Bud Meristem Research Articles

Gibberellin Treatment Toward Off-crop Season as a Practical Tool to Increase Yield in ‘Orri’ Mandarin

Multiannual fruit bearing in fruit trees varies from regular bearing, with an almost steady yield from season to season, to alternate bearing, during which a year with a high fruit load (on-crop) is followed by a year of a low fruit load (off-crop). ‘Orri’ mandarin [Temple (Citrus temple hort. ex Y. Tanaka) × Dancy (Citrus tangerine hort. ex Tanaka)] exhibits a nonregular bearing pattern: steady for a few years and alternate for others. In nonregular or alternate-bearing cultivars, fruit load is thought to regulate flowering induction and development negatively the following year. In citrus, the bud meristem develops into a leafless inflorescence (generative), leafy inflorescence (mixed type, containing leaves and flowers in various ratios), or vegetative shoot, or remains dormant. Mixed-type inflorescences contribute to most of the final yield. Gibberellins inhibit flowering when applied at relatively high concentrations during the flowering induction period in the winter, but they are suggested to induce yield when applied at relatively low concentrations. We determined the effect of mild gibberellin application in an off-crop year on the productivity of ‘Orri’ mandarin, and whether it occurs through the induction of mixed-type inflorescences. Low-concentration, low-frequency gibberellin treatments were applied to trees during the winter when fruit load was high, resulting in a greater number of mixed vs. generative inflorescences at anthesis. An average increase of 40% in fruit number and yield weight was recorded in off-crop seasons at harvest, whereas no change was recorded in on-crop seasons. We discuss treatment efficiency in on-crop and off-crop years as a practical tool for increasing yield in low-crop seasons of ‘Orri’ mandarin.

Identification of an ethylene-responsive and cell wall-secreting β-1,3-glucanase, VvGLU1, in the early cell regrowth of grape winter buds triggered by exogenous dormancy releasers

BackgroundGrape (Vitis vinifera) crops encounter significant challenges in overcoming bud endodormancy in warm winter areas worldwide. Research on the mechanisms governing bud dormancy release has focused primarily on stress regulation; however, cell wall regulation of bud meristem regrowth mechanism during the dormancy release remains obscure.ResultsIn this study, transmission electron microscopy revealed significant changes in the grape bud cell wall following hydrogen cyanamide (HC) treatment, accompanied by an increase in β-1,3-glucanase activity. We then investigated the potential contribution of β-1,3-glucanases (GLUs) to the regulation of cell wall remodeling. Forty-eight VvGLUs distributed in clades α, β, and γ were identified and nominated based on the genome data of V. vinifera. Three γ-clade VvGLUs (VvGLU1, VvGLU16, and VvGLU32) were upregulated by dormancy-releasing stimuli, including HC, sodium azide (AZ), ethylene and hypoxia. Among these, VvGLU1 presented increased gene transcription and protein expression in response to HC and ethylene treatment. The VvGLU1 promoter positively responded to ethylene, and its activity could be activated by VvERF57. Using both immunogold labeling and GFP fusion protein analysis, we observed that VvGLU1 localized in the endoplasmic reticulum, accumulated in the vacuole, and was secreted into the cell wall during HC-triggered dormancy release.ConclusionsBased on these findings, we propose that ethylene-regulated VvGLU1 plays a pivotal role in cell wall remodeling, thereby facilitating the regrowth of the bud meristem.

Auxin treatment reduces inflorescences number and delays bud development in the alternate bearing Citrus cultivar Murcott mandarin.

Specific cultivars of many commercial fruit tree undergo cycles of heavy fruit load (ON-crop) one year, followed by low fruit load (OFF-crop) the next (termed alternate bearing). Fruit load may affect flowering at various developmental stages, and its presence is suggested to generate a flowering-inhibitory signal. In a previous report, we showed that the presence of fruit induces polar auxin transport from the fruit into the stem, interfering with indole acetic acid (IAA) release from the bud, and thus elevating its levels in the bud meristem. To better understand the relationship between auxin homeostasis in the bud and flowering, IAA or 2,4-Dichlorophenoxyacetic acid (2,4-D) were applied with the polar auxin transport blocker 2,3,5-triiodobenzoic acid (TIBA) to OFF-crop 'Murcott' mandarin trees during the flowering-induction period. The treatment reduced inflorescences number and delayed bud development. Transcriptome analysis following the treatment revealed a reduction in the expression of a few flowering-control genes, including LEAFY and SQUAMOSA PROMOTER BINDING PROTEIN-LIKE. In addition, genes related to carbohydrate metabolism were reduced. We suggest that the elevation of auxin levels in the bud by heavy fruit load directly affects the expression of flowering-control, flower-development, and developmental genes.

Genetic and epigenetic control of dormancy transitions throughout the year in the monoecious cork oak.

Bud dormancy plays a vital role in flowering regulation and fruit production, being highly regulated by endogenous and environmental cues. Deployment of epigenetic modifications and differential gene expression control bud dormancy/break cycles. Information on how these genetic and epigenetic mechanisms are regulated throughout the year is still scarce for temperate trees such as Quercus suber. Here, the expression levels of CENTRORADIALIS-LIKE (CENL) and DORMANCY-ASSOCIATED PROTEIN 1 (QsDYL1) during seasonal cycles of bud development, suggesting that QsCENL may be implicated in growth cessation in Q. suber and that QsDYL1 is a good dormancy marker. As gene expression can be regulated by the activity of chromatin modifiers, we have analysed the expression of these genes and the deposition of epigenetic marks in dormant versus non-dormant bud meristems. The DNA methyl transferases CHROMOMEHTYLASE 3 (QsCMT3) and METHYLTRANSFERASE 1 (QsMET1) were more expressed in the transition between dormancy to bud swelling. QsCMT3 was also highly expressed during the late stages of active bud formation. Conversely, the HISTONE ACETYLTRANSFERASE 1 (QsHAC1) was up-regulated during growth cessation and dormancy when compared to bud swelling. These results indicate that epigenetic regulation is implicated in how bud development progresses in Q. suber, which can be observed in the different profile deposition of the repressive and active marks, 5mC and H3K18Ac/H3K4me, respectively. The identification of bud-specific genetic and epigenetic profiling opens new possibilities to predict the relative rate of dormancy/growth of the bud stages, providing tools to understand how trees respond to the current challenges posed by climate change.

Similar chilling response of dormant buds in potato tuber and woody perennials.

Bud dormancy is a survival strategy that plants have developed in their native habitats. It helps them endure harsh seasonal changes by temporarily halting growth and activity until conditions become more favorable. Research has primarily focused on bud dormancy in tree species and the ability to halt growth in vegetative tissues, particularly in meristems. Various plant species, such as potato, have developed specialized storage organs, enabling them to become dormant during their yearly growth cycle. Deciduous trees and potato tubers exhibit a similar type of bud endodormancy, where the bud meristem will not initiate growth, even under favorable environmental conditions. Chilling accumulation activates C-repeat/dehydration responsive element binding (DREB) factors (CBFs) transcription factors that modify the expression of dormancy-associated genes. Chilling conditions shorten the duration of endodormancy by influencing plant hormones and sugar metabolism, which affect the timing and rate of bud growth. Sugar metabolism and signaling pathways can interact with abscisic acid, affecting the symplastic connection of dormant buds. This review explores how chilling affects endodormancy duration and explores the similarity of the chilling response of dormant buds in potato tubers and woody perennials.

Zonal Chemical Signal Pathways Mediating Floral Induction in Apple.

Phytohormones that trigger or repress flower meristem development in apple buds are thought to be locally emitted from adjacent plant tissues, including leaves and fruitlets. The presence of fruitlets is known to inhibit adjacent buds from forming flowers and thus fruits. The resulting absence of fruitlets the following season restores flower-promoting signalling to the new buds. The cycle can lead to a biennial bearing behaviour of alternating crop loads in a branch or tree. The hormonal stimuli that elicit flowering is typically referred to as the floral induction (FI) phase in bud meristem development. To determine the metabolic pathways activated in FI, young trees of the cultivar 'Ruby Matilda' were subjected to zonal crop load treatments imposed to two leaders of bi-axis trees in the 2020/2021 season. Buds were collected over the expected FI phase, which is within 60 DAFB. Metabolomics profiling was undertaken to determine the differentially expressed pathways and key signalling molecules associated with FI in the leader and at tree level. Pronounced metabolic differences were observed in trees and leaders with high return bloom with significant increases in compounds belonging to the cytokinin, abscisic acid (ABA), phenylpropanoid and flavanol chemical classes. The presence of cytokinins, namely adenosine, inosine and related derivatives, as well as ABA phytohormones, provides further insight into the chemical intervention opportunities for future crop load management strategies via plant growth regulators.

Molecular Insights into the Accelerated Sprouting of and Apical Dominance Release in Potato Tubers Subjected to Post-Harvest Heat Stress.

Climate change-induced heat stress (HS) increasingly threatens potato (Solanum tuberosum L.) production by impacting tuberization and causing the premature sprouting of tubers grown during the hot season. However, the effects of post-harvest HS on tuber sprouting have yet to be explored. This study aims to investigate the effects of post-harvest HS on tuber sprouting and to explore the underlying transcriptomic changes in apical bud meristems. The results show that post-harvest HS facilitates potato tuber sprouting and negates apical dominance. A meticulous transcriptomic profiling of apical bud meristems unearthed a spectrum of differentially expressed genes (DEGs) activated in response to HS. During the heightened sprouting activity that occurred at 15-18 days of HS, the pathways associated with starch metabolism, photomorphogenesis, and circadian rhythm were predominantly suppressed, while those governing chromosome organization, steroid biosynthesis, and transcription factors were markedly enhanced. The critical DEGs encompassed the enzymes pivotal for starch metabolism, the genes central to gibberellin and brassinosteroid biosynthesis, and influential developmental transcription factors, such as SHORT VEGETATIVE PHASE, ASYMMETRIC LEAVES 1, SHOOT MERISTEMLESS, and MONOPTEROS. These findings suggest that HS orchestrates tuber sprouting through nuanced alterations in gene expression within the meristematic tissues, specifically influencing chromatin organization, hormonal biosynthesis pathways, and the transcription factors presiding over meristem fate determination. The present study provides novel insights into the intricate molecular mechanisms whereby post-harvest HS influences tuber sprouting. The findings have important implications for developing strategies to mitigate HS-induced tuber sprouting in the context of climate change.

MADS-box protein PpDAM6 regulates chilling requirement-mediated dormancy and bud break in peach.

Bud dormancy is crucial for winter survival and is characterized by the inability of the bud meristem to respond to growth-promotive signals before the chilling requirement (CR) is met. However, our understanding of the genetic mechanism regulating CR and bud dormancy remains limited. This study identified PpDAM6 (DORMANCY-ASSOCIATED MADS-box) as a key gene for CR using a GWAS (Genome-Wide Association Study) analysis based on structural variations (SVs) in 345 peach (Prunus persica (L.) Batsch) accessions. The function of PpDAM6 in CR regulation was demonstrated by transiently silencing the gene in peach buds and stably overexpressing the gene in transgenic apple (Malus × domestica) plants. The results showed an evolutionarily conserved function of PpDAM6 in regulating bud dormancy release, followed by vegetative growth and flowering, in peach and apple. The 30-bp deletion in the PpDAM6 promoter was substantially associated with reducing PpDAM6 expression in low-CR accessions. A PCR marker based on the 30-bp indel was developed to distinguish peach plants with non-low and low CR. Modification of the H3K27me3 marker at the PpDAM6 locus showed no apparent change across the dormancy process in low- and non-low-chilling requirement cultivars. Additionally, H3K27me3 modification occurred earlier in low-CR cultivars on a genome-wide scale. PpDAM6 could mediate cell-cell communication by inducing the expression of the downstream genes PpNCED1 (9-cis-epoxycarotenoid dioxygenase 1), encoding a key enzyme for ABA biosynthesis, and CALS (CALLOSE SYNTHASE), encoding callose synthase. We shed light on a gene regulatory network formed by PpDAM6-containing complexes that mediate CR underlying dormancy and budbreak in peach. A better understanding of the genetic basis for natural variations of CR can help breeders develop cultivars with different CR for growing in different geographical regions.

Chilling induces sugar and ABA accumulation that antagonistically signals for symplastic connection of dormant potato buds.

Endodormancy (ED) is a crucial stage in the life cycle of many perennial plants. ED release requires accumulating a certain amount of cold exposure, measured as chilling units. However, the mechanism governing the effect of chilling on ED duration is poorly understood. We used the potato tuber model to investigate the response to chilling as associated with ED release. We measured the accumulation of specific sugars during and after chilling, defined as sugar units. We discovered that ED duration correlated better with sugar units accumulation than chilling units. A logistic function was developed based on sugar units measurements to predict ED duration. Knockout or overexpression of the vacuolar invertase gene (StVInv) unexpectedly modified sugar units levels and extended or shortened ED, respectively. Silencing the energy sensor SNF1-related protein kinase 1, induced higher sugar units accumulation and shorter ED. Sugar units accumulation induced by chilling or transgenic lines reduced plasmodesmal (PD) closure in the dormant bud meristem. Chilling or knockout of abscisic acid (ABA) 8'-hydroxylase induced ABA accumulation, in parallel to sweetening, and antagonistically promoted PD closure. Our results suggest that chilling induce sugar units and ABA accumulation, resulting in antagonistic signals for symplastic connection of the dormant bud.

Genome-Wide Identification of the KNOX Gene Family in Japanese Apricot (Prunus mume Sieb. et Zucc.) and Functional Characterization of PmKNAT2 Genes.

The Knotted1-like Homeobox gene is crucial for plant morphological development and growth. Physicochemical characteristics, phylogenetic relationships, chromosomal localization, cis-acting elements, and tissue-specific expression patterns of the 11 PmKNOX genes found in the Japanese apricot genome in this study were examined. Proteins of 11 PmKNOX were soluble proteins with isoelectric points between 4.29 and 6.53, molecular masses between 15.732 and 44.011 kDa, and amino acid counts between 140 and 430. The identified PmKNOX gene family was split into three subfamilies by jointly constructing the phylogenetic tree of KNOX proteins in Japanese apricot and Arabidopsis thaliana. Combined outcomes of the analyzed conserved motifs and gene structures of the 11 PmKNOX genes from the same subfamily displayed comparable gene structure and motif patterns. The 11 PmKNOX members were distributed across six chromosomes, while two sets of PmKNOX genes were found to be collinear. Analysis of the 2000 bp promoter upstream of the coding region of the PmKNOX gene revealed that most PmKNOX genes might be involved in the physiological metabolism, growth and development processes of plants. The PmKNOX gene expression profile revealed that these genes were expressed at varying levels in different tissues, and most of them were linked to the meristems of leaf and flower buds, suggesting that PmKNOX may be involved in plants' apical meristems. In Arabidopsis thaliana, functional validation of PmKNAT2a and PmKNAT2b revealed that these two genes might be involved in regulating leaf and stem development. In addition to laying the groundwork for future research on the function of these genes, understanding the evolutionary relationships between members of the PmKNOX gene family provides opportunities for future breeding in Japanese apricots.

Integrative Analysis of the GRAS Genes From Chinese White Pear (Pyrus bretschneideri): A Critical Role in Leaf Regeneration.

GRAS is a transcription regulator factor, which plays an important role in plant growth and development. Previous analyses found that several GRAS functions have been identified, such as axillary bud meristem formation, radial root elongation, gibberellin signaling, light signaling, and abiotic stress. The GRAS family has been comprehensively evaluated in several species. However, little finding is on the GRAS transcription factors (TFs) in Chinese white pear. In this study, 99 PbGRAS were systemically characterized and renamed PbGRAS1 to PbGRAS99 according to their chromosomal localizations. Phylogenetic analysis and structural features revealed that could be classified into eight subfamilies (LISCL, Ls, SHR, HAM, SCL, PAT, SCR, and DELLA). Further analysis of introns/exons and conserved motifs revealed that they are diverse and functionally differentiated in number and structure. Synteny analysis among Pyrus bretschenedri, Prunus mume, Prunus avium, Fragaria vesca, and Prunus persica showed that GRAS duplicated regions were more conserved. Dispersed duplication events are the most common mechanism and may play a crucial role in the expansion of the GRAS gene family. In addition, cis-acting elements of the PbGRAS gene were found in promoter regions associated with hormone and environmental stress responses. Notably, the expression pattern detected by qRT-PCR indicated that PbGRAS genes were differentially expressed under gibberellin (GA), abscisic acid (ABA), and auxin (IAA) conditions, which are responsive to abiotic stress. PbGRAS89 and PbGRAS99 were highly expressed at different stages of hormone treatment and may play important role in leaf development. Therefore, we selected PbGRAS89 and PbGRAS99 to clone and construct pCAMBIA1301-PbGRAS89, 99 and transferred them into Arabidopsis thaliana. Finally, we observed and compared the changes of overexpressed plants and wild-type plants during regeneration. This method was used to analyze their roles in leaf regeneration of Chinese white pear. In addition, we also constructed pCAMBIA1305-PbGRAS89, 99, and transferred them into onion cells to determine the subcellular localization. Subcellular localization experiments showed that PbGRAS89 and PbGRAS99 were localized in the nucleus. In summary, the results of this study indicate that PbGRAS89 and PbGRAS99 are mainly responsible for leaf regeneration of Chinese white pear, which plays a positive role in callus formation and provides rich resources for studying GRAS gene functions.

Metabolic Pathways for Observed Impacts of Crop Load on Floral Induction in Apple.

The triggers of biennial bearing are thought to coincide with embryonic development in apple and occurs within the first 70 days after full bloom (DAFB). Strong evidence suggests hormonal signals are perceived by vegetative apple spur buds to induce flowering. The hormonal response is typically referred to as the floral induction (FI) phase in bud meristem development. To determine the metabolic pathways activated in FI, young trees of the biennial bearing cultivar ‘Nicoter’ and the less susceptible cultivar ‘Rosy Glow’ were forced into an alternate cropping cycle over five years and an inverse relationship of crop load and return bloom was established. Buds were collected over a four-week duration within 70 DAFB from trees that had maintained a four-year biennial bearing cycle. Metabolomics profiling was undertaken to determine the differentially expressed pathways and key signalling molecules associated with biennial bearing. Marked metabolic differences were observed in trees with high and low crop load treatments. Significant effects were detected in members of the phenylpropanoid pathway comprising hydroxycinnamates, salicylates, salicylic acid biosynthetic pathway intermediates and flavanols. This study identifies plant hormones associated with FI in apples using functional metabolomics analysis.

In vitro Regeneration of Avocado (Persea Americana) West Indian Rootstock cv.lula Via Tissue Culture

Avocado (Persea Americana Mill) is a subtropical fruit and is highly recommended for its nutritional value. Avocado is known for its sensitivity to biotic and a biotic stress. One way to overcome this problem is to graft on tolerance rootstocks that are mainly obtained via seeds that are subjected to genetic variation. Two different types of explants: axillary bud and shot tip meristem were used in this study. Axillary buds gave the best results in terms of the maximum number of shoots when compared to the apical meristem in all treatments, regardless of the media type. The highest shoot induction in Woody Plant Medium (WP) was better than Murashige and Skooge( MS) medium regardless of the explant type. Explant responded better in BAP- containing medium than TDZ and KN. The maximum number of shoots obtained from axillary bud was 4 shoots/explant when cultured in WP medium supplemented with BAP (1.5mg/l). When apical meristems were used as explant, the best result obtained was 2.5 shoots/explant cultured in WP medium supplemented with BAP (1.5mg/l). For shoot length, axillary buds responded better than apical meristem when cultured in BAP containing medium regardless of medium type. The maximum shoot length (4.8 cm) was obtained from axillary bud cultured in WP media supplemented with BAP (1.5mg/l). For rooting, 50% of explant formed root at IBA (1.0 mg/l) when cultured in WP medium. The best number of roots (3.2 roots/explant) was obtained in MS medium supplemented with IBA (1.0 mg/l).

Overexpression of the AtWUSCHEL gene promotes somatic embryogenesis and lateral branch formation in birch (Betula platyphylla Suk.)

Birch (Betula platyphylla Suk.) is a deciduous tree with medicinal and ornamental value. During the process of genetic transformation, somatic embryos do not easily develop into transgenic plants, which is a limitation in genetic breeding. The Arabidopsis thaliana WUSCHEL (AtWUS) gene, which is a transcription factor, plays an important role in maintaining and regulating stem cell characteristics, which determines whether the stem cell population is differentiated. To explore methods for inducing somatic embryogenesis (SE) in birch, we overexpressed the AtWUS gene and transferred it to birch. The expression of AtWUS increased the SE rate from 101.4 to 717.1%. The expression of the AtWUS gene led to the downregulation of BpWUS gene expression in both calli and globular embryos as well as bud meristems. The expression of a few genes, i.e., BpLEC1 (LEAFY COTYLEDON 1), BpLEC2 (LEAFY COTYLEDON 2) and BpFUS3 (FUSCA 3), was upregulated during both embryogenesis and bud meristem development. However, BpABI3 (ABSCISIC ACID INSENSITIVE 3) gene expression was upregulated only in calli embryos, while BpSTM (SHOOT MERISTEMLESS) and BpCUC2 (CUP-SHAPED COTYLEDON 2) gene expression was upregulated only in bud meristems. This result indicated that overexpression of the AtWUS gene promoted SE by increasing the expression of SE-related genes. In conclusion, this study focused on the role of the AtWUS gene in birch SE and the molecular mechanism by which SE was promoted. This work indicates that overexpression of the WUSCHEL gene from Arabidopsis thaliana in birch can promote somatic embryogenesis and increase the development of lateral branches and buds.

Evolution analysis of FRIZZY PANICLE (FZP) orthologs explored the mutations in DNA coding sequences in the grass family (Poaceae).

FRIZZY PANICLE (FZP), an essential gene that controls spikelet differentiation and development in the grass family (Poaceae), prevents the formation of axillary bud meristems and is closely associated with crop yields. It is unclear whether the FZP gene or its orthologs were selected during the evolutionary process of grass species, which possess diverse spike morphologies. In the present study, we adopted bioinformatics methods for the evolutionary analysis of FZP orthologs in species of the grass family. Thirty-five orthologs with protein sequences identical to that of the FZP gene were identified from 29 grass species. Analysis of conserved domains revealed that the AP2/ERF domains were highly conserved with almost no amino acid mutations. However, species of the tribe Triticeae, genus Oryza, and C4 plants exhibited more significant amino acid mutations in the acidic C-terminus region. Results of the phylogenetic analysis showed that the 29 grass species could be classified into three groups, namely, Triticeae, Oryza, and C4 plants. Within the Triticeae group, the FZP genes originating from the same genome were classified into the same sub-group. When selection pressure analysis was performed, significant positive selection sites were detected in species of the Triticeae and Oryza groups. Our results show that the FZP gene was selected during the grass family’s evolutionary process, and functional divergence may have already occurred among the various species. Therefore, researchers investigating the FZP gene’s functions should take note of the possible presence of various roles in other grass species.

Floral initiation in gooseberry (Ribes uva-crispa L.) and its control by daylength and temperature

ABSTRACT The morphogenetic changes of the bud meristem during floral initiation in gooseberry were examined by scanning electron microscopy. Six floral stages, similar to those reported for black currants, were identified. We also studied the environmental control of shoot growth and floral initiation of cvs. Mucurines, Pax and Xenia in two experiments in daylight phytotron compartments at 12, 18 and 24°C. Under natural daylength conditions at Ås, Norway (69°40’N), shoot growth started to decline by mid-August and ceased in early September. Cessation of growth was associated with floral initiation at 18 and 12°C, while at 24°C, only ‘Mucurines’ initiated floral primordia. Floral Stage 2 was reached by 3 September in ‘Mucurines’ and ‘Xenia’ at 18 and 12°C and nearly 2 weeks later in ‘Pax’. In a second experiment with controlled photoperiods, all cultivars ceased growing and initiated flowering in 10-h SD within 2–3 weeks, while in 20-h LD, growth continued for 8 weeks without floral initiation. Under 10-h SD conditions, all cultivars initiated flowers also at 24°C. Flowering performance in the following spring verified these results. We conclude that gooseberry is an obligatory SD plant with a critical photoperiod of 15–16 h.

Dancing on the platform: Lability of floral organs of Beilschmiedia appendiculata (Lauraceae).

Floral characters are important for the systematics of the Lauraceae. However, structure and development of the flowers remain poorly known in the family. In this study, we observed the variation and early development of flowers of Beilschmiedia appendiculata, which belongs to the Cryptocarya clade of the family. The results indicate that the shoot apical meristems (SAMs) of the floral buds are enlarged and become a platform for the programmed initiation of the floral organs; floral organs develop basically in an acropetal pattern; phyllotaxis is whorled, initiation of floral primordia within a whorl is asynchronous; floral merosity is extremely variable, for example, dimerous, trimerous, tetramerous, dimerous plus trimerous, and trimerous plus tetramerous. In addition, this species has lost the innermost staminal whorl and glands are not closely associated with stamens of the third staminal whorl, which is unusual in the family Lauraceae. Our new observations broaden our knowledge of the variation of floral structure in Beilschmiedia and pose a fundamental question regarding the ecology underlying the lability of floral organs in B. appendiculata.

Nitrogen management can inhibit or induce the sprouting of potato tubers: Consequences of regulation tuberization

Regulation of tuber dormancy and sprouting are pivotal for postharvest storage, sales, and seed breeding of potatoes (Solanum tuberosum L.). Nitrogen is an essential mineral nutrient required in potato production, which directly influences tuber development and quality. However, the effects of nitrogen on the post-harvest dormancy of potato tubers remain unclear, and their association with the initial tuber development are poorly understood. The aim of this study was to clarify the effects of nitrogen application rate on potato tuber dormancy and the associated physiological mechanisms. We obtained the tubers of different commercial potato cultivars (E shu3, Z shu5, and H shu3) at three nitrogen levels (0, 210, and 315 kg N ha−1) through field experiment, and then stored the tubers at room temperature (25 ℃) in the dark for 0–16 weeks. The dormancy period and alkaloid accumulation of potato tubers were analyzed, and the quality of seed tubers was evaluated by examining eye sprouting and replanting. We also conducted a pot experiment to explore the differences in tuber and stolen development of one potato cultivar (H shu3) at the three nitrogen levels. The carbohydrate and phytohormone contents in the apical bud meristem of dormant tubers and the enlarged subapical region of stolons were measured. The results showed that a reduction in the nitrogen application rate extended the dormancy period of potato tubers by 3–6 weeks and thereby reduced the risk of alkaloid accumulation caused by tuber sprouting, which was favorable for potato storage and sales. From the perspective of seed potato breeding, nitrogen application markedly increased the number of sprouting eyes, resulting in more stems and higher tuber yield after replanting. Compared to the control, nitrogen application promoted the sprouting of eyes at the apical bud of potato tubers, improved associated α-amylase activity and sucrose content, and increased gibberellin 1 (GA 1) content by 6.0 times. Nitrogen application also facilitated stolon elongation and growth, increased associated GA 1 content by 2.2 times, and delayed the enlargement of the subapical region to form tubers by 6–15 d. Taken together, the results indicate that nitrogen management (increasing or reducing nitrogen application rate) can be used as an agricultural practice to regulate potato tuber dormancy and sprouting. The intrinsic link between regulation of tuber dormancy by nitrogen application rate and its effects on tuber development is attributable to the regulation of tuberization. This research provides abundant physiological information for tuber dormancy and development in potatoes.

Effects of the in vitro behavior of micropropagated plants on the stability of variegation in Yucca gloriosa, Phormium tenax, and Cordyline australis cultivars

Cultivars with variegated foliage could be difficult to obtain in large-scale production of true-to-type plants. To determine the micropropagation potentialities of ornamental variegated monocotyledons in an industrial and commercial context, to define the stability of their variegated phenotypes, and to understand how and when off-type plants appear, the shoot tips of a variegated cultivar of three different species : Yucca gloriosa ‘Variegata’, Phormium tenax ‘Jessie’ and Cordyline australis ‘Pink Passion’ were introduced in vitro for propagation. The propagation rates and the variegation stability were estimated by separately monitoring each plant obtained during the several successive subcultures. During the in vitro process, samples were periodically fixed and studied by staining histological sections of the shoot tips. Leaf tissues were studied by light and confocal microscopy.After three-four subcultures, the multiplication rates obtained were stabilized at around 2.5–3 for Yucca, 1.4–1.7 for Phormium, and 1.2–1.7 for Cordyline. The number of off-type plants obtained after six multiplication cycles was around 10 % for Yucca, 25 % for Phormium and 60 % for Cordyline. The histology study showed that the axillary bud meristems (AxM) are totally (Yucca and Cordyline) or partially (Phormium) repressed by shoot apical meristem (SAM) in PGR-free medium. In the presence of BAP or BAP and NPA, only AxM were observed for Yucca, Phormium mainly developed AxM and some adventitious bud meristems (AdM), and Cordyline developed both AxM and AdM. The leaf section observations revealed that the three variegated cultivars turned out to be three periclinal chimeras.This histological study carried out on these cultivars highlights major differences in the development and in vitro multiplication behavior of three different genera belonging to the order Asparagales (clade monocotyledons). The variegation stability of these chimeric cultivars depends on their propensity to propagate by adventitious meristems.

AfLFY, a LEAFY homolog in Argyranthemum frutescens, controls flowering time and leaf development

Flowering is important for plant propagation and survival, and it is also closely related to human life. Identifying the molecular mechanisms underlying flower development is essential for plant improvement and breeding. Flower development is a complex physiological process that is regulated by multiple genes. LFY genes play important roles in the floral meristem transition and act as crucial integrators in regulating the floral gene network. Argyranthemum frutescens is an ornamental species cultivated for floral displays, yet little is known about molecular mechanisms driving its flower development. In this study, the LEAFY gene homologue, AfLFY, was identified and cloned from A. frutescens, and its role and expression patterns were characterized. Two distinct copies of AfLFY were found in the A. frutescens genome and both sequences contained a 1248 bp open reading frame that encoded 415 amino acids. The putative protein sequences have a typical LFY family domain. In addition, AfLFY was expressed at the highest levels in young leaves of the vegetative stage and in the shoot apical bud meristem of the reproductive stage. Phylogenetic analysis showed that AfLFY was most closely related to DFL from Chrysanthemum lavandulifolium. Subcellular localization studies revealed that AfLFY localized to the nucleus. Heterologous expression of AfLFY in transgenic tobacco plants shortened its period of vegetative growth, converted the lateral meristems into terminal flowers and promoted precocious flowering. In addition, transgenic plants exhibited obvious morphological changes in leaf shape. qRT-PCR analysis indicated that the expression levels genes related to flowering, FT, SOC1, and AP1 were significantly upregulated in AfLFY transgenic plants. Our findings suggested that the AfLFY gene plays a vital role in promoting flowering and leaf development in A. frutescens. These results laid a foundation for us to understand the mechanism of AfLFY in regulation flowering, and the results will be helpful in improving A. frutescens through molecular breeding.