The abundance of minor chlorophyll a/b-binding proteins CP29 and LHCI of barley (Hordeum vulgare L.) during leaf senescence is controlled by light.

The abundance of the minor light-harvesting complexes CP29 and LHCI generally declines during the senescence of barley leaves. When light intensity declined due to clouding during the senescence of flag leaves from barley plants grown under field conditions, the levels of both light-harvesting complexes temporarily increased in parallel with photosystem II-efficiency [F(v)/F(m)]. A sudden shift from high light conditions to low light conditions during the growth of barley plants in a growth chamber also resulted in an increase in the abundance of minor light-harvesting complexes and a parallel increase in F(v)/F(m) as well as in the chlorophyll a+b-content of senescing primary foliage leaves. Northern blot analyses with a cDNA probe specific for the barley Lhcb4 gene encoding CP29 showed that the light-dependent changes in the abundance of CP29 during senescence are paralleled by corresponding changes in the transcript level. The results indicate that adjustments of the levels of minor light-harvesting complexes during senescence under high light conditions may serve in the prevention of photo-oxidative damage to the photosynthetic reaction centres and under low light in ensuring efficient photosynthesis of the residual photosynthetic reaction centres.