These were mounted with a xylene-based mountant DPX after dehydration through ethanol and Histoclear. Microscope slides were examined under bright field with an Olympus BX50 light microscope and images were recorded using Fujichrome or a digital camera attached to an Olympus analySIS B imaging system.
Some of the images were captured with Nomarski optics. An antisense L. Microscope slide sections were rehydrated in ethanol series and taken through pre-hybridization treatments according to a modified protocol Drews et al. The slides were washed and prepared for immunodetection following the manufacturer's protocol Roche. Finally, the slides were washed in saline solution and mounted with an aqua-based mounting medium Shandon Immu-mount.
Ten seed pods were collected from each of the surviving plants, and the M 2 seeds were extracted and packaged. Twelve M 2 seeds from each plant were sown into seedling trays and grown in glasshouse conditions.
Screening of the M 2 progeny plants commenced about 2 weeks after seedling emergence, and putative mutants were transplanted into individual planter bags when the seedlings were well established. M 3 seeds of the putative mutant plants were collected, sown and these M 3 progeny plants were used for the initial morphological analysis. There are two distinct patterns of shoot branching in L.
Basal branching refers to the branching pattern observed in the cotyledonary region, and aerial branching to the development of branches above the cotyledon. Figure 1 provides a schematic comparison of the branching architectures of wild-type Lotus Fig. In wild-type Arabidopsis , axillary shoots usually develop in the axils of rosette and cauline leaves but not in the cotyledons Grbic and Bleecker, In Lotus , axillary shoots develop in the axils of all leaves and the cotyledons, throughout the vegetative and reproductive development of the plant.
Additional axillary shoots, referred to as accessory shoots, also develop alongside the primary axillary shoots. Diagram showing wild-type Lotus A and wild-type Arabidopsis B branching architecture. The primary shoot is indicated by a black arrow. Floral meristems are indicated by closed circles. Cotyledons are indicated by green ovals, and leaves by grey ovals.
Numbers indicate the order of emergence of axillary and accessory buds. In Lotus , the first pair of axillary buds, referred to as primary axillary buds, is morphologically visible in the cotyledon axils early in the vegetative development of the plant Fig. These buds develop into lateral shoots as soon as they are initiated, without being subject to any apparent inhibition exerted by the primary SAMs Fig.
Additional axillary buds, referred to as accessory buds, continue to develop in the axils of cotyledons, repeating largely the development pattern of the primary shoot, resulting in numerous lateral shoots Fig. A new accessory bud forms on the stem side of the cotyledon axil at the basal region of the next older bud Fig. New accessory buds appear at regular time intervals at approx.
Shoot branching patterns in Lotus japonicus. A A 2-week-old Lotus seedling. B A 5-week-old plant. C A mature Lotus shoot.
D Cotyledonary node of a 5-week-old plant; the cotyledon has been abscised. E A 3-week-old seedling. Above the cotyledons, primary axillary buds are morphologically visible in the axils of leaves early in the vegetative development of the plant Fig. Accessory buds also form in the aerial axils of Lotus Fig. However, if accessory buds formed at aerial nodes do develop into lateral shoots, this occurs mostly in the axils closest to the cotyledon Fig.
The pattern of shoot branch development in the cotyledonary node region appears to be reiterated in culture-grown detached cotyledons Fig. Cotyledons were detached from 1-week-old culture-grown seedlings and allowed to grow in a tissue culture medium to observe the proliferative branching pattern. At the time that the cotyledon was detached, a primary axillary bud had already initiated at the cotyledon axil and came off with the detached cotyledon stalk Fig.
Within 2 months of culture, accessory buds continued to be initiated at the basal region of the primary axillary bud Fig. All these buds developed into shoots in a pattern similar to that of the cotyledonary buds in an intact seedling. No other buds formed in any other part of the detached cotyledon. SEM images showing A a newly detached cotyledon and B a detached cotyledon after growth in culture medium for 2 months. New accessory buds are indicated by arrows.
In a mature embryo of Lotus , the SAM appears as a mound of smaller, less vacuolated, densely stained cells Fig. Significantly, a portion of this group of densely stained cells extends beyond the apical dome to include a flanking zone that remains in direct continuity with the SAM. Upon seed germination, an axillary meristem is anatomically visible as a group of densely staining cells in the axil of a cotyledon Fig.
Furthermore, groups of densely staining cells are positioned where additional axillary meristems subsequently initiated Fig. Accessory meristems develop between the axillary bud and the cotyledon Fig. In a more mature plant, when the cotyledons have abscised, additional accessory buds develop in between the basal region of the next two older accessory buds Fig.
Longitudinal sections of A mature embryo, B newly imbibed seed, C 4-day-old seedling and D day-old seedling, showing densely staining meristematic tissues. H A transverse section through the cotyledonary node of a more mature seedling. In longitudinal sections of Lotus at different stages of development Fig. The high sequence similarity of the putative LjSTM-like gene to Arabidopsis STM and the similar meristem-specific patterns of expression in Arabidopsis and Lotus is the basis for using the expression pattern of LjSTM-like gene transcripts to describe the pattern of axillary meristem development in Lotus.
In Fig. LjSTM-like transcripts accumulated in the subepidermal cellular layers in the axil of the cotyledon as shown by a longitudinal section of a 2-day-old seedling Fig. The accumulation of LjSTM-like transcripts in these groups of cells in the cotyledon axils is associated with initiation sites of primary axillary meristems Fig.
As the axillary meristems developed into buds, LjSTM-like transcript accumulation persisted in the cotyledon axils, at the basal region of the primary axillary bud, coinciding with the positions where accessory meristems subsequently arise Fig.
No transcript accumulation was observed in the newly formed leaves of the axillary bud Fig. As a negative control, tissues hybridized with the sense probe showed no staining Fig. In a transverse section of a more mature Lotus seedling, LjSTM-like transcripts accumulate in cells adjacent to the basal region of axillary or accessory buds Fig.
Vector NTI was used to make the alignment and the deduced distance tree. Identical residues are darkly shaded. Similar residues are lighly shaded. Dashed lines indicate gaps introduced by the programme to attain maximum alignment. P1 and P2 leaf primordia curve around the SAM. Longitudinal sections of D a 4-day-old seedling showing transcript accumulation in the axillary meristems.
E In a 7-day-old seedling, transcript accumulation is restricted to the shoot apical meristem of an axillary bud.
A A 2-day-old seedling. A plane and a green line indicate the positions of a sagittal longitudinal section as shown in B and a transverse section as shown in C , respectively. In situ hybridization shows that LjSTM-like transcripts accumulate in the cotyledon axils of a 7-day-old seedling as shown in adjacent median longitudinal sections D and E.
As the bud develops, LjSTM-like transcript accumulation is restricted to the shoot apical meristem of the new axillary bud as shown in E. An example of a primary meristem is the apical meristem. Apical meristems are meristematic tissues located in the apices of plant, e. See also:. Stems primarily provide plants structural support. This tutorial includes lectures on the external form of a woody twig and the origin and development of stems.
Also included are the different modified stems that carry out special functions. Read More. Plant organs are comprised of tissues working together for a common function. The different types of plant tissues are meristematic, simple, secretory, and complex tissues. If this genetic change is not functioning properly, then flowering will not occur.
The second genetic event follows the commitment of the plant to form flowers. The sequential development of plant organs suggests that a genetic mechanism exists in which a series of genes are sequentially turned on and off.
This switching is necessary for each whorl to obtain its final unique identity. In the simple ABC model of floral development, three gene activities termed A, B, and C-functions interact to determine the developmental identities of the organ primordia singular: primordium within the floral meristem. The ABC model of flower development was first developed to describe the collection of genetic mechanisms that establish floral organ identity in the Rosids and the Asterids; both species have four verticils sepals, petals, stamens and carpels , which are defined by the differential expression of a number of homeotic genes present in each verticil.
In the first floral whorl only A-genes are expressed, leading to the formation of sepals. In the second whorl both A- and B-genes are expressed, leading to the formation of petals. In the third whorl, B and C genes interact to form stamens and in the center of the flower C-genes alone give rise to carpels.
For example, when there is a loss of B-gene function, mutant flowers are produced with sepals in the first whorl as usual, but also in the second whorl instead of the normal petal formation. In the third whorl the lack of B function but presence of C-function mimics the fourth whorl, leading to the formation of carpels also in the third whorl. ABC model of flower development : Class A genes blue affect sepals and petals, class B genes yellow affect petals and stamens, class C genes red affect stamens and carpels.
Most genes central in this model belong to the MADS-box genes and are transcription factors that regulate the expression of the genes specific for each floral organ. Privacy Policy. Skip to main content. Plant Form and Physiology. Search for:. Plant Development. Meristems Plant meristematic tissues are cells that divide in order to give rise to various organs of the plant and keep the plant growing.
Learning Objectives Discuss the attributes of meristem tissue and its role in plant development and growth. Key Takeaways Key Points Mitotic cell division happens in plant meristems, which are composed of a group of self-renewing stem cells from which most plant structures arise.
Meristematic tissue has a number of defining features, including small cells, thin cell walls, large cell nuclei, absent or small vacuoles, and no intercellular spaces. The apical meristem the growing tip functions to trigger the growth of new cells in young seedlings at the tips of roots and shoots and forming buds. The apical meristem is organized into four meristematic zones: 1 central zone, 2 peripheral zone, 3 medullary meristem and 3 medullary tissue.
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