Plant Developrment Part II for MSc Biology

Plant Developrment Part II for MSc Biology

• 1.
  An Overview ofPlant Development (Part II) Post-embryonic Phase [From Developmental Biology, Eighth Edition, by Scott F. Gilbert, published by Sinauer Associates, Inc.] Susan R. Singer Laurence McKinley Gould Professor of the Natural Sciences, Carleton College Reporter: Kimberly Rose P. Balmeo
• 2.
  An Overview ofPlant Development (Part II)  Germination  Vegetative Growth  The Vegetative-to-Reproductive Transition  Senescence
• 3.
  Germination  the resumptionof the growth of the seed embryo after the period of dormancy  In order to takes place  A period of After-ripening  Seed-Environment Interaction  Stratification (requirement of chilling)  Imbibition (rehydration)  Scarification (scratched or etched)
• 4.
  Germination  During germination Gibberellins trigger the breakdown of starch into sugar.  Light trigger differentiation of chloroplast  Radicle
• 5.
  Vegetative Growth  Whenthe shoot emerges from the soil, most of the sporophyte body plan which will emerge from meristems remains to be elaborated.
• 6.
  Meristems  Apical Meristem Shoot  Root  Lateral Meristem  Intercalary Meristem
• 7.
  Apical Meristems
• 8.
  Apical Meristems Angiosperm meristems havetwo or three outer layers of cells that are histologically distinct (L1, L2, and L3). If a cell is shifted to a new layer, it generally develops like the other cells in that layer. FIGURE 20.21 Organization of the shoot apical meristem. (A)
• 9.
  Apical Meristems Chimeric Tabaco Plant oL1 layer always lacks chlorophyll (except in guard cells o L2 genetically unable to produce chlorophyll o L3 remains green FIGURE 20.21 Organization of the shoot apical meristem. (B)
• 10.
  Apical Meristems Control byIntercellular Signals • WUS and STM proteins act to keep meristem cells in an undifferentiated state • while the products of the CLAVATA genes CLV1, CLV2, and CLV3all limit the number of undifferentiated meristem cells. FIGURE 20.21 Organization of the shoot apical meristem. (B)
• 11.
  Meristems  Apical Meristem Shoot  Root  Lateral Meristem – secondary growth  Intercalary Meristem – inserted in the stems of monocot between mature tissues
• 12.
  Root Development  Radialand axial patterning – from embryogenesis throughout development as the primary root grows and lateral roots emerge from pericycle
• 13.
  Root Development  Cellsare plastic and that position is the primary determinant of fate in early root development  There are two layers of root ground tissue  outer layer - cortex  inner layer - endodermis  SCARECROW (SCR) genes - asymmetrical cell division in the initial layer of cells  SHORT-ROOT (SHR) genes - responsible for endodermal cell specification
• 14.
  Root Development  Distributionof the plant hormone auxin organizes the axial pattern.  A peak in auxin concentration at the root tip must be perceived for normal axial patterning
• 15.
  Shoot Development  ApicalDominance  Branching patterns are regulated by the shoot tip  Plant Hormones  Auxin - suppresses the outgrowth of axillary bud  Cytokinin - release buds from apical dominance  Axillary buds can initiate their own axillary buds  environmental signals  maximizes light capture  Asymmetrical tree crowns form when two trees grow very close to each other  shoot architecture is genetically regulated
• 16.
  Shoot Development  Phyllotaxy- involves communication among existing and newly forming leaf primordial  the mature sporophyte is created by stacking node/internode units together  mechanisms for maintaining geometrically regular spacing of leaves on a plant
• 17.
  Shoot Development  cells’commitment to become a leaf  research indicates that the youngest visible leaf primordia are not determined to make a leaf; rather, programming for leaf development occurs only later  establishment of the leaf axes  morphogenesis Leaf Shape  Apoptosis  Differential cell growth
• 18.
  Patterning in Leaves DORSAL-VENTRAL / adaxial side-abaxial side  PHABUL OSA (PHB) and PHAVOLUTA (PHV) genes initially have uniformly expressed RNA throughout the primordium  proteins are receptors for an adaxial signal, which leads to the accumulation of PHB and PHV on the adaxial leaf surface  KANADI (KAN) genes initiate abaxial cell differentiation  Abaxial fate also appears to be specified by three members of the YABBY gene family
• 19.
  Patterning in Leaves
• 20.
  Patterning in Leaves SIMPLE AND COMPOUND LEAVES Whether simple and compound leaves develop by the same mechanism is an open question  Class I KNOX genes are homeobox genes that include STM and the KNOTTED 1 (KN1) gene in maize – mutation causes meristem-like bumps to form on maize leaves  When KN1, or the tomato homologue LeT6, with a promoter from cauliflower mosaic virus, the gene is expressed at high levels throughout the plant, and the leaves become "super compound"  In response to overexpression of KN1 Simple leaves become more lobed (but not compound),  consistent with the hypothesis that compound leaves may be an extreme case of lobing in simple leaves  consistent with the hypothesis that compound leaves are modified shoots.
• 21.
  Patterning in Leaves SIMPLE AND COMPOUND LEAVES Whether simple and compound leaves develop by the same mechanism is an open question  Class I KNOX genes are homeobox genes that include STM and the KNOTTED 1 (KN1) gene in maize – mutation causes meristem-like bumps to form on maize leaves  In wild-type plants KNOX genes stimulate meristem initiation and growth  YABBY genes (some) - function by downregulating KNOX genes - Control KN1 gene
• 22.
  Patterning in Leaves SIMPLE AND COMPOUND LEAVES Whether simple and compound leaves develop by the same mechanism is an open question  When KN1, or the tomato homologue LeT6, with a promoter from cauliflower mosaic virus, the gene is expressed at high levels throughout the plant, and the leaves become "super compound"  In response to overexpression of KN1 Simple leaves become more lobed (but not compound),  hypotheses compound leaves may be an extreme case of lobing in simple leaves compound leaves are modified shoots
• 23.
  Patternng in Leaves (A)a wildtype plant (B) a mouse ears mutant, with increased leaf complexity, (C) a transgenic plant that uses a viral promoter to overexpress the tomato homologue (LeT6) of the KN1gene from maize. FIGURE 20.26 Overexpression of Class 1 KNOXgenes in tomato
• 24.
  Patternng in Leaves (A)Wild-type pea plant (B) The tl mutant, in which tendrils are converted to leaflets (C) The af mutant, in which leaflets are converted to tendrils (D) An af tl double mutant, which results in a “parsley leaf” phenotype FIGURE 20.28 Leaf morphology mutants in peas
• 25.
  Vegetative-to-Reproductive Transition  vegetative andreproductive structures of the shoot are all derived from the shoot meristem formed during embryogenesis  Maximal reproductive success in angiosperms depends on the timing of flowering and on balancing the number of seeds produced with the resources allocated to individual seeds  a signal from the leaves moves to the shoot apex and induces flowering
• 26.
  Vegetative-to-Reproductive Transition  Signals toflowering  environmental conditions Photoperiodism Chronological age of the plant Size of plant Temperature  The nature of the flowering signal, however, remains unknown.
• 27.
  Vegetative-to-Reproductive Transition  JUVENILITY  juvenilephase - the plant cannot produce reproductive structures even if all the appropriate environmental signals are present EARLY PHASE CHANGE (EPC) gene in maize is required to maintain the juvenile state Arabidopsis juvenility gene HASTY (HST), necessary for microRNA processing and export from the nucleus. Loss of-function mutants undergo early phase change because microRNAs are trapped in the nucleus
• 28.
  Vegetative-to-Reproductive Transition  FLORAL SIGNALS The “black box” between environmental signals and the production of a flower is vanishing rapidly  CONSTANS (CO) responds to day length, promoting flowering under long-day conditions, activates transcription of a gene called FLOWERING LOCUS T (FT).  FT is transcribed only in the leaves, but the transcript travels through the phloem (transport tissue) from the leaf to the shoot and is likely translated when it arrives at the shoot meristem
• 29.
  Floral Signals Leaves andmeristems have undergone a juvenile-to-adult phase change to develop competence to respond to environmental signals before they can produce floral promoters FIGURE 20.30 The vegetative-to-reproductive transition.
• 30.
  Senescence  developmental programleading to death, is closely linked to flowering in many angiosperms  Fruit ripening (and ultimately overripening) is an example of organ senescence  Monocarpic plants flower once and then senesce.  Polycarpic plants, such as the bristlecone pine, can live thousands of years (4,900 years is the current record) and flower repeatedly. 