what are the steps of leaf development

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What is leaf development process?

Leaf development starts from the PZ of the meristem and the process involves leaf initiation from SAM, primary patterning, and proliferation. The initiation starts with the polarization of PZ into adaxial (upper) and abaxial (lower) regions during the early development.

What is the initiation of leaf?

The initiation of leaf commences with a lateral protrusion on the apical meristem. This is leaf buttress. Later leaf primordium develops on leaf buttress. The initial lateral protrusion results from periclinal division. The two growth zones —tunica and corpus variously participate in the development of leaf primordium.

What are the stages of leaf formation?

Leaf formation. Leaves are structures which are derived from stems. The initial stages of leaf formation are the same for monocots and dicots. Variations in morphogenesis between the shoots of monocot and dicot plants occur at a later stage.

What is the ontogenetic process of leaves?

Most leaves appear simple at first sight and they consist of only a few cell types. Despite that, many developmental processes are involved in leaf ontogeny, including positioning and initiation of leaf primordia, specification of leaf identity, establishment of dorsiventrality, the control of cell division and expansion, and pattern formation.

What are the stages of leaf development?

Afterward, the transformation of the small leaf primordium to a mature leaf is controlled by at least six distinct processes: cytoplasmic growth (4), cell division (5), endoreduplication (6), transition between division and expansion (7), cell expansion (8) and cell differentiation (9) into stomata (9a), vascular ...

What are the three stages during development of leaf?

Epidermal growth and final leaf form is influenced by genetic and physiological inputs regulating patterns of cell proliferation. Epidermal cell division, growth, and expansion occur simultaneously during several stages of leaf development.

What are the main events in the initiation and development of a leaf?

The early events in leaf development have been divided into three main processes (Foster, 1936, Steeves and Sussex, 1989, Smith and Hake, 1992), namely, the initiation of the leaf primordium, the establishment of dorsiventrality, and the development of a marginal meristem.

What is the process of a leaf?

The main function of a leaf is to produce food for the plant by photosynthesis. Chlorophyll, the substance that gives plants their characteristic green colour, absorbs light energy. The internal structure of the leaf is protected by the leaf epidermis, which is continuous with the stem epidermis.

Where do leaves develop?

Leaf growth On the surface of the apical meristem in the bud, a new meristem is formed. This new meristem is called a leaf primordium where cells divide and grow into a leaf. Soon after leaves develop, a new bud primordium (meristem) is formed at the base of each leaf stem.

What are the different types of leaf?

There are two different types of leaves – simples leaves and compound leaves. The other types of leaves include acicular, linear, lanceolate, orbicular, elliptical, oblique, centric cordate, etc.

What is the first step in the process of plant growth?

The first step in the process of plant growth is seed germination. The seed germinates when favourable conditions for growth exist in the environment. In absence of such favourable conditions the seeds do not germinate and goes into a period of suspended growth or rest.

What is the origin of leaf?

Leaves originate on the flanks of the shoot apex. A local concentration of cell divisions marks the very beginning of a leaf; these cells then enlarge so as to form a nipple-shaped structure called the leaf buttress.

What is shoot development?

The new growth from seed germination that grows upward is a shoot where leaves will develop. In the spring, perennial plant shoots are the new growth that grows from the ground in herbaceous plants or the new stem or flower growth that grows on woody plants. In everyday speech, shoots are often synonymous with stems.

What are the 5 parts of a leaf?

Apex: tip of the leaf • Margin: edge of the leaf • Veins: carry food/water throughout leaf; act as a structure support • Midrib: thick, large single vein along the midline of the leaf • Base: bottom of the leaf • Petiole: the stalk that joins a leaf to the stem; leafstalk • Stipule: the small, leaf-like appendage to a ...

What are the 4 functions of a leaf?

CONTENTSPhotosynthesis.Transpiration.Guttation.Storage.Defense.

What are the 3 main functions of a leaf?

These are:Photosynthesis.Transpiration.Photosynthesis.

What are new leaves called?

bud Add to list Share. The young part of a plant that's almost ready to flower or unfurl new leaves is called the bud. As a verb, bud also means to grow or develop.

Which phase represents the longest period in leaf development?

The third phase of leaf development, expansion, encompasses a much longer time period and represents an increase in surface area and volume of several thousandfold.

What is leaf ontogeny?

Leaf ontogeny: Stomata density on both leaf surfaces (if stomata are present) of herbaceous plants increases in the expanding leaf when stomata are initiated (for examples see Table 1.1), and then decreases at first rapidly and then gradually more slowly towards the end of leaf life.

What is the origin of leaf?

Leaves originate on the flanks of the shoot apex. A local concentration of cell divisions marks the very beginning of a leaf; these cells then enlarge so as to form a nipple-shaped structure called the leaf buttress.

What are the phases of leaf development?

Leaf development follows three continuous and overlapping phases, initiation, primary morphogenesis (PM), also referred to as morphogenesis, and secondary morphogenesis (SM), also referred to as differentiation [1].

How does the leaf develop?

Leaf development starts from the PZ of the meristem and the process involves leaf initiation from SAM, primary patterning, and proliferation. The initiation starts with the polarization of PZ into adaxial (upper) and abaxial (lower) regions during the early development. The polarity is the result of two HD-Zip III genes: PHABULOSA (PBH) and PHAVOLUTA (PHV) expressed in adaxial sites of the leaf. The expression is controlled by miR165/166 and AGO1 and AGO10 interactions. miR165/166 are produced in abaxial regions and induce the degradation of HD-Zip III mRNAs. This creates a polarity gradient in the region (high to lower miR165/166 concentrations in abaxial and adaxial regions, respectively), and leaf polarity is achieved (Fig. 9 A; [32] ).

Where are primary plasmodesmata modified?

nigrum protoplasts ( Ehlers and Kollmann, 1996 ). Evidence from electron microscopic studies suggests that the majority of these primary plasmodesmata are modified by the lateral fusion of neighboring plasmodesmata at the middle lamella region of the cell walls and the subsequent addition of new cytoplasmic strands containing the ER and the plasma membrane across the existing cell walls ( Ding et al., 1992a, 1993; Itaya et al., 1998) ( Fig. 9 ). In some cases, new cytoplasmic strands seem to be added to a primary plasmodesma without fusion of neighboring primary plasmodesmata ( Ding et al., 1992a, 1993; Itaya et al., 1998 ). Volk et al. (1996) have also demonstrated the formation of branched plasmodesmata via the modification of primary plasmodesmata as a function of leaf development between several cell types in C. melo and C. pepo. Because these modifications involve the de novo addition of cytoplasmic strands containing ER across the existing cell walls, they have been considered as a type of secondary plasmodesmata ( Ding et al., 1992a, 1993; Ding and Lucas, 1996 ). More specifically, they are referred to as “complex secondary plasmodesmata” ( Ding, 1998 ). Some workers ( Ehlers and Kollmann, 1996) have raised concerns about the use of “secondary plasmodesmata” to describe these “branched” plasmodesmata, as they are not formed entirely de novo across existing cell walls. Ehlers and Kollmann (1996) suggested that these plasmodesmata are still primary in nature and should be called modified or branched plasmodesmata. However, as just discussed, primary plasmodesmata can branch by different mechanisms, and the term “branched plasmodesmata” can hardly account for the differences. The use of “complex secondary plasmodesmata” to describe a specific class of “branched” plasmodesmata, the developmental origin of which is known, represents an extension of the classical definition of secondary plasmodesmata necessary to describe new findings ( Ding, 1998 ).

What control is involved in leaf serration?

Leaf morphology, size, laminar growth, and serration are also dependent on small RNAs for developmental control. Leaf serrations are controlled by the talk between auxin and CUC2 gene. The expression of CUC2 gene in the leaf indents promote the flow of auxin to the edges of leaves where auxin represses the CUC2 and serrations are produced. The control of serration development is dependent on the miR164, which is a repressor of the CUC2 gene. Similarly, relative concentrations of CUC2 and auxin also seem to have facilitated the evolution of compound leaves and their development ( Fig. 9 B; [31] ).

How does auxin transport contribute to leaf development?

One major question is: how is this process coordinated? Auxin gradients may contribute to leaf development by coordinating growth , and, for example, the differentiation and patterning of veins. An auxin maximum at the apical tip of the leaf primordium is established through auxin transport early in development (Reinhardt et al., 2003 ), and is maintained by the induction of auxin biosynthesis at the tip, and later on also in the hydathodes at the margins of the leaf primordium. It has been suggested that this process allows the formation of a distal–proximal auxin gradient ( Benkova et al., 2003 ), which is important for controlled cell division and expansion, and gradients formed by auxin transport from the leaf tip have been suggested to be important for midvein development ( Mattsson et al., 1999; Zgurski et al., 2005 ).

How do transcription factors affect leaf development?

The transcription factors can act as switches to initiate differential gene expression by binding to specific cis -elements of target-gene promoters for the activation and suppression of target genes. Out of total number (2491) of genes Guo et al. (2004) identified 134 (5.4% ESTs) genes encoding for target transcription factors that provide important understanding of the regulatory pathways of the senescence program. In senescing leaves, NAC and WRKY transcription-factors are two largest groups of senescence-related transcription factors. Among them, NAC transcriptional factors are exclusively present in plants and involved in controlling organ development and response to pathogens while the WRKY transcription-factor group is elicited by salicylic acid and respond against the pathogen attack. The expression of WRKY transcription-factor group members are up-regulated during defense response and leaf senescence. Previously, involvement of WRKY6, WRKY18, WRKY22/29 and WRKY53 has been found in leaf senescence ( Robatzek and Somssich, 2002 ).

How does salinity affect the growth of a plant?

Salinity affects the leaf development by inducing changes in osmotic potential to reduce the ability of plants for water and nutrient uptake during the first phase. During this phase reduction in leaf area suggests a decrease in water intake to prevent the salt stress. During the second phase of ion toxicity, Na+ accumulates in the leaf blade and transpiration stream, especially in the older leaves, which do not expand failing to dilute the ionic toxicity effect whereas, young leaves show expansion in response which lowers the toxicity of ions. This phenomenon leads to the death of the older leaves. When the older leaves die at a rate higher than that of the emergence of new leaves, the ability of plants for photosynthesis is greatly reduced which results in overall reduction in growth rate ( Munns and Tester, 2008 ). Ali et al. (2004) performed a study to understand the effects of salinity on leaf and other yield parameters of 18 rice cultivars using an artificial saline soil medium. The results demonstrated a significant reduction in leaf area of rice plants with the increase in salinity levels. The leaf size depends on the processes of cell division and cell elongation. Results observed by Ali et al. (2004) for the reduction in the leaf area were attributed to suppressed cell division.

What are the processes that occur in the development of a leaf?

Despite that, many developmental processes are involved in leaf ontogeny, including positioning and initiation of leaf primordia, specification of leaf identity, establishment of dorsiventrality, the control of cell division and expansion, and pattern formation. This report highlights and reviews some of what we know about the genetic circuitry that underlies leaf form, as discussed at a workshop on “Leaf Development” held February 11 through 13, 2002, at the Instituto Juan March (Madrid).

How do shoot meristems produce leaves?

Shoot meristems produce leaves on their flanks in regular patterns called phyllotaxy. As leaves are initiated, meristem cells divide and replace the cells that have just been committed to initiating a leaf primordium. Thus, the meristem balances self-renewal with organ initiation. The regular pattern of leaf initiation allows one to predict where the next leaf will appear. Leaves that have just appeared as bumps from the meristem are in Plastochron 1 and are referred to as P 1 leaves. The cells in the meristem that will become the next leaf are designated P 0. The P 0 cells, although still part of the meristem, soon become radically different from adjacent cells. They divide at higher rates, their growth axis changes from isodiametric to axial, they loose their indeterminate nature, and they gain leaf cell identity. Even more amazing, the boundary that establishes the P 0 cells from the meristem is continually being remade and reinterpreted with every initiating leaf.

Where is Knotted1 expressed?

A Knotted1-like homeobox gene in Arabidopsis is expressed in the vegetative meristem and dramatically alters leaf morphology when overexpressed in transgenic plants.

Which protein acts as differentiation-promoting transcription factor of the vascular meristems?

The Arabidopsis ATHB-8 HD-ZIP protein acts as differentiation-promoting transcription factor of the vascular meristems.

Which gene encodes symmetric leaf lamina?

The ASYMMETRIC LEAVES2 gene of Arabidopsis thaliana, required for formation of a symmetric flat leaf lamina, encodes a member of a novel family of proteins characterized by cysteine repeats and a leucine zipper.

Does Knox cause leaf dissection?

It has been proposed that differential regulation of KNOX genes may be involved in the generation of dissected leaf morphology ( Hareven et al., 1996; Janssen et al., 1998 ). Tsiantis also reported that the dominant Mouse ear mutation of tomato ( Lycopersicon esculentum) increases leaf dissection, a phenotype that is suppressed by the constitutive GA response procera mutation, suggesting again that GA acts antagonistically to KNOX genes in simple (Arabidopsis) and compound (tomato) leaves.

What are the dividing zones of a leaf?

The dividing zones are the marginal meristems, through the activity of which the leaf gains its laminat e form. In each meristem the outer file of cells, or marginal initials, contributes the epidermal layers by continued division. The cells below, the submarginal initials, provide the tissue of the inner part of the leaf.

Where is the cell division of a leaf?

Usually a certain number of cell layers is defined in the mesophyll (the parenchyma between the epidermal layers of a foliage leaf). Cell division is not limited to the region of the marginal meristems but continues throughout the leaf in each of the layers, always in the same plane, until the final cell number is approached.

What is the apical growth of a leaf?

Apical growth dominates in the tobacco-leaf primordium until a height of about 0.5 millimetre (0.02 inch) is reached. Thereafter, the buttress becomes more and more flattened in the transverse plane by laterally oriented cell divisions and further expansion growth on either side. The dividing zones are the marginal meristems, through the activity of which the leaf gains its laminate form. In each meristem the outer file of cells, or marginal initials, contributes the epidermal layers by continued division. The cells below, the submarginal initials, provide the tissue of the inner part of the leaf. Usually a certain number of cell layers is defined in the mesophyll (the parenchyma between the epidermal layers of a foliage leaf). Cell division is not limited to the region of the marginal meristems but continues throughout the leaf in each of the layers, always in the same plane, until the final cell number is approached. The rate then declines, ceasing in the different layers at different times. Divisions usually end first in the epidermis, then in the lower mesophyll layers of a leaf such as that of tobacco, and last in the main photosynthetic tissue, the palisade layer, just beneath the upper epidermis.

How does the primordium develop?

In the development of the maize leaf, the primordium arises first as a prominence some distance below the apical dome. The zone of division and growth extends laterally around the apex so that a complete collar forms; then the margins overlap. Meanwhile the original tip zone continues to elongate, eventually surpassing the stem apex. Tip growth declines thereafter, and further increase in cell number results from meristematic activity at the base. The early development of the vascular system is unlike that in dicotyledons, for several parallel procambial strands, rather than a single midrib, are initiated. The first of these grow toward the apex, but, as tip growth ceases, procambial strands form above and extend toward the base, passing through the node, or point of insertion of the leaf primordium, and into the stem below. As the leaf extends in length, the tissues begin to mature first at the tip, and a wave of differentiation passes down toward the base, where cell division and extension growth may continue long after the tip of the leaf is mature. Protection for this immature and succulent tissue of the leaf base is afforded by the sheaths of older leaves surrounding it.

How is a tobacco leaf vascular pattern determined?

The vascular pattern in a tobacco leaf is determined early in the development of the vessel primordium. A procambial strand is formed by the elongation of narrow axial cells, and this extends both toward the base and toward the apex, eventually linking with the procambium of the stem.

How do new cells contribute to the growth of the primordium?

In the early growth of the leaf primordium, new cells are contributed mainly by meristematic activity at the pole directed away from the stem, so that the buttress extends in length. The subsequent distribution of growth varies among the different groups of vascular plants according to the shape of the mature leaf.

What is the leaf buttress?

A local concentration of cell divisions marks the very beginning of a leaf; these cells then enlarge so as to form a nipple-shaped structure called the leaf buttress. The cells of the leaf buttress may be derived from the tunica alone or from both the tunica and the corpus.