title: Effects of salt stress on the structure and function of the photosynthetic apparatus in Cucumis sativus and its protection by exogenous putrescine.
abstract: With the objective to clarify the physiological significance of polyamines (PAs) in the photosynthetic apparatus, the present study investigated the effects of salt stress with and without foliar application of putrescine (Put) on the structure and function of the photosynthetic apparatus in cucumber. Salt stress at 75 mM NaCl for 7 days resulted in a severe reduction of photosynthesis. The fast chlorophyll afluorescence transient analysis showed that salt stress inhibited the maximum quantum yield of PSII photochemistry (F(v)/F(m)), mainly due to damage at the receptor side of PSII. In addition, salt stress decreased the density of active reaction centers and the structure performance. The microscopic analysis revealed that salt stress-induced destruction of the chloroplast envelope and increased the number of plastoglobuli along with aberrations in thylakoid membranes. Besides, salt stress caused a decrease in the content of endogenous PAs, conjugated and bound forms of spermidine and spermine in particular, in thylakoid membranes. However, applications of 8 mM Put alleviated the salt stress-mediated decrease in net photosynthetic rates (Pn) and actual efficiency of PSII(Φ(PSII)). Put increased PAs in thylakoid membranes and overcame the damaging effects of salt stress on the structure and function of the photosynthetic apparatus in salt-stressed plant leaves. Put application to control plants neither increased PAs in thylakoid membranes nor affected photosynthesis. These results indicate that PAs in chloroplasts play crucial roles in protecting the thylakoid membranes against the deleterious influences of salt stress. In addition, the present results point to the probability that the salt-induced dysfunction of photosynthesis is largely attributable to the loss of PAs in the photosynthetic apparatus.
authors.affiliation: Key Laboratory of Southern Vegetable Crop Genetic Improvement in Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing 210095, Jiangsu Province, People's Republic of China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Shu
authors.forename: Shi-Rong
authors.initials: SR
authors.lastname: Guo
authors.forename: Jin
authors.initials: J
authors.lastname: Sun
authors.forename: Ling-Yun
authors.initials: LY
authors.lastname: Yuan
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D018553:Cucumis sativus / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D005453:Fluorescence; D058503:Mesophyll Cells / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D010777:Photochemistry; D010788:Photosynthesis / Q000187:drug effects*; D045332:Photosystem II Protein Complex / Q000187:drug effects*; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D011073:Polyamines / Q000378:metabolism*; D011700:Putrescine / Q000494:pharmacology*; D036226:Seedlings / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D012965:Sodium Chloride / Q000494:pharmacology*; D013095:Spermidine / Q000378:metabolism; D013096:Spermine / Q000378:metabolism; D013312:Stress, Physiological; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D045332:Photosystem II Protein Complex; D011073:Polyamines; D002734:Chlorophyll; D013096:Spermine; D012965:Sodium Chloride; D013095:Spermidine; D011700:Putrescine