and the beginning of flowering from April 5 to 28. Vegetative buds begin to wake up as a whole later than generative ones, with the exception of varieties and hybrids bred from crosses with plum and alpine plum. Beginning swelling buds, flushing buds and leaves in the second and third decade of April, on average on April 11, 21 and 25, respectively. Correlation analysis showed the presence of a positive correlation between the majority of generative and vegetative traits of varieties and forms of apricot, significant at the level of P ≤ 0,05. An inaccurate correlation was found between the trait “bud swelling” and all generative traits. According to the results of cluster analysis, the proximity of most of the cultivars of Dagestan origin to each other was established, with the exception of the Khonobakh variety and its varieties, which turned out to be closer to the Central Asian varieties, which is probably due to its allochthonous origin. The scientific novelty of the study is to assess the phenological phases of flowering and swelling of apricot cultivar leaves under the conditions of the Tsudakhar experimental base showed that the majority of Dagestan cultivars are early flowering (13 samples from 22) and medium (7), while in European and Central Asian prevail varieties of medium and late flowering.

Comparative transcriptomic analysis of the flower induction and development of the Lei bamboo (Phyllostachys violascens)

BackgroundBamboo is a very important forest resource. However, the prolonged vegetative stages and uncertainty of flowering brings difficulties in bamboo flowers sampling. Until now, the flowering mechanism of bamboo is still unclear.ResultsIn this study, three successive stages of flowering buds and the corresponding vegetative buds (non-flowering stage) from Lei bamboo (Phyllostachys violascens) were collected for transcriptome analysis using Illumina RNA-Seq method. We generated about 442 million clean reads from the above samples, and 132,678 unigenes were acquired with N50 of 1080 bp. A total of 7266 differentially expressed genes (DEGs) were determined. According to expression profile and gene function analysis, some environmental stress responsive and plant hormone-related DEGs were highly expressed in the inflorescence meristem formation stage (TF_1) while some floral organ development related genes were up-regulated significantly in floral organs determination stage (TF_2) and floral organs maturation (TF_3) stage, implying the essential roles of these DEGs in flower induction and maturation of Lei bamboo. Additionally, a total of 25 MADS-box unigenes were identified. Based on the expression profile, B, C/D and E clade genes were more related to floral organs development compared with A clade genes in Lei bamboo.ConclusionsThis transcriptome data presents fundamental information about the genes and pathways involved in flower induction and development of Lei bamboo. Moreover, a critical sampling method is provided which could be benefit for bamboo flowering mechanism study.

Response of “White Robin” Peach Trees Cv. (Prunus persica L.) to Cultivation Under Plastic Covering Conditions and Foliar Application by Hydrogen Cyanamide and Garlic Extract

A field experiment was carried out during 2018 and 2019 seasons on 4 years old ‘White Robin’ peach trees cv. (Prunus persica L.), to investigate the effect of cultivation peach trees under plastic covering conditions (PC) with combination of hydrogen cyanamide (HC at 0.5%) as a Dormex and garlic extract (GE at 1%) on floral and vegetative bud break time, vegetative growth parameters, fruit set, yield and fruit quality of this cultivar. Eight treatments, HC alone, GE alone, HC + GE, PC alone, PC + HC, PC + GE, PC + HC + GE and control were applied. The application of HC and GE under PC, resulted in earlier buds break and harvesting period by 10 and 20 days, respectively. Moreover, it shortened the period between both of flower and vegetative buds break and onset to end fruit harvesting by 10 days. It significantly increased shoot length, diameter and leaf area compared to control and other treatments. Furthermore, it improved fruit physical and chemical properties beside increasing the yield by 30%. All studied parameters gradually improved by other investigated treatments as follow: PC + HC, PC + GE, PC alone, HC and GE, HC alone then GE alone compared by control. Plastic covering might be useful for early peach cultivars for advancing fruit maturity and improving yield and fruit quality, that will be more suitable for exportation and profitable for growers under conditions of Egypt.

6-Hydroxyisocaryophyllene and Isocaryophyllenic Acid from Birch Vegetative Buds

The new isocaryophyllene derivatives: 6-hydroxyisocaryophyllene [(1R,4Z,6R,9S)-8-methylene-11,11-dimethylbicyclo[7.2.0]undec-4-ene-6-ol], epoxide of 6-hydroxyisocaryophyllene [(6R)-hydroxy-(4R,5S)-epoxyisocaryophyllene [(1R,4R,5S,6R,9S)-4.5-epoxy-8-methylene-11,11-dimethylbicyclo[7.2.0]undeco-6-ol], (6R)-acetoxyisocaryophyllene [(6R)-acetoxy-(1R,4Z,9S)-8-methylene-11,11-dimethylbicyclo[7.2.0]undec-4-ene], isocaryphyllenic acid [(1R,4E,9S)4-carboxy-8-methylene-11,11-dimethylbicyclo[7.2.0]undec-4-ene] were first detected in the birch vegetative buds. 6-Hydroxyisocaryophyllene and epoxide of 6-hydroxyisocaryophyllene are isolated by from the Betula pendula Roth. birch buds etheric extract by chromatography on silica gel. (6R)-Acetoxyisocaryophyllene was synthesized. The structure of 6-hydroxyisocaryophyllene and epoxide of 6-hydroxyisocaryophyllene isolated from the buds were determined by NMR spectroscopy. Caryophyllenic acids are isolated from the ether extract with an aqueous solution of alkali. Caryophyllenic acids are separated by chromatography on silica gel. The structures of caryophyllenic acid and isocaryphyllenic acid isolated from the Betula grandifolia Litv., B. albo-sinensis Burk., B. fusca Pall.ex Georg, B. obscura A. Kotula, B. litwinowii Doluch., B. hallii Howell, B. grandifolia Litv. birch buds were determined by X-ray diffraction analysis. The physico-chemical characteristics and NMR data of 6-hydroxyisocaryophyllene, epoxide of 6-hydroxyisocaryophyllene and all the isolated acids are given. The obtained mixtures of compounds were analyzed by gas chromatography–mass spectrometry (GC-MS). The gas chromatographic retention indices of all identified compounds were determined.

Responses in growth and phenolics accumulation to lateral bud removal in male and female saplings of Populus tremula (L.) under simulated climate change

The responses in growth and defense after tissue damage are highly variable in plants depending on species, damaged-tissue type and the intensity of damage. The prevailing abiotic conditions can also influence these responses. In this study, our aim was to examine how the removal of lateral vegetative buds affects the growth and accumulation of phenolics in saplings of the dioecious Populus tremula grown under simulated climate change. For three growing seasons, the saplings were grown under ambient conditions (control), elevated temperature (+2°C) and elevated UV radiation (30%) (UVB and UVA as its control), or a combination of these. In the fourth growing season, all saplings were grown under ambient conditions. The bud removal was performed twice – in summer and autumn – in the third year. The responses of growth and the accumulation of phenolics to the bud removal were measured at the end of the fourth growing season. Removal of 5% of the lateral buds resulted in higher leaf, stem and total plant biomass in both sexes of P. tremula saplings, compared to intact plants. The effects were greater in the temperature-treated plants, especially in the temperature-treated females. The concentrations of flavonoids and condensed tannins were higher in the bud-removed individuals. The concentration of condensed tannins was also higher in the males than in the females, opposite to the concentration of phenolic acids. There was no significant interaction between bud removal and UVB treatment on either growth or phenolics. Our results suggest that plants can allocate resources to both growth and defense simultaneously in response to tissue loss, and that global warming can modify the responses to some extent.

<p><strong><em>Begonia medeiroii</em></strong><strong> (Begoniaceae), a new species endemic to Santa Catarina, southern Brazil</strong></p>

We describe here Begonia medeiroii, a narrow endemic species from the Atlantic Rainforest. The conservation status of this species was assessed as critically endangered according to IUCN criteria. This species resembles to B. catharinensis and B. hirtella in some characteristics, differing among other features due the presence of adventitious vegetative buds on the adaxial surface of the leaves.

Impact of Chilling Requirement on Budburst, Floral Development and Hormonal Level in Buds of Early and Late Apple Varieties (<i>Malus</i> <i>sylvestris, </i>Mill) under Natural Conditions

In order to produce the physiological bases for choosing early- flowering varieties that may avoid the depleted low winter temperatures, the early and late- opining apple variety Barkhar, Local and Strakhan (Malus sylvestris) were wont to study the relation between the seasonal changes and these balance of endogenous hormones and flower opining date. An improved understanding of the factors governing budburst and development, and their underlying mechanisms is crucial for management of trees performance and yielding. This study investigated variations in chilling requirements, bud burst and development in early and late varieties of apple trees. The budburst and hormonal profile of flower and vegetative buds of early and late varieties were additionally investigated. Results showed less bud burst in late varieties than in early ones. In the former, there were increased in promoters (indole-3-acetic acid and gibberellins) at budburst. Although endogenous inhibitors levels of abscisic acid were considerably reduced by bud development in all varieties. We conclude that late varieties (Strakhan) are less economical in manufacturing new growth, as indicated by less bud vigor at budburst than early varieties (Barkhar and local) and show a marked differential hormonal pattern throughout bud development compared to early varieties.

INTRODUCTION RESULTS OF COTONEASTER MEDIK IN THE STEPPE CONDITIONS OF THE REPUBLIC OF KHAKASSIA

Cotoneaster is an ornamental shrub that has been used in Khakassia since the end of the 20th century not only for the improvement of populated areas but also for the forestation. In the Ключевые слова: кизильник, интродукция, ритм роста и развития, озеленение, засушливые условия, Хакасия arboretum of the Institute, more than 40 varieties of cotoneaster of different origin were tested. The paper identifies promising new cotoneaster varieties for immigration into the landscapes of the region. Currently, an inventory has established 12 varieties of cotoneaster. According to the duration of spring development, the studied varieties can be divided into two groups: dissolving vegetative buds in the second and third decades of April - 75% (C. foveolatus, C. intergerrimus, C. lucidus, C. melanocarpus var. Laxiflora, C. nitens, C. oliganthus, C. racemiflorus, C. soongoricus, C. zeravschanicus). In the second group there are varieties in which the vegetative buds bloom in the first and second decades of May - 25% (C. melanocarpus, C. divaricatus, C. pannosus). The cotoneaster bloom period averages 16 ± 2 days. Most of the characterized varieties (54.5%) bloom in the third decade of May, flowering 36.3% falls on the first decade of June. The average vegetation period for woody plants in Khakassia reaches 165 days. Cotoneaster, having an East Asian locality, is close to this value. The vast majority of the considered varieties (75%) has winter hardness at the level of I point. 16.6% of the varieties freeze over in some years (winter hardness II point). The largest weight is 1000 pcs. seed belongs to Cotoneaster oliganthus, C. racemiflorus, and C. melanocarpus. Soil germination of seeds in different vatieties of Cotoneaster varies from 4.4 to 24.4%. The highest rate was fixed in the shaggy cotoneaster (C. pannosus) from South-Western China. For a more complete assessment, each of the studied varieties was assigned an introduction score. The highest fifth point of introduction is characterized by seven species, or 58.3%. Four types have a fourth score - 33.3%. Based on a comprehensive assessment of the prospects of the studied cotoneaster varieties it was found that 67% of the varieties are quite promising. The promising varieties such as C. pannosus, C. melanocarpus var. laxiflora, as well as C. zeravschanicus (during vegetative propagation) for landscaping in Khakassia.

Physiological and Transcriptomic Analysis Reveals Distorted Ion Homeostasis and Responses in the Freshwater Plant Spirodela polyrhiza L. under Salt Stress.

Duckweeds are a family of freshwater angiosperms with morphology reduced to fronds and propagation by vegetative budding. Unlike other angiosperm plants such as Arabidopsis and rice that have physical barriers between their photosynthetic organs and soils, the photosynthetic organs of duckweeds face directly to their nutrient suppliers (waters), therefore, their responses to salinity may be distinct. In this research, we found that the duckweed Spirodela polyrhiza L. accumulated high content of sodium and reduced potassium and calcium contents in large amounts under salt stress. Fresh weight, Rubisco and AGPase activities, and starch content were significantly decreaseded in the first day but recovered gradually in the following days and accumulated more starch than control from Day 3 to Day 5 when treated with 100 mM and 150 mM NaCl. A total of 2156 differentially expressed genes were identified. Overall, the genes related to ethylene metabolism, major CHO degradation, lipid degradation, N-metabolism, secondary metabolism of flavonoids, and abiotic stress were significantly increased, while those involved in cell cycle and organization, cell wall, mitochondrial electron transport of ATP synthesis, light reaction of photosynthesis, auxin metabolism, and tetrapyrrole synthesis were greatly inhibited. Moreover, salt stress also significantly influenced the expression of transcription factors that are mainly involved in abiotic stress and cell differentiation. However, most of the osmosensing calcium antiporters (OSCA) and the potassium inward channels were downregulated, Na+/H+ antiporters (SOS1 and NHX) and a Na+/Ca2+ exchanger were slightly upregulated, but most of them did not respond significantly to salt stress. These results indicated that the ion homeostasis was strongly disturbed. Finally, the shared and distinct regulatory networks of salt stress responses between duckweeds and other plants were intensively discussed. Taken together, these findings provide novel insights into the underlying mechanisms of salt stress response in duckweeds, and can be served as a useful foundation for salt tolerance improvement of duckweeds for the application in salinity conditions.

Posttranscriptional Regulation of RhBRC1 (Rosa hybrida BRANCHED1) in Response to Sugars is Mediated via its Own 3' Untranslated Region, with a Potential Role of RhPUF4 (Pumilio RNA-Binding Protein Family).

The shoot branching pattern is a determining phenotypic trait throughout plant development. During shoot branching, BRANCHED1 (BRC1) plays a master regulator role in bud outgrowth, and its transcript levels are regulated by various exogenous and endogenous factors. RhBRC1 (the homologous gene of BRC1 in Rosa hybrida) is a main branching regulator whose posttranscriptional regulation in response to sugar was investigated through its 3′UTR. Transformed Rosa calluses containing a construction composed of the CaMV35S promoter, the green fluorescent protein (GFP) reporter gene, and the 3′UTR of RhBRC1 (P35S:GFP::3′UTRRhBRC1) were obtained and treated with various combinations of sugars and with sugar metabolism effectors. The results showed a major role of the 3′UTR of RhBRC1 in response to sugars, involving glycolysis/the tricarboxylic acid cycle (TCA) and the oxidative pentose phosphate pathway (OPPP). In Rosa vegetative buds, sequence analysis of the RhBRC1 3′UTR identified six binding motifs specific to the Pumilio/FBF RNA-binding protein family (PUF) and probably involved in posttranscriptional regulation. RhPUF4 was highly expressed in the buds of decapitated plants and in response to sugar availability in in-vitro-cultured buds. RhPUF4 was found to be close to AtPUM2, which encodes an Arabidopsis PUF protein. In addition, sugar-dependent upregulation of RhPUF4 was also found in Rosa calluses. RhPUF4 expression was especially dependent on the OPPP, supporting its role in OPPP-dependent posttranscriptional regulation of RhBRC1. These findings indicate that the 3′UTR sequence could be an important target in the molecular regulatory network of RhBRC1 and pave the way for investigating new aspects of RhBRC1 regulation.

Preliminary phytochemical screening of Vatankura (Ficus bengalensis) with milk and in water extract

Every human being has inherent, intense desire to continue his (one's) own race; to become a mother is one of the most cherished desires of every woman. Infertility is defined as “a disease of the reproductive system defined by the failure to achieve a pregnancy after 12 or more of regular unprotected sexual intercourse”. In Ayurveda, this condition is considered as Vandhvatva. It is a Universal phenomenon occurring both in developing and under developing countries. A great demand from Ayurveda in the field of infertility has been established due to its unique concept about effective and cheaper therapy without any side effects. Vata (Ficus bengalensis) is such a drug which is widely available and is having many mentioning in the classics for its effectiveness in Stree Vandhyatwa. Its vegetative buds are used in the treatment of Vandyatwa.

First record of Azalea rough bollworm, Earias roseifera (Lepidoptera: Nolidae) in Europe

The first record of the Azalea rough bollworm, Earias roseifera Butler, 1881 in Europe is reported. Larvae were collected on twigs, sprouts and buds of several azalea hybrids growing in a botanical garden in the province of Como (Northern Italy). The larvae fed mainly on the flower and vegetative buds, which resulted in a significant reduction in the amount of blossom. Specimens were identified using both morphological characters and a molecular analysis of the DNA barcode (COX1 sequence).

Effects of low chill supplying on dormancy dynamics of different apple tree cultivars

The experiment was developed in an orchard located at Arroio do Padre, Brazil. The objective of this research was to evaluate the behaviour of different apple tree cultivars grown under subtropical climate. Three cultivars of apple trees with varying chilling requirements were used: ‘Eva’ (low-chilling), ‘Castel Gala’ (medium-chilling) and ‘Mollie’s Delicious’ (high-chilling). Two biological tests were performed to determine the dormancy dynamics; the Tabuenca’s test, which determines the water content inside buds and the single-node cutting test, to estimate the dormancy depth. To perform these tests, long shoots bearing vegetative buds and short shoots bearing floral buds from each cultivar were regularly collected during the winter period of 2015. Dormant state in vegetative buds was evaluated by the single-node cutting test and in floral buds by the Tabuenca’s test. The dormancy process is affected by the lack of cold temperatures. High temperature variation during the rest period did not allow the cultivars to reach a deep stage of dormancy, making dormancy phases difficult to differentiate. Results demonstrate that all cultivars presented superficial dormancy (ecodormancy) during the whole winter, and the bud bursting capacity is attached to favourable growth conditions. This research may be helpful for future achievements in the area of tree phenology under atypical conditions and could be expanded to screen more cultivars.

The Phenological Growth Stages of Sapindus mukorossi According to BBCH Scale

Sapindus mukorossi is a native tree in southern China that has multiple useful functions, including high landscaping, ecological, esthetic, and economic values. More importantly, its fruits are being rapidly developed as raw materials for bioenergy and saponin production in southern China. To provide a standardized phenological description of the species, this study firstly used the BBCH (Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie) scale. In total, eight principal stages—i.e., bud, leaf and shoot development, inflorescence emergence, flowering, fruit development, fruit maturity, senescence and beginning of dormancy—and 58 secondary stages were described. It ranges from vegetative bud dormancy to the onset of the next beginning of the dormancy, using a two-digit numerical coding system. In addition to the descriptions, we provide photographic images of some major developmental stages to standardize morphological characteristics and the phenological observation of S. mukorossi. This study will be an asset for biological researches and cultivation management in Sapindus, and will provide valuable information for other fruit trees.

Frost Survival Mechanism of Vegetative Buds in Temperate Trees: Deep Supercooling and Extraorgan Freezing vs. Ice Tolerance.

In temperate climates, overwintering buds of trees are often less cold hardy than adjoining stem tissues or evergreen leaves. However, data are scarce regarding the freezing resistance (FR) of buds and the underlying functional frost survival mechanism that in case of supercooling can restrict the geographic distribution. Twigs of 37 temperate woody species were sampled in midwinter 2016 in the Austrian Inn valley. After assessment of FR, infrared-video-thermography and cryo-microscopy were used to study the freezing pattern in and around overwintering vegetative buds. Only in four species, after controlled ice nucleation in the stem (−1.6 ± 0.9°C) ice was observed to immediately invade the bud. These buds tolerated extracellular ice and were the most freezing resistant (−61.8°C mean LT50). In all other species (33), the buds remained supercooled and free of ice, despite a frozen stem. A structural ice barrier prevents ice penetration. Extraorgan ice masses grew in the stem and scales but in 50% of the species between premature supercooled leaves. Two types of supercooled buds were observed: in temporary supercooling buds (14 species) ice spontaneously nucleated at −20.5 ± 4,6°C. This freezing process appeared to be intracellular as it matched the bud killing temperature (−22.8°C mean LT50). This response rendered temporarily supercooled buds as least cold hardy. In 19 species, the buds remained persistently supercooled down to below the killing temperature without indication for the cause of damage. Although having a moderate midwinter FR of −31.6°C (LT50), some species within this group attained a FR similar to ice tolerant buds. The present study represents the first comprehensive overview of frost survival mechanisms of vegetative buds of temperate trees. Except for four species that were ice tolerant, the majority of buds survive in a supercooled state, remaining free of ice. In 50% of species, extraorgan ice masses harmlessly grew between premature supercooled leaves. Despite exposure to the same environmental demand, midwinter FR of buds varied intra-specifically between −17.0 and −90.0°C. Particularly, species, whose buds are killed after temporary supercooling, have a lower maximum FR, which limits their geographic distribution.

Blueberry Gall Midge on Southern Highbush Blueberry in Florida

Blueberry gall midge is a small fly native to North America that feeds on blueberries and cranberries. It can be found throughout the United States, including Florida, where its larvae feed on southern highbush blueberry and rabbiteye floral and vegetative buds. Reports of blueberry gall midge damage on southern highbush blueberry in Florida have become more common in recent years, in some cases significantly impacting yield where there was severe feeding damage to floral buds. This 3-page fact sheet written by Oscar Liburd and Doug Phillips and published by the UF/IFAS Department of Entomology and Nematology will inform growers how to scout for, identify, and control blueberry gall midge. http://edis.ifas.ufl.edu/in1239

Propagation from Basal Epicormic Meristems Remediates an Aging-Related Disorder in Almond Clones

The asexual propagation of clonal crops has allowed cultivation of superior selections for thousands of years. With time, some clones deteriorate from genetic and epigenetic changes. Non-infectious bud-failure (NBF) in cultivated almond (Prunus dulcis) is a commercially important age-related disorder that results in the failure of new vegetative buds to grow in the spring, with dieback of terminal shoots, witches-brooming of surviving buds, and deformed bark (roughbark). The incidence of NBF increases with clone age, including within individual long-lived trees as well as nursery propagation lineages. It is not associated with any infectious disease agents. Consequently, nursery practices emphasize the establishment of foundation-mother blocks utilizing propagation-wood selected from proven and well-monitored propagation-lineages. Commercial propagation utilizes axillary shoot buds through traditional budding or grafting. This study examines NBF development using basal epicormic buds from individual trees of advanced age as an alternative source of foundation stock. Results show the age-related progression of NBF is suppressed in these epicormic meristems, possibly owing to their unique origins and ontogeny. NBF development in commercial orchards propagated from foundation blocks established from these sources was similarly dramatically suppressed even over the 10- to 20-year expected commercial orchard-life. Foundation-stock stability can be further maintained through appropriate management of propagation source-trees, which requires accurate knowledge of meristem origin and development.

Engineering Tree Seasonal Cycles of Growth Through Chromatin Modification.

In temperate and boreal regions, perennial trees arrest cell division in their meristematic tissues during winter dormancy until environmental conditions become appropriate for their renewed growth. Release from the dormant state requires exposure to a period of chilling temperatures similar to the vernalization required for flowering in Arabidopsis. Over the past decade, genomic DNA (gDNA) methylation and transcriptome studies have revealed signatures of chromatin regulation during active growth and winter dormancy. To date, only a few chromatin modification genes, as candidate regulators of these developmental stages, have been functionally characterized in trees. In this work, we summarize the major findings of the chromatin-remodeling role during growth-dormancy cycles and we explore the transcriptional profiling of vegetative apical bud and stem tissues during dormancy. Finally, we discuss genetic strategies designed to improve the growth and quality of forest trees.

Deep supercooling enabled by surface impregnation with lipophilic substances explains the survival of overwintering buds at extreme freezing.

The frost survival mechanism of vegetative buds of angiosperms was suggested to be extracellular freezing causing dehydration, elevated osmotic potential to prevent freezing. However, extreme dehydration would be needed to avoid freezing at the temperatures down to −45°C encountered by many trees. Buds of Alnus alnobetula, in common with other frost hardy angiosperms, excrete a lipophilic substance, whose functional role remains unclear. Freezing of buds was studied by infrared thermography, psychrometry, and cryomicroscopy. Buds of A. alnobetula did not survive by extracellular ice tolerance but by deep supercooling, down to −45°C. An internal ice barrier prevented ice penetration from the frozen stem into the bud. Cryomicroscopy revealed a new freezing mechanism. Until now, supercooled buds lost water towards ice masses that form in the subtending stem and/or bud scales. In A. alnobetula, ice forms harmlessly inside the bud between the supercooled leaves. This would immediately trigger intracellular freezing and kill the supercooled bud in other species. In A. alnobetula, lipophilic substances (triterpenoids and flavonoid aglycones) impregnate the surface of bud leaves. These prevent extrinsic ice nucleation so allowing supercooling. This suggests a means to protect forestry and agricultural crops from extrinsic ice nucleation allowing transient supercooling during night frosts.