Under non-stressed conditions the net photosynthetic rate (PN) of the mutant plants cbp20 of Arabidopsis was similar to that of the wild type (WT). In response to water deprivation, however, PN started to decrease later in the mutants and remained substantially higher. Thermoluminescence measurements showed that the lipid peroxidation induced by severe water stress was also less pronounced in the mutant than in the WT. Both soil gravimetric and plant water potential data showed that cbp20 mutants lose water more slowly than the WT plants. The drought-induced decline in Fv/Fm, the quantum efficiency of photosystem 2, and photochemical quenching parameters also started later in the cbp20 mutants than in the WT plants. Thus the restricted gas exchange in the cbp20 mutants does not impair the photosynthetic performance of the plant; however, under drought improved water retention provides significant protection for the photosynthetic apparatus. and R. Bacsó ... [et al.].
Unlike mulberry (Morus alba, M.a.), paper mulberry (Broussonetia papyrifera, B.p.) can acclimate to Karst soil and incline to alien invasion. The photosynthetic parameters, diurnal changes of carbonic anhydrase, and chlorophyll fluorescence induction, and water potential were measured on sunny days (SD) and cloudy days (CD). Photosynthetic midday depression occurred in B.p. but not in M.a. The irradiance-and CO2-saturated photosynthetic rates of B.p. were significantly higher than those of M.a. There was no significant difference in water use efficiency between the two species on a SD. The maximum fluorescence, maximum quantum yield, photochemical quenching, and relative electron transport rate in the leaves of B.p. were much higher than those in M.a. The activity of carbonic anhydrase (CA) of B.p., on either an SD or a CD, was much greater than that of M.a. Higher transpiration rate (E) and net photosynthetic rate (PN) of B.p. resulted in the lack of water in mesophyll cells. Although a higher CA activity of B.p. supplied both water and CO2 for the photosynthesis of mesophyll cells, water in mesophyll cells was the factor limiting photosynthesis, and the intercellular CO2 concentration of B.p. was high and stable. and Y.-Y. Wu ... [et al.].
We compared light-saturated photosynthetic rates and their stomatal limitations among Cryptomeria japonica trees with a similar height but different current growth rates. Although
slow-growing trees had a lower stomatal conductance and a higher carbon isotope ratio in shoots, the stomatal limitations in photosynthesis were not different. Large mesophyll CO2 diffusion resistance contributed to the low photosynthetic rate of the
slow-growing trees., T. Tange ... [et al.]., and Obsahuje bibliografii
Photosynthetic water use efficiency (PWUE), stomatal conductance (gs), and water potential were measured at two different positions in the tree crown of two emergent tropical tree species (Shorea beccariana Burck, Dryobalanops aromatica Gaertn. f.). The trees were about 50 m high, in a tropical rain forest in Sarawak, East Malaysia. In both species, gs at the upper crown position at midday was lower than at the lower crown position, even though both positions were exposed to full sunlight; the difference was greater in S. beccariana. Hydraulic limitation occurs in the upper crown position in both species. A midday depression was observed in the photon saturated photosynthetic rate in both species, especially at the upper crown. However, PWUE was markedly higher in the upper crown than the lower crown at midday, even though no morphological adjustment was observed in the leaves; this difference was greater in S. beccariana. and Y. Kitahashi ... [et al.].
We compared responses of maize, tomato, and bean plants to water stress. Maize reached a severe water deficit (leaf water potential -1.90 MPa) in a longer period of time as compared with tomato and bean plants. Maize stomatal conductance (gs) decreased at mild water deficit. gs of tomato and bean decreased gradually and did not reach values as low as in maize. The protein content was maintained in maize and decreased at low water potential (ψw); in tomato it fluctuated and also decreased at low ψw; in bean it gradually decreased. Ribulose-1,5-bisphosphate carboxylase/oxygenase activity remained high at mild and moderate stress in maize and tomato plants; in bean it remained high only at mild stress. and M. Castrillo ... [et al.].
Environmental factors that influence stomatal conductance (gs) interact through a complex network of signal transduction and have therefore highly interdependent effect.
In the present study we examined how plant water status affects stomatal sensitivity to the change of CO2 concentration ([CO2]). We investigated the short-term dynamic of stomatal response to a sudden [CO2] increase (from 400 to 700 µmol(CO2) mol-1) in maize supplied with different amounts of water (resulting ψw = -0.35, -0.52 and -0.75 MPa). Gas exchange measurements were performed in short logging intervals and the response was monitored under two different levels of water vapour pressure deficit (VPD) of 1 and 2 kPa in order to observe the impact of air humidity. Generalized logistic curves were fitted to standardized stomatal response data, which enabled us to objectively estimate the level (relative decrease of g s) and the dynamics of the response.
Soil water stress and high VPD significantly decreased relative stomatal closure in response to [CO2] rise, but simultaneously accelerated stomatal response to [CO2], as revealed by shorter half life (t1/2). VPD significantly affected the response of well-watered plants. In contrast, a fast stomatal reaction of water-deprived plants was predetermined by a low xylem water potential (ψw) of the leaf and the influence of air humidity was minor. and J. Hladnik ... [et al.].
High irradiance promotes decreases in the quantum yield in plants, which reduce the photosynthetic rate. The excess of light in combination with water deficit can intensify the response of plants to stress, especially in species susceptible to those factors. The aim of the present study was to characterize the photosynthetic activity of young jatobá-do-cerrado (Hymenaea stigonocarpa Mart. ex Hayne) trees under different irradiance conditions, both alone and/or in combination with water deficit. Four irradiances [45, 230, 510, and 1,700 μmol(photon) m-2 s-1] and two levels of water in soil (90% and 50% of field capacity) were used. Gas exchange, water potential, and chlorophyll a fluorescence were measured. The highest rates of photosynthesis were observed under irradiances of 230 and 510 μmol(photon) m-2 s-1. Irradiance of 1,700 μmol(photon) m-2 s-1 led to the photoinhibition of photosynthesis, as indicated by a reduced maximum quantum yield of PSII, effective quantum yield ratio, and electron transport rate, as well as higher nonphotochemical quenching. The most stressful to young H. stigonocarpa plants was high irradiance, while water deficit did not intensify the response to light stress., A. C. Costa, S. L. Rezende-Silva, C. A. Megguer, L. M. F. Moura, M. Rosa, A. A. Silva., and Obsahuje bibliografii
In order to address the question of how elevated CO2 concentration (EC) will affect the water relations and leaf anatomy of tropical species, plants of Jatropha gossypifolia L. and Alternanthera crucis (Moq.) Bondingh were grown in five EC open top chambers (677 μmol mol-1) and five ambient CO2 concentration (AC) open top chambers (454 μmol mol-1) with seasonal drought. No effect of EC was found on morning xylem water potential, leaf osmotic potential, and pressure potential of plants of J. gossypifolia. In A. crucis EC caused a significant increase in morning xylem water potential of watered plants, a decrease in osmotic potential, and an increase of 24-79 % in pressure potential of moderately droughted plants. This ameliorated the effects of drought. Stomatal characteristics of both leaf surfaces of J. gossypifolia and A. crucis showed time-dependent, but not [CO2]-dependent changes. In J. gossypifolia the thickness of whole leaf, palisade parenchyma, and spongy parenchyma, and the proportion of whole leaf thickness contributed by these parenchymata decreased significantly in response to EC. In A. crucis EC caused an increase in thickness of whole leaf, bundle sheath, and mesophyll, while the proportion of leaf cross-section comprised by the parenchymata remained unchanged. These effects disappeared with time under treatment, suggesting that acclimation of the leaf anatomy to the chambers and to EC took place in the successive flushes of leaves produced during the experiment. and E. Rengifo, R. Urich, A. Herrera.