title: The photoprotective role of spermidine in tomato seedlings under salinity-alkalinity stress.
abstract: Polyamines are small, ubiquitous, nitrogenous compounds that scavenge reactive oxygen species and stabilize the structure and function of the photosynthetic apparatus in response to abiotic stresses. Molecular details underlying polyamine-mediated photoprotective mechanisms are not completely resolved. This study investigated the role of spermidine (Spd) in the structure and function of the photosynthetic apparatus. Tomato seedlings were subjected to salinity-alkalinity stress with and without foliar application of Spd, and photosynthetic and morphological parameters were analyzed. Leaf dry weight and net photosynthetic rate were reduced by salinity-alkalinity stress. Salinity-alkalinity stress reduced photochemical quenching parameters, including maximum photochemistry efficiency of photosystem II, quantum yield of linear electron flux, and coefficient of photochemical quenching (qP). Salinity-alkalinity stress elevated nonphotochemical quenching parameters, including the de-epoxidation state of the xanthophyll cycle and nonphotochemical quenching (NPQ). Microscopic analysis revealed that salinity-alkalinity stress disrupted the internal lamellar system of granal and stromal thylakoids. Exogenous Spd alleviated the stress-induced reduction of leaf dry weight, net photosynthetic rate, and qP parameters. The NPQ parameters increased by salinity-alkalinity stress were also alleviated by Spd. Seedlings treated with exogenous Spd had higher zeaxanthin (Z) contents than those without Spd under salinity-alkalinity stress. The chloroplast ultrastructure had a more ordered arrangement in seedlings treated with exogenous Spd than in those without Spd under salinity-alkalinity stress. These results indicate that exogenous Spd can alleviate the growth inhibition and thylakoid membrane photodamage caused by salinity-alkalinity stress. The Spd-induced accumulation of Z also may have an important role in stabilizing the photosynthetic apparatus.
authors.affiliation: College of Horticulture, Northwest Agricultural & Forest University, Yangling, China; Key Laboratory of Protected Horticultural Engineering in Northwest, Ministry of Agriculture, Shaanxi Yangling, China.
authors.forename: Lipan
authors.initials: L
authors.lastname: Hu
authors.affiliation: College of Horticulture, Northwest Agricultural & Forest University, Yangling, China; Key Laboratory of Protected Horticultural Engineering in Northwest, Ministry of Agriculture, Shaanxi Yangling, China.
authors.forename: Lixia
authors.initials: L
authors.lastname: Xiang
authors.affiliation: College of Horticulture, Northwest Agricultural & Forest University, Yangling, China; Key Laboratory of Protected Horticultural Engineering in Northwest, Ministry of Agriculture, Shaanxi Yangling, China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.affiliation: College of Horticulture, Northwest Agricultural & Forest University, Yangling, China; Key Laboratory of Protected Horticultural Engineering in Northwest, Ministry of Agriculture, Shaanxi Yangling, China.
authors.forename: Xiaoting
authors.initials: X
authors.lastname: Zhou
authors.affiliation: College of Horticulture, Northwest Agricultural & Forest University, Yangling, China; Key Laboratory of Protected Horticultural Engineering in Northwest, Ministry of Agriculture, Shaanxi Yangling, China.
authors.forename: Zhirong
authors.initials: Z
authors.lastname: Zou
authors.affiliation: College of Horticulture, Northwest Agricultural & Forest University, Yangling, China; Key Laboratory of Protected Horticultural Engineering in Northwest, Ministry of Agriculture, Shaanxi Yangling, China.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Hu
mesh_terms: D002734:Chlorophyll / Q000737:chemistry; D002736:Chloroplasts / Q000648:ultrastructure; D018551:Solanum lycopersicum / Q000502:physiology*; D046529:Microscopy, Electron, Transmission; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000502:physiology; D010858:Pigmentation; D017382:Reactive Oxygen Species / Q000737:chemistry; D054712:Salinity; D012492:Salts / Q000737:chemistry; D036226:Seedlings / Q000502:physiology*; D013095:Spermidine / Q000502:physiology*; D020524:Thylakoids / Q000648:ultrastructure; D024341:Xanthophylls / Q000737:chemistry
chemical_list: D045332:Photosystem II Protein Complex; D017382:Reactive Oxygen Species; D012492:Salts; D024341:Xanthophylls; D002734:Chlorophyll; D013095:Spermidine