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. 199-220drhodes@purdue.edu

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 types

6

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

ABA and signal transduction – ABA induces activation of genes

11

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

ABA activation of the receptor and signaling

Finkelstein et al. (2008) Annu Rev Plant Biol

14

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

GA affects seed development

16

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 biosynthesis and storage product mobilization for seed germination

18

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

(d)

Seed germination and seedling emergence from the soil

22