Action spectrum of photosynthesis Fig 39.3

Fig Seedling germination may depend on light

Phytochrome: a reversible receptor Fig 39.15

Hey, want to swap some pollen?

I don’t have any flowers.

I guess I will have to find another plant.

I hate when that happens. You give really good pollen.

Fig Plants use day length to synchronize flowering

The critical period is actually night length Fig 39.13

Phytochrome regulates flowering time Fig 39.14

Plants use night length to determine the season.

What about daily time... the circadian clock

Circadian Rhythms: daily patterns set by light (northern flying squirrel)

(oxalis) (sunflower tracking) Phytochrome sets the circadian clock

The molecular identity of the circadian clock is unknown

CCA1 is a transcription factor that regulates some photosynthetic genes

Overexpression of CCA1 in transgenic Arabidopsis plants abolished the circadian rhythms of several genes with dramatically different phases. /Research/Tobin/research. html

Plants were created that lack a functional CCA1 gene cla.edu/Research/T obin/research.html

With no CCA1 protein, phytochrome induction of Lhcb RNA is reduced to 60% of the normal level. a.edu/Research/Tobin /research.html

Plants overexpressing CCA1 had delayed flowering. Furthermore, leaf movement rhythms were abolished

CCA1 is part of the oscillator, but it is not THE oscillator/clock.

Enjoy your break...