Limitations in photosystem function and photosynthetic electron flow were investigated during leaf senescence in two field-grown plants, i.e., Euphorbia dendroides L. and Morus alba L., a summer- and winter-deciduous, shrub and tree, respectively. Analysis of fast chlorophyll (Chl) a fluorescence transients and post-illumination fluorescence yield increase were used to assess photosynthetic properties at various stages of senescence, the latter judged from the extent of Chl loss. In both plants, the yield of primary photochemistry of PSII and the content of PSI remained quite stable up to the last stages of senescence, when leaves were almost yellow. However, the potential for linear electron flow along PSII was limited much earlier, especially in E. dendroides, by an apparent inactivation of the oxygen-evolving complex and a lower efficiency of electron transfer to intermediate carriers. On the contrary, the corresponding efficiency of electron transfer from intermediate carriers to final acceptors of PSI was increased. In addition, cyclic electron flow around PSI was accelerated with the progress of senescence in E. dendroides, while a corresponding trend in M. alba was not statistically significant. However, there was no decrease in PSI activity even at the last stages of senescence. We argue that a switch to cyclic electron flow around PSI during leaf senescence may have the dual role of replenishing the ATP and maintaining a satisfactory nonphotochemical energy quenching, since both are limited by hindered linear electron transfer., C. Kotakis, A. Kyzeridou, Y. Manetas., and Obsahuje bibliografii
Vochysia divergens Pohl is considered to be a flood-adapted, light-demanding pioneer species that has been invading grasslands of the Brazilian Pantanal. In these areas, a successful invasion requires an ability to tolerate physiologically wide fluctuations in surface hydrology and shading induced by a dense cover of grasses and other vegetation. We evaluated how flooding and shading affected the photosynthetic performance of V. divergens saplings by measuring light-saturated gas exchange (net photosynthetic rate, PN; stomatal conductance, gs), and intercellular CO2 (PN/Ci) and photosynthetic photon flux density
(PN/PPFD) response curves over a 61-d field experiment. Shading and flooding reduced significantly light-saturated PN and gs and affected multiple aspects of the leaf gas exchange response of V. divergens to variations in PPFD and CO2. Flooding influenced the physiology of this species more than shading. Given the success of V. divergens at invading and expanding in seasonally flooded areas of the Pantanal, the results were surprising and highlighted the physiological ability of this species to tolerate suboptimal conditions. However, the consistently higher light-saturated PN and gs under nonflooded conditions suggested that the invasive success of V. divergens might not be related to its physiological potential during flooding, but to situations, when flooding recedes during the dry season and soil water availability is adequate. and A. C. Dalmolin ... [et al.].
Photosynthetic properties of carnivorous plants have not been well characterized and the extent to which photosynthesis contributes to carbon gain in most carnivorous plants is also largely unknown. We investigated the photosynthetic light response in three carnivorous plant species, Drosera rotundifolia L. (sundew; circumpolar and native to northern British Columbia, Canada), Sarracenia leucophylla Rafin. ('pitcher-plant'; S.E. United States), and D. capensis L. (sundew; Cape Peninsula, South Africa), using portable gas-exchange systems to explore the capacity for photosynthetic carbon gain in carnivorous plant species. Maximal photosynthetic rates (1.32-2.22 μmol m-2 s-1 on a leaf area basis) and saturating light intensities (100 to 200 μmol PAR m-2 s-1) were both low in all species and comparable to shade plants. Field or greenhouse-grown D. rotundifolia had the highest rates of photosynthesis among the three species examined. Dark respiration, ranging from -1.44 (S. leucophylla) to -3.32
(D. rotundifolia) μmol m-2 s-1 was high in comparison to photosynthesis in the species examined. Across greenhouse-grown plants, photosynthetic light compensation points scaled with light-saturated photosynthetic rates. An analysis of gas-exchange and growth data for greenhouse-grown D. capensis plants suggests that photosynthesis can account for all plant carbon gain in this species. and B. M. Bruzzese ... [et al.].
Plants are constantly subjected to variations in their surrounding environment, which affect their functioning in different ways. The influence of environmental factors on the physiology of plants depends on several factors including the intensity, duration and frequency of the variation of the external stimulus. Water deficit is one of the main limiting factors for agricultural production worldwide and affects many physiological processes in plants. The aim of this study was to analyse the effects of different rates of induced water deficit on the leaf photosynthetic responses of soybean (Glycine max L.) and cowpea (Vigna unguiculata L.). The plants were subjected to two types of water deficit induction: a rapid induction (RD) by which detached leaves were dehydrated by the exposure to air under controlled conditions and a slow induction (SD) by suspending irrigation under greenhouse conditions. The leaf gas exchange, chlorophyll (Chl) a fluorescence, and relative water content (RWC) were analysed throughout the water-deficit induction. V. unguiculata and G. max demonstrated similar dehydration as the soil water percentage declined under SD, with V. unguiculata showing a greater stomatal sensitivity to reductions in the RWC. V. unguiculata plants were more sensitive to water deficit, as determined by all of the physiological parameters when subjected to RD, and the net photosynthetic rate (PN) was sharply reduced in the early stages of dehydration. After the plants exposed to the SD treatment were rehydrated, V. unguiculata recovered 65% of the PN in relation to the values measured under the control conditions (initial watering state), whereas G. max recovered only 10% of the PN. Thus, the better stomatal control of V. unguiculata could enable the maintenance of the RWC and a more efficient recovery of the PN than G. max., S. C. Bertolli, G. L. Rapchan, and G..M. Souza., and Obsahuje bibliografii
When cells get metals in small excess, mechanisms of avoidance occur, such as exclusion, sequestration, or compartmentation. When the excess reaches sub-lethal concentrations, the oxidative stress, that toxic metals trigger, leads to persistent active oxygen species. Biomolecules are then destroyed and metabolism is highly disturbed. At the chloroplast level, changes in pigment content and lipid peroxidation are observed. The disorganized thylakoids impair the photosynthetic efficiency. The Calvin cycle is also less efficient and the photosynthetic organism grows slowly. When an essential metal is given together with a harmful one, the damages are less severe than with the toxic element alone. Combined metals and phytochelatins may act against metal toxicity. and M. Bertrand, I. Poirier.
In an experimental site for reforestation of degraded area, three-year-old plants of Bertholletia excelsa Humb. & Bonpl. were subjected to different fertilization treatments: T0 = unfertilized control, T1 = green fertilization (branches and leaves) and T2 = chemical fertilization. Higher net photosynthetic rates (PN) were observed in T1 [13.2±1.0 μmol(CO2) m-2 s-1] compared to T2 [8.0±1.8 μmol(CO2) m-2 s-1] and T0 [4.8±1.3 μmol(CO2) m-2 s-1]. Stomatal conductance (g s), transpiration rate (E) and water use efficiency (WUE) of individuals of T1 and T2 did not differ significantly, however, they were by 88, 55 and 63%, respectively, higher in T1 than in the control. The mean values of variable fluorescence (Fv), performance index (P.I.) and total chlorophyll [Chl (a+b)] were higher in T1. Our results indicate that green fertilization improves photosynthetic structure and function in plants of B. excelsa in young phase. and M. J. Ferreira, J. F. C. Gonçalves, J. B. S. Ferraz.
The photosynthetic performances of regenerated protoplasts of Bryopsis hypnoides, which were incubated in seawater for 1, 6, 12, and 24 h, were studied using chlorophyll (Chl) fluorescence and oxygen measurements. Results showed that for the regenerated protoplasts, the pigment content, the ratios of photosynthetic rate to respiration rate, the maximal photosystem II (PSII) quantum yield (Fv/Fm), and the effective PSII quantum yield (ΦPSII) decreased gradually along with the regeneration progress, indicated that during 24 h of regeneration there was a remarkable reduction in PSII activity of those newly formed protoplasts. We assumed that during the cultivation progress the regenerated protoplasts had different photosynthetic vigor, with only some of them able to germinate and develop into mature thalli. The above results only reflected the photosynthetic features of the regenerated protoplasts at each time point as a whole, rather than the actual photosynthetic activity of individual aggregations. Further investigation suggested a relationship between the size of regenerated protoplasts and their viability. The results showed that the middle-sized group (diameter 20-60 μm) retained the largest number of protoplasts for 24 h of growth. The changes in Fv/Fm and ΦPSII of the four groups of differently sized protoplasts (i.e. < 20, 20-60, 60-100, and > 100 μm) revealed that the protoplasts 20-60 μm in diameter had the highest potential activity of the photosynthetic light energy absorption and conversion for several hours. and F. Lü, G. C. Wang, J. F. Niu.
Photosynthesis and leaf traits of five species in genus Cypripedium were compared in natural habitats and transplant nursery to develop effective strategy for cultivation and conservation. Among five species, C. guttatum had the highest photosynthetic capacity
(PNmax) in the natural habitat and nursery, while C. lichiangense the lowest. The differences in PNmax among species were correlated with leaf N content (LNC) and leaf dry mass per unit area (LMA). After transplanting from natural habitats to nursery, the
PNmax of C. lichiangense and C. yunnanense decreased, that of C. guttatum increased, while those of C. flavum and C. tibeticum remained relatively constant. The variations in LNC and biochemical efficiency would be responsible for the differences in
PNmax between plants in natural habitats and in the nursery, but not the relative stomatal limitation. After transplanting, the Fv/Fm of C. lichiangense and C. yunnanense were declined. Meanwhile, the temperature ranges maintaining 90 % PNmax of C. lichiangense and C. yunnanense were narrower than those of the other three species. Thus the biochemical process in five species played a major role in the differences of PNmax after transplanting, and the widespread species had higher photosynthetic adaptability than the narrow-spread species. and S.-B. Zhang ... [et al.].
Salt stress causes extensive losses to agricultural crops, including wheat, throughout the world and has been the focus of wide research. Though, information is scarce on the potential of ancient wheat relatives in tackling this major limiting factor. Thus, six hulled tetraploid wheat genotypes (HW) were compared to a
free-threshing durum wheat genotype (FTW) under different NaCl concentrations, ranging from 0 to 150 mM, at early growth stages in a sand culture experiment. Salt stress induced significant declines in the leaf chlorophyll (Chl) a, Chl b, total Chl, and carotentoid contents; the extent of the declines was greater in FTW compared to HW. Mean leaf proline (3.6-fold) and Na+ (1.58-fold) concentrations and Na+/K+ (2.48-fold) drastically increased with 150 mM of NaCl; the magnitude of the increases was greater in HW compared to FTW. While the carotenoids concentration decreased with progressive salinity both in HW and FTW, the activities of antioxidant enzymes, i.e., catalase, ascorbate peroxidase, and peroxidase were reduced in FTW, but remained unchanged in HW. The above responses to 150 mM NaCl were associated with a significant decrease in shoot dry mass of FTW and lack of significant changes in that of HW. Findings of the present study could help pave the way for further studies on physiological and molecular mechanisms of salt tolerance in these durum wheat relatives., S. Tabatabaei, P. Ehsanzadeh., and Seznam literatury
European beech (Fagus sylvatica L.) seedlings of three different origins were used to evaluate the effect of water deficit and recovery during the most vulnerable phase of forest tree life. Gas-exchange characteristics and fluorescence rapid light curves were studied in the seedlings from a warm region (PV1, 530 m a.s.l.), seedlings from a moderately warm region (PV2, 625 m a.s.l.), optimal for beech, and in seedlings from a cool region (PV3; 1,250 m a.s.l.). Changes in photosynthetic characteristics caused by water deficit were similar, but their intensity was dependent on the origin of the seedlings. Simulation of drought conditions by the interruption of watering led to a decrease in the efficiency of primary photochemistry in PSII, with the most significant decrease in the PV2 seedlings. Conversely, water deficit affected most significantly gas exchange in PV3, where the recovery process was also the worst. The PV1 demonstrated the highest resistance to water deficit. Drought-adaptation of beech seedlings at non-native sites seems to be linked to water availability and to the origin of the beech seedlings., E. Pšidová, Ľ. Ditmarová, G. Jamnická, D. Kurjak, J. Majerová, T. Czajkowski, A. Bolte., and Obsahuje bibliografii