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Start Over Coverage 385-391

2. Changes in properties of phosphoenolpyruvate carboxylase with induction of Crassulacean acid metabolism (CAM) in the C4 plant Portulaca oleracea

Creator:
Mazen, A. M. A.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
malic acid
Language:
Multiple languages
Description:
Aiming at understanding the odd case of CAM expression by a C4 plant, some properties of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31, orthophosphate: oxaloacetate carboxylyase, phosphorylating) were comparatively studied in leaves of CAM-expressing and non-expressing Portulaca oleracea L. plants. CAM expression was induced by growing plants under an 8-h photoperiod and under water-stress. CAM induction in leaves of these plants (designated as CAM) is indicated by the nocturnal acidification and by the clear diurnal oscillation pattern and amplitude of acidity, malic acid, and PEPC activity characteristic of CAM plants. Treatment of the other plant group (designated as C4) by growth under a 16-h photoperiod and well-watered conditions did not induce expression of the tested criteria of CAM in plants. In these C4 plants, the mentioned CAM criteria were undetectable. PEPC from CAM and C4Portulaca responded differently to any of the studied assay conditions or effectors. For example, extent and timing of sensitivity of PEPC to pH change, inhibition by malate, activation by glucose-6-phosphate or inorganic phosphate, and the enzyme affinity to the substrate PEP were reversed with induction of CAM from the C4-P. oleracea. These contrasting responses indicate distinct kinetic and regulatory properties of PEPC of the two modes. Thus by shifting to CAM in the C4Portulaca a new PEPC isoform may be synthesised to meet CAM requirements. Simultaneous occurrence of both C4 and CAM is suggested in P. oleracea when challenged with growth under stress.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

4. Physiological response of eight Mediterranean maquis species to low air temperatures during winter

Creator:
Varone, L. and Gratani, L.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
carotenoids, chlorophyll, cold events, evergreen species, photosynthesis, and stomatal conductance
Language:
Multiple languages
Description:
We analyzed the physiological response of the Mediterranean evergreen species (Arbutus unedo L., Cistus incanus L., Erica arborea L., Erica multiflora L., Phillyrea latifolia L., Pistacia lentiscus L., Quercus ilex L., and Rosmarinus officinalis L.) to winter low air temperatures. In occasion of two cold events, in February 2005 (T min = 1.8 °C), and January 2006 (T min = 3.1 °C and minimum T air = -0.40 °C during the nights preceding the measurements), R. officinalis, C. incanus, and E. multiflora had the highest net photosynthetic rate (PN) decrease (73 %, mean value) with respect to the winter PN maximum, followed by A. unedo (62 %), P. latifolia and P. lentiscus (54 %, mean value), E. arborea (49 %), and Q. ilex (44 %). Among the considered species, Q. ilex was able to maintain PN near the maximum for 150 min during the day, A. unedo, P. lentiscus, E. arborea, P. latifolia, E. multiflora, and R. officinalis for 60 min, and C. incanus for 30 min. The calculated mean winter daily PN ranged from 7.9±0.6 (Q. ilex) to 2.8±0.5 (R. officinalis) µmol(CO2) m-2 s-1. During the study period, chlorophyll (Chl) content decreased by 36 % on an average in the two cold events, and the carotenoid (Car) to Chl ratio increased by 133 % in Q. ilex, having the highest value in January 2006. Principal component analysis underlined the highest cold resistance of Q. ilex by high PN and high Car/Chl ratio. On the contrary, R. officinalis and C. incanus had the lowest cold resistance by the highest PN decrease and the lowest Car/Chl (C. incanus). Thus, winter stress could be an additional limitation to Mediterranean evergreen species production, and the capacity of the species to maintain PN near 90-100 % during winter is determinant for biomass accumulation. and L. Varone, L. Gratani.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public