Leaf Blade Formation Research Articles

Polar auxin transport modulates early leaf flattening

The flattened leaf form is an important adaptation for efficient photosynthesis, and the developmental process of flattened leaves has been intensively studied. Classic microsurgery studies in potato and tomato suggest that the shoot apical meristem (SAM) communicates with the leaf primordia to promote leaf blade formation. More recently, it was found that polar auxin transport (PAT) could mediate this communication. However, it is unclear how the expression of leaf patterning genes is tailored by PAT routes originating from SAM. By combining experimental observations and computer model simulations, we show that microsurgical incisions and local inhibition of PAT in tomato interfere with auxin transport toward the leaf margins, reducing auxin response levels and altering the leaf blade shape. Importantly, oval auxin responses result in the bipolar expression of SlLAM1 that determines leaf blade formation. Furthermore, wounding caused by incisions promotes degradation of SlREV, a known regulator of leaf polarity. Additionally, computer simulations suggest that local auxin biosynthesis in early leaf primordia could remove necessity for external auxin supply originating from SAM, potentially explaining differences between species. Together, our findings establish how PAT near emerging leaf primordia determines spatial auxin patterning and refines SlLAM1 expression in the leaf margins to guide leaf flattening.

Interplay between the shoot apical meristem and lateral organs.

Tissues and organs within a living organism are coordinated, but the underlying mechanisms are not well understood. The shoot apical meristem (SAM) continually produces lateral organs, such as leaves, from its peripheral zone. Because of their close proximity, SAM and lateral organs interact during plant development. Existing lateral organs influence the positions of newly formed organs to determine the phyllotaxis. The SAM not only produces lateral organs, but also influences their morphogenesis. In particular, the SAM promotes leaf polarity determination and leaf blade formation. Furthermore, lateral organs help the SAM to maintain homeostasis by restricting stem cell activity. Recent advances have started to elucidate how SAM and lateral organs patterning and growth are coordinated in the shoot apex. In this review, we discuss recent findings on the interaction between SAM and lateral organs during plant development. In particular, polar auxin transport appears to be a commonly used coordination mechanism.

Suppression of Leaf Blade Development by BLADE-ON-PETIOLE Orthologs Is a Common Strategy for Underground Rhizome Growth.

Rhizomes are modified stems that grow horizontally underground in various perennial species, a growth habit that is advantageous for vigorous asexual proliferation. In Oryza longistaminata, a rhizomatous wild relative of cultivated rice (Oryza sativa), leaves in the aerial shoots consist of a distal leaf blade and a proximal leaf sheath [1]. Leaf blade formation is, however, suppressed in rhizome leaves. In O.sativa, BLADE-ON-PETIOLE (BOP) genes are the main regulators of proximal-distal leaf patterning [2]. During the juvenile phase of O.sativa, BOP expression is maintained at high levels by the small regulatory RNA microRNA156 (miR156), leading to formation of leaves consisting predominantly of the sheath. Here, we show that in O.longistaminata, high expression of BOPs caused by miR156 was responsible for suppression of the blade in rhizomes and that bop loss-of-function mutants produced leaves consisting of the leaf blade only. Rhizome growth in soil was also hampered in the mutants due to a severe reduction in rhizome tip stiffness. Leaf blade formation is also suppressed in the stolons of Zoysia matrella, a monocot species, and in the rhizomes of Houttuynia cordata, a dicot species, indicating that leaf blade suppression is widely conserved. We also show that strong expression of BOP homologs in both rhizome and stolon leaves rather than in aerial leaves is another conserved feature. We propose that suppression of the leaf blade by BOP is an evolutionary strategy that has been commonly recruited by both rhizomatous and stoloniferous species to establish their unique growth habit.

The Diverse Roles of Auxin in Regulating Leaf Development.

Leaves, the primary plant organs that function in photosynthesis and respiration, have highly organized, flat structures that vary within and among species. In recent years, it has become evident that auxin plays central roles in leaf development, including leaf initiation, blade formation, and compound leaf patterning. In this review, we discuss how auxin maxima form to define leaf primordium formation. We summarize recent progress in understanding of how spatial auxin signaling promotes leaf blade formation. Finally, we discuss how spatial auxin transport and signaling regulate the patterning of compound leaves and leaf serration.

Effects of light, temperature and nitrogen on Scilla hyacinthoides germination and seedling development

Summary Scilla hyacinthoides (Asparagaceae, subfamily Scilloideae) is a perennial deciduous bulbous geophyte, growing naturally in the Mediterranean region. During recent years in Israel there have been attempts to grow S. hyacinthoides horticulturally as a cut flower or a water-saving garden ornamental. Hence, information on germination and seedling development is timely and much needed for future plant selection. The specific objectives of the present study were to describe germination and seedling development, to define the temperature requirements for germination and growth, and to determine the factors involved in developmental seedling plasticity. S. hyacinthoides seeds exhibit physiological dormancy. Germination was inhibited by light and by high temperatures. The germination is epigeal. High temperatures induced end-of-season seedling dormancy and lead to increased seedling mortality. The cotyledon serves as a photosynthetic leaf, while the leaves lack blades and function as scales. Application of nitrogen compounds changed the axial patterning of leaves by inducing leaf blade formation and increased seedling dry weight. In conclusion, S. hyacinthoides germination and seedling development are highly plastic and are influenced by light, temperature and nitrogen availability. Such plasticity is of great benefit in the unpredictable Mediterranean climate.

Early stages of leaf development in has mutant of Arabidopsis thaliana

The elucidation of molecular mechanisms underlying the leaf development can be facilitated by the detailed anatomical study of leaf development mutants. We present an analysis of leaf anatomy and morphogenesis during early developmental stages in has mutant of Arabidopsis thaliana. The recessive has mutation affects a number of aspects in plant development, including the shape and size of both cotyledons and leaves. The earliest developmental observations suggest almost synchronous growth of the first two leaf primordia of has mutant. No significant disruption of the cell division pattern in the internal tissue is observed at the earliest stages of development, with the major anatomical difference compared to wild type primordia being the untimely maturation of mesophyll tissue cells in has mutant. At the stage of leaf blade formation, structure disruption becomes clearly evident, by irregular arrangement of the cell layers and the lack of polarity in juvenile has leaves. One distinguishing feature of the mutant leaf anatomy is the absence of mesophyll tissue differentiation. Altered has mutant leaf morphology could be at least partially accounted for by the ectopic STM activity that was found at the base of leaf primordia during early stages of leaf development in has plants.

Harmfulness of wheat leaf rust in the eastern part of forest-steppe of Ukraine

The comparison of data obtained as a result of artificial inoculation in the period of leaf blade formation with the data received as a result of inoculating older plants in the natural infectious background shows that the drop in the weight of grains from a spike and the weight of 1000 grains depends on the degree of affect. It directly depends on the efficiency of resistance genes and on the stage of plants' development when the affect took place. So infection at an earlier stage of plants' development results in more harmful damage of the pathogen than infection at later stages. In the artificial infectious background (infection of plants in the early period of leaf flag formation) the decrease in grain weight from a spike is between 0.7–35%; weight of 1000 grain is between 0.5–13.9%. In the background of a later natural infection of the plants with a moderate development of the disease the indices of harmfulness in much lower and is between 0.9–14.5% and 0.1–5.5%, respectively. The decrease of 1000 grains weight is significantly lower as compared to the weight of grain from a spike which is obviously connected to the fact that in the lower and central deeply affected spikelets grain are not formed.

VARICOSE, a WD-domain protein, is required for leaf blade development.

To gain insight into the processes controlling leaf development, we characterized an Arabidopsis mutant, varicose (vcs), with leaf and shoot apical meristem defects. The vcs phenotype is temperature dependent; low temperature growth largely suppressed defects, whereas high growth temperatures resulted in severe leaf and meristem defects. VCS encodes a putative WD-domain containing protein, suggesting a function involving protein-protein interactions. Temperature shift experiments indicated that VCS is required throughout leaf development, but normal secondary vein patterning required low temperature early in leaf development. The low-temperature vcs phenotype is enhanced in axr1-3 vcs double mutants and in vcs mutants grown in the presence of polar auxin transport inhibitors, however, vcs has apparently normal auxin responses. Taken together, these observations suggest a role for VCS in leaf blade formation.

The Arabidopsis thaliana rlp mutations revert the ectopic leaf blade formation conferred by activation tagging of the LEP gene.

Activation tagging of the gene LEAFY PETIOLE (LEP) with a T-DNA construct induces ectopic leaf blade formation in Arabidopsis, which results in a leafy petiole phenotype. In addition, the number of rosette leaves produced prior to the onset of bolting is reduced, and the rate of leaf initiation is retarded by the activation tagged LEP gene. The ectopic leaf blade results from an invasion of the petiole region by the wild-type leaf blade. In order to isolate mutants that are specifically disturbed in the outgrowth of the leaf blade, second site mutagenesis was performed using ethane methanesulphonate (EMS) on a transgenic line that harbours the activation-tagged LEP gene and exhibits the leafy petiole phenotype. A collection of revertant for leafy petiole (rlp lines was isolated that form petiolated rosette leaves in the presence of the activated LEP gene, and could be classified into three groups. The class III rlp lines also display altered leaf development in a wild-type (non-transgenic) background, and are probably mutated in genes that affect shoot or leaf development. The rlp lines of classes I and II, which represent the majority of revertants, do not affect leaf blade outgrowth in a wild-type (non-transgenic) background. This indicates that LEP regulates a subset of the genes involved in the process of leaf blade outgrowth, and that genetic and/or functional redundancy in this process compensates for the loss of RLP function during the formation of the wild-type leaf blade. More detailed genetic and morphological analyses were performed on a selection of the rlp lines. Of these, the dominant rlp lines display complete reversion of (1) the leafy petiole phenotype, (2) the reduction in the number of rosette leaves and (3) the slower leaf initiation rate caused by the activation-tagged LEP gene. Therefore, these lines are potentially mutated in genes for interacting partners of LEP or in downstream regulatory genes. In contrast, the recessive rlp lines exhibit a specific reversion of the leafy petiole phenotype. Thus, these lines are most probably mutated in genes specific for the outgrowth of the leaf blade. Further functional analysis of the rlp mutations will contribute to the dissection of the complex pathways underlying leaf blade outgrowth.

Activation tagging of the two closely linked genes LEP and VAS independently affects vascular cell number.

The complex dominant Arabidopsis thaliana mutant lettuce (let) shows the conversion of the leaf petiole into a leaf blade caused by an ectopic leaf blade formation. This is the result of the activation tagging of the LEAFY PETIOLE (LEP) gene encoding an AP2/EREBP-like transcription factor. Here, we report that in addition to this leafy petiole phenotype, the size of the vascular bundles is increased in all aerial organs in let as a result of an increase in the number of xylem, phloem (pro)cambial and pericycle cells. This vascular phenotype is caused by activation tagging of the two genes VASCULAR TISSUE SIZE (VAS) and LEP. These genes are closely linked and arranged in tandem. Activation tagging of LEP only caused a specific increase in the number of xylem cells. This increased xylem cell number, together with the ectopic leaf blade formation, indicates that LEP functions as a cell division-promoting factor. The activation tagging of VAS only resulted in a specific increase in phloem (pro)cambial and pericycle cells. We conclude that activation tagging of LEP and VAS results in additive phenotypes. Insertional mutants for LEP and VAS display wild-type vascular development, indicating the relevance of activation tagging for functional analysis of novel genes involved in plant development.