Transcript Figure 4.1

Chapter 4
From Embryo to Establishment
© 2012 by John Wiley & Sons, Ltd.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.1 Diagram showing asymmetric expression of genes in the two-celled
embryo. MONOPTEROS (MP), BODENLOS (BDL) and WOX 2 are expressed only
in the smaller apical cell (which will become the embryo proper), while WOX8,
WOX9 and PIN7 are expressed only in the larger basal cell. Within that cell, the
PIN7 protein is localized at the apical end.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.2 Formation of the hypophysis, based on activity of a mobile transcription
factor. In the pro-embryo (pe), IAA induces the degradation of BDL protein. This
releases MP, which activates auxin transport via PIN1; thus, auxin is moved to the
apical cell of the suspensor(s). This transport of auxin is necessary, but not sufficient
for hypophysis formation; another mobile signal is also needed. That signal is the
transcription factor TOM7, synthesis of which is up-regulated in the pro-embryo by
MP. Reproduced by permission from Schlereth, A. et al.(2010) Nature 464, 913–916
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.3 (a) Diagram showing the main stages in a developing eudicots embryo.
(b) The mature embryo in situ in the seed. Reproduced with permission from Bryant,
J (1985), Seed Physiology, Edward Arnold. London.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.4 General overview of events in seed development and maturation. Notes
on DNA endoreduplication: (1) there are some species in which DNA
endoreduplication does not occur in the storage tissue (e.g. cotyledons of Brassica
napus, oil-seed rape or canola). (2) DNA endoreduplication occurs early in
embryogenesis in the embryo suspensor (not indicated in this diagram).
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.5 Structures of stachyose and raffinose. Images from Yikrazuul, Wikimedia
Commons.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.6 Processing of eudicot storage proteins. Top: 7S vicilin-type proteins. Three different-sized
polypeptides are generated from one precursor. Each of these polypeptides may be glycosylated, with the
extent of glycosylation varying between species. Bottom: 11S legumin-type proteins. After removal of the
signal peptide (see text), the protein is folded so that an intramolecular S-S bridge can form. At this stage, the
protein assembles into a trimer and then the linking peptide is removed. Each molecule of legumin now
consists of two polypeptides held to together by an S-S bridge and assembled into a trimer with two other
legumin molecules. Trimers are transported to protein bodies, where they join in pairs to form the final
hexameric product. Redrawn with permission from page 1034 in Buchanan, B. et al. (2002), Biochemistry
and Molecular Biology of Plants, ASPB, Rockville, MD and Figure 1 in Krochko, JE and Bewley, JD (1988).
Electrophoresis 9, 751–763.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.6 Continued
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.7 Section of a cotyledon of pea (Pisum sativum) after one day of imbibition.
S = Starch grain; P = Protein body. The arrows indicate phosphatase activity
adjacent to the cell wall. Phosphatases mobilize stored phosphates, e.g. in phytic
acid. Picture is cropped from Figure 1 in Bowen, ID and Bryant, JA (1978).
Protoplasma 97, 241–250
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.8 Formation of oleosomes (oil bodies) during seed maturation. Redrawn,
with permission, from p 516 in Buchanan, B. et al. (2002), Biochemistry and
Molecular Biology of Plants, ASPB, Rockville, MD and Figure 4 in Huang, AHC,
(1992) Annual Review of Plant Biology 43, 177–200.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.9 A model for the overall genetic regulation of seed development,
maturation and early germination in Arabidopsis thaliana. Details of ABI, FUS and
LEC functions are given in the text. During the early phases of germination, GA
represses embryogenesis-type activities. Also involved in this repression are the
chromatin-remodelling factor (see Chapter 3), PICKLE (PKL) and the transcriptional
repressors HS12 and HSL1. The latter appear to be specific for events in which
sugars have a regulatory role. Reproduced by permission from Santos-Mendoza m.
et al. (2008) Plant Journal 54, 608–620.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.10 Formation of protein bodies in cereals. Prolamin-type and globulin-type
(i.e. glutelins) exhibit different modes of synthesis and storage. Prolamins are laid
down into the ER lumen, which balloons out and pinches off to make protein bodies.
Globulins (glutelins) are transported from the ER via the Golgi to be deposited in the
vacuole. From Buchanan B. et al. (2002) Biochemistry and Molecular Biology of
Plants, ASPB, Rockville, MD, p 1035
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.11 An apomictic species, Orange Hawkweed (Hieraceum auranticum). Like
many apomictic plants, Hieraceum species also reproduce via stolons.
Photograph by Nancy Zack.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.12 (a) Dispersal on the coats of animals is achieved by seeds or fruit
armed with hooks, as seen in this picture of a ‘seed’ head of burdock, Arctium lappa.
The ‘seeds’ are actually one-seeded fruit known as achenes. Photo: Mike Vallender.
(b) Several different seed or fruit morphologies are adapted for wind dispersal,
including the ‘parachute’ seeds of dandelion (Taraxacum), the small seeds of poppy
(Papaver spp) in their ‘pepperpot’ fruit and the winged fruit of Acer species,
illustrated in this picture of sycamore, Acer pseudoplatanus. Photograph taken in
Haddenham, Buckinghamshire, UK by Margot Hodson.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.13 The explosive seed pods of Impatiens (in this picture, I. glandulifera).
When ripe, the pods explode on touch, scattering the seeds over a range of several
metres and often, as in the picture, detaching completely the pod from the flower
stalk Photograph by R. V. Albitsky, reproduced by permission under the Creative
Commons Attribution Share Alike Licence.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.14 Ethylene response element (ERE). Genes that are responsive to
ethylene possess in their promoters two (usually) copies of an 11bp sequence that
contains two adjacent GCC motifs. The 5bp sequence immediately upstream of the
GCC motifs shows some variation. Transcription factors that bind to EREs all
possess a 59 amino acid domain that binds to the GCC motifs.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.15 Development of polygalacturonase (a wall-softening enzyme) activity in
tomato fruit (black squares) and suppression of its activity in GM plants carrying at
antisense version of the polygalacturonase gene (white squares). MG = mid-green
stage of development. From Lea, P and Leegood, R (1999) Plant Biochemistry and
Molecular Biology, Wiley, Chichester, p 318.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.16 Breakdown of starch during germination and early seedling growth.
Starch consists of two types of polymer of a-D-glucose. Amylase is formed of
straight chains of glucose units joined by 1→4 linkages. Amylopectin is a branched
polymer; the branches are formed by 1→6 linkages and all the other linkages are
1→4. Total breakdown of these molecules to yield glucose requires the cooperation
of several enzymes.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.17 The glyoxylate cycle and its role in mobilizing lipids in fat-storing seeds.
From Lea, P and Leegood, R. (1999) Plant Biochemistry and Molecular Biology,
Wiley, Chichester, page 131.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.18 Diagram to illustrate control of the mobilization of reserves in
germinating barley seeds. (1) The embryo secretes gibberellic acid (GA) to the
aleurone layer. (2) In response to GA, the aleurone cells synthesize hydrolytic
enzymes and secrete them into the endosperm. (3) The hydrolysis products are
taken up by the embryo. The diagram is a very simplified version of the real thing. In
particular, the reader should note that the embryo is growing actively during this time
and that germination (defined as emergence of the radicle) occurs well before the
hydrolysis of the reserves. From Bryant, J. (1985), Seed΄Physiology, Edward Arnold,
London.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.19 Most GA response elements (GAREs) are set within a broader domain
– the GA response complex (GARC). There are some ‘stand-alone’ GAREs which
are longer than those set within GARCs Key: E = enhancer. Note: the diagram is not
to scale. From Lea, P and Leagood, R. (1999) Plant Biochemistry and Molecular
Biology, Wiley, Chichester, p 323.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.20 Styles of germination: (a) In pea (Pisum sativum), germination is hypogeal; cotyledons remain
below ground. (b) In common bean (Phaseolus vulgaris), germination is epigeal; cotyledons appear above
ground and, after mobilization of stored reserves, they wither and die. (c) In castor bean (Ricinus communis),
germination is also epigeal but the cotyledons become photosynthetic and live on for some time. (d) Onion
(Allium cepa) is a monocot that exhibits epigeal germination. Reproduced with permission from Raven PH et
al. (2005), Biology of Plants, 7th edition, Freeman, NY, pp 506–507
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.
Figure 4.21 Interaction of GA and phytochrome in the early growth of seedlings. In
the dark, the phytochrome-interacting factor, PIF4, promotes elongation. However,
this is inhibited by the DELLA proteins. In the presence of GA, DELLA proteins are
degraded (see Chapter 3.6, section 3.6.4). This allows the growth-promoting effects
of both PIF4 and GA to occur, and the seedling becomes etiolated. In the light, PIF4
is bound by phytochrome-B, thus inhibiting PIF4’s promotion of cell elongation. GA
still causes degradation of DELLA proteins, thus allowing the ‘normal’ GA-mediated
cell elongation. The seedlings are not etiolated.
Functional Biology of Plants
Martin J. Hodson and John A. Bryant
© 2012 by John Wiley & Sons, Ltd.