Are symplast tolerance to intense drought conditions and xylem vulnerability to cavitation coordinated? An integrated analysis of photosynthetic, hydraulic and leaf level processes in two Mediterranean drought-resistant species

10 Pags., 2 Tabls., 10 Figs.In the last decades, plant resistance to drought conditions has been studied intensively both at whole-tree level and at tissue level. These studies have highlighted the role of xylem cavitation in the global resistance of plants to drought. In this paper, we investigate the coordination among several symplastic variables during intense drought conditions and its relationship to resistance to xylem cavitation. We selected 2-year-old seedlings of Pistacia lentiscus L. and Quercus coccifera L., two Mediterranean drought-resistant species with differences in both xylem vulnerability to cavitation and survival rates under field conditions. Drought provoked large decreases in photosynthetic rates and predawn Fv/Fm ratios, as well as less marked decreases in actual PSII efficiency (due to decreases in both intrinsic PSII efficiency and photochemical quenching). Photosynthetic pigment composition remained fairly unchanged down to water potentials of −8 MPa, despite inter-conversions within the xanthophyll cycle in both species. Cell membrane injury and proline accumulation followed similar patterns, and were much more intense in P. lentiscus than in Q. coccifera. Comparisons between variables revealed that both species: (i) followed a drought avoidance strategy, (ii) were very resistant to drought conditions at symplastic level, and (iii) showed an overall good relationship between apoplast (xylem cavitation) and symplast resistance (membrane stability, PSII functionality, proline accumulation and pigment composition). Differences between species in functional symplastic and apoplastic characteristics are discussed.We thank JS Pereira (ISA, Portugal) for helpful suggestions and comments on a preliminary version of the manuscript. We also thank CITA-DGA for technical support, Carmen Pérez for her help with proline analyses and J. Scheiding for the English revision of the manuscript. This work was supported by Generalitat Valenciana R&D projects (Grupos 03/155 and GV 05/208), the Spanish Ministry of Environment (MARM, Project ESTRES 063/SGTB/2007/7.1), MICINN (SUM2008-00004-C03-03 and CGL2008-03649) and Consolider-Ingenio (GRACCIE CSD2007-00067). FM, AA and EGP wish to thank the Gobierno de Aragón (A03 and A54 research groups) for financial support.Peer reviewe

Are symplast tolerance to intense drought conditions and xylem vulnerability to cavitation coordinated? An integrated analysis of photosynthetic, hydraulic and leaf level processes in two Mediterranean drought-resistant species

10 Pags., 2 Tabls., 10 Figs.In the last decades, plant resistance to drought conditions has been studied intensively both at whole-tree level and at tissue level. These studies have highlighted the role of xylem cavitation in the global resistance of plants to drought. In this paper, we investigate the coordination among several symplastic variables during intense drought conditions and its relationship to resistance to xylem cavitation. We selected 2-year-old seedlings of Pistacia lentiscus L. and Quercus coccifera L., two Mediterranean drought-resistant species with differences in both xylem vulnerability to cavitation and survival rates under field conditions. Drought provoked large decreases in photosynthetic rates and predawn Fv/Fm ratios, as well as less marked decreases in actual PSII efficiency (due to decreases in both intrinsic PSII efficiency and photochemical quenching). Photosynthetic pigment composition remained fairly unchanged down to water potentials of −8 MPa, despite inter-conversions within the xanthophyll cycle in both species. Cell membrane injury and proline accumulation followed similar patterns, and were much more intense in P. lentiscus than in Q. coccifera. Comparisons between variables revealed that both species: (i) followed a drought avoidance strategy, (ii) were very resistant to drought conditions at symplastic level, and (iii) showed an overall good relationship between apoplast (xylem cavitation) and symplast resistance (membrane stability, PSII functionality, proline accumulation and pigment composition). Differences between species in functional symplastic and apoplastic characteristics are discussed.We thank JS Pereira (ISA, Portugal) for helpful suggestions and comments on a preliminary version of the manuscript. We also thank CITA-DGA for technical support, Carmen Pérez for her help with proline analyses and J. Scheiding for the English revision of the manuscript. This work was supported by Generalitat Valenciana R&D projects (Grupos 03/155 and GV 05/208), the Spanish Ministry of Environment (MARM, Project ESTRES 063/SGTB/2007/7.1), MICINN (SUM2008-00004-C03-03 and CGL2008-03649) and Consolider-Ingenio (GRACCIE CSD2007-00067). FM, AA and EGP wish to thank the Gobierno de Aragón (A03 and A54 research groups) for financial support.Peer reviewe