Dark development Photosynthesis Nutrient uptake Respiration Dormancy Phytohormones Gene regulation Enzymes Long distance transport The Cell Membranes 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 Germination HORT 301 – Plant Physiology Taiz & Zeiger Chapter 20 & 23 Finkelstein et al. (2008) Annu Rev Plant Biol 59: Finch-Savage and Leubner-Merzger (2006) New Phytol 171: Hartmann & Kester et al. (2002) Plant Propagation, pp

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 germinates Pollen 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

Graham et al. 2006, Plant Biology Auxin regulates embryo development – first discovered plant hormone Hormone – chemical messengers produced in one cell and transported Regulate mechanisms and processes 4

Graham et al. Plant Biology 2006 Seed development – embryogenesis and endosperm development in ovule Embryonic axis Cotyledons and endosperm – storage of polysaccharides, lipids and proteins Seed 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 germination Primary 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 Biol 8

Primary Seed Dormancy – exogenous and endogenous factors Fruit and seed coat Inhibitors Impermeable 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 tolerance Drought → 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 germination After ripening (cool & dry storage) - decline in ABA levels Stratification and light – increase in GA levels Finch-Savage & Leubner-Metzger New Phytol

GA affects seed development 16

Finkelstein et al. Annu Rev Plant Biol 2008 Gibberellins and germination GAs 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↓s Hartmann and Kester et al (2002) Plant Propagation 21

(d) Seed germination and seedling emergence from the soil 22