title: Response of transglutaminase activity and bound putrescine to changes in light intensity under natural or controlled conditions in Quercus ilex leaves.
abstract: In order to further study a previously observed relationship between polyamine (PA) content and changes in irradiation, we examined the level of free and bound PAs, the activity of transglutaminase (TGase, EC 2.3.2.13) and chlorophyll fluorescence in holm oak (Quercus ilex L.) leaves in response to different levels of light intensity and amount. A diurnal trend of free and bound putrescine (F-Put and B-Put, respectively) and TGase activity was observed in plants under natural conditions in the forest, with the highest value corresponding to the maximum light intensity and amount of light received by the leaves. In another set of experiments, potted Q. ilex plants in experimental fields were subjected to a range of periods of natural photosynthetic photon flux density (PPFD) by covering or not covering the whole trees. Under a natural photoperiod (uncovered leaves), B-Put content and TGase activity paralleled the diurnal PPFD pattern, reaching a maximum at the highest PPFD; prior to this maximum, free PAs showed a significant rise. Plants that were in darkness until midday and suddenly exposed to high light intensity showed enhanced TGase activity, resulting in the maximum accumulation of B-Put. The involvement of the accumulation of B-Put reflected in the changes of the B-Put/bound spermidine ratio during the photoprotective responses to high light stress in forest plants is discussed in relation to the chlorophyll fluorescence parameters observed.
authors.affiliation: Unitat Fisiologia Vegetal, Departament de Biologia Vegetal, Facultat Biologia, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Pintó-Marijuan
authors.forename: Marina
authors.initials: M
authors.lastname: de Agazio
authors.forename: Massimo
authors.initials: M
authors.lastname: Zacchini
authors.forename: Maria Asunción
authors.initials: MA
authors.lastname: Santos
authors.forename: Josep Maria
authors.initials: JM
authors.lastname: Torné
authors.forename: Isabel
authors.initials: I
authors.lastname: Fleck
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D005470:Fluorometry / Q000379:methods; D008027:Light; D009757:Nylons / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology* / Q000378:metabolism / Q000528:radiation effects; D010940:Plant Proteins / Q000378:metabolism; D011700:Putrescine / Q000378:metabolism*; D029963:Quercus / Q000201:enzymology* / Q000378:metabolism / Q000528:radiation effects; D011503:Transglutaminases / Q000378:metabolism*
chemical_list: D009757:Nylons; D010940:Plant Proteins; D002734:Chlorophyll; D011503:Transglutaminases; D011700:Putrescine