Petunia Cultivars Research Articles

Efficacy and Optimal Timing of Warm-white or Red + Far-red LED Lamps in Regulation of Flowering in Long-day Ornamentals

When natural days are short, photoperiodic lighting at the end or beginning of the day (day extension) or in the middle of the night (night break) promotes flowering of long-day plants. The objective of this study was to compare broad-spectrum warm-white light-emitting diodes (LEDs) and red (R) + far-red (FR) LEDs at flowering regulation when delivered at different timings in the night period. We performed a greenhouse experiment on four long-day ornamentals [coreopsis (Coreopsis grandiflora) ‘Early Sunrise’, snapdragon (Antirrhinum majus) ‘Liberty Classic Yellow’, petunia (Petunia ×hybrida) ‘Easy Wave Burgundy Star’, and petunia ‘Wave Purple Improved’]. We grew plants under a truncated 8-hour photoperiod with or without low-intensity (∼2 μmol·m−2·s−1) nighttime lighting from warm-white or R+FR LEDs. For each light quality, we delivered four timings: 1) 8 hours after dusk; 2) 8 hours before dawn; 3) 4 hours after dusk + 4 hours before dawn; and 4) 4-hour night break. The effectiveness of floral promotion was determined by time from the treatment onset to the first open flower. Coreopsis flowered similarly under all lighting treatments, irrespective of light quality and timing, but did not flower under the short-day treatment by the end of the experiment. At flowering, coreopsis was 18% to 19% shorter under white than R+FR LEDs. In contrast, snapdragon flowered 9 to 20 days later under white than R+FR LEDs, when delivered for 8 hours at night, but flowered similarly under these two lamp types as a 4-hour night break. Compared with the short-day treatment, white and R+FR LEDs promoted flowering of both petunia cultivars, although flowering generally occurred later under white than R+FR LEDs. Snapdragon and petunia ‘Easy Wave Burgundy Star’ developed 30% to 122% more lateral branches under white than R+FR LEDs, when delivered for 8 hours at night. The effectiveness of warm-white LEDs was generally unaffected by timing, although it was most promotive of flowering in snapdragon when delivered for 8 hours before dawn. For R+FR LEDs, 8-hour day-extension lighting was generally more effective than 4-hour night-break lighting, irrespective of timing. We conclude when delivered for 8 hours at night, warm-white LEDs are generally less effective than R+FR LEDs at promoting flowering of long-day ornamentals but similarly effective as 4-hour night-break lighting. The effectiveness of day-extension lighting is generally independent of timing, although for R+FR LEDs, 8 hours after-dusk and/or before-dawn lighting was generally more effective than 4-hour night-break lighting.

Effect of irrigation levels on the physiological responses of petunia cultivars for selection

The selection of drought-tolerant varieties is essential to address the anticipated water stress in plants. This study assessed the drought tolerance of two petunia cultivars (Petunia Grandiflora and Falcon F1 (white). A pot experiment was conducted with the four irrigation levels, which included the irrigation interval of one day (control, T0), three days (T1), five days (T2), and seven days (T3). Under T1, the Grandiflora cultivar produced the tallest plants (43.0 cm). The plant height gradually decreased as the irrigation interval grew longer. Overall, the size of the Grandiflora was observed to be higher than the Falcon F1 cultivar. The Grandiflora cultivar produced the longest roots (6.2 cm) in T0, followed by the Falcon, which had roots with a length of 5.6 cm. The root length of Grandiflora was found to be 5.5 cm and 5.0 cm in T1 and T2, while Falcon F1 produced 5.2 and 4.6 cm roots, respectively. Petunia Grandiflora surpassed Falcon F1 (white) regarding root dry weight for all treatments. In addition, when water was provided after a 3-day gap (T1), the Petunia Grandiflora cultivar produced the highest root-shoot ratio (3.52) using fresh weight. Petunia Grandiflora had the highest chlorophyll concentration of 2.68 mg g−1, followed by the Falcon F1 (white) cultivar in T1. The Grandiflora produced the highest total chlorophyll levels (4.04 mg g−1) when water was added after a one-day break, followed by Falcon F1 (white), which had total chlorophyll values of 3.42 mg g−1 under control compared to other irrigation treatments. Hence, Grandiflora performed the best; therefore, this study will help the cultivators adapt to drought environments using drought-resistant cultivars. Due to this fact, most people buy these flowers as seedlings rather than starting them from seeds, and this research is significant for flower nurseries.

Physiological changes besides the enhancement of pigmentation in Petunia hybrida caused by overexpression of PhAN2, an R2R3-MYB transcription factor.

Ectopic expression of PhAN2 in vegetative tissue can improve regeneration and adventitious rooting but inhibit axillary bud outgrowth of petunia, while overexpression specifically in flowers could shorten longevity. Anthocyanin 2 has been only treated as a critical positive regulation factor of anthocyanin biosynthesis in petunia flowers. To determine if this gene had other functions in plant growth, we overexpressed this gene in an an2 mutant petunia cultivar driven by promoters with different strengths or tissue specificity. Various physiological processes of transformants in different growth stages and environments were analyzed. Besides the expected pigmentation improvement in different tissues, the results also showed that ectopic expression of AN2 could improve the regeneration skill but inhibit the axillary bud germination of in vitro plants. Moreover, the rooting ability of shoot tips of transformants was significantly improved, while some transgenic lines' flower longevity was shortened. Gene expression analysis showed that the transcripts level of AN2, partner genes anthocyanin 1 (AN1), anthocyanin 11 (AN11), and target gene dihydroflavonol 4-reductase (DFR) was altered in the different transgenic lines. In addition, ethylene biosynthesis-related genes 1-aminocyclopropane-1-carboxylic acid synthase (ACS1) and ACC oxidase (ACO1) were upregulated in rooting and flower senescence processes but at different time points. Overall, our data demonstrate that the critical role of this AN2 gene in plant growth physiology may extend beyond that of a single activator of anthocyanin biosynthesis.

Management of Botrytis cinerea in Petunia Using Cultivar Resistance and Biorational Products

Botrytis cinerea causes blight on the leaves, stems, and flowers of petunia ( Petunia × hybrida), a popular annual bedding plant. Our objectives were to evaluate (i) four standard and nine Wave petunia cultivars for resistance to Botrytis blight and (ii) 10 biorational products compared with the standard fungicide fenhexamid and an untreated control to limit disease. According to the final disease assessment and area under the disease progress curve (AUDPC) data, ‘Sophistica Blackberry’ had significantly less disease than ‘Tidal Wave Cherry’ in all trials. Tidal Wave Cherry also had significantly more disease according to ratings and AUDPC data than ‘Easy Wave Red Improved’, ‘Wave Purple Classic’, ‘Tidal Wave Silver’, ‘Shock Wave Red’, and ‘Easy Wave Blue’ in trials 1 and 3, whereas in trial 2, these differences were not observed. When evaluated on Shock Wave Red petunia, Prestop ( Gliocladium catenulatum) provided significant B. cinerea control and was similar to the fungicide standard Decree (fenhexamid) in both trials. According to the final disease severity assessment, treatment with Botector ( Aureobasidium pullulans), Zio ( Pseudomonas chlororaphis), or LifeGard ( Bacillus mycoides) also provided control similar to the fungicide standard but was significantly different from the untreated control in one trial only. Results from this study illustrate that certain biorational products can limit B. cinerea when used in conjunction with a cultivar that has disease resistance that limits the impact of the pathogen.

Protoplast isolation and transient gene expression in different petunia cultivars.

The protocol optimized for Petunia hybrida cv. Mirage Rose produced high protoplast yields in 3 out of other 11 cultivars (Damask White, Dreams White, and Opera Supreme White). Factors optimized in the protoplast transfection process showed that the best transfection efficiency (80%) was obtained using 2.5 × 105 protoplast density, 40% polyethylene glycol (PEG) concentration, 10µg plasmid DNA, and 15min of transfection time. Assessing the usability of the protocol for other cultivars (Damask White, Dreams White, and Opera Supreme White), a reasonable protoplast transfection efficiency (⁓50%) was observed in the cultivars Dreams White and Opera Supreme White, with lower efficiency (⁓50%) observed in the cv. Damask White. The transient expression of enhanced green fluorescent protein (eGFP) in the nucleus of the transfected protoplasts of all cultivars was confirmed using PCR. This system could be valuable for genome editing of unwanted genes in petunias using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) technology. Furthermore, it could contribute to other studies on protein subcellular localization, protein-protein interactions, and functional gene expression in the petunias.

Ammonium and nitrate impact petal color traits and amino acid profiles differently in <i>Petunia</i>

Nitrogen (N) is vital for ornamental plants to fulfill fundamental cellular functions. Effects of inorganic N including nitrate and ammonium on ornamental traits at the biochemical level are less reported. Given that the continuously increased concentration of CO₂ in atmosphere has greater negative effects on nitrate reduction than ammonium utilization in C₃ plants, it is vital for us to dissect various effects of different inorganic N forms on flower development, which will lead to a better understanding of the metabolic regulation of ornamental traits. In this study, <italic>Petunia x hybrida</italic> cv 'Mitchell Diploid' (MD) plants at 6~8-leaf stage were treated hydroponically with the same and regular amount of inorganic N for one month but in three different forms, 1mM NH₄NO₃ as the control (NH₄NO₃), 2mM NH₄Cl alone (NH₄-N) and 2mM NaNO₃ alone (NO₃-N). Results indicated that relative to the control, effects of NH₄-N and NO₃-N treatment alone on plant growth, N utilization and distribution, petal color traits and petal amino acid profiles were different by varying degrees. We have confirmed that NH₄-N could specifically increase ¹⁵N distribution to floral tissues, change the amino acid profiles in petals which in turn bring changes to petal colors. Results with four commercially available petunia cultivars with different flower colors also validated our findings. This study has been designed to specifically investigate effects of ammonium or nitrate as the sole source of inorganic N on the developmental and chemical features of floral tissues in <italic>Petunia</italic>.

Dissecting genetic diversity and genomic background of Petunia cultivars with contrasting growth habits

The cultivated petunia (Petunia ×hybrida) is derived from the progenitor species P. axillaris and P. integrifolia. The hybridization dates back only to the 1830s, though intensive breeding efforts have yielded cultivars exhibiting incredible diversity for many traits, including growth habit, flower color, and flower size. Until now, little is known about the genetic diversity and genomic background of modern cultivars. Here we selected a panel of 13 cultivars with contrasting growth habits and three wild species (the progenitors and P. exserta) to estimate the genomic contribution from the ancestral species and to study whether the variation of the genetic origin could be associated with different breeding programs or morphological variability. Transcriptome sequencing identified 1,164,566 SNPs representing 98.4% (32,451) of the transcripts that cover 99.2% (of 52,697,361 bp) of the P. axillaris transcriptome. Cultivars with an upright growth habit had more homozygous alleles and more P. axillaris-derived alleles than trailing cultivars, while mounded cultivars had intermediate heterozygosity. Unlike previous studies, we found the proportions of alleles derived from each progenitor species varied across cultivars but overall were not biased toward one progenitor species, suggesting diverse selection during cultivar development. For trailing cultivars, alleles potentially introgressed from other wild species (“out” alleles) were enriched. The “out” alleles were clustered in particular regions of chromosomes, suggesting that these regions may be hotspots of introgression. Transcripts in these regions were enriched with gene ontology terms associated with growth habit. This study provides novel insight into the contributions of progenitor species to the genomic background of modern petunia cultivars and identifies genome regions that may harbor genes conferring the trailing growth habit for further exploration.

Simultaneous targeting of duplicated genes in Petunia protoplasts for flower color modification via CRISPR-Cas9 ribonucleoproteins.

We obtained a complete mutant line of Petunia having mutations in both F3H genes via Cas9-ribonucleoproteins delivery, which exhibited a pale purplish pink flower color. The CRISPR-Cas system is now revolutionizing agriculture by allowing researchers to generate various desired mutations in plants at will. In particular, DNA-free genome editing via Cas9-ribonucleoproteins (RNPs) delivery has many advantages in plants; it does not require codon optimization or specific promoters for expression in plant cells; furthermore, it can bypass GMO regulations in some countries. Here, we have performed site-specific mutagenesis in Petunia to engineer flower color modifications. We determined that the commercial Petunia cultivar 'Madness Midnight' has two F3H coding genes and designed one guide RNA that targets both F3H genes at once. Among 67 T0 plants regenerated from Cas9-RNP transfected protoplasts, we obtained seven mutant lines that contain mutations in either F3HA or F3HB gene and one complete mutant line having mutations in both F3H genes without any selectable markers. It is noteworthy that only the f3ha f3hb exhibited a clearly modified, pale purplish pink flower color (RHS 69D), whereas the others, including the single copy gene knock-out plants, displayed purple violet (RHS 93A) flowers similar to the wild-type Petunia. To the best of our knowledge, we demonstrated a precedent of ornamental crop engineering by DNA-free CRISPR method for the first time, which will greatly accelerate a transition from a laboratory to a farmer's field.

Isolation of the Histone Lysine Methyltransferase Gene PhSDG8 and Characterization of Function in Shoot Branching

Petunia (Petunia ×hybrida) is an important ornamental plant, and its branch development has become a hot research topic. In this study, PhSDG8, an ortholog of SET domain group 8 (SDG8), was cloned from the petunia cultivar Mitchell Diploid. It had an open reading frame (ORF) of 5070 bp and encoded 1689 amino acids, with Suppressor variegation 3–9, Enhancer of zeste, Trithorax (SET), Zinc finger-cysteine and tryptophan conserved (Zf-CW), associated with SET (AWS) and Post SET domains. The predicted amino acid sequence of PhSDG8 was most closely related to Nicotiana sylvestris ASHH2 (NsASHH2). Expression analysis revealed that PhSDG8 expressed highest in the stems and lowest in the axil. Subcellular localization analysis showed that PhSDG8 was localized in the nucleus. Overexpression of PhSDG8 reduced the branch number of Arabidopsis thaliana sdg8-2. The silencing of PhSDG8 resulted in an increase in the number of branches of petunia and significant upregulation of PhUGT74E2. These results suggested that PhSDG8 may be a candidate gene for regulating the branching of petunia.

Mechanical stimulation affects growth dynamics, IAA content and activity of POD and IAA oxidase in Petunia x atkinsiana

Ornamental plants are bred and purchased for their aesthetical features such as colorful flowers and leaves, as well as compact and elegant stature. Petunia is one of the most popular bedding plants for urban areas and gardens, therefore, control of its growth and branching is essential. In commercial horticulture, the most common method to control growth dynamics is via growth regulators. Mechanical stimulation is proposed as an environmentally friendly alternative to chemical regulators. In this study, the efficiency of MS was tested on two cultivars of Petunia x atkinsiana. A brushing apparatus was set to stroke apical parts of young plants 40, 60 or 80 times per day between 14 March and 25 April. Several parameters, such as stem length, the number of branches, mature leaf area, the number of open flowers, were measured four times during the whole experiment: three times during the stimulation period, on 20 March, 4 and 25 April, and the last time on 18 May, three weeks after the stimulation stopped. For biochemical analyses, 1 cm apical stem fragments were collected on 20 March, 25 April and 18 May. The results show that MS affects the growth dynamics in petunia, but the response appears to be cultivar specific. In both cultivars, brushing with 80 strokes per day produced the most spectacular effects in growth reduction. On the last day of brushing the POD and IAA oxidase activities in the strongly reacting cultivar were the highest in plants rubbed 80 x per day. The results indicate that MS can be very effective in controlling stem growth in at least some cultivars of petunia, replacing hormonal treatments.

Protoplast Isolation and Shoot Regeneration from Protoplast-Derived Callus of Petunia hybrida Cv. Mirage Rose.

Despite the increasing use of protoplasts in plant biotechnology research, shoot regeneration from protoplasts remains challenging. In this study, we investigated the factors involved in protoplast isolation, callus induction, and shoot regeneration in Petunia hybrida cv. Mirage Rose. The following conditions were found to be most optimal for protoplast yield and viability: 0.6 M mannitol, 2.0% cellulase, and 6 h digestion time. A plating density of 10 × 104 protoplasts/mL under osmoticum condition (0.58 M mannitol) showed high microcolony viability in liquid culture. The Kao and Michayluk medium was found to be appropriate for callus proliferation from microcalli under a 16-h light photoperiod. Calli cultured in Murashige and Skoog medium containing 1.0 mg/L 6-benzylaminopurine and 0.2 mg/L 3-indole butyric acid showed the highest shoot regeneration frequency and number of shoots obtained per explant. Random amplification of polymorphic DNA analysis showed that the protoplast-derived shoots exhibited the same banding patterns as those of donor plants. Collectively, these findings can contribute to solving problems encountered in protoplast isolation and shoot regeneration in other petunia cultivars and related species. As the protocol developed by us is highly reproducible, it can be applied in biotechnology research on P. hybrida cv. Mirage Rose.

Event-specific qualitative polymerase chain reaction analysis for two T-DNA copies in genetically modified orange Petunia

In 2017, various orange coloured petunia on the market turned out to be genetically modified (GM) without an official authorization for commercialization. Sequence analysis suggested these undeclared plants most probably originated from a plant transformation experiment performed in the 1980s. For a deeper understanding how GM petunia entered classical breeding programmes worldwide, and whether they originated from a single source or not, we undertook a molecular genetic characterization of the T-DNA integration sites in different GM petunia cultivars and breeding lines. By means of genome walking, we isolated different T-DNA sequences, which are located at the junctions between the T-DNA(s) and the petunia DNA. Based on the results obtained we conclude that there are at least two T-DNA copies of different lengths. This is supported by Southern blot analysis. For T-DNA1, the 3′-junction sequence was isolated, whereas the 5′-junction remained unclear. In contrast, for T-DNA2, the 5′-junction sequence was isolated, whereas the sequence isolated from the 3′-region consists only of T-DNA, but did not include the junction from the T-DNA to the petunia DNA. We developed primers for event-specific PCRs and screened a set of three orange GM petunia cultivars and 126 GM offspring from a commercial breeding program. We show that both T-DNA copies are present in all our tested GM petunia samples, which underpins the assumption of a single transgenic origin of the undeclared GM petunia. Most likely, the two T-DNAs are integrated in close proximity into the petunia genome.

Differential Temperature Sensitivity of Flowering Time and Crop Quality Parameters of 20 Seed-propagated Petunia Cultivars

Twenty petunia (Petunia ×hybrida) cultivars were grown at 14, 17, and 20 °C to quantify the impact of temperature on time to flowering, flowering and development rates, and crop quality parameters. Increasing temperature increased vegetative development rates and reduced time to flower (TTF) for all cultivars. Linear functions generated to describe the effects of temperature on the flowering rate (1/TTF) revealed considerable variability in the temperature sensitivity of flowering rates across cultivars. The minimum temperature for the rate of progress toward flowering (Tbase) ranged from 0.15 °C for ‘Damask Purple’ to 7.1 °C for ‘Wave Purple’. The crop quality parameters plant height and branch and flower bud number were all influenced by interactions between cultivar and temperature. Plant height at flowering was unaffected by temperature for 13 of the 20 cultivars, whereas the height of five cultivars was lower at 20 °C compared with 14 °C, and two cultivars were shortest at 17 °C. The branch number of six cultivars was lower at 14 °C than at 17 or 20 °C, whereas three cultivars produced more branches at 17 °C compared with 20 °C. The branch number of 11 cultivars was not impacted by temperature. For 11 of the 20 cultivars, the flower bud number was greater at 14 °C than at 20 °C, whereas temperature did not influence the flower bud number for the other nine cultivars. The results of this work could help to improve production efficiency by allowing cultivars to be placed in temperature-response groups based on the temperature sensitivity of flowering time and/or crop quality parameters.

Expression of CCD4 gene involved in carotenoid degradation in yellow-flowered Petunia × hybrida

Petunia is a popular commercial bedding plant that comes in many colors, but there are no petunia cultivars with deep yellow petals. The carotenoid degradation gene carotenoid cleavage dioxygenase (CCD4) was isolated from white and yellow-flowered petunia and we found the 226-bp insertion of a non-autonomous transposable element tourist-like miniature-inverted repeat (MITE) in the coding region of CCD4 only in yellow cultivars. The insertion interrupts gene expression because of a premature stop codon after the TE insertion and could form secondary structures in hairpin RNA that could then be processed into a mature miRNA. Here, the normal function of CCD4 isolated from a white cultivar was introduced to a yellow cultivar. The transformants showed more fading pale-yellow flowers and carotenoid content was decreased. These results indicate that transformed CCD4 expression promoted carotenoid degradation and the lack of CCD4 expression results in more carotenoid accumulation in wild-type yellow-flowered petunia.

Direct shoot regeneration of three Petunia cultivars

A tissue culture system for acquiring high efficiency regeneration of Petunia was optimized. Leaf explants of Alvan, Large Flower Alvan (LF Alvan) and Mahalat cultivars of Petunia hybrida were cultured separately on MS medium including various concentrations of TDZ and BA without auxin in order to assess direct shoot regeneration. Alvan showed the highest frequency of shoot regeneration (100%) and the highest mean number of shoots per explant (25.33) on MS containing 2 mg/l TDZ. For LF Alvan cultivar the highest percentage of shoot organogenesis (100%) and the highest mean number of shoots per explant (18.20) were observed when MS medium containing 1 mg/l BA was used. With the Mahalat cultivar the maximum rate of direct regeneration was obtained on MS supplemented with 0.5 and 1 mg/l BA (80%). The mean number of shoots per explant (9.63) was obtained when 2 mg/l TDZ was used. Regenerated shoots were successfully elongated (2 to 3 cm in length) and transferred into half-strength MS as the rooting medium supplemented with 0.1 mg/l NAA. The shoots were successfully rooted, acclimatized and transferred to the greenhouse.

Development of an efficient virus-induced gene silencing method in petunia using the pepper phytoene desaturase (PDS) gene

Virus-induced gene silencing (VIGS) is widely used for functional analysis of genes in plants. Because of the variation in its effectiveness among plant species, the VIGS system is normally optimized using the phytoene desaturase (PDS) gene as a visible indicator. In this study, we optimized an efficient VIGS system for petunias using the PDS gene isolated from pepper (Capsicum annuum) plants as a visible indicator. Application of the CaPDS gene effectively induced gene silencing in the petunia cultivars Mirage Rose, Mirage Pink, and Picobella Blue. However, silencing effectiveness was observed to be limited by genotypes and inoculation methods; apical meristem application was the appropriate method, whereas the highest silencing effectiveness among the cultivars was found in Picobella Blue. In addition, it was found that higher silencing effectiveness was associated with higher degradation of the endogenous PhPDS mRNA. Moreover, in terms of plant age and temperatures, 3-week-old plants grown at 20 °C day/18 °C night showed high silencing effectiveness for all cultivars. Taken together, infection of apical meristem of 3-week-old plants grown at 20 °C day/18 °C night with pTRV2-CaPDS exhibited the highest silencing effectiveness of all cultivars. Therefore, this study indicated the effectiveness of the CaPDS in the VIGS experiment with petunias, as well as the involvement of different factors in the mechanism influencing silencing effectiveness in petunias. These results will enable high-throughput functional analysis of genes associated with commercially important traits in petunias. CaPDS gene effectively induced gene silencing in the petunia cultivars, however, higher silencing effectiveness was observed to be limited by genotypes, inoculation methods, plant age, inoculation temperature, and presence of endogenous PhPDS mRNA.

Inhibition of post-transcriptional gene silencing of chalcone synthase genes in petunia picotee petals by fluacrypyrim.

In petals of picotee petunia (Petunia hybrida) cultivars, margin-specific post-transcriptional gene silencing (PTGS) of chalcone synthase A (CHSA) inhibits anthocyanin biosynthesis, resulting in marginal white tissue formation. In this study, we found that a low molecular mass compound, fluacrypyrim, inhibits PTGS of CHSA, and we explored the site-specific PTGS mechanism of operation. Fluacrypyrim treatment abolished the picotee pattern and eliminated site-specific differences in the levels of anthocyanin-related compounds, CHSA expression, and CHSA small interfering RNA (siRNA). In addition, fluacrypyrim abolished the petunia star-type pattern, which is also caused by PTGS of CHSA. Fluacrypyrim treatment was effective only at the early floral developmental stage and predominantly eliminated siRNA derived from CHS genes; i.e. siRNA derived from other genes remained at a comparable level. Fluacrypyrim probably targets the induction of PTGS that specifically operates for CHS genes in petunia picotee flowers, rather than common PTGS maintenance mechanisms that degrade mRNAs and generate siRNA. Upon treatment, the proportion of colored tissue increased due to a shift of the border between white and colored sites toward the margin in a time- and dose-dependent manner. These findings imply that the fluacrypyrim-targeted PTGS induction is completed gradually and its strength is attenuated from the margins to the center of petunia picotee petals.

Regulation of flowering by green light depends on its photon flux density and involves cryptochromes.

Photoperiodic lighting can promote flowering of long-day plants (LDPs) and inhibit flowering of short-day plants (SDPs). Red (R) and far-red (FR) light regulate flowering through phytochromes, whereas blue light does so primarily through cryptochromes. In contrast, the role of green light in photoperiodic regulation of flowering has been inconsistent in previous studies. We grew four LDP species (two petunia cultivars, ageratum, snapdragon and Arabidopsis) and two SDP species (three chrysanthemum cultivars and marigold) in a greenhouse under truncated 9-h short days with or without 7-h day-extension lighting from green light (peak = 521 nm) at 0, 2, 13 or 25 μmol m-2 s-1 or R + white (W) + FR light at 2 μmol m-2 s-1 . Increasing the green photon flux density from 0 to 25 μmol m-2 s-1 accelerated flowering of all LDPs and delayed flowering of all SDPs. Petunia flowered similarly fast under R + W + FR light and moderate green light but was shorter and developed more branches under green light. To be as effective as R + W + FR light, saturation green photon flux densities were 2 μmol m-2 s-1 for LDP ageratum and SDP marigold and 13 μmol m-2 s-1 for LDP petunia. Snapdragon was the least sensitive to green light. In Arabidopsis, cryptochrome 2 mediated promotion of flowering under moderate green light, whereas both phytochrome B and cryptochrome 2 mediated that under R + W + FR light. We conclude that 7-h day-extension lighting from green light-emitting diodes can control flowering of photoperiodic ornamentals and that in Arabidopsis, cryptochrome 2 mediates promotion of flowering under green light.

Characteristics of Floral Scent Compounds in a New Fragrant Petunia Cultivar TX-794 ‘Evening Scentsation’

Characteristics of Floral Scent Compounds in a New Fragrant Petunia Cultivar TX-794 ‘Evening Scentsation’

Phenylpropanoid Scent Compounds in Petunia x hybrida Are Glycosylated and Accumulate in Vacuoles.

Floral scent has been studied extensively in the model plant Petunia. However, little is known about the intracellular fate of scent compounds. Here, we characterize the glycosylation of phenylpropanoid scent compounds in Petunia x hybrida. This modification reduces scent compounds' volatility, reactivity, and autotoxicity while increasing their water-solubility. Gas chromatography–mass spectrometry (GC–MS) analyses revealed that flowers of petunia cultivars accumulate substantial amounts of glycosylated scent compounds and that their increasing level parallels flower development. In contrast to the pool of accumulated aglycones, which drops considerably at the beginning of the light period, the collective pool of glycosides starts to increase at that time and does not decrease thereafter. The glycoside pool is dynamic and is generated or catabolized during peak scent emission, as inferred from phenylalanine isotope-feeding experiments. Using several approaches, we show that phenylpropanoid scent compounds are stored as glycosides in the vacuoles of petal cells: ectopic expression of Aspergillus niger β-glucosidase-1 targeted to the vacuole resulted in decreased glycoside accumulation; GC–MS analysis of intact vacuoles isolated from petal protoplasts revealed the presence of glycosylated scent compounds. Accumulation of glycosides in the vacuoles seems to be a common mechanism for phenylpropanoid metabolites.