The Diurnal Changes of PS Ⅱ and Absorbed Light Allocation in Leaves of Alfalfa(Medicago sativa L.)

doi:10.7668/hbnxb.2009.S2.029

Abstract

Abstract: A study was conducted, using chlorophyll fluorescence technique and a local alfalfa variety Yuedongzhixing as experimental material, to investigate the diurnal changes of PS Ⅱ and maximum quantum efficiency of photosystem Ⅱ photochemistry(Fv/Fm) in alfalfa leaves. The data acquired in this study showed that the diurnal changes of Fv/Fm and actual photochemical efficiency of PS Ⅱ (φPS Ⅱ) were related to light intensity, the functional photosystem Ⅱ reaction centers were decreased to cause significant photoinhibition. With the increasing of photosynthetic actual irradiation (PAR)to simulate PAR diurnal change, and φPS Ⅱ decreased, nonphotochemical quenching (NPQ)increased, and the fraction of excited energy allocated to PS Ⅱ increased to enhance PS Ⅱ burden carrying excited energy. These results indicated that photoinhibition in alfalfa leaves were caused primarily by increasing of excited energy allocated to PS Ⅱ to enhance reversible inactivation of PS Ⅱ centers except NPQ increasing. With the decreasing of PAR, Fv/Fm and φPS Ⅱ increased, NPQ and unbalance index of excited energy allocated to PS Ⅱ and PS Ⅰ (β/α -1) declined respectively. This indicated that the recovery of PS Ⅱ photochemical efficiency was caused primarily by renewing PS Ⅱ activation owing to unloading the energy burden of PS Ⅱ.

Key words: Medicago sativa L., Chlorophyll fluorescence, Nonphotochemical quenching, State transition

CLC Number:

S541.9

YANG Dan-xia, SUN Guang-yu, CAI Dun-jiang, HU Yan-bo. The Diurnal Changes of PS Ⅱ and Absorbed Light Allocation in Leaves of Alfalfa(Medicago sativa L.)[J]. ACTA AGRICULTURAE BOREALI-SINICA, doi: 10.7668/hbnxb.2009.S2.029.

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