Phytochrome and flowering.When is the right time to flower?

• Unreliable indicators of time of year– Temperature – Moisture – Light levels

• Reliable: length of day/night – Varies with season– Varies with latitude

• Detected by phytochrome

Sunlight

Mostly red

A little far red

Pr

Pfr

In sunlight

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

In sunlight most P gets converted to Pfr form.

Pr

Pfr

Start of night

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

Most P in Pfr form.

Pfr

In the dark

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPr

Pfr

Pfr

Pfr form changes gradually to Pr form.

Pr

Pr

Pr

Pr

Pfr

After a short night

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPr

Pfr

Pfr

much Pfr still remains.

Pr

Pr

Pr

Pr

Pfr

Later in the night

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

PfrPfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

more Pfr changes to Pr.

Pr

Pr

Pr

Pr

Pfr

After a long night

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPr

Pfr

Pfr

all the Pfr is gone.

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

PrPr

Pr

PrPr

Pr

Pr

Pr

Pfr

Next day

Pfr

PrPr

Pr

Pr

Pr

Pr

Pr

Pr

Pr

Pfr

Pfr

Pfr

Pfr

Pfr

PfrPfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pfr

Pr

Pfr

Pfr

Most P gets converted to Pfr form again.

Long day plant = Short night plants

• Needs short night to flower• Needs Pfr still present at end of night• Pfr promotes flowering for LDPs

Short day plant = Long night plant

• Needs long night to flower• Needs Pfr gone at end of night• Pfr inhibits flowering for SDPs

Can trick a SDP into not flowering with a brief flash of red light during the long night, this resets much of its phytochrome to Pfr form.

LDP SDP

Long day: Pfr remains at end of short night.

Pfr promotes flowering for LDPs.

Pfr inhibits flowering for SDPs.

Short day: Pfr gone at end of long night.

Lack of Pfr promotes flowering for LDPs.

Lack of Pfr inhibits flowering for SDPs.

Blue light responses, chapter 18

1. Phototropism

2. Stomatal opening

3. Chlorophyll and carotenoid synthesis

4. Inhibition of hypocotyl elongation

5. Altered gene expression

Phototropism - directional growthtoward light.

Most evident indark-grown seedlings.

Characteristic blue-light action spectrum Fig. 18.1

“”three finger” pattern

Figure 18.2

How does bending toward light happen?

Mechanically, what’s going on?

1. Collapse of cells on near side

2. Increased growth on far side, no change on near side.

3. Reduced growth on near side, no change on far side.

Wild type

Mutant

Blue light response causes differentialgrowth by slowingcell expansion on near side.

Blue light responseis very rapid.

Fig. 18.6 Blue light depolarizesthe plasmamembranebefore reducinggrowth rate

Blue light andstomatal opening

The blue lighteffect is not due to increasedphotosynthesis

Fig. 18.11. Action spectrum for blue lightstimulated stomatal opening in red light background.

Blue light stimulates guard cell H+ pumps.

Blue light stimulates a proton pump on guard cell plasmamembrane

Blue light regulates osmotic relations of guard cells:1. H+, K+, Cl- fluxes at plasmamembrane2. Malate synthesis increases3. Sucrose synthesis increases4. K+, Cl-, malate, and sucrose accumulate in vacuole