Plant growth, development and differentiation(6 hr)- Plant growth and

development- Plant cell differentiation- Plant hormones and their controls in plant development- Control of flowering

Cosgrove D.J. 1997. Plant Cell 9: 1031-1041

Stress relaxation of cell wall

Acid growth theoryGrowth hormone auxin induces

elongation growth of plant cells.

Growing cell wall extend much faster at acidic pH than at neutral pH.

Auxin-induced growth is associated with wall acidification.

-IAA +IAA

Acid growth theory

Hager A. et al. 1991 Planta 185: 527-537

(a) stem and coleoptile sections excrete protons in response to auxin, lowering the pH of the apoplast.

(b) treatment of auxin-sensitive tissues with acidic buffers of pH 5.0 can cause cells to elongate at rates comparable to that induced by auxin.

(c) neutral buffers infiltrated into the apoplast can inhibit auxin-induced growth.

(d) the fungal toxin fusicoccin, whose main action is to promote extensive acidification of the apoplast, also causes rapid cell elongation.

Evidences supporting the Acid Growth Theory

Growth curve

Figure 1   Growth of the unicellular green alga Chlamydomonas. Growth is assessed by a count of the number of cells per milliliter at increasing times after the cells are placed in fresh growth medium. Temperature, light, and nutrients provided are optimal for growth. An initial lag period during which cells may synthesize enzymes required for rapid growth is followed by a period in which cell number increases exponentially. This period of rapid growth is followed by a period of slowing growth in which the cell number increases linearly. Then comes the stationary phase, in which the cell number remains constant or even declines as nutrients are exhausted from the medium.

“unicellular organism”

Growth curve

วดัการเติบโตจาก- น้ำ�าหนักสด- น้ำ�าหนักแห้ง- ปรมิาตร- ความสงู- ฯลฯ

ท่ีระยะเวลาต่าง ๆ Sh

oot

dry

wei

ght

(kg)

“multicellular organism”

Reproductive development

การเขา้สูร่ะยะเจรญิพนัธุ ์(reproductive stage) ควบคมุโดยปัจจยัสิง่แวดล้อม เชน่ อุณหภมูแิละจำานวนชัว่โมงแสง เนื้อเยื่อเกิดการเจรญิเป็น floral meristem

inflorescence

ท้ำาอยา่งไร พชืจะออกดอก

“ท้ำาอยา่งไร พชืจะออกดอก”

๑. รูจ้กัธรรมชาติของพชืต้นนั�น

๒. เขา้ใจกลไกควบคมุการออกดอก

sun /shade plant

tropical/

temperate

annual/

perennial

etc.

signal/ receptor/

gene expression

ทบทวนโครงสรา้งดอก

เนื�อเยื่อเจรญิ: floral meristemโครงสรา้งของดอก ชั�นของดอก (whorl) 4 ชั�น

Flowering genes

ABC model: three floral organ identity genesHomeotic

mutation

Flowering signals and receptors

Short-day plants

Long-day plants

Photoperiod: day length controls of flowering

Phytochrome control of flowering

Vernalization: cold promotes flowering

Taiz and Zeiger (2002)

Four developmental pathway for flowering

เขา้ใจกลไกควบคมุการออกดอกsignalภายใน: hormone

(gibberellins), circadian rhythm

(physiological clock)ภายนอก: light, temperature,

humidity, nutrientreceptorphytochrome (light); ?

(temperature)gene expressionmeristem identity genes /

floral organ identity genes/ cadastral genes