Young Leaf Primordia Research Articles

Vitrification cryo-foil method for shoot tip cryopreservation and virus eradication in apple

Establishment of a new method for improved shoot tip cryopreservation is crucial to facilitate the long-term preservation of plant germplasm as well as the use of cryotherapy for pathogen eradication. The present study reported a vitrification (V) cryo-foil method for shoot tip cryopreservation and virus eradication in apple. Shoot tip regrowth levels after cryopreservation were comparable among V cryo-foil (53 %), V cryo-plate (46 %) and conventional droplet vitrification (Dr-vi, 48 %). The V cryo-foil is more efficient to perform than Dr-vi as more shoot tips can be cryopreserved by one person. In the histological study applying an image-overlaying strategy, shoot tips cryopreserved by V cryo-foil showed a higher survival chance in the youngest leaf primordia than in the apical dome. When V cryo-foil was tested for virus eradication, fifty-five percent (55 %) of cryo-derived shoots were free of the apple stem pitting virus (ASPV), while none and less than 10 % were free of the apple stem grooving virus (ASGV) and the apple chlorotic leaf spot virus (ACLSV), respectively. Thus, these two viruses were efficiently preserved by V cryo-foil cryopreservation. Noticeably, although the shoot regrowth level was reduced to 27 %, a higher frequency (81 %) of ASPV eradication was achieved when a reduced duration of cryoprotectant exposure was applied in V cryo-foil, supporting the use of insufficient cryoprotection for improved virus eradication.

Cellular insights of beech leaf disease reveal abnormal ectopic cell division of symptomatic interveinal leaf areas.

The beech leaf disease nematode, Litylenchus crenatae subsp. mccannii, is recognized as a newly emergent nematode species that causes beech leaf disease (BLD) in beech trees (Fagus spp.) in North America. Changes of leaf morphology before emergence from the bud induced by BLD can provoke dramatic effects on the leaf architecture and consequently to tree performance and development. The initial symptoms of BLD appear as dark green, interveinal banding patterns of the leaf. Despite the fast progression of this disease, the cellular mechanisms leading to the formation of such aberrant leaf phenotype remains totally unknown. To understand the cellular basis of BLD, we employed several types of microscopy to provide an exhaustive characterization of nematode-infected buds and leaves. Histological sections revealed a dramatic cell change composition of these nematode-infected tissues. Diseased bud scale cells were typically hypertrophied and showed a high variability of size. Moreover, while altered cell division had no influence on leaf organogenesis, induction of cell proliferation on young leaf primordia led to a dramatic change in cell layer architecture. Hyperplasia and hypertrophy of the different leaf cell layers, coupled with an abnormal proliferation of chloroplasts especially in the mesophyll cell layers, resulted in the typical interveinal leaf banding. These discrepancies in leaf cell structure were depicted by an abnormal rate of cellular division of the leaf interveinal areas infected by the nematode, promoting significant increase of cell size and leaf thickness. The formation of symptomatic BLD leaves is therefore orchestrated by distinct cellular processes, to enhance the value of these feeding sites and to improve their nutrition status for the nematode. Our findings thus uncover relevant cellular events and provide a structural framework to understand this important disease.

FLOWERING REPRESSOR AAA+ ATPase 1 is a novel regulator of perennial flowering in Arabis alpina.

Arabis alpina is a polycarpic perennial, in which PERPETUAL FLOWERING1 (PEP1) regulates flowering and perennial traits in a vernalization-dependent manner. Mutagenesis screens of the pep1 mutant established the role of other flowering time regulators in PEP1-parallel pathways. Here we characterized three allelic enhancers of pep1 (eop002, 085 and 091) which flower early. We mapped the causal mutations and complemented mutants with the identified gene. Using quantitative reverse transcriptase PCR and reporter lines, we determined the protein spatiotemporal expression patterns and localization within the cell. We also characterized its role in Arabidopsis thaliana using CRISPR and in A. alpina by introgressing mutant alleles into a wild-type background. These mutants carried lesions in an AAA+ ATPase of unknown function, FLOWERING REPRESSOR AAA+ ATPase 1 (AaFRAT1). AaFRAT1 was detected in the vasculature of young leaf primordia and the rib zone of flowering shoot apical meristems. At the subcellular level, AaFRAT1 was localized at the interphase between the endoplasmic reticulum and peroxisomes. Introgression lines carrying Aafrat1 alleles required less vernalization to flower and reduced number of vegetative axillary branches. By contrast, A. thaliana CRISPR lines showed weak flowering phenotypes. AaFRAT1 contributes to flowering time regulation and the perennial growth habit of A. alpina.

Early leaf development in Euterpe oleracea Mart. (Arecaceae, Arecoideae): Leaflets, pinnae or segments?1

Euterpe oleracea presents long leaves with divisions in the blade frequently referred to as leaflets or pinnae, as if they were compound. The purpose of this article is to present the first leaf ontogeny study for this species. Buds of dissected E. oleracea were classified according to their size and morphology and examined under scanning electron and light microscopy. The youngest leaf primordia are conical. The first foldings in the leaf blade appear in primordia ca. 0.8 mm in length and already have procambium. When young leaves reach 1.5 mm long, these plications separate from one another. Segments change their orientation throughout leaf development. Leaf blade in E. oleracea is initially entire (nonplicate), becoming plicate at a later stage, and plications separate from each other as a final step. This developmental process has some similarities with what is observed in other palm species. According to early stages of the leaf ontogeny, these plants have simple pinnatisect and not compound pinnate leaves. The use of terminology such as “leaflets” or “pinnae” is incongruent with simple leaves, and we recommend that adult leaf blade subdivisions of Arecaceae should be called “leaf segments” instead. This work contributed to the understanding of histological changes during palm leaf development, being a contemporary report on both histological and micromorphological study on palm leaf ontogeny.

Reflections on the Triptych of Meristems That Build Flowering Branches in Tomato.

Branching is an important component determining crop yield. In tomato, the sympodial pattern of shoot and inflorescence branching is initiated at floral transition and involves the precise regulation of three very close meristems: (i) the shoot apical meristem (SAM) that undergoes the first transition to flower meristem (FM) fate, (ii) the inflorescence sympodial meristem (SIM) that emerges on its flank and remains transiently indeterminate to continue flower initiation, and (iii) the shoot sympodial meristem (SYM), which is initiated at the axil of the youngest leaf primordium and takes over shoot growth before forming itself the next inflorescence. The proper fate of each type of meristems involves the spatiotemporal regulation of FM genes, since they all eventually terminate in a flower, but also the transient repression of other fates since conversions are observed in different mutants. In this paper, we summarize the current knowledge about the genetic determinants of meristem fate in tomato and share the reflections that led us to identify sepal and flower abscission zone initiation as a critical stage of FM development that affects the branching of the inflorescence.

Network analyses identify a transcriptomic proximodistal prepattern in the maize leaf primordium.

The formation of developmental boundaries is a common feature of multicellular plants and animals, and impacts the initiation, structure and function of all organs. Maize leaves comprise a proximal sheath that encloses the stem, and a distal photosynthetic blade that projects away from the plant axis. An epidermally derived ligule and a joint-like auricle develop at the blade/sheath boundary of maize leaves. Mutations disturbing the ligule/auricle region disrupt leaf patterning and impact plant architecture, yet it is unclear how this developmental boundary is established. Targeted microdissection followed by transcriptomic analyses of young leaf primordia were utilized to construct a co-expression network associated with development of the blade/sheath boundary. Evidence is presented for proximodistal gradients of gene expression that establish a prepatterned transcriptomic boundary in young leaf primordia, before the morphological initiation of the blade/sheath boundary in older leaves. This work presents a conceptual model for spatiotemporal patterning of proximodistal leaf domains, and provides a rich resource of candidate gene interactions for future investigations of the mechanisms of blade/sheath boundary formation in maize.

Rapid, high efficiency virus-mediated mutant complementation and gene silencing in Antirrhinum

BackgroundAntirrhinum (snapdragon) species are models for genetic and evolutionary research but recalcitrant to genetic transformation, limiting use of transgenic methods for functional genomics. Transient gene expression from viral vectors and virus-induced gene silencing (VIGS) offer transformation-free alternatives. Here we investigate the utility of Tobacco rattle virus (TRV) for homologous gene expression in Antirrhinum and VIGS in Antirrhinum and its relative Misopates.ResultsA. majus proved highly susceptible to systemic TRV infection. TRV carrying part of the Phytoene Desaturase (PDS) gene triggered efficient PDS silencing, visible as tissue bleaching, providing a reporter for the extent and location of VIGS. VIGS was initiated most frequently in young seedlings, persisted into inflorescences and flowers and was not significantly affected by the orientation of the homologous sequence within the TRV genome. Its utility was further demonstrated by reducing expression of two developmental regulators that act either in the protoderm of young leaf primordia or in developing flowers. The effects of co-silencing PDS and the trichome-suppressing Hairy (H) gene from the same TRV genome showed that tissue bleaching provides a useful marker for VIGS of a second target gene acting in a different cell layer. The ability of TRV-encoded H protein to complement the h mutant phenotype was also tested. TRV carrying the native H coding sequence with PDS to report infection failed to complement h mutations and triggered VIGS of H in wild-type plants. However, a sequence with 43% synonymous substitutions encoding H protein, was able to complement the h mutant phenotype when expressed without a PDS VIGS reporter.ConclusionsWe demonstrate an effective method for VIGS in the model genus Antirrhinum and its relative Misopates that works in vegetative and reproductive tissues. We also show that TRV can be used for complementation of a loss-of-function mutation in Antirrhinum. These methods make rapid tests of gene function possible in these species, which are difficult to transform genetically, and opens up the possibility of using additional cell biological and biochemical techniques that depend on transgene expression.

Simple and Divided Leaves in Ferns: Exploring the Genetic Basis for Leaf Morphology Differences in the Genus Elaphoglossum (Dryopteridaceae).

Despite the implications leaves have for life, their origin and development remain debated. Analyses across ferns and seed plants are fundamental to address the conservation or independent origins of megaphyllous leaf developmental mechanisms. Class I KNOX expression studies have been used to understand leaf development and, in ferns, have only been conducted in species with divided leaves. We performed expression analyses of the Class I KNOX and Histone H4 genes throughout the development of leaf primordia in two simple-leaved and one divided-leaved fern taxa. We found Class I KNOX are expressed (1) throughout young and early developing leaves of simple and divided-leaved ferns, (2) later into leaf development of divided-leaved species compared to simple-leaved species, and (3) at the leaf primordium apex and margins. H4 expression is similar in young leaf primordia of simple and divided leaves. Persistent Class I KNOX expression at the margins of divided leaf primordia compared with simple leaf primordia indicates that temporal and spatial patterns of Class I KNOX expression correlate with different fern leaf morphologies. However, our results also indicate that Class I KNOX expression alone is not sufficient to promote divided leaf development in ferns. Class I KNOX patterns of expression in fern leaves support the conservation of an independently recruited developmental mechanism for leaf dissection in megaphylls, the shoot-like nature of fern leaves compared with seed plant leaves, and the critical role marginal meristems play in fern leaf development.

Following Spatial Distribution of Photosynthetic Pigments Across the Development of a Leaf using Hyperspectral Fluorescence Microscopy

Leaves on plants undergo a transition from a sink (a net carbon importer) to a source (a net carbon exporter) during their development. This conversion from sink to a photosynthetic source marks a fundamental transition in the physiology of the leaf, profoundly altering the carbohydrate metabolism and acting as one of the major determinants of plant performance. Hence a considerable amount of study is underway to understand its biochemical and structural characteristics. In plants, the process by which undifferentiated plastids differentiate into mature functional chloroplasts begins in the shoot apical meristem (SAM) and young leaf primordia (sink tissue), and continues along leaf development. In this work, we follow the spatial distribution of these plastids and their abundance of photosynthetic pigments in a gradient from sink to source by imaging laser induced fluorescence using a home-built laser scanning hyperspectral microscope. The line-scanning hyperspectral microscope combines fast scanning with optical sectioning to record 4-D datasets with spatial (x, y, z) and spectral (λ) information. We will present three dimensional observations of photosynthetic pigment carrying plastids in C4 plants during the different phases of leaf cell development.

Initial proplastid-to-chloroplast differentiation in the developing vegetative shoot apical meristem of Arabidopsis

In dicot plants, the process by which undifferentiated plastids, termed proplastids, differentiate into mature functional chloroplasts begins in the shoot apical meristem (SAM) and young leaf primordia, and continues along leaf development. In this work, we followed initial chloroplast biogenesis in cells of the SAM in Arabidopsis, during the early stages of germination, using chlorophyll fluorescence as a marker. We found that cells bound to form the SAM in the mature seed embryo lack chlorophyll, while plastids in the rest of the embryo cells are somewhat developed. The initial appearance of chlorophyll in the SAM occurred two days after the onset of germination, was not expedited by higher light intensities, and required a light period of between five to ten hours within these two days. In addition, we found that biogenesis of chloroplasts occurred only in the upper layer of the SAM, as opposed to the two central subtending cell layers. This pattern was maintained, mirroring the developmental status of plastids in the mature vegetative SAM. The work also presents another model for studying proplastid-to-chloroplast development, in which differentiation can be followed in SAM cells in a defined time-wise fashion.

Photosynthesis in Ranunculus asiaticus L.: The Influence of the Hybrid and the Preparation Procedure of Tuberous Roots.

Ranunculus asiaticus L. is a quantitative long-day geophyte, grown in a cold greenhouse for cut flowers and potted plants. Flowering in ranunculus is a complex process, strongly steered by temperature and photoperiodism. Vernalization of rehydrated tuberous roots anticipate sprouting and leaf rosette formation and flowering. It is known that the time for flowering and the sensitivity to cold treatment, in terms of flowering anticipation, varies in numerous hybrids, while no information seems to be available on the influence of hybrids and on the vernalization on the photosynthetic process and primary metabolite profiling. We investigated the influence of two ranunculus hybrids, MDR and MBO, and two preparation procedures of tuberous roots, only rehydration (Control, C) and rehydration followed by vernalization (V), on the photosynthesis and photochemistry of plants grown in a climatic chamber, under a controlled environment. In addition, in MBO plants, in which the vernalization showed the main effects, carbohydrate, amino acid and protein levels were also investigated. In control plants, the response of leaf photosynthesis, to increasing white light, revealed higher photosynthetic activity in MDR than in MBO. The quantum yield of PSII (ϕPSII), electron transport rate (ETR) and non-photochemical quenching (NPQ) did not differ between the two hybrids. The maximal photochemical efficiency (Fv/Fm) was higher in MBO than in MDR and showed a decrease in both hybrids after vernalization. The preparation treatment of propagation material affected the light response of photosynthesis in the two hybrids differently, which increased in plants from vernalized tuberous roots, compared to those from only rehydrated in MBO and decreased in MDR, in accordance to the effects of vernalization observed in leaf photosynthetic pigments. In MBO vernalized tuberous roots, starch was rapidly degraded, and the carbon skeletons used to synthesize amino acids. Control plants of MBO, developed more leaves than those of MDR and a consequent larger plant leaf area. Compared to only rehydration, vernalization of rehydrated tuberous roots increased the plant leaf area in both the hybrids. Compared to the control, vernalized tuberous roots of MBO showed higher concentrations of sucrose and free amino acids, which could act as a long-distance signal promoting floral transition in young leaf primordia.

Model for the role of auxin polar transport in patterning of the leaf adaxial-abaxial axis.

Leaf adaxial-abaxial polarity refers to the two leaf faces, which have different types of cells performing distinct biological functions. In 1951, Ian Sussex reported that when an incipient leaf primordium was surgically isolated by an incision across the vegetative shoot apical meristem (SAM), a radialized structure without an adaxial domain would form. This led to the proposal that a signal, now called the Sussex signal, is transported from the SAM to emerging primordia to direct leaf adaxial-abaxial patterning. It was recently proposed that instead of the Sussex signal, polar transport of the plant hormone auxin is critical in leaf polarity formation. However, how auxin polar transport functions in the process is unknown. Through live imaging, we established a profile of auxin polar transport in and around young leaf primordia. Here we show that auxin polar transport in lateral regions of an incipient primordium forms auxin convergence points. We demonstrated that blocking auxin polar transport in the lateral regions of the incipient primordium by incisions abolished the auxin convergence points and caused abaxialized leaves to form. The lateral incisions also blocked the formation of leaf middle domain and margins and disrupted expression of the middle domain/margin-associated marker gene WUSCHEL-RELATED HOMEOBOX 1 (SlWOX1). Based on these results we propose that the auxin convergence points are required for the formation of leaf middle domain and margins, and the functional middle domain and margins ensure leaf adaxial-abaxial polarity. How middle domain and margins function in the process is discussed.

A novel role for STOMATAL CARPENTER 1 in stomata patterning.

BackgroundGuard cells (GCs) are specialised cells within the plant epidermis which form stomatal pores, through which gas exchange can occur. The GCs derive through a specialised lineage of cell divisions which is specified by the transcription factor SPEECHLESS (SPCH), the expression of which can be detected in undifferentiated epidermal cells prior to asymmetric division. Other transcription factors may act before GC specification and be required for correct GC patterning. Previously, the DOF transcription factor STOMATAL CARPENTER 1 (SCAP1) was shown to be involved in GC function, by activating a set of GC–specific genes required for GC maturation and activity. It is thus far unknown whether SCAP1 can also affect stomatal development.ResultsHere we show that SCAP1 expression can also be observed in young leaf primordia, before any GC differentiation occurs. The study of transgenic plants carrying a proSCAP1:GUS-GFP transcriptional fusion, coupled with qPCR analyses, indicate that SCAP1 expression peaks in a temporal window which is coincident with expression of stomatal patterning genes. Independent scap1 loss-of-function mutants have a reduced number of GCs whilst SCAP1 over expression lines have an increased number of GCs, in addition to altered GC distribution and spacing patterns. The study of early markers for stomatal cell lineage in a background carrying gain–of–function alleles of SCAP1 revealed that, compared to the wild type, an increased number of protodermal cells are recruited in the GC lineage, which is reflected in an increased number of meristemoids.ConclusionsOur results suggest an early role for SCAP1 in GC differentiation. We propose that a function of SCAP1 is to integrate different aspects of GC biology including specification, spacing, maturation and function.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0851-z) contains supplementary material, which is available to authorized users.

The INDETERMINATE DOMAIN Protein BROAD LEAF1 Limits Barley Leaf Width by Restricting Lateral Proliferation

Variation in the size, shape, and positioning of leaves as the major photosynthetic organs strongly impacts crop yield, and optimizing these aspects is a central aim of cereal breeding [1, 2]. Leaf growth in grasses is driven by cell proliferation and cell expansion in a basal growth zone [3]. Although several factors influencing final leaf size and shape have been identified from rice and maize [4-14], what limits grass leaf growth in the longitudinal or transverse directions during leaf development remains poorly understood. To identify factors involved in this process, we characterized the barley mutant broad leaf1 (blf1). Mutants form wider but slightly shorter leaves due to changes in the numbers of longitudinal cell files and of cells along the leaf length. These differences arise during primordia outgrowth because of more cell divisions in the width direction increasing the number of cell files. Positional cloning, analysis of independent alleles, and transgenic complementation confirm that BLF1 encodes a presumed transcriptional regulator of the INDETERMINATE DOMAIN family. In contrast to loss-of-function mutants, moderate overexpression of BLF1 decreases leaf width below wild-type levels. A functional BLF1-vYFP fusion protein expressed from the endogenous promoter shows a dynamic expression pattern in the shoot apical meristem and young leaf primordia. Thus, we propose that the BLF1 gene regulates barley leaf size by restricting cell proliferation in the leaf-width direction. Given the agronomic importance of canopy traits in cereals, identifying functionally different BLF1 alleles promises to allow for the generation of optimized cereal ideotypes.

Callose Deposition in Plasmodesmata and Viroid Invasion of the Shoot Apical Meristem.

Callose Deposition in Plasmodesmata and Viroid Invasion of the Shoot Apical Meristem.

Three vitrification-based cryopreservation procedures cause different cryo-injuries to potato shoot tips while all maintain genetic integrity in regenerants

We previously reported successful cryopreservation of shoot tips of potato ‘Zihuabai’ by three vitrification-based protocols. In the present study, cryo-injury to shoot tips and genetic stability in regenerants recovered from cryopreserved shoot tips by the three vitrification-based protocols were further investigated. The results showed that sucrose preculture caused no obviously different injuries, while dehydration with plant vitrification solution 2 (PVS2) was the step causing major damage to cells of shoot tips, regardless of the cryogenic procedures. Compared with droplet-vitrification and encapsulation–vitrification, vitrification caused the most severe injury to cells of the shoot tips, thus resulting in much longer time duration for shoot recovery and much lower shoot regrowth rate. Cells in apical dome and the youngest leaf primordia were able to survive and subsequently some of them regrew into shoots following all three vitrification-based cryopreservation procedures. Analyses using inter-simple sequence repeat (ISSR) and amplified fragment length polymorphism (AFLP) markers in shoots regrown from all three vitrification-based protocols did not find any polymorphic bands. The results reported here suggest that vitrification-based cryo-procedures can be considered promising methods for long-term preservation of potato genetic resources.

Invasion of shoot apical meristems by Chrysanthemum stunt viroid differs among Argyranthemum cultivars.

Chrysanthemum stunt viroid (CSVd) is a damaging pathogen attacking Argyranthemum plants. Our study attempted to reveal distribution patterns of CSVd in shoot apical meristems (SAM) and to explore reasons for differential ability of CSVd to invade SAM of selected Argyranthemum cultivars. Symptom development was also observed on greenhouse-grown Argyranthemum plants. Viroid localization using in situ hybridization revealed that the ability of CSVd to invade SAM differed among cultivars. In diseased ‘Yellow Empire’ and ‘Butterfly’, CSVd was found in all tissues including the uppermost cell layers in the apical dome (AD) and the youngest leaf primordia 1 and 2. In diseased ‘Border Dark Red’ and ‘Border Pink’, CSVd was detected in the lower part of the AD and elder leaf primordia, leaving the upper part of the AD, and leaf primordia 1 and 2 free of viroid. Histological observations and transmission electron microscopy showed similar developmental patterns of vascular tissues and plasmodesmata (PD) in the SAM of ‘Yellow Empire’ and ‘Border Dark Red’, while immunolocalization studies revealed a major difference in the number of callose (β-1, 3-glucan) particles deposited at PD in SAM. A lower number of callose particles were found deposited at PD of SAM of ‘Yellow Empire’ than ‘Border Dark Red’. This difference is most likely responsible for the differences in ability of CSVd to invade SAM among Argyranthemum cultivars.

The sequence of cell divisions in the I tunic layer of Actinidia arguta Planch in light of the development of twin cell complexes

In <em>Actinidia arguta</em>, the I tunc layer is formed by four cell complexes which descend from single initials. These initials are positioned in a corner of their complex, around the meristem axis. The meristematic activity of the I tunic layer depends on the formative divisions of the initials; the entire I tunic layer above the youngest leaf primordia is formed during the time the initials undergo only 4-8 divisions. In light of the development of the twin cell complexes. it is impossible for cells to be displaced from the I tunic layer into the meristem. The supposition is set forth that the impermanent. mericlinal sectors on variegated perinclinal chimeras develop due to periclinal cleavages within the subcomplexes which derive from tissue mother cells. Whereas. the cell initials do not undergo periclinal divisions and are not displaced.

Distribution of insoluble polysaccharides in the shoot apex of Rhododendron arboreum Linn. during the annual growth cycle

Starch grains occur all over the dormant shoot apex of <em>Rhododendron arboreum</em> except in the bud scales. They are abundant in the peripheral, rib and pith meristem cells. as well as in the youngest leaf primordia. Tannin is present in the entire dormant bud hut for the cells of the apical meristem and leaf primordia. Gradually, tannin degradation into numerous globules occurs. This is concomitant with the disappearance of starch grains and indicates the earliest structural manifestation of spring awakening by meristematic activity in the buds. The weak affinity of tannin globules to PAS is due to their hydrolysis which releases glucose for metabolic activities. Thus, a parallelism seems to exist between the metabolism of tannins and starch in relation to the various phases of bud development.

Ontogenetic variation of phyllotaxis and apex geometry in vegetative shoots of Sedum maximum (L.) Hoffm.

Phyllotaxis of vegetative shoots of <em>Sedum maximum</em> (L.) Hoffm. is variable and unstable. Phyllotactic transitions proceeding either between two whorled, two spiral or a whorled and a spiral pattern occur during shoot ontogeny. A general rule is that in the course of these transitions numbers of contact parastichies increase or much less often diminish. During most common transitions only a single parastichy is added to or subtracted from the already existing contact parastichy pattern. This applies both to the transitions between a spiral and a whorled and to those between two spiral patterns. More parastichies appear only when phyllotaxis changes from one whorled pattern to another. These transitions, however, are the least common in <em>S. maximum</em>. Parameters of apex geometry differ significantly in shoots exhibiting different contact parastichy numbers. The sequence of phyllotactic patterns arranged according to an increasing apical dome area or area ratio, as well as decreasing plastochron ratio (both as defined by Richards) is the same as their sequence based on increasing numbers of contact parastichies. This in turn is the sequence of patterns as they appear during shoot ontogeny. The only parameter which remains relatively constant is the area of the youngest leaf primordium. This implies that during phyllotactic transitions in <em>S. maximum</em> the area ratio changes mainly due to the increase of the apical dome. It seems that in <em>S. maximum</em> this ontogenetic increase of the apical dome, which on the other hand is typical for many plants, somehow differs from these cases where such a change alters only contact parastichy numbers within the same phyllotactic series.