Damage of PS II during senescence of Spirodela polyrrhiza explants under long-day conditions and its prevention by 6-benzyladenine.
The chlorophyll a (Chl a) fluorescence technique was applied to investigate damage of PS II during senescence of excised half-fronds in Spirodela polyrrhiza P143. The green explants showed a typical Chl a fluorescence transient, OJIP. After cultivation of explants under long-day conditions for 8 days, all the J, I, and P steps disappeared, but a clear K band, an indication of senescence, was observed. JIP-test showed that at this time point, the photosynthetic performance index (PI) dropped to zero and the active reaction center (RC) per leaf cross-section (RC/CS) declined to 18%. As the oxygen-evolving complex (OEC) and the chlorophyll content all remained above 42%, it is proposed that the decline in RC contributes more to the appearance of the K band. Supplementation of 6-benzyladenine (6-BA) into the medium at the beginning of cultivation caused dramatic increase in PI, OEC, RC/CS, and chlorophyll content, and at any time before the 8th day reversed the senescence process of the explants. When 6-BA was added after 8 days of cultivation, the PI did not increase anymore, RC/CS and OEC were maintained at 22% and above 40%, respectively, and chlorophyll content decreased continuously further. These data support a view that the decline in RC is crucial for initiation of the irreversible senescence phase of explants cultivated under long-day conditions.
Liu
Qingdai
Q
Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, 300071 Tianjin, China.
Zhu
Yerong
Y
Tao
Hanlin
H
Wang
Ningning
N
Wang
Yong
Y
D001593:Benzyl Compounds; D002734:Chlorophyll; D000077194:Chlorophyll A; D005453:Fluorescence; D007701:Kinetin / Q000502:physiology*; D019684:Magnoliopsida / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000502:physiology*; D011687:Purines
D001593:Benzyl Compounds; D045332:Photosystem II Protein Complex; D011687:Purines; D002734:Chlorophyll; C480551:benzylaminopurine; D007701:Kinetin; D000077194:Chlorophyll A