Vegetative growth. Development of root and shoot

Size: px

Start display at page:

Download "Vegetative growth. Development of root and shoot"

Verity Bryant
5 years ago
Views:

1 Vegetative growth Development of root and shoot

2 Shoot morphology Mature plant with repeating units controled by environemtal and hormone signal Shoot architect is controlled genetically Asymetric growth when two plants growing near each other Stacking node internode units

3 Germination is by growth of embryo hypocotyle and epicotyle: produce seedling Seedling development: The development after germination is more environmentally controlled, controlled instead by light, which, among other effects, acts on the seedling by inhibiting production of plant growth regulators called brassinosteroids. Mutations in genes required for production or reception of the brassinosteroid signal cause the stem of the seedling to go green, slow its elongation, and open its cotyledons prematurely, Photomorphogenesis also while it is in the dark.

4 Fate of SAM added cells Cell leaving SAM produce three fundamental cell layers. Predetermined d in SAM? Fate map by surgical manipulation, mutation. Experiment proved Fate depends mostly on position rather than linage. Depends on intercellular l signals. Each pieces of SAM form a complete functional meristem. Mutation, induction of polyploidy, layer specific marker help to trace fate. ATML1 expressed ecl exclusively siel in L1 in arabidopsis. Unusual periclinal division in L1 and L2 the displace cell are absorbed by adjacent layer Linage play a role in specification but fate can be respecified by interaction with other cells.

5 Lineage versus Position in the Specification of Cell llfates in the Shoot Fate determined by linage but change in cell position change cell cell contact and may change fate. Cell marked at centre of meristem give marked character at upper leaves and marked cell from peiphery give marked kd character at basal leave and stem The cells are more commited at priphery than towards centre

6 Apical meristem growth results axillarymeristem For branching new shoot apical meristems must be created, tddepending di on events in the shoot apex. Axillary bud is formed at each developing node, in the axil between the leaf primordium and the stem, Axillary bud is a nest of cells, derived from the apical meristem, that keep meristematic character. The meristems either remain dormant or can grow to branch or flower

7 Gentic control of Plant topology in maize Simple mutations in some genes can transform plant structure by changing the behavior of meristem cells: Study of Maize and its wild ancester teosinte Teosinte is branched but change in 5 genetic loci produced modern maize oneofthe of gene is Teosinte branched 1 (TB1) Mutant maize with defective TB1 (loss of function) no inhibition of axillary bud change to branch with tassel ear growth is inhibited. In wild with active TB1 the axillary bud grow but produce ear TB1 in wild and maize active but differ in expression. In maize mutation in regulatory region boosted the level of TB1 expression In Breeding:body change without changing protein character Low TB1 expression High TB1 expression

8 Hormonal control Plant hormones have powerful influences on plant development. They include the, Auxin, gibberellins, cytokinins, i abscisic i acid, the gas ethylene, and the brassinosteroids. Auxin produced in apical bud and leaf supress axillary bud growth- Apical ldominance Cytokinin can release bud dormancy Growth regulator effects are modulated by the other growth regulators, auxinalone promote root formation, but in conjunction with gibberellin it can promote stem elongation, with cytokinin, it can suppress lateral shoot out growth, and with ethylene it can stimulate lateral root growth. Auxin also controls the detailed patterns of cell specialization in the apical meristem.

9 Differentiation depends on orientation of cell division and expansion Plant tcells cannot crawl ca and dshuffle eas the epa plant grows; but they can divide, and they can swell, stretch, and bend determine division growth and dff differentiation The morphogenesis depends on division, growth (l (elongation) of cell differentiation. orderly cell divisions followed by strictly orientedcellexpansionsdeterminedby expansions determined cellusoe deposition in wall which is controlled by microtubuls orientation

10 . Plant hormones are samall molecules they can enter cellwall. Each growth regulator has multiple effects, Each character is influenced by many hormones. The characters are modulated dby the growth regulators, as well as by environmental cues and nutritional status

11 Shoot development By the activity of SAM both differentiated and meristematic cells (SAM and others) cause continuous growth and development Apical meristem also give outgrowth with limited growth like primodrdia for leaves and flower Continuous activityof the meristem produces an ever increasing number of similar modules, each consisting of a node with stem, leaf, and bud connected by internode Characteristic repetitively ypatterned structure phytomere Apical dominance affect axillary bud growth Hormonal control: role of Auxin/cytokinins Phylotaxy, the leaf arrangement chemical chemicalandphysicaland interaction of new leaf primordia with apex and other primordia. Environemntal stress also affect Only few phylotactic mutant known

12 Regular pattern formation provide attractive structures

13 Growth of meristem results successive layers of primordia Shoot apex with meristem and leaf primordia

14 Mutation in Pin1 will not effect shoot growth but without leaf giving pin like structure. Pin1 is auxin transporter and mutant show defect in auxin distribution Application of auxin in one side start diferentiation of leaf or flower (A) Pin distribution is asymetric more concentrated where primordia is differentiating (B, C, D). Pin1 gene is upregulated by auxin Pin1 asymetricdistributed also in individual cell (D) that control flow of auxin to particular side of cell. In established primordium Pin distribution change and auxin transport toward vascular tissue.

15 Lateral Inhibition to Produce Regular Spacing pattern The differentiation of one cell or group of cells is prevented by signals produced from another: to delay the initiation of successive lateral organs and to generate regular spacing patterns The periodic initiation of lateral organs by the SAM plastochron, defines a developmental unit. Plastochorn gives the shoot time to extend before the next organisinitiated initiated. Shootsare thus composed of nodes and internodes, the nodes bearing the lateral organs (usually leaves). The formation of one primordium inhibits the formation of the next until a certain time has passed

16 Activity of SAM and aerial growth of plant producing phytomers SAM gives series of lateral organs Arrangement of leaves on nodes is the phyllotaxy Periodic initiationof of successive primordia form modularunits units consisting of a lateral organ (leaf), axillary bud, node and subtending internode. Each unit is called a phytomer Phytomers show developmental gradient along apical basal axis, youngest at the apex Plastochron provide time to primordium to grow Phytomer grows by cell proliferation and cell expansion by removing new leaf primordium as soon as they have formed the next leaf primordium emerge as expected, but the position of the one after that is altered. It is shifted toward the site of excision. Lateral inhibition (differentiation of one cell prevented by signal from neighbouring cells) is used to delay the emergence of succesive organ primordia and to ensure the correct spacing of leaves.

17 spacing patterns are produced by lateral inhibition. A. Initially all cells are undifferentiated (white) and inhibit each other s differentiation equally (T bars). (B) Random fluctuations in the level of inhibition then cause some cells to assert dominance, and cause the surrounding cells to lose their inhibitory activity. (C) Eventually, the dominant cells differentiate and completely inhibit the surrounding cells. Organs are arranged in definite pattern due to lateral inhibition

18 At genes for trichome differentiation are isolated like TRYPTICHON (TRY), GLABROUS1 (GL1), GL2, GL3, and TRANSPARENT TESTA GLABRA (TTG). TRY appears to be involved in the lateral inhibition process. In try mutant, trychomes are formed in clusture. Mutations in GL1, GL2, GL3, and TTG reduce the number of trichomes involved in trychome development. Weak ttg andgl1 alsoproduce trychomes inclusture TTGandGL1 GL1 control trichome spacing The control is complicated by the existence ofa number of other regulators, such as the MYB like protein AtMYB23 that functionally overlaps with GL1 and the putative negative regulators CAPRICE (CPC) and COTYLEDON TRICHOME1 (COT1).

Specification of organ Determinate in maize: predetermined number of phytomers (18+ tassel)

primordium is controlled by signal from existing primordia.

20 Specification of organ Determinate in maize: predetermined number of phytomers (18+ tassel) Indeterminate in Arabidopsis: phytomersnot fixed If flattened: series of concentric circles inner younger and higher. Alternate phylotaxy in maize and spiral in maize Allocation of cell to particular primordium is controlled by signal from existing primordia. Signal to a top producing primordia comes from lower phytomer not from meristem. Culture of SAM after producing certain number of phytomer in maize is deprogrammed and produce another entire plant

21 Leaf development Difference in auxin distribution and PIN gene family involved Includes cell comited to develop into leaf, leaf axis formation and morphogenesis Young leaf primordia arenot differentiated asthey can develop to complete plant in culture. Programing for leaf development is latter Rdil Radial symetry of leaf primordia change to dorsiventral flat. Dorsoventral, proximal distal and lateral axes are established The unique shapes of leaves result from regulation of cell division and differential cell expansion as the leaf blade develops, p, in some also selective cell death Adaxial and abaxial side in leaf blade

22 In At PHABULOSA (PHB) and PHAVOLOTA (PHV) initially uniformly expressed in adaxial and abaxial side. PHB and PHV are the receptor for adaxial signal accumulate at adaxial side. PHB and PHV excluded from abaxial side by degrading their RNA by microrna and supressing PHB and PHV transcription by methylation. Gain of function mutant by disruption of microrna RNAlead to develop two adaxial side KANADI (KAN) expressed at abaxial side of cotyl., leaves and floral organ for abaxial differentiation. KAN and PHB/PHV mutually suppress eachother in two sides

23 PHB /PHV, and KAN gene mutually supress each others expression. Adaxial and abaxial patterning in Arabidopsis leaf. Genetically controlled by PHB,PHV, PHV KAN, YABBY family genes. PHB and PHV proteins for adaxial differentiation where as KAN and YABBY protein for abaxial differentiation

24 Phylotaxy with precise spacing: as existing primordia affect the new leaf primordia Removal of newest leaf primordia do not affect the position of next primordia but affect the one after that shifted towards the site of excision. Terminal ear 1 gene of maize espressed in horseshoe, the open end of horse shoe alternate t like the phylotaxy, hlt the gene repress leaf develoment. Leaf growth begins with extension of petiole and leaf lamina grow latter Leaf primordia may grow to branch, infloresence, flower or other organs like thorn the fate is determined dafter emergence controlled by meristem.

25 Phylotaxy

26 spacing patterns are produced by lateral inhibition. A. Initially all cells are undifferentiated (white) and inhibit each other s differentiation equally (T bars). (B) Random fluctuations in the level of inhibition then cause some cells to assert dominance, and cause the surrounding cells to lose their inhibitory activity. (C) Eventually, the dominant cells differentiate and completely inhibit the surrounding cells. Organs are arranged in definite pattern due to lateral inhibition

lam1 mutant of tobacco fail to proliferate meristem either side of midrib so no lamina development, in fat mutant abnormal cell division in dorsoventral axis result thickened leaf, but petiole grow

27 lam1 mutant of tobacco fail to proliferate meristem either side of midrib so no lamina development, in fat mutant abnormal cell division in dorsoventral axis result thickened leaf, but petiole grow normal. tangled 1 mutation in maize result irregular pattern instead of parrell venation due to randomly oriented cell division but overall morphology of leaf is unaffected Augustifolia mutant of At shows narrow leaves wherre as rotundifolia shows round leaves. Apical basal and lateral expansion are independent growth The leaf margin growth is late events in leaf morphogenesis Simple and compound leaves Whether simple and compound leaves develop by the same mechanism? Compound leaf are highly lobed simple leaves or modified shoot?

28 Overexpresion of Class 1 KNOX genes (KN1 Maize homologue of LeT6) in tomato (C) with super compound leaf. Simple leaf of wild type plant (A), Mouse ear mutant with complex leaf (B) In tomato KN1 decrease the expression of gene for GA synthesis KNAT1 overexpression in At resulted lobed leaf instead of simpleleaf leaf. At highest expression inflorescence form at base of lobe.

29 Intl mutanttendril is changed to leaflet (B) in af mutant leaflets In tl mutant tendril is changed to leaflet (B), in af mutant leaflets are converted to tendril (C), in tl af mutantresuults parsley leaf phenotype. (A) is normal pea plant

Lineage versus Position in the Specification of Cell llfates in the Root RAM cells derive from embryo

cap that is continually replenished as the cells are sloughed off.

Cells produce from RAM elongate when reach certain distance In differentiation zone cell differntiate,

30 Lineage versus Position in the Specification of Cell llfates in the Root RAM cells derive from embryo proper and hypophysis RAM gives rise to the differentiated cells of the root, but also to a distal root cap that is continually replenished as the cells are sloughed off. Lateral roots emerge from pericycle Zones of cell division, cell elongation and cell differentiation Cells produce from RAM elongate when reach certain distance In differentiation zone cell differntiate, develop root hairs in epidermis. Laser ablation experiments showed that the cells are plastic and position detemine the fate in early development

32 RAM promeristem with a quiescent center surrounded by proliferative initial cells that give rise to the file meristem it and dthe distal root cap. The Arabidopsis promeristem has three layers. The lower layer comprises 12 central cells (RCI) that produce the root cap and 16 surrounding cells (ELI) that generate the lateral root cap and the epidermis. The middle layer comprises the four cells of the quiescent center (QC) and eight surrounding cells that give rise to the endodermis and cortex (CEI). Finally, the upper layer of stele initials (PI and SI) gives rise to the pericycle and vascular Bundles The cortical/endodermal initial cells divide to produce one initial cell and one daughter cell. The daughter cell then goes on to divide to produce one cortical cell and one endodermal cell, which enter the file meristem. The process is repeated throughout root growth

33 CEI: cortical endodermal initial QC: quiscent center PI: pericycle initial VI: vascular initial Ablation experiments shown that cell fates are dependent predominantly on position rather than linage D: daughter cell C: cortical cell E: endodermal cell

34 Arabidopsis Root mutant study Shoot SCRexpression in root and shoot Green layer Mutants of root radial organization revealed genes with layer specific activity. Two type of ground tissue outer cortex and inner endodermissurrounding stele Scarcrow (scr) and Short root (shr) mutants with single layer of ground tissue: ECI fail to divide SCR responsible for asymmetric division of CEI producing small endodermal cell and larger cortical cell, SHR responsible for endodermis specification. shr do not develop endodermis. Auxin distribution important: a peak in auxin concentration at root tip for normal axil patterning. Distinct gene expression in root and shoot development but SCR and SHR genes express in both root and shoot (Fig) SCR and SHR in shoot for gravitropic response related to normal endodermis formation.

35 Wild scr mutant shr mutant Small endodermal and large cortical cell Single mutnt layer. SCR gene responsible for asymetric division SHR responsible for endodermis specification shr mutant with layer without endodermal feature, Distinct gene expression in root and shoot development but SCR and SHR genes express in both root and shoot In pinocchio mutant CEI fail to divide differentiation of endodermis cortex missing. Axial patterning in root is governed by distribution of hormone Auxin highest at tip

36 References TwymanR M : Molecular Biology of Development, University of York, York, UK Copyright 2003, Elsevier Ltd. Twyman:R.M. Developmental Biology ShrivastavLalit M : Plant growth and development Gilbert, Scott F: Developmental biology

Outline. Leaf Development. Leaf Structure - Morphology. Leaf Structure - Morphology

Outline. Leaf Development. Leaf Structure - Morphology. Leaf Structure - Morphology Outline 1. Leaf Structure: Morphology & Anatomy 2. Leaf Development A. Anatomy B. Sector analysis C. Leaf Development Leaf Structure - Morphology Leaf Structure - Morphology 1 Leaf Structure - Morphology