Jatropha curcas, one of the most important energy plant resources, is vulnerable to chilling. To evaluate the effects of chilling on photosynthesis of J. curcas and intraspecific differences in chilling tolerance, seedlings of twelve populations were treated with the temperature of 4-6°C for five consecutive nights with normal environmental temperature during the day. Night chilling treatment decreased light-saturated photosynthetic rate (Pmax) significantly for all populations. Stomatal limitation could not explain the decreased Pmax because intracellular CO2 concentration was not significantly reduced by night chilling in all populations (with only one exception). The decreased soluble-protein content, which may be related to the increased malondialdehyde (MDA) content, contributed to the decreased Pmax. The increased MDA content indicated that oxidative stress occurred after night chilling, which was associated with the larger decrease in Pmax compared with the decrease in actual photochemical efficiency of photosystem II, and the slight increase in thermal dissipation of excessive energy. After five-day recovery, MDA (with two exceptions) and Pmax still did not recover to the levels as those before night chilling treatment for all populations, indicating that J. curcas was vulnerable to chilling. Chilling tolerance was significantly different among populations. Populations originating from high elevations had greater chilling-tolerant abilities than populations originating from low elevations, showing a local adaptation to environmental temperatures of origins. Our study shed light on the possibility to find or breed chilling-tolerant genotypes of J. curcas. and Y.-L. Zheng ... [et al.].
Gas exchange and fluorescence parameters were measured simultaneously in two Zea mays L. cultivars (Liri and 121C D8) to assess the relationship between the quantum yield of electron transport (ΦPS2) and the quantum yield of CO2 assimilation (ΦCO2) in response to photosynthetic photon flux density (PPFD). The cv. Liri was grown under controlled environmental conditions in a climate chamber (CC) while cv. 121C D8 was grown in CC as well as outdoors (OT). By exposing the two maize cultivars grown in CC to an increasing PPFD, higher photosynthetic and photochemical rates were evidenced in cv. Liri than in cv. 121C D8. In Liri plants the ΦPS2/ΦCO2 ratio increased progressively up to 27 with increasing PPFD. This suggests that the reductive power was more utilised in non-assimilatory processes than in CO2 assimilation at high PPFD. On the contrary, by exposing 121C D8 plants to increasing PPFD, ΦPS2/ΦCO2 was fairly constant (around 11-13), indicating that the electron transport rate was tightly down regulated by CO2 assimilation. Although no significant differences were found between ΦPS2/ΦCO2 of the 121C D8 maize grown under CC and OT by exposing them to high PPFD, the photosynthetic rate and photochemical rates were higher in OT maize plants. and N. D'Ambrosio, C. Arena, A. Virzo de Santo.
Responses of the photosynthetic electron transport system of chloroplasts to exogenous proline application were evaluated in young and mature leaves of Arabidopsis thaliana plants under optimal growth conditions. Exogenous proline application (10 mM) during the 4th week of growth increased proline accumulation in young leaves more than in mature leaves, and possibly due to its degradation producing NADPH, decreased significantly the ratio of NADP+/NADPH in both leaf types compared with controls (without proline). However, the ratio of NADP+/NADPH remained significantly higher in the young leaves, suggesting lower proline degradation which resulted in less reduced plastoquinone pool than that in the mature leaves, under both low light [130 μmol(photon) m-2 s-1] and high light [1,200 μmol(photon) m-2 s-1] treatments. The young leaves seemed to adjust nonphotochemical fluorescence quenching in order to maintain a better PSII quantum yield. We concluded that under optimal growth conditions exogenous proline results in overreduction of the plastoquinone pool and blockage of photosynthetic electron flow due to accumulation of NADPH. We suggest that optimum concentrations of proline are required for optimal PSII photochemistry., I. Sperdouli, M. Moustakas., and Obsahuje seznam literatury
The impact of grazing by domestic goats, Capra hircus, on the photochemical apparatus of three co-ocurring Mediterranean shrubs, Erica scoparia, Halimium halimifolium, and Myrtus communis was evaluated. Seasonal course of gas exchange, chlorophyll fluorescence and photosynthetic pigment concentrations were measured in the field in grazed and ungrazed plants. Net photosynthetic rate was higher in grazed plants of E. scoparia and H. halimifolium in May, while there were not significant differences in M. communis. Photosynthetic enhancement in grazed plants of E. scoparia could be explained largely by higher stomatal conductance. On the other hand, the lack of differences in stomatal conductance between grazed and ungrazed plants of
H. halimifolium could indicate that carboxylation efficiency, and ribulose-1,5-bisphosphate (RuBP) regeneration may have been enhanced by grazing. Overall grazing has little effect on the photochemical (PSII) apparatus, however grazed plants of M. communis showed chronic photoinhibition in the short term. Finally, seasonal variations recorded on photosynthesis, photochemical efficiency and pigment concentrations may be a physiological consequence of environmental factors, such as summer drought and competition for light, rather than an adaptation to grazing. and S. Redondo-Gómez ... [et al.].
Nostoc muscorum cells showed metal-induced decrease in the relative growth, pigment contents, O2 evolution, and Hill activity in response to lead (Pb2+) and cadmium (Cd2+) treatment, which was further accentuated with increase in metal exposure time and metal concentration. I50 concentrations (50% growth inhibitory concentrations) of Pb2+ and Cd2+ for growth of N. muscorum were 55 and 21 μg mL-1, respectively. These results indicated that the cells of N. muscorum were more susceptible to Cd2+ in comparison to Pb2+. The O2 production was relatively more sensitive to both heavy metals (I50: 16 and 10 μg mL-1 of Pb2+ and Cd2+, respectively) than the Hill activity (I50: 61 and 39 μg mL-1 of Pb2+ and Cd2+, respectively). Further, measurement of Hill activity in the presence of metals and electron donors showed that inhibition sites of both Pb2+ and Cd2+ were located on the oxidizing site of PSII. The chlorophyll a (Chl a) and phycobilisome (PB) fluorescence emission spectra showed that energy transfer from Chl a and PB to PSII reaction center was more susceptible to Cd2+ than Pb2+., S. Dixit, D. P. Singh., and Obsahuje bibliografii
Fe, Mn, and Zn affected the chlorophyll (Chl) content whereas Fe deficiency caused larger reduction of total chlorophyll content than Mg and Zn deficiencies. Mg deficient mango had a higher Chl a/b ratio than the respective healthy plants. The foliar contents of Fe, Zn, and Mg in the deficient leaves were lower than the critical level. Nutrient deficiency significantly affected the Fv/Fm ratios as observed from the Chl fluorescence induction curves. Fe deficiency resulted in larger reduction of variable fluorescence than Mg and Zn deficiency. and K, Balakrishnan, C. Rajendran, G. Kulandaivelu.
The photosynthetic responses to elevated CO2 concentration (EC) at ambient and ambient +4°C temperature were aßsessed in the second leaf of rice (Oryza sativa L.) seedlings. The duration of different leaf developmental phases, as characterised by changes in photosynthetic pigment contents and photochemical potential, was protracted in the seedlings grown under EC. On the other hand, a temporal shift in the phases of development with an early onset of senescence was observed in the seedlings grown under EC at ambient +4°C temperature. The contents of carotenoids, ß-carotene, and xanthophyll cycle pigments revealed that EC downregulated the protective mechanism of photosynthetic apparatus against oxidative damages, whereas this mechanism assumed higher significance under EC at ambient +4°C temperature. We observed an enhancement in electron transport activity, photochemical potential, and net photosynthesis in spite of a loss in photostasis of photosynthesis under EC. On the other hand, the loss in photostasis of photosynthesis was exacerbated under EC at ambient +4°C temperature due to the decline in electron transport activity, photochemical potential, and net photosynthesis., S. Panigrahi, M. K. Pradhan, D. K. Panda, S. K. Panda, P. N. Joshi., and Seznam literatury
By measurement of gas exchange and chlorophyll fluorescence, the effects of salt shock on photosynthesis and the mechanisms to protect photosynthetic machinery against photodamage during salt shock were investigated in leaves of Rumex seedlings. Salt shock induced significant decrease in photosynthesis both in 21 and 2 % O2. In 21 % O2, quantum yield of photosystem 2 (PS2) electron transport (ΦPS2) decreased slightly and qP remained constant, suggesting that the excitation pressure on PS2 did not increase during salt shock. In 2 % O2, however, both ΦPS2 and qP decreased significantly, suggesting that the excitation pressure on PS2 increased during salt shock. NPQ increased slightly in 21 % O2 whereas it increased significantly in 2 % O2. The data demonstrated that during salt shock a considerable electron flow was allocated to oxygen reduction in the Mehler-peroxidase reaction (MPR). Under high irradiance and in the presence of saturating CO2, the susceptibility of PS2 to photoinhibition in salt-shocked leaves was increased when the electron flow to oxygen in MPR was inhibited in 2 % O2. Hence, MPR is important in photoprotection of Rumex seedlings during salt shock. and H.-X. Chen ... [et al.].
The plants of Prosopis juliflora growing in northern India are exposed to large variations of temperature, vapour pressure deficits (VPD), and photosynthetic photon flux density (PPFD) throughout the year. Under these conditions P. juliflora had two short periods of leaf production, one after the winter season and second after summer, which resulted in two distinct even aged cohorts of leaves. In winter with cold nights (2-8 °C) and moderate temperatures during the day, the plants showed high rates of photosynthesis. In summer the midday temperatures often reached <45 °C and plants showed severe inhibition of photosynthesis. The leaves of second cohort appeared in July and showed typical midday depression of photosynthesis. An analysis of diurnal partitioning of the absorbed excitation energy into photochemistry showed that a smaller fraction of the energy was utilised for photochemistry and a greater fraction was dissipated thermally, further the photon utilisation for photochemistry and thermal dissipation is largely affected by the interaction of irradiance and temperature. The plants showed high photochemical efficiency of photosystem 2 (PS2) at predawn and very little photoinhibition in all seasons except in summer. The photoinhibition in summer was pronounced with very poor recovery during night. Since P. juliflora exhibited distinct pattern of senescence and production of new leaves after winter and summer stress period, it appeared that the ontogenic characteristic together with its ability for safe dissipation of excess radiant energy in P. juliflora contributes to its growth and survival. and P. A. Shirke, U. V. Pathre.
The Amazonian peach palm (Bactris gasipaes Kunth) has been grown for heart-of-palm production under subtropical conditions. As we did not see any substantial study on its photosynthesis under Amazonian or subtropical conditions, we carried out an investigation on the diurnal and seasonal variations in photosynthesis of peach palms until the first heart-of-palm harvest, considering their relationship with key environmental factors. Spineless peach palms were grown in 80-L plastic pots, under irrigation. Gas exchange and chlorophyll fluorescence emission measurements were taken in late winter, mid spring, mid summer and early autumn, from 7:00 to 18:00 h, with an additional chlorophyll fluorescence measurement at 6:00 h. The highest net CO2 assimilation (PN), observed in mid summer, reached about 15 μmol m-2 s-1, which was about 20% higher than the maximum values found in autumn and spring, and 60% higher than that in winter The same pattern of diurnal course for PN was observed in all seasons, showing higher values from 8:00 to 9:00 h and declining gradually from 11:00 h toward late afternoon. The diurnal course of stomatal conductance (gs) followed the same pattern of
PN, with the highest value of 0.6 mol m-2 s-1 being observed in February and the lowest one (0.23 mol m-2 s-1) in September. The maximal quantum yield of photosystem II (Fv/Fm) was above 0.75 in the early morning in all the months. The reversible decrease was observed around midday in September and October, suggesting the occurrence of dynamic photoinhibition. A significant negative correlation between the leaf-air vapour pressure difference (VPDleaf-air) and PN and a positive correlation between PN and gs were observed. The photosynthesis of peach palm was likely modulated mainly by the stomatal control that was quite sensible to atmospheric environmental conditions. Under subtropical conditions, air temperature (Tair) and VPDleaf-air impose more significant effects over PN of peach palm than an excessive photosynthetic photon flux density (PPFD). The occurrence of dynamic photoinhibition indicates that under irrigation, peach palms appeared to be acclimated to the full-sunlight conditions under which they have been grown. and M. L. S. Tucci ... [et al.].