Seasonal fluctuations in photoprotective (xanthophyll cycle) and photoselective (chlorophylls) capacity in eight Mediterranean plant species belonging to two different growth forms

Abstract

Xanthophyll cycle components and their pool sizes were seasonally examined in eight Mediterranean plant species from two different growth forms (drought semi-deciduals and evergreen sclerophylls), in an attempt to correlate possible fluctuations in the above parameters with potentially photoinhibitory conditions. The xanthophyll cycle was common in all species examined and was functional throughout the year. In semi-deciduals, the maximum midday values for conversion state, defined as the ratio (zeaxanthin + antheraxanthin)/(violaxanthin + zeaxanthin + antheraxanthin), and the maximum xanthophyll pool sizes, expressed on a Chl basis, were recorded during the dry summer, indicating that the period of water shortage may be the most demanding for a high photoprotective potential. However, the data suggests that sclerophylls may also need a high photoprotective potential during winter, since the xanthophyll pool sizes were equally high during both summer and winter. Corresponding spring and autumn values were low. Furthermore, winter pre-dawn conversion state values were the highest recorded amongst all species studied, indicating that the mildly low winter temperatures may be a considerable stress factor for these plants. It is assumed that by preserving high concentrations of zeaxanthin and antheraxanthin overnight, sclerophylls retain high energy dissipation activity early in the morning, when minimum temperatures, coinciding with high photon fluence rates, are likely to drive the photosynthetic apparatus to potentially harmful overexcitation. Of significance may be the fact that almost all species show a minimum in chlorophyll content during the summer. In this way, overexcitation is alleviated and the photoprotective action of carotenoids per chlorophyll molecule is enhanced.

Drought resistance and recovery of photosystem II activity in a Mediterranean semi-deciduous shrub at the seedling stage

“…Changes of NPQ process development in our case indicated that decrease of F v /F m was not due to photodamage and that heat dissipation process though still persistent under severe water stress is not fully functional. Under similar RWC, Kyparissis et al (2000) recorded the highest photoprotective potential (xanthophyll pool size) of mature P. fruticosa plants in the field. Therefore, seedlings appeared to be less efficient than the mature plants against the increased demand for thermal energy dissipation during severe water stress, but similar regarding recovery after re-watering (Kyparissis et al 2000, Montanaro et al 2007).…”

“…In the present work we investigated PSII resistance to water stress in seedlings of the malacophyllous, dimorphic, semi-deciduous Mediterranean shrub Phlomis fruticosa L. Overall photosynthesis (gas exchange measurements), as well as ecophysiology of mature plants of P. fruticosa have been thoroughly investigated in our laboratory and a big repertoire of adaptations (morphological, biochemical and physiological) against adverse Mediterranean summer has been found (Grammatikopoulos and Manetas 1994, Grammatikopoulos et al 1995, Kyparissis et al 1997, Grammatikopoulos 1999, Karavatas and Manetas 1999, Kyparissis et al 2000. However, seedlings and young plants are expected to be more sensitive to water stress than their mature individuals (Fenner 1987, Padilla and Pugnaire 2007, Fotelli et al 2000.…”

Acclimation to light in seedlings of Quercus petraea (Mattuschka) Liebl. and Quercus pyrenaica Willd. planted along a forest-edge gradient

“…Such excess is partly related to the absorption of light and the capacity of a plant to use it in photosynthesis. Low A max together with a high chlorophyll concentration in the more exposed seedlings of Q. petraea is likely to increase such imbalance, triggering NPQ (Faria et al 1998;Kyparissis et al 2000;Martínez-Ferri et al 2000;Williams et al 2003). The rapid onset of NPQ suggested a higher sensitivity to elevated PPFD in Q. petraea.…”

Phenotypic plasticity blurs ecotypic divergence in the response of Quercus coccifera and Pinus halepensis to water stress

“…The low plasticity detected for Xuorescence characters indicates that both the species maintain their photochemical eYciency by adjustments of other physiological characters, such as modiWcations of Quercus garrigue Quercus rock Pinus garrigue Pinus rock either photorespiration, pigment content or antioxidant capacity, especially in P. halepensis. This higher plasticity of P. halepensis for pigment and antioxidant characters could be related to the photoinhibition-avoiding strategy found in this species, since it would be a mechanism to reduce light absorption by PSII, dissipate excess energy and prevent overexcitation (Kyparissis et al 2000, Martínez-Ferri et al 2000. Phenotypic plasticity in response to water explained over 75% of the total variability among individual plants.…”