Inflorescence Elongation Research Articles

Integrated Multi-Omics Analysis to Reveal the Molecular Mechanisms of Inflorescence Elongation in Medicago sativa.

The morphological architecture of inflorescence influences seed production. The regulatory mechanisms underlying alfalfa (Medicago sativa) inflorescence elongation remain unclear. Therefore, in this study, we conducted a comparative analysis of the transcriptome, proteome, and metabolome of two extreme materials at three developmental stages to explore the mechanisms underlying inflorescence elongation in alfalfa. We observed the developmental processes of long and short inflorescences and found that the elongation capacity of alfalfa with long inflorescence was stronger than that of alfalfa with short inflorescences. Furthermore, integrative analysis of the transcriptome and proteome indicated that the phenylpropanoid biosynthesis pathway was closely correlated with the structural formation of the inflorescence. Additionally, we identified key genes and proteins associated with lignin biosynthesis based on the differential expressed genes and proteins (DEGs and DEPs) involved in phenylpropanoid biosynthesis. Moreover, targeted hormone metabolome analysis revealed that IAA, GA, and CK play an important role in the peduncle elongation of alfalfa inflorescences. Based on omics analysis, we detected key genes and proteins related to plant hormone biosynthesis and signal transduction. From the WGCNA and WPCNA results, we furthermore screened 28 candidate genes and six key proteins that were correlated with lignin biosynthesis, plant hormone biosynthesis, and signaling pathways. In addition, 19 crucial transcription factors were discovered using correlation analysis that might play a role in regulating candidate genes. This study provides insight into the molecular mechanism of inflorescence elongation in alfalfa and establishes a theoretical foundation for improving alfalfa seed production.

Transcriptome Analysis Reveals the Molecular Mechanism of Grape Inflorescence Elongation after Applying Microbial Fertilizers

Microbial fertilizers can activate and promote nutrient absorption and help inflorescence elongation. To understand the molecular mechanisms governing grape (Vitis vinifera) inflorescence elongation after microbial fertilizer application, we comprehensively analyzed the transcriptome dynamics of ‘Summer Black’ grape inflorescence at different leaf stages. With the development of ‘Summer Black’ grape inflorescence, gibberellic acid content gradually increased and was clearly higher in the microbial fertilizer group than in the corresponding control group. In addition, the microbial fertilizer and control groups had 291, 487, 490, 287, and 323 differentially expressed genes (DEGs) at the 4-, 6-, 8-, 10-, and 12-leaf stages, respectively. Kyoto Encyclopedia of Genes and Genomes pathway annotation revealed that most upregulated DEGs were enriched in starch and sucrose metabolism pathways at the 6-, 8-, and 10-leaf stages. Weighted gene coexpression network analysis identified stage-specific expression of most DEGs. In addition, multiple transcription factors and phytohormone signaling-related genes were found at different leaf stages, including basic helix-loop-helix proteins, CCCH zinc finger proteins, gibberellin receptor GID1A, 2-glycosyl hydrolases family 16, protein TIFY, MYB transcription factors, WRKY transcription factors, and ethylene response factor, suggesting that many transcription factors play important roles in inflorescence elongation at different developmental stages. These results provide valuable insights into the dynamic transcriptomic changes of inflorescence elongation at different leaf stages.

Molecular characterization of Satsuma mandarin (Citrus unshiu Marc.) VASCULAR PLANT ONE-ZINC FINGER2 (CuVOZ2) interacting with CuFT1 and CuFT3.

Shortening the juvenility is a burning issue in breeding fruit trees such as Satsuma mandarin (Citrus unshiu Marc.). Decreasing the breeding period requires a comprehensive understanding of the flowering process in woody plants. Throughout the Arabidopsis flowering system, FLOWERING LOCUS T (FT) interacts with other transcription factors (TFs) and functions as a transmissible floral inducer. In a previous study, a VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1)-like TF from the Satsuma mandarin, CuVOZ1, showed protein-protein interaction with two citrus FTs in a yeast two-hybrid (Y2H) system and precocious flowering in Arabidopsis. In this study, another VOZ, CuVOZ2, was isolated from the Satsuma mandarin 'Aoshima' and protein-protein interaction was confirmed between CuVOZ2 and CuFTs. No apical meristem (NAM) and zinc coordination motifs were identified within the N-terminal of CuVOZ2. Docking simulation predicted that interactions between CuVOZ2 and CuFTs might occur in domain B of CuVOZ2, which contains a zinc finger motif. According to docking predictions, the distances between the amino acid residues involved ranged from 1.09 to 4.37 Å, indicating weak Van der Waals forces in the interaction. Cys216, Cys221, Cys235, and His239 in CuVOZ2 were suggested to bond with a Zn2+ in the Zn coordination motif. Ectopic expression of 35SΩ:CuVOZ2 in Arabidopsis affected the flowering time, length of inflorescence and internode, and number of siliques, suggesting that CuVOZ2 might regulate both vegetative and reproductive development, act as a trigger for early flowering, and be involved in the elongation of inflorescence possibly in a slightly different way than CuVOZ1.

Gibberellic Acid for Table Grape Inflorescence Elongation: Is It Worth It?

<h3>Background and goals</h3> Gibberellic acid (GA₃) is sometimes used at prebloom to help controlling cluster compactness, but controversy has been raised regarding its efficacy, particularly in table grape production. A trial was established to evaluate prebloom GA₃ on rachis length. <h3>Methods and key findings</h3> In GA₃ treated and untreated clusters rachises were divided in three arbitrary segments. The increase in length of each segment was evaluated from a month before bloom until the beginning of summer. Prebloom GA₃ rapidly triggered rachis growth in length, but only in the middle and distal portions of the inflorescence. The top area was not affected. The following standard table grape cluster tipping eliminated the cluster distal portion and all GA₃ related rachis growth. GA₃ treated clusters had longer segments removed compared to untreated ones. Shot berries and rachis thickness were also increased, but cluster and berry weight remained the same. <h3>Conclusions and significance</h3> The effects of GA₃ on rachis length at prebloom, can be discarded by other required standard table grapes practices. The negative and cumulative effects should be considered when analyzing its usefulness. Knowing the benefits and disadvantages of this practice will help table grape growers to optimize plant growth regulator programs.

Trichoderma spp. Improves Flowering, Quality, and Nutritional Status of Ornamental Plants

Scientists all over the world conduct research to determine the influence of Trichoderma spp. on various groups of plants, mostly crops. However, there is little information on the influence of these fungi on ornamental plants. Therefore, the authors of this study analyzed the influence of Trichoderma spp. on the growth, flowering, quality, and nutritional status of ornamental plants. The research showed that Trichoderma spp. in this group of plants stimulate the elongation and thickening of shoots and the formation of leaves. These fungi also stimulate or inhibit leaf elongation. They also accelerate the flowering of plants, stimulate the elongation of inflorescence shoots and inflorescences, and the development of flowers. Apart from that, Trichoderma spp. positively influence the content of chlorophyll and carotenoids in leaves, and they stimulate the uptake of micro- and macroelements.

Ectopic expression of two CAULIFLOWER genes from mango caused early flowering in Arabidopsis

APETALA1 (AP1), CAULIFLOWER (CAL) and FRUITFULL (FUL) were homologous genes with redundant functions in the process of flower transformation and floral development in Arabidopsis. Two CALs genes, MiCAL1 and MiCAL2, were cloned from mango (Mangifera indica L.). Their full-length sequences contained 717 bp and 714 bp, encoding 239 and 238 amino acids, respectively. Both the MiCAL1 and MiCAL2 proteins contained typical MADS-box and K-box domains and therefore belonged to the CAL-like protein family. MiCAL1 and MiCAL2 were expressed in all tissues at the inflorescence elongation stage and flowering stage, with the highest expression in the leaves at the flowering stage. They had similar expression patterns during flower development, with the highest expression levels in leaves during flower differentiation and the lowest expression levels during fruit development. Overexpression of MiCAL1 and MiCAL2 resulted in significantly earlier flowering in Arabidopsis. Overexpression of MiCAL1 resulted in terminal flowers with normal flower organs, while overexpression of MiCAL2 induced partially variation in floral organs but had no effect on inflorescences. Yeast two-hybrid (Y2H) experiments showed that MiCAL1 and MiCAL2 can interact with several flower-related proteins as well as stress response proteins, such as SEP1, SVP1, SVP2, SOC1G and Di19-4. These results suggest that these two MiCALs genes may have an important influence on mango flowering.

Flowering, Nutritional Status, and Content of Chloroplast Pigments in Leaves of Gladiolus hybridus L. ‘Advances Red’ after Application of Trichoderma spp.

In this study, we attempt to assess the influence of Trichoderma spp. on the flowering and nutritional status of Gladiolus hybridus L. ‘Advances Red’, as well as on the content of chlorophyll a + b and carotenoids in the leaves. During both years of the experiment, there was a treatment in which Trichoderma fungi were not used (control), and in another treatment, plants were treated with these fungi. After five weeks of cultivation, when leaf apexes were visible above the surface of the substrate, each plant was irrigated with a suspension (20 mL) of mix of Trichoderma spp. (T. viride Schumach-Tv14, T. harzianum Rifai-Thr2, T. hamatum/Bonord/Bainier-Th15). The treatment of the plants Trichoderma-spp. improved their uptake of macro- (P, K and Ca) and micronutrients (Zn, Fe and B), and increased the chlorophyll a + b and carotenoids in their leaves. Trichoderma spp. accelerated the flowering of Gladiolus hybridus L. ‘Advances Red’ by 10–14 days. The fungi stimulated the elongation of inflorescence shoots and inflorescences, in which the number of flowers increased, but flower diameter did not change. Trichoderma spp. improved the nutrients uptake, chlorophyll a + b and carotenoids, and flowering; hence, Trichoderma spp. treatment is suggested for enhancing inflorescence and inflorescence shoots in Gladiolus hybridus.

The Novel Cucurbitaceae miRNA ClmiR86 Is Involved in Grafting-Enhanced Phosphate Utilization and Phosphate Starvation Tolerance in Watermelon.

Watermelon (Citrullus lanatus) is a globally important Cucurbitaceae crop in which grafting is commonly used to improve stress tolerance and enhance nutrient utilization. However, the mechanism underlying grafting-enhanced nutrient assimilation remains unclear. Here, we demonstrate the possible involvement of a novel Cucurbitaceae miRNA, ClmiR86, in grafting-enhanced phosphate-starvation tolerance via CALCINEURIN B-LIKE INTERACTING PROTEIN KINASE 5 (ClCIPK5) suppression in watermelon. Transcript analyses revealed that the induction of ClmiR86 expression was correlated with the downregulation of ClCIPK5 in squash-grafted watermelon under phosphate starvation. In addition, the differential expression of ClmiR86 in various watermelon genotypes was consistent with their phosphate utilization efficiency. Furthermore, ClmiR86 overexpression in Arabidopsis enhanced root growth and phosphate uptake under phosphate starvation and promoted inflorescence elongation under normal conditions. These results suggest that the ClmiR86–ClCIPK5 axis is involved in phosphate starvation response as well as grafting-enhanced growth vigor and phosphate assimilation. The present study provides valuable insights for investigating long-distance signaling and nutrient utilization in plants.

Isolation and characterization of two APETALA1-Like genes from mango (Mangifera indica L.)

APETALA1 (AP1) encodes a key MADS-box transcription factor that plays a crucial role in the floral transition and floral organ development. Here we describe two AP1 homologues gene MiAP1-1 and MiAP1-2 from mango (Mangifera indica L.). The full-length MiAP1-1 and MiAP1-2 were 960 bp and 906 bp, respectively, including 741 bp and 744 bp open reading frame encoding 247 and 248 amino acids, respectively. MiAP1-1 and MiAP1-2 exhibited high expression levels in floral organs and low transcript levels in vegetative organs. MiAP1-1 was more highly expressed in leaves during the floral transition stage, while MiAP1-2 was more highly expressed in leaves during the floral transition stage, floral differentiation stage and inflorescence elongation stage. Overexpression of MiAP1-1 and MiAP1-2 in Arabidopsis resulted in significant early flowering, meanwhile MiAP1-2 in transgenic tobacco also promote early flowering. Ectopic expression of MiAP1-1 and MiAP1-2 causes different flower phenotypes. MiAP1-1 caused the side branch flower organs mutate, while MiAP1-2 produced terminal flowers in the main stem shoots and also in the side branch. Several floral integrator genes were upregulated in the overexpression transgenic plant lines. These observations indicated that the two MiAP1 homologue genes in mango functions in the floral transition and floral organ development.

Flowering and nutritional status of Gladiolus hybridus L. 'Black Velvet' following gibberellin treatment

Flowering and nutritional status in Gladiolus hybridus L. ‘Black Velvet’ were assessed following gibberellic acid treatment (GA&lt;sub&gt;3&lt;/sub&gt;). Treatment were applied to corm (12–14 diameter) by soaking for 30 min in water solutions of GA&lt;sub&gt;3&lt;/sub&gt; at 100, 350 and 600 mg/dm&lt;sup&gt;3 &lt;/sup&gt;with a control consisting of soaking-in water. All GA&lt;sub&gt;3&lt;/sub&gt; treatments inhibited elongation of inflorescence shoots and stimulated spike elongation. None of the tested concentrations affected the number of developing flowers in the spike, except for the 100 mg/dm&lt;sup&gt;3&lt;/sup&gt; in the 2nd year of the study. All GA&lt;sub&gt;3&lt;/sub&gt; treatments stimulated calcium uptake, but had no effect on the uptake of other macronutrients. All the GA&lt;sub&gt;3&lt;/sub&gt; treatments increased manganese content in leavesbud did not affect copper content. GA&lt;sub&gt;3&lt;/sub&gt; at 600 mg/dm&lt;sup&gt;3&lt;/sup&gt; stimulated uptake of iron and boron at 600 mg/dm&lt;sup&gt;3&lt;/sup&gt; but inhibited both at lower concentrations. Zinc uptake was stimulated at 100 mg/dm&lt;sup&gt;3 &lt;/sup&gt;but inhibited at higher concentration.

Monoecious Mutant Reveals New Insights into Male and Female Inflorescence Development in the Chinese Bayberry (Morella rubra)

To identify the dynamic differences in transcriptome and gene expression in chinese bayberry flowers of different sex types, the female ‘Fugong-1’ (WT) and its monoecious mutant (MT) were used as experimental materials. Using Illumina HiSeq™ 2500, flowers at the inflorescence germination, inflorescence elongation, and initial flowering stages were sequenced by RNA-seq technology and 6 libraries were obtained. After sequence assemble, 84,945 unigenes greater than 200 bp were found and the total length was 71.66 Mb. Transcriptomic expression analysis of the six libraries indicated that there was only 297 genes showed different expression at the inflorescence germination stage between MT and WT, the difference of which was the minimum. At the elongation stage and the initial flowering stage, such numbers increased to 787 and 2722, respectively. Gene ontology (GO) functional enrichment analysis revealed that the enriched differentially expressed genes (DEGs) included those related with transcription in DNA-templated (GO: 0006355), pollen exine formation (GO: 0010584), plasma membrane (GO: 0005886), sequence-specific DNA binding transcription factor activity (GO: 0003700), and 2-alkenal reductase [NAD(P)] activity (GO: 0032440) GO categories, etc. Among these processes, pollen exine formation plays an important role in pollen cell wall synthesis and sporopollen participates in the biosynthesis of sporopollenin. High expression levels of these related genes were closely related to the MT’s male flower traits during the initial flowering stage, which resulted in the male characteristics in MT flower. This study provides important foundation for further mining important genes and regulating factors controlling the sex differentiation of flowers in chinese bayberry.

Can a high red: Far red ratio replace temperature-induced inflorescence development in Phalaenopsis?

Phalaenopsis is one of the most economically important ornamental crops in the Netherlands, but due to its growth requirements during its various developmental stages, it is a costly crop to grow in terms of energy. Warming the greenhouse in the winter during the vegetative phase, and cooling the greenhouse to 19°C in the summer to induce flowering costs a great deal of energy. Because flower induction is primarily controlled by altering the balance of plant hormones, it might well be possible to steer flower induction by changing the light spectrum instead of changing the temperature. The objective of the present study was to investigate the role of the light spectrum on bud break and inflorescence elongation in Phalaenopsis. To this end an experiment was designed with two Phalaenopsis cultivars, Quincy and Red Stones in a matrix of temperature and spectral treatments. Light treatments were used with a relatively high red to far-red ratio (R:FR) and therefore a high phytochrome photostationary state (PSS) value of 0.85, and with a relatively lower R:FR ratio resulting in a PSS value of 0.71, similar to that of natural daylight. Our hypothesis was that low temperature treatments can, at least partially, be substituted by a light spectrum with a high PSS value in order to suppress apical dominance of the primary flowering inflorescence and thus realize multiple inflorescences. A cooling period (19°C) of 8 weeks always resulted in a high percentage of multiple inflorescences, both from Red Stones as well as Quincy. This implies that a flower induction period of 8 weeks with cooling is effective, regardless of the light spectrum. An induction period of 8 weeks with “red light” always resulted in a high percentage of multiple inflorescences, regardless of the temperature (19 or 22°C). A cooling period (19°C) of 4 weeks followed by 4 weeks 22°C only resulted in a higher percentage of multiple inflorescences under the light spectrum with a high PSS value during the second 4 week-period. This suggests that the plant hormones responsible for bud break and inflorescence elongation, can be stimulated by light with a high PSS value, as well as by a cool phase. In order to stimulate multiple flowering inflorescences, the temperature and/or light spectrum during the second 4-week-period appears to be more important than during the first 4-week-period of the induction phase. Presumably this is due to suppression of the apical dominance of the first emerging inflorescence by low temperature and/or relatively high R:FR ratio during this phase. This also implies that the energy costly cool-induction period during the summer can be replaced, at least in part, by red light or a relatively high R:FR.

EFFECT OF UNICONAZOLE ON FLOWERING, YIELD AND FRUIT QUALITY ON DURIAN

This study was aimed to investigate the effect of uniconazole (UCZ) on inducing early flowering, fruit yield and quality in durian cultivar ‘Monthong’. In the 1st year, a single foliar spray at a high concentration of 2,500 mg L-1 UCZ was made, compared to multiply sprays of 1.5 mg L-1 brown seaweed extracts, a conventionally used solution. The results showed that UCZ sprayed at mature leaf stage after 2nd leaf flushing could hasten flower emergence. UCZ very strongly inhibited inflorescence length, shortening the fruit stalk. There was no significant effect of UCZ on fruit yield but UCZ reduced fruit size. Analysis of fresh fruit showed that UCZ decreased both fresh weight and normal seeds. In vivo pollen germination, observation showed that UCZ delayed pollen tube growth. In the 2nd year, the experiment was conducted to find a suitable concentration for early durian fruiting. Lower concentrations of UCZ could induce both early flowering and more flowering branches than non-chemical application. All lower concentrations of UCZ had no effect on fruit yield. Spraying of 100 mg L-1 UCZ had no effect on suppression of inflorescence elongation and fruit size. UCZ at 250 and 500 mg L-1 inhibited only fruit width, whereas no other fruit size characteristics were suppressed. All lower concentration of UCZ decreased both fresh weight and the number of normal seeds. These results suggest that UCZ promoted flowering in durian by shortening the time of bud release. The reduction of pollen tube growths caused by UCZ could be attributed to the inhibition of normal seed development. We recommended the lower concentration of UCZ at 100 mg L-1 for early durian production.

Effects of Paclobutrazol Sprays on Inflorescences of Three Potted Moth Orchid Clones

Inflorescences of some moth orchid (Phalaenopsis and Doritaenopsis) hybrids can become very tall, which can pose shipping challenges for commercial producers and be unwieldy for consumers. We determined the efficacy of paclobutrazol as a foliar spray to inhibit inflorescence elongation of these genera and intergeneric hybrids. A single application of 15, 30, or 45 mg·L−1 palcobutrazol at a volume of 0.2 L·m−2 was applied to Doritaenopsis Miss Saigon, Doritaenopsis Andrew, and Phalaenopsis ‘Smart Thing’ grown at 23 °C to induce flowering. Applications were made after inflorescence emergence but before flower initiation (inflorescences were 1 to 2 cm long) or after flower initiation (inflorescences were 10 to 18 cm long). None of the paclobutrazol applications inhibited total inflorescence elongation of ‘Smart Thing’ or Miss Saigon. However, paclobutrazol inhibited inflorescence elongation from treatment until first flowering of Andrew by 19% to 23% when plants were treated with 15 or 45 mg·L−1 before flower initiation and 30 or 45 mg·L−1 after flower initiation. One or more concentrations of paclobutrazol applied after flower initiation reduced the length of the internode between the first and second flower on all three orchid clones. Paclobutrazol delayed flowering only on Miss Saigon (by 2 days) and only when applied after flower initiation. Paclobutrazol application did not affect the number of inflorescences or flowers, diameter of the first flower, number of new leaves formed, or increase in leaf span. Growers are advised to perform small-scale trials with paclobutrazol solutions starting at 30 to 45 mg·L−1 within 1 week of inflorescence emergence, although higher concentrations may be appropriate for the most vigorous varieties. Furthermore, a late spray application can cause unwanted crowding of the flowers.

ENVIRONMENTAL AND HORMONAL REGULATION OF FLOWERING IN PHALAENOPSIS ORCHIDS: A MINI REVIEW

Phalaenopsis, Doritaenopsis, and their related hybrids are the most common commercially produced flowering potted orchids. Temperature regulates flower initiation and development of Phalaenopsis; inflorescence initiation (sometimes referred to as spiking) occurs in mature plants after at least 2 to 4 weeks of temperatures below 26°C under otherwise favorable conditions. Flowering of many hybrids is increasingly delayed as the daily duration at ≥28°C increases and can be completely suppressed with extended high-temperature exposure. Once an inflorescence has developed, time to open flower is a function of temperature and variety. Exogenous application of gibberellic acid (GA) can be used to increase inflorescence length, but more commonly, chemicals that inhibit the biosynthesis of active GA are used to suppress inflorescence elongation. In addition, cytokinins such as benzyladenine can increase inflorescence number of Phalaenopsis when applied near the onset of exposure to inductive temperatures. However, in some hybrids, inflorescences can develop abnormally if cytokinins are applied at an excessive rate or after flower initiation. Collectively, commercial producers of Phalaenopsis and their related hybrids can manipulate flowering by controlling temperature and applying chemicals that influence endogenous hormone levels to produce architecturally desirable and floriferous plants for predetermined market dates.

Development and morphology of flowers and inflorescences in Balanophora papuana and B. elongata (Balanophoraceae)

Extreme modification and reduction in floral morphology presents an obstacle to determining the evolutionary relationships and homologies of the holoparasites in Balanophoraceae. Developing flowers and inflorescences of two dioecious species, Balanophora papuana and B. elongata, were compared to each other and to the monoecious B. fungosa. Intermingled with flowers in the male inflorescences are bracts (B. elongata) or bract parts (B. papuana). In the latter, early cessation of bract tip growth results in two half-bracts, which become displaced during inflorescence elongation, thus disproving the view that these bract-like structures are axial in nature. Male flower primordia emerge in positions axillary to the dividing bracts, and both arise in a spiral sequence. This pattern is modified in B. papuana by the formation of pseudowhorls of four. In both species, the staminate flowers consist of a generally four-merous perianth and a synandrium of congenitally fused stamens. Male flower and bract ontogeny (but not pollen sacs) conform to patterns seen in other angiosperms. More problematic are the carpellate flowers whose primordia arise in irregular order between club-shaped, radially symmetrical organs called claviform bodies. The interpretation that these bodies are homologous to the peltate bracts of Helosideae appears plausible, but cannot explain their nonspiral initiation and radial symmetry.

Interactions of temperature and photoperiod in the control of flowering of latitudinal and altitudinal populations of wild strawberry (Fragaria vesca)

Floral induction and development requirements of a range of latitudinal and altitudinal Norwegian populations of the wild strawberry Fragaria vesca L. have been studied in controlled environments. Rooted runner plants were exposed to a range of photoperiods and temperatures for 5 weeks for floral induction and then transferred to long day (LD) at 20°C for flower development. A pronounced interaction of temperature and photoperiod was shown in the control of flowering. At 9°C, flowers were initiated in both short day (SD) and LD conditions, at 15 and 18°C in SD only, whereas no initiation took place at 21°C regardless of daylength conditions. The critical photoperiod for SD floral induction was about 16 h and 14 h at 15 and 18°C, respectively, the induction being incomplete at 18°C. The optimal condition for floral induction was SD at 15°C. A minimum of 4 weeks of exposure to such optimal conditions was required. Although the populations varied significantly in their flowering performance, no clinal relationship was present between latitude of origin and critical photoperiod. Flower development of SD‐induced plants was only marginally advanced by LD conditions, while inflorescence elongation and runnering were strongly enhanced by LD at this stage. The main shift in these responses took place at photoperiods between 16 and 17 h. Unlike all other populations studied, a high‐latitude population from 70°N (‘Alta’) had an obligatory vernalization requirement. Although flowering and fruiting in its native Subarctic environment and after overwintering in the field in south Norway, this population did not flower in the laboratory in the absence of vernalization, even with 10 or 15 weeks of exposure to SD at 9°C. Flowering performance in the field likewise indicated a vernalization requirement of this high‐latitude population.

The BIG gene is involved in regulation of sulfur deficiency‐responsive genes in Arabidopsis thaliana

The Arabidopsis thaliana mutants altered sulfur response 1‐1 (asr1‐1) and asr1‐2 were isolated using the green fluorescent protein gene (GFP), as a marker, driven by a sulfur deficiency‐responsive promoter containing the βSR fragment, which is responsible for the induction of gene expression under sulfur deficiency. In the asr1 mutants, the expression of three sulfur deficiency‐responsive genes βSR‐driven GFP, sulfate transporter 2;2 (SULTR2;2) and adenosine‐5′‐phosphosulfate reductase 1 (APR1) were induced in medium containing a normal sulfate concentration. The ASR1 locus was mapped to a 53‐kb region on the upper arm of chromosome III; this is also the region of the BIG gene, which encodes a calossin‐like protein necessary for the polar transport of auxin. The morphology of the asr1 mutants, i.e. reduced leaf size and inflorescence elongation, resembled that of big mutants. Using nucleotide sequence analysis of the BIG gene, we identified independent nonsense mutations in asr1‐1 and asr1‐2. To confirm that ASR1 was BIG, we established lines of transgenic A. thaliana carrying a transfer DNA (T‐DNA) insertion in the BIG gene. In these T‐DNA insertion mutants, mRNA levels of βSR‐driven GFP and APR1 were upregulated in normal sulfate medium. The F1 plants from crosses between asr1‐1 and T‐DNA insertion lines exhibited reduced leaf size and inflorescence length, indicating that ASR1 was indeed BIG. Taken together, the present results established that BIG is involved in the regulation of βSR‐driven GFP and APR1 mRNA level gene expression. Indole‐3‐acetic acid also upregulated βSR‐driven GFP and APR1 together with SULTR2;2 mRNA level, suggesting that the big effect on βSR‐driven GFP and APR1 is a pleiotropic aspect of the BIG gene.

AtVAM3 is Required for Normal Specification of Idioblasts, Myrosin Cells

Myrosin cells in Capparales plants are idioblasts that accumulate thioglucoside glucohydrolase (TGG, also called myrosinase), which hydrolyzes glucosinolates to produce toxic compounds for repelling pests. Here, we show that AtVAM3 is involved in development of myrosin cells. It has been shown that yeast VAM3 is a Q(a)-SNARE that is involved in vesicle transport of vacuolar proteins and vacuolar assembly. We found that two Arabidopsis atvam3 alleles, atvam3-3 and atvam3-4/ssm, accumulate large amounts of TGG1 and TGG2 that are enzymatically active. An immunogold analysis revealed that TGGs were specifically localized in the vacuole of myrosin cells in atvam3 mutants. This result indicates that TGGs are normally transported to vacuoles in these mutants and that AtVAM3 is not essential for vacuolar transport of the proteins. We developed a staining method with Coomassie brilliant blue that detects myrosin cells in whole leaves by their high TGG content. This method showed that atvam3 leaves have a larger number of myrosin cells than do wild-type leaves. Myrosin cells were scattered along leaf veins in wild-type leaves, while they were abnormally distributed in atvam3 leaves. The mutants developed a network of myrosin cells throughout the leaves: myrosin cells were not only distributed continuously along leaf veins, but were also observed independent of leaf veins. The excess of myrosin cells in atvam3 mutants might be responsible for the abnormal abundance of TGGs and the reduction of elongation of inflorescence stems and leaves in these mutants. Our results suggest that AtVAM3 has a plant-specific function in development of myrosin cells.

Relationships of disease and leaf area variables with yield in the Alternaria helianthi–sunflower pathosystem

Three field experiments were carried out in 1997/1998, 1998/1999 and 1999/2000 to investigate the relationship between severity (S) of alternaria leaf spot, caused by Alternaria helianthi, area under disease progress curve (AUDPC), healthy leaf area index at any given day (HLAI), healthy leaf area duration (HAD), radiation intercepted by healthy leaf area at any given day (HRI), total healthy leaf area absorption (HAA), and yield components of sunflower sown on four dates. AUDPC showed a relationship with yield in two years, following the negative exponential model coefficient of determination (R2 = 0·79 and 0·60). The HAD–yield relationship was linear for each of three trials (0·73 &lt; R2 &lt; 0·83). Among the integral variables analysed, the HAA–yield relationship was the best, fitted by the exponential model (0·77 &lt; R2 &lt; 0·89). Single‐point models using disease severity, HLAI and HRI to estimate yield at various times during the crop season were tested. The slope of the severity–yield relationship was stable from the R1 (inflorescence visible) growth stage. The HLAI–yield relationship was stable between R1 and R6 (anthesis completed) and increased from the R7 (first phase of achene development) stage. The HRI–yield relationship was variable and not stable. The relationship between severity and yield in the R3 (second phase of inflorescence elongation) growth stage proved that plants with disease severity higher than 10% had yield lower than 500 kg ha−1, regardless of the sowing date. This value can be used as a damage threshold for the disease. Disease severity can be used as an independent variable in a sunflower–alternaria leaf spot management system and can be used to produce recommendations at the research level, such as genetic breeding for disease resistance or studies on sowing date.