Darkdevelopment
Photosynthesis
Nutrient uptake
Respiration
DormancyPhytohormonesGene regulationEnzymes
Long distance transport
The CellMembranes and Wall
Photoreceptors
Phytochrome
Water and transpiration
Secondary metabolism
Biotic and abiotic stress
Flowering
Fertilization and embryogenesis
Seed and fruit development
Dormancy and senescence
Germination
Seed Development, Dormancy and GerminationHORT 301 – Plant PhysiologyTaiz & Zeiger Chapter 20 & 23
Finkelstein et al. (2008) Annu Rev Plant Biol 59:387-415Finch-Savage and Leubner-Merzger (2006) New Phytol 171:521-523
Hartmann & Kester et al. (2002) Plant Propagation, pp. [email protected]
1
Hartmann and Kester et al. Plant Propagation 2002
Angiosperm flower is the reproductive structure - stamen (male reproductive structure) and pistil (female reproductive structure)
2
Pollination and fertilization Pollen associates with stigma and germinatesPollen tube moves through style towards the mycropyle Generative nuclei fuse with the egg (zygote) and the polar nuclei (endosperm)
Hartmann & Kester et al. Plant Propagation 2002
3
Graham et al. 2006, Plant Biology
Auxin regulates embryo development – first discovered plant hormone Hormone – chemical messengers produced in one cell and transportedRegulate mechanisms and processes
4
Graham et al. Plant Biology 2006
Seed development – embryogenesis and endosperm development in ovuleEmbryonic axis Cotyledons and endosperm – storage of polysaccharides, lipids and proteinsSeed coat – develops from integuments of the ovule
5
Hartmann & Kester et al. Plant Propagation 2002
Seed maturation involves desiccation – 5 to 20% moisture content
7
Dormancy stages during seed maturation and germinationPrimary dormancy induction occurs during seed maturation
Dormancy maintenance is associated with desiccation tolerance
Dormancy release – seeds remain quiescent until environmental conditions are favorable for germination
Finkelstein et al. (2008) Annu Rev Plant Biol8
Primary Seed Dormancy – exogenous and endogenous factors Fruit and seed coat InhibitorsImpermeable seed coat Seed coat pigments (e.g. flavanoids) – cross-link cell walls to increase mechanical resistance and reduce permeability
9
Finch-Savage & Leubner-Metzger New Phytol 2006
Abscisic acid (ABA) and gibberellin (GA) regulate dormancy and dormancy release
ABA – induces and maintains dormancy Gibberellin (GA) – enhances dormancy release
10
Precocious germination (vivipary) caused by the ABA-deficient vivipary 14 (vp14) mutation
vp14
VP14 encodes NCED a rate limiting enzyme in ABA biosynthesis
12
ABA function in seed germination and desiccation toleranceDrought → ABA biosynthesis/accumulation → ABA receptor (signal transduction) → transcription factors → dormancy genes (seed dormancy/desiccation tolerance genes)
13
Seed dormancy release and germinationAfter ripening (cool & dry storage) - decline in ABA levels
Stratification and light – increase in GA levels
Finch-Savage & Leubner-Metzger New Phytol 200615
Finkelstein et al. Annu Rev Plant Biol 2008
Gibberellins and germinationGAs induce hydrolytic enzyme gene expression - mobilize storage product reserves and degrade seed coat cell wall
17
GA signal transduction necessary for seed germination – α-amylase synthesis and secretion from the aleurone to the starchy endosperm
19
Hartmann & Kester et al. Plant Propagation 2002
Three phases of seed germination - imbibition, lag and radicle emergence from the seed coat
Lag – minimal water uptake but high metabolic activity
Imbibition – period of rapid water uptake
20
Radical emergence from the seed coat – cell expansion driven by turgor pressure (water potential gradient) and water uptake
↓s
Hartmann and Kester et al (2002) Plant Propagation 21