Different enhancement of senescence induced by metabolic products of Alternaria alternata in tobacco leaves of different ages.
The purpose of this study was to explore the mechanisms by which Alternaria alternata damages tobacco (Nicotiana tabacum) leaves. Treatment with A. alternata metabolic products enhanced senescence in leaves of different ages, as indicated by the significant decrease in chlorophyll, soluble protein, photosynthetic O(2) evolution and catalase (CAT, EC 1.11.1.6) activity as well as an increase in H(2)O(2) content. The induction of senescence by A. alternata metabolic products increased as the age of the leaves increased. A. alternata metabolic products greatly influenced the behavior of photosystem II (PSII) in the leaves: oxygen evolving complex (OEC) activity and electron transport from primary quinone electron acceptor of PS II (Q(A)) to secondary quinone electron acceptor of PS II (Q(B)) were both significantly inhibited. This inhibition also became more pronounced in older leaves. In vitro experiments revealed that, without the influence of natural senescence, the A. alternata metabolic products directly inhibited the activity of a commercial CAT solution and inhibited photosynthetic O(2) evolution, which resulted in excess PSII excitation pressure and an overaccumulation of H(2)O(2) in leaf segments. These results suggest that the significant declines in photosynthesis and CAT activity induced by the metabolic products of A. alternata were important contributors to the overaccumulation of reactive oxygen species (ROS), which accelerated senescence in tobacco leaves. The fact that the enhancement of senescence was getting more pronounced with the age of tobacco leaves might be related to the fact that older leaves already had higher H(2)O(2) levels and less antioxidant activity as reflected in lower CAT activity.
State Key Lab of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an 271018, China.
Yu-Jiao
YJ
Jia
Dan-Dan
DD
Cheng
Wei-Bin
WB
Wang
Hui-Yuan
HY
Gao
Ai-Xin
AX
Liu
Xin-Min
XM
Li
Qing-Wei
QW
Meng
D000528:Alternaria / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000378:metabolism / Q000382:microbiology / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D014026:Nicotiana / Q000378:metabolism / Q000382:microbiology* / Q000502:physiology
D045332:Photosystem II Protein Complex; D017382:Reactive Oxygen Species; D002734:Chlorophyll; D006861:Hydrogen Peroxide; D002374:Catalase