Phytochrome Action Plant Physiology 2009 UNI

The pigment phytochrome Detects R and FR light Provides information about environment Answers 3 questions for plant –Am I in the light? –Do I have plants as neighbors or above me? –Is it time to flower?

Seed location? Red light from sun penetrates to seed. No light from sun to this deep seed. Seed germinates.No germination. Red light to seed = near surface

Why bother? Seeds store materials to start growth Must reach light before running out of stored materials Small seeds –Need to be very near surface –Often need light for germination Germinating plants straighten & open leaves at surface, too

Plant neighbors? Far red reflected from other plants. Red absorbed by other plants. Far red enriched = neighbors

Why does this matter? Neighboring plants are threats –Might grow taller, shade you Solution –Grow at least as tall as neighbors –Need to know that you have neighbors Isolated plants typically shorter than crowded plants –Other reasons, too

Under other plants? Red absorbed by other plants. Far red reflected from other plants or transmitted. Far red enriched = understory

Why important? Best growth strategy for understory plants is different than for plants in open Need to know whether –Shaded by other plants OR –Just cloudy OR –Late in day (low light)

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

Red-absorbing phytochrome Far red absorbing phytochrome Interconverted Two forms of the same compound Total amount same Phytochrome has 2 forms PrPr P fr PrPr

In red light PrPr P fr P r absorbs red light, changes to P fr form. P fr doesn’t absorb red light, stays the same.

In far red light PrPr P fr P fr absorbs far red light, changes to P r form. P r doesn’t absorb far red light, stays the same. PrPr

PrPr In pure light P fr In pure far red light, all the phytochrome ends up in the P r form. In pure red light, all the phytochrome ends up in the P fr form.

Sunlight Mostly red A little far red

PrPr P fr In sunlight P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr In sunlight most P gets converted to P fr form.

PrPr P fr Start of night P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr Most P in P fr form.

P fr In the dark P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr P fr form changes gradually to P r form. PrPr PrPr PrPr PrPr

P fr After a short night P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr P fr still left. PrPr PrPr PrPr PrPr

LDP = SNP Needs short night Needs P fr still present at end of night P fr promotes flowering for LDPs

P fr Later in the night P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr More P fr changes to P r. PrPr PrPr PrPr PrPr

P fr After a long night P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr All the P fr is gone. PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr

PrPr P fr Day dawns P fr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr PrPr Most P gets converted to P fr form again.

SDP = LNP Needs long night Needs P fr gone at end of night P fr inhibits flowering for SDPs

LDP SDP Long day: P fr left at end of short night. P fr promotes flowering for LDPs. P fr inhibits flowering for SDPs. Short day: P fr gone at end of long night. No P fr to promote flowering for LDPs. No P fr to inhibit flowering for SDPs.

Waiting for the right time Plants grow leaves until it is time to flower LDPs wait until the day is long enough –Really night short enough –Some time before June 21 SPDs wait until the day is short enough –Really night long enough –Some time after June 21 Flower opening happens later

Day neutral plants Flower when mature enough Maybe other environmental signals (temp?) Day length (dark length) doesn’t matter

Through the year May June July August September October Specific flowers at specific times.

Phytochrome tells plants If they are near the surface About their plant neighbors Whether it is time to flower And lots more