Putrescine is a main polyamine found in animals, plants and microbes, but the molecular mechanism underlying its mode of action is still obscure. In vivo chlorophyll a fluorescence in tobacco leaf discs indicated that putrescine treatment affects the energization of the thylakoid membrane. Molecular dissection of the electron transport chain by biophysical and biochemical means provided new evidence that putrescine can play an important bioenergetic role acting as a cation and as a permeant natural buffer. We demonstrate that putrescine increases chemiosmotic ATP synthesis more than 70%. Also a regulation of the energy outcome by small changes in putrescine pool under the same photonic environment (i.e., photosynthetically active radiation) is shown. The proposed molecular mechanism has at least four conserved features: (i) presence of a membrane barrier, (ii) a proton-driven ATPase, (iii) a DeltapH and (iv) a pool of putrescine.

The sensitivity of the photosynthetic apparatus to ultraviolet-B (UV-B) irradiation was studied in cultures of unicellular green alga Scenedesmus obliquus incubated in low light (low photosynthetically active radiation intensity [LL]) and high light (high photosynthetically active radiation intensity [HL]) conditions, treated or not with exogenous polyamines. Biochemical and physicochemical measurements showed that UV-B radiation induces a decrease in the thylakoid-associated putrescine (Put) and an increase in spermine (Spm), so that the reduction of Put/Spm ratio leads to the increase of light-harvesting complex II (LHCII) size per active reaction center and, consequently, the amplification of UV-B effects on the photosynthetic apparatus. The separation of oligomeric and monomeric forms of LHCII from isolated thylakoids showed that UV-B induces an increase in the oligomeric forms of LHCII, which was more intense in LL than in HL. By manipulating the LHCII size with exogenous polyamines, the sensitivity degree of the photosynthetic apparatus to UV-B changed significantly. Specifically, the addition of Put decreased highly the sensitivity of LL culture to UV-B because of the inhibitory effect of Put on the LHCII size increasing, whereas the addition of Spm enhanced the UV-B injury induced in HL culture because of the increasing of LHCII size. The ability of the photosynthetic apparatus to recover the UV-B induced changes was also investigated.

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The biosynthesis of the polyamines spermidine (Spd) and spermine (Spm) from putrescine (Put) is catalysed by the consequent action of two aminopropyltransferases, spermidine synthase (SPDS EC: 2.5.1.16) and spermine synthase (SPMS EC: 2.5.1.22). Two cDNA clones coding for SPDS and SPMS homologues in the nitrogen-fixing nodules of the model legume Lotus japonicus were identified. Functionality of the encoded polypeptides was confirmed by their ability to complement spermidine and spermine deficiencies in yeast. The temporal and spatial expression pattern of the respective genes was correlated with the accumulation of total polyamines in symbiotic and non-symbiotic organs. Expression of both genes was maximal at early stages of nodule development, while at later stages the levels of both transcripts declined. Both genes were expressed in nodule inner cortical cells, vascular bundles, and central tissue. In contrast to gene expression, increasing amounts of Put, Spd, and Spm were found to accumulate during nodule development and after maturity. Interestingly, nodulated plants exhibited systemic changes in both LjSPDS and LjSPMS transcript levels and polyamine content in roots, stem and leaves, in comparison to uninoculated plants. These results give new insights into the neglected role of polyamines during nodule development and symbiotic nitrogen fixation (SNF).

The sensitivity of the photosynthetic apparatus to ultraviolet-B (UV-B) irradiation was studied in cultures of unicellular green alga Scenedesmus obliquus incubated in low light (low photosynthetically active radiation intensity [LL]) and high light (high photosynthetically active radiation intensity [HL]) conditions, treated or not with exogenous polyamines. Biochemical and physicochemical measurements showed that UV-B radiation induces a decrease in the thylakoid-associated putrescine (Put) and an increase in spermine (Spm), so that the reduction of Put/Spm ratio leads to the increase of light-harvesting complex II (LHCII) size per active reaction center and, consequently, the amplification of UV-B effects on the photosynthetic apparatus. The separation of oligomeric and monomeric forms of LHCII from isolated thylakoids showed that UV-B induces an increase in the oligomeric forms of LHCII, which was more intense in LL than in HL. By manipulating the LHCII size with exogenous polyamines, the sensitivity degree of the photosynthetic apparatus to UV-B changed significantly. Specifically, the addition of Put decreased highly the sensitivity of LL culture to UV-B because of the inhibitory effect of Put on the LHCII size increasing, whereas the addition of Spm enhanced the UV-B injury induced in HL culture because of the increasing of LHCII size. The ability of the photosynthetic apparatus to recover the UV-B induced changes was also investigated.

The sensitivity of the photosynthetic apparatus to ultraviolet‐B (UV‐B) irradiation was studied in cultures of unicellular green alga Scenedesmus obliquus incubated in low light (low photosynthetically active radiation intensity [LL]) and high light (high photosynthetically active radiation intensity [HL]) conditions, treated or not with exogenous polyamines. Biochemical and physicochemical measurement showed that UV‐B radiation induces a decrease in the thylakoid‐associated putrescine (Put) and an increase in spermine (Spm), so that the reduction of Put/Spm ratio leads to the increase of light‐harvesting complex II (LHCII) size per active reaction center and, consequently, the amplification of UV‐B effects of the photosynthetic apparatus. The separation of oligomeric and monomeric froms of LHCII from isolated thylakoids showed that UV‐B induces an increase in the oligomeric forms of LHCII, which was more intense in LL than in HL. By manipulating the LHCII size with exogenous polyamines, the sensitivity degree of the photosynthetic apparatus to UV‐B changed significantly. Specifically, the addition of Put decreased highly the sensitivity of LL culture to UV‐B because of the inhibitory effect of Put on the LHCII size increasing, wheres the addition of Spm enhanced the UV‐B injury induced in HL culture because of the increasing of LHCII size. The ability of the photosynthetic apparatus to recover the UV‐B induced changes was also investigated.

No abstract

Υποβλήθηκε ως µέρος των απαιτήσεων για τον τίτλο του ∆ιδάκτορα στο µεταπτυχιακό πρόγραµµα ΕΠΕΑΕΚ µε τίτλο «ΜΟΡΙΑΚΗ ΒΙΟΛΟΓΙΑ ΚΑΙ ΒΙΟΤΕΧΝΟΛΟΓΙΑ ΦΥΤΩΝ» του Τµήµατος Βιολογίας του Πανεπιστηµίου Κρήτης ΠΕΡΙΛΗΨΗ XV βλαβερές δράσεις της UVB λογω της ανταγωνιστικής δράσης της υψηλής έντασης της PAR-ακτινοβολίας.