Response of the photosynthetic apparatus to a flowering-inductive period by water stress in Citrus

The photosynthetic responses to a flowering-inductive water-stress period and recovery were studied and compared in two Citrus species. Under greenhouse conditions, Fino lemon and Owari satsuma trees were subjected to moderate (-2 MPa at predawn) and severe (-3 MPa) water stress levels and were re-watered after 60 days. Vegetative growth was inhibited during the stress assays, and strong defoliation levels were reported, especially in Fino lemon. In both species, bud sprouting was induced after re-watering. Flowers and vegetative shoots developed in Owari satsuma after a drought period, and the development was independent of the stress level. In Fino lemon, vegetative shoots and flowers were primarily formed after moderate and severe stress, respectively. The photosynthetic rate and stomatal conductance were reduced by water stress, and a marked increase in water-use efficiency at the moderate water deficit level was observed. Nevertheless, the photosynthetic apparatus was not damaged, since the maximum quantum yield, photosynthetic pigment concentrations and Rubisco level and activity did not change. Furthermore, the measured malonyldialdehyde (MDA) and peroxidase activity indicated that oxidative stress was not specifically triggered by water stress in our study. Therefore, the gas exchange, fluorescence and biochemical parameters suggested that diffusional limitations to photosynthesis predominated in both of the studied Citrus species, and explained the rapid recovery of the photosynthetic parameters after rehydration. The net CO 2 fixation rate and stomatal conductance were recovered within 24 h in Fino lemon, whereas 3 days were required in Owari satsuma. This suggests the presence of some metabolic limitations in the latter species. Furthermore, the sensibility of the defoliation rates, the accumulation of proline and the stomatal behaviour in response to water stress indicated a higher drought tolerance of Fino lemon, according to its better acclimation to hot climates. © 2011 Springer-Verlag.The authors thank Dr. J. Moreno and co-workers from the Departamento de Bioquimica of the Universidad de Valencia for his help and support in the Rubisco assays, and Dr. F. Fornes, Dr. A. Calatayud and Dr. E. Primo-Millo for the critical review of the manuscript. This work was funded by the Universitat Politecnica de Valencia, Spain (Ayudas para primeros proyectos de investigacion PAID06-06).Ávila Reséndiz, C.; Guardiola Barcena, JL.; González Nebauer, S. (2012). Response of the photosynthetic apparatus to a flowering-inductive period by water stress in Citrus. Trees - Structure and Function. 26(3):833-840. https://doi.org/10.1007/s00468-011-0657-4S833840263Addicott FT (1982) Abscission. University of California Press, BerkeleyBajji M, Kinet JM, Lutts S (1998) Salt stress effects on roots and leaves of Atriplex halimus L. and their corresponding callus. Plant Sci 137:131–142Barbera G, Fatta-del-Bosco G, Lo-Cascio B (1985) Effect of water stress on lemon summer bloom: the Forzatura technique in the Sicilian citrus industry. Acta Hortic 171:391–397Bates LS, Waldren RP, Teare ID (1973) Rapid determination of free proline for water stress studies. Plant Soil 39:205–207Bota J, Medrano H, Flexas J (2004) Is photosynthesis limited by decreased Rubisco activity and RuBP content under progressive water stress? New Phytol 162:671–681Bradford MM (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 72:248–254Cassin J, Bourdeaut A, Fougue V, Furon V, Gaillard JP, LeBourdelles J, Montagut G, Moreuil C (1969) The influence of climate upon blooming of Citrus in tropical areas. Proc Int Soc Citrus 1:315–323Castel JR, Buj A (1990) Response of Salustiana oranges to high frequency deficit irrigation. Irrig Sci 11:121–127Chaikiatitiyos S, Menzel CM, Rasmussen TS (1994) Floral induction in tropical fruit trees: effects of temperature and water supply. J Hortic Sci 69:397–415Chaves MM, Flexas J, Pinheiro C (2009) Photosynthesis under drought and salt stress: regulation mechanisms from whole plant to cell. Ann Bot 103:551–560Costa JM, Ortuño MF, Chaves M (2007) Deficit irrigation as a strategy to save water: physiology and potential application to horticulture. J Integr Plant Biol 49:1421–1434Davenport TL (1990) Citrus flowering. Hortic Rev 12:249–408Davies FS, Albrigo LG (1994) Citrus. CAB International, Wallingford, pp 126–134Domingo R, Ruiz-Sánchez MC, Sánchez-Blanco MJ, Torrecillas A (1996) Water relations, growth and yield of Fino lemon trees under regulated deficit irrigation. 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Physiol Plant 86:648–652García-Sánchez F, Syvertsen JP, Gimeno V, Botía P, Pérez-Pérez JG (2007) Responses to flooding and drought stress by two citrus rootstock seedlings with different water-use efficiency. Physiol Plant 130:532–542Genty B, Briantais JM, Baker NR (1989) The relationship between quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence. Biochim Biophys Acta 990:87–92Gómez-Cadenas A, Tadeo FR, Talon M, Primo-Millo E (1996) Leaf abscission induced by ethylene in water-stressed intact seedlings of Cleopatra mandarin requires previous abscisic acid accumulation in roots. Plant Physiol 112:401–408Gordo O, Sanz JJ (2010) Impact of climate change on plant phenology in Mediterranean ecosystems. Glob Chang Biol 16:1082–1106Heath RL, Packer L (1968) Photoperoxidation in isolated chloroplasts. I. Kinetics and stoichiometry of fatty acid peroxidation. 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ORGANOSOLV PULPING-VII - DELIGNIFICATION SELECTIVITY OF FORMIC-ACID PULPING OF EUCALYPTUS-GRANDIS

Eucalyptus grandis wood was ca. 80% delignified in 79-92% (v v-1) formic acid containing 0.22% (w v-1) HCl as a catalyst under reflux and mechanical stirring for 90 min. Pulps obtained under these conditions presented pulp yield, Kappa number and Klason lignin in the ranges of 44-52%, 30-40 and 8-10%, respectively. The presence of water in the experiments with the more diluted formic acid concentration (79%) showed a beneficial effect on the pulp fiber length and pulp yield. Formic acid sawdust treatments were carried out under the best chip pulping conditions. Plots of yield versus lignin loss show comparable delignification selectivity for sawdust and chips. The most selective pulping experiments were those with 79% formic acid employing a mechanical stirrer blade of polytetrafluorethylene (PTFE) and those with 99% formic acid using a stainless steel blade.47324725

ORGANOSOLV PULPING .5. FORMIC-ACID DELIGNIFICATION OF EUCALYPTUS-GLOBULUS AND EUCALYPTUS-GRANDIS

Organosolv pulping mediated by formic acid was evaluated. Wood of Eucalyptus globulus and Eucalyptus grandis was cooked with formic acid under different conditions of solvent ratio (formic acid:water), catalyst concentration, temperature and time of treatment. For E. globulus, the best results for sawdust samples were obtained at 90-degrees-C after 90 min of cooking, with a solvent ratio of 80:20 (vv-1), a charge (wood:solvent ratio) of 1:30 and 0.44% (wv-1) of catalyst. In the case of E. globulus chips, the concentration of catalyst used was 0.22%, the charge was 1:10, and soaking and preheating were used. For a sample of E. globulus soaked in water for 72 h, the pulp yield was 56%, Kappa number 22 and reject content 1.6%. E. grandis wood needed more drastic conditions. Cooking of E. grandis chips with formic acid (99%) at 95-degrees-C, 0.22% catalyst, charge 1:10, resulted in a pulp yield of 43%. The Kappa number was 31, reject content 0.1% and the cellulose and Klason lignin contents were 88% and 8%, respectively.3711

NONPOLLUTING WOOD AND PULP DELIGNIFICATION - BIOMIMETIC LIGNINASE SYSTEM

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Changes in growth and soil microbial communities in reciprocal grafting clones between Populus deltoides males and females exposed to water deficit conditions

Key message. Our findings highlight that male-rooted clones (M/M and F/M) of Populus deltoides are more water-deficit tolerant than female-rooted clones (F/F and M/F), as shown by a smaller decrease in total biomass and net photosynthetic rate in the male-rooted clones. Context. It has been reported that graft clones (female scion and male rootstock) in poplars may be an option to mitigate the effects of water deficit on plants. However, the extent to which grafting mitigates the effect of soil water deficit on soil microorganisms remains poorly understood. Aims. The research was designed to investigate the effects of soil water deficit on plant growth, soil microbial communities, and soil enzymatic activities of the reciprocal graft clones of P. deltoides. Methods. Four different graft clones (female shoot scion and female rootstock, F/F; male shoot scion and female rootstock, M/F; male shoot scion and male rootstock scion, M/M; and female shoot scion and male rootstock, F/M) in P. deltoides were used. Two watering regimes, irrigation and soil water deficit (i.e., non-irrigation conditions, natural levels of precipitation) were included in the experiments. The microbial community structure was quantified using phospholipid fatty acid. Results. Under water deficit, the decreases in total biomass, net photosynthetic rates, and leaf nitrogen content were more evident in M/M and F/M than in F/F and M/F. Bacterial phospholipid fatty acids (PLFAs) and actinomycetal PLFAs remained unaffected in the four graft clones. In contrast, during soil water deficit, fungal PLFAs were higher in M/M and F/M soil coincided with higher extracellular activities of β-1,4-N-acetyl-glucosaminidase and leucine aminopeptidase. Conclusion. Male-rooted clones (M/M and F/M) are more tolerant to water deficit than female-rooted clones (F/F and M/F). It is possible that the better performance of M/M and F/M, when exposed to water deficit, is associated mainly with higher fine root activity, greater specific root length and root/shoot ratio as well as increased fungal PLFAs