Recovery Of Pn Research Articles

Ecophysiological Recovery of Micropropagated Olive Cultivars: Field Research in an Irrigated Super-High-Density Orchard

This research focuses on the seasonal patterns of the ecophysiological recovery of four olive cultivars (Arbequina, Coratina, Frantoio, and Urano), both micropropagated and self-rooted, grown in a mature, irrigated, super high-density (SHD) orchard under Mediterranean conditions (Southern of Italy). The aim was to observe the impact of the micropropagation method on the ecophysiological responses. Ecophysiological parameters, including leaf water potential (LWP), stomatal conductance (gs), net photosynthetic rate (Pn), and transpiration rate (E) were assessed. Self-rooted trees consistently exhibited superior gs, E, and Pn recovery compared to the micropropagated ones. ‘Arbequina’ maintained elevated levels of Pn under water-deficit conditions. ‘Coratina’ exhibited increases in gs and E after irrigation. ‘Frantoio’ demonstrated recovery capabilities, with lower LWP and higher Pn under stress. ‘Urano’ micropropagated trees achieved higher gs values in mid-summer, while self-rooted trees sustained higher Pn later in the season. This field research highlighted the important role of the propagation method in optimizing the physiological performance of olive cultivars in SHD orchards. Furthermore, it highlighted the necessity of long-term studies on the effects of propagation methods and their interactions with other farming practices.

Sensitivity and Regulation of Diel Photosynthesis in Red-Fleshed Pitaya (Hylocereus polyrhizus) Micropropagules under Mannitol-Induced Water Stress/Rehydration Cycle In Vitro

Climate change-induced prolonged water stress (WS) affects crassulacean acid metabolism photosynthesis in pitaya (Hylocereus), limiting crop productivity through insufficient photosynthate. To document how WS/rehydration affects diel photosynthesis, red-fleshed pitaya (H. polyrhizus) micropropagules were studied for 5 weeks in a mannitol-induced water potential gradient replaced with moderate (MWS; −1.0 MPa in week 2; −0.5 MPa for the rest) or intensified (IWS; −1.0 and −1.5 MPa in weeks 2 and 3; −0.5 MPa for the rest) WS in vitro. Net photosynthetic rate (Pn) and integrated net CO2 uptake (INCU) were measured using an Arduino-based photosynthesis system. Micropropagules under MWS had similar Pn in weeks 5 and 1, whereas the control (−0.5 MPa) increased. Pn recovery did not occur after IWS. The average relative INCU was similar in the control and MWS, but lower in IWS. The Pn difference increased with WS, becoming more evident at dawn (Phase II), evening (Phase IV), and predawn the next day (Phase I), and occurred earlier in Phases IV and I under IWS. MWS did not reduce photosynthesis, demonstrating that the photosynthetic regulation could respond to short-term WS in pitaya and indicating the potential of watering for Pn recovery at evening and predawn under IWS.

Simulating the effects of low-temperature stress on wheat biomass growth and yield

Low-temperature stress in late spring poses a serious threat to winter wheat production. In three-year environment-controlled phytotron experiments at both elongation and booting stages, we observed that short-term low-temperature stress decreased leaf area and stem, limited leaf photosynthetic system, and severely reduced grain yield, especially in the low-temperature sensitive cultivar. To better quantify the effects of low-temperature stress on leaf photosynthesis rate (Pn), leaf area index (LAI), biomass partitioning, and grain yield, the lethal temperature at 50% mortality (LT50), low-temperature damage index (LDI), and process-based algorithms were proposed and incorporated into the WheatGrow model. The algorithms take into account the effects of low-temperature with different durations and reflected a low-temperature sensitivity of cultivars at different growth periods by using LT50. The improved WheatGrow model could reproduce well the observed dynamics of the decrease of Pn during the treatment period, recovery of Pn after cold treatments, and the damage to LAI and biomass accumulation under the low-temperature stress treatments. Compared to the original model, RMSE of Pn, LAI, total aboveground biomass, and grain yield in the improved WheatGrow model were reduced by 63 to 77% under low-temperature stress. Although the newly developed algorithms expand crop modeling capacity into quantifying the impacts of low-temperature stress on wheat productivity, further assessments with observed data under field conditions are still required, especially for obtaining suitable parameters at the regional scale.

Maize (Zea mays L.) physiological responses to drought and rewatering, and the associations with water stress degree

A thorough understanding of the plant drought response mechanism and the relationships between plant functional traits and drought will help to improve the key biophysical process parameterization scheme in ecological and crop growth models. In this study, a drought level evaluation indicator, named water stress degree (Dws), was established by synthetically considering soil water content (WC), evapotranspiration, and drought duration to obtain a quantitative description of drought level. The maize physiological and functional traits responses to drought and subsequent rewatering were also investigated. Drought-rewatering field experiments with no water addition for 40 days during the vegetative period (VP) and reproductive period (RP) were respectively conducted at Jinzhou Agrometerological Experimental Station, northeast China in 2014 and 2016. The Dws values indicated that there were significant differences between growth stages and between years because the environmental conditions in 2014 and 2016 were different during the maize growth periods. Furthermore, Dws was larger in 2016 than in 2014 during the VP and RP. Leaf photosynthesis had a certain adaptability to drought, and the transpiration rate (E) drought response (DR) was quicker than the photosynthetic rate (Pn) response, and Pn recovery was greater than E recovery when the plants were rewatered during the VP. However, leaf photosynthesis is more sensitive to drought and less available to recover as normal in subsequent rewatering during the RP than the VP, which was intensified as Dws rose between 2014 and 2016. In addition, the leaf WC drought response was faster than the photosynthetic DR during the VP and RP, and leaf and stalk WCs responded more rapidly to drought during the VP than the RP. The decrease in ear WC during the earlier grouting period was larger in the VP than in the RP treatment. However, the drought-induced decrease in daily sap flow rate (DSF) during the RP was larger than during the VP, while the differences in DSF drought response and DSF recovery during rewatering were attributed to the inter-annual variation in Dws. Furthermore, the drought-caused reductions in leaf, stalk, and plant total dry matters and in leaf and stalk WCs had positively exponential or linear relationships with Dws. The results can help to understand the disaster-causing mechanism of drought-stricken maize.

Pyrrhotite depression studies with DETA and SMBS on a Ni‐Cu sulphide ore

AbstractPyrrhotite (Po) is a common gangue mineral in Ni‐Cu sulphide ores (pentlandite {Pn}‐chalcopyrite {Cp}) and can be difficult to reject under certain circumstances. This paper summarizes the results of a lab‐scale flotation study on a reactive ore with a high Po/Pn ratio (7.5), 42 % hexagonal Po content (of total Po), and 85.9 % Ni deportment in Pn (remainder Ni largely reporting to Po), making Po rejection challenging and Ni recovery/grade targets difficult to obtain. The main objective was to assess whether the ore could be processed “as received” to achieve high Pn recovery (>85 %) while ensuring low Po recovery (<20 %), which will typically yield acceptable final concentrate grades after cleaning stages. Baseline testing showed Po depression was difficult by conventional means and required depressants. The test work was centered around the use of DETA (diethylenetriamine) for its proven effectiveness for Po depression (used with sodium metabisulphite (SMBS)). Several strategies were tested: DETA alone; DETA/SMBS; sulphuric acid/DETA/SMBS with/without aeration; and DETA/SMBS with concentrate regrind. The DETA was found to be effective as a Po depressant (both hexagonal and monoclinic Po) on this challenging ore. Overall, the DETA/SMBS with concentrate regrind exhibited the best results (∼11 % Po recovery at ∼85 % Pn recovery) and was found to be sufficient in achieving the outlined targets.

Physiological responses of young Brazil nut (Bertholletia excelsa) plants to drought stress and subsequent rewatering

The Brazil nut tree (Bertholletia excelsa Bonpl.) is widely distributed in the Amazon region. It is subject to different rainfall regimes, particularly in El Niño years. Here, we demonstrate how biomass growth, gas exchange and biochemical traits of young B. excelsa plants were affected by imposed drought stress and subsequent rehydration. Four-month-old young plants were acclimated in a greenhouse for 15 days and received daily irrigation, after this period they were separated into two treatment: well-watered (control plants, WW) and water deficit (drought-stressed plants, DS). After 58 days of water deficit, the net photosynthetic rate (Pn) of the plants in the DS treatment regime reached values close to zero, water use efficiency significantly increased, and midday leaf water potential (Ѱleaf) reached a mean value of −4.7 MPa. The recovery of Pn and Ѱleaf to control levels was re-established after 16 days of rehydration. The DS treatment regime led to lower level of biomass (37%) when compared to plants in the WW treatment regime. The DS treatment plants had higher leaf concentrations of total soluble sugars, whereas the starch content was higher in the WW treatment regime. Our results suggest that (i) B. excelsa has a high physiological plasticity with respect to drought stress and (ii) the recovery of physiological traits was followed by the recovery of the absolute growth rates of the DS plants in the short term. These ecophysiological responses demonstrate the strong potential of this species for establishment in forest plantations in the Amazon region and its resilience during drought events.

English

To investigate drought-induced changes in morphophysiological characteristics, seedlings of two genotypes of Jatropha curcas (CNPAE 183 and CNPAE 191) were grown under two watering regimes: irrigated (-33.1 to 13.5 to kPa) and water deficit (-409.5 to 49.5 to kPa) for 55 days, followed by six days of rehydration (DAR). Withholding water led to a significant reduction (p<0.05) of leaf water potential (ΨW) and an increase in relative water content (RWC). The values of net photosynthetic rate (PN), stomatal conductance to water vapor (gS) and transpiration (E) were significantly (p<0.05) reduced 21 and 34 days after starting treatment (DAST) in plants of genotypes CNPAE 183 and CNPAE 191, respectively. After 6 DAR, only CNPAE 191 achieved a recovery of PN and E. Moreover, significantly (p<0.05) lower gS was measured in recovering plants of both genotypes, as compared to the controls. Drought stress led to reductions of 57 and 65% in whole-plant hydraulic conductance (KL) in genotypes CNPAE 183 and CNPAE 191, respectively. Full recovery of KL was observed after 6 DAR. The average water consumption was 18% lower in plants subjected to water shortage, as compared to irrigated plants. However, drought-induced reduction in growth led to lower biomass water use efficiency (WUEbiomass) in plants subjected to water deficit. The effect of water stress was more intense in CNPAE 183 than in CNPAE 191, regarding the growth variables (leaf area, height and diameter), dry mass and root volume. Moreover, a delay in the effect of water stress in genotype CNPAE 191 was also observed, which suggests a higher tolerance of this genotype as compared to CNPAE 183. Altogether, the results showed strong drought-induced stomatal limitation of carbon assimilation and growth in J. curcas. Slight genotypic differences were detected, CNPAE 191 being less sensitive to the imposed experimental conditions than CNPAE 183.   Key words: Hydraulic conductivity, root volume, tolerance, leaf gas exchange, water relations, water status.

Photosynthetic responses of a wheat (Asakaze)-barley (Manas) 7H addition line to salt stress

The photosynthetic responses to salt stress were examined in a wheat (Triticum aestivum L. cv. Asakaze)–barley (Hordeum vulgare L. cv. Manas) 7H addition line having elevated salt tolerance and compared to the parental wheat genotype. For this purpose, increasing NaCl concentrations up to 300 mM were applied and followed by a 7-day recovery period. Up to moderate salt stress (200 mM NaCl), forcible stomatal closure, parallel with a reduction in the net assimilation rate (P N), was only observed in wheat, but not in the 7H addition line or barley. Since the photosynthetic electron transport processes of wheat were not affected by NaCl, the impairment in P N could largely be accounted for the salt-induced decline in stomatal conductance (g s), accompanied by depressed intercellular CO2 concentration and carboxylation efficiency. Both, P N and nonstomatal limitation factors (Lns) were practically unaffected by moderate salt stress in barley and in the 7H addition line due to the sustained g s, which might be an efficient strategy to maintain the efficient photosynthetic activity and biomass production. At 300 mM NaCl, both P N and g s decreased significantly in all the genotypes, but the changes in P N and Lns in the 7H addition line were more favourable similar to those in wheat. The downregulation of photosynthetic electron transport processes around PSII, accompanied by increases in the quantum yield of regulated energy dissipation and of the donor side limitation of PSI without damage to PSII, was observed in the addition line and barley during severe stress. Incomplete recovery of P N was observed in the 7H addition line as a result of declined PSII activity probably caused by enhanced cyclic electron flow around PSI. These results suggest that the better photosynthetic tolerance to moderate salt stress of barley can be manifested in the 7H addition line which may be a suitable candidate for improving salt tolerance of wheat.

Interspecific grafting to enhance physiological resilience to flooding stress in tomato (Solanum lycopersicum L.)

Tomato (Solanum lycopersicum L.) is highly susceptible to flooding stress. In order to improve its flooding tolerance, the study was conducted to determine the effect of grafting tomato plants (cv. Arka Rakshak, AR) onto different eggplant (Solanum melongena L.) rootstocks [BPLH-1, Arka Neelkanth (AN), Mattu Gulla (MG) and Arka Keshav (AK)] against flooding during rainy season (July-September). The tomato plants were subjected to flooding stress at flowering stage for 6 days by submerging in a tank with the water level at 2.0cm above the soil surface in the pots. The gas exchange parameters, photosynthesis rate (PN), stomatal conductance (gs) and internal CO2 concentration (Ci), chlorophyll fluorescence, leaf water potential (ψL) and chlorophyll content showed a lesser decline in eggplant rootstock grafted plants as compared with self-grafted and ungrafted plants. In general, eggplant rootstock grafted plants exhibited better survival, enhanced physiological adaptation and improved fruit yield over the self-grafted and ungrafted plants under flooding. Between the rootstock grafted plants, the graft combinations AR/AN and AR/BPLH-1 were more efficient in sustaining the above attributes. Flooding conditions favoured accumulation of total sugar, reducing sugar, sucrose and individual sugar like sucrose and glucose in the leaves of grafted and ungrafted plants and the eggplant rootstocks grafted plants under flooding conditions accumulated higher sugars and starch as compared with self-grafted and ungrafted plants. Among the grafts, AR/AN showed in high sugar and starch accumulation under flooding. The recovery was better in eggplant rootstock grafted plants as reflected by recovery of PN, gs and ψL, and decline in sugar and starch levels. The study indicated that the eggplant rootstock grafting is of great relevance in improving physiological tolerance in tomato under flooding. Among the eggplant rootstock grafted tomato plants, AR/AN showed better survival and plant yield after experiencing flooding.

Stomatal Development and Associated Photosynthetic Characteristics of Watermelon (Citrullus lanatus) Plug Seedlings during Light Storage

Illumination during storage was proven to extend the storability of seedlings, but little attention has been given to the underlying mechanism. To determine how light conditions affect photosynthetic status in watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] plug seedlings, differences of stomatal development and relative photosynthetic characteristics of expanding new leaves when stored for 8 days at 15 °C in light at a photosynthetic photon flux (PPF) of 15 μmol·m−2·s−1 or darkness were investigated. The stomatal density (SD) increased with time to a peak and then decreased from the start of storage in light to the subsequent transplantation. Dark storage retarded the stomatal development and delayed the appearance of the peak of SD. Compared with those under dark storage, light-stored seedlings showed significantly higher SD and stomatal index (SI) in leaves accompanied by higher maximal photochemical efficiency of PSII (Fv/Fm) and quantum yield of PSII (ΦPSII). During storage in darkness, Fv/Fm and ΦPSII declined steeply with increasing storage duration but recovered gradually to reach the same level of those in light at the fourth day after transplanting. Seedlings stored in light for 8 days showed higher net photosynthesis rate (Pn), stomatal conductance (gS), intercellular CO2 concentration (Ci), and transpiration rate (Tr) than in darkness. The post-storage recovery of Pn, gS, and Tr were closely related to the SI, which ensured the fast recovery of photosynthesis during the early stage of transplanting. In agreement with the change of SD, no differences in Pn, gS, Ci, and Tr between light and dark storage were observed after 8 days of transplantation. Seedlings stored in light appeared vigorous and the shoot dry weight was significantly higher than that of dark-stored ones. Although seedlings in dark storage had a poor appearance during storage, they showed inhibited regrowth potentials during the subsequent transplanting stage. This study exhibited that light in short-term storage contributed to maintaining stomatal development as well as photosynthetic efficiency in watermelon, which could also extend to post-storage for ensuring the transplant quality of seedlings after removal from storage.

Pyrrhotite flotation and its selectivity against pentlandite in the beneficiation of nickeliferous ores: An electrochemistry perspective

Pyrrhotite (Po) is one of the most abundant sulfide minerals in processing industry and must be rejected in most cases. Particularly, Po rejection and its selectivity against pentlandite (Pn) have long been a challenge due to similarities in the mineral composition of the two minerals and the collectorless flotation characteristics of Po. Xanthates have been widely used to promote sulfide mineral flotation; however, in the presence of xanthates, the redox potential established at the mineral/solution interface is most important, determining the flotation performance. In this paper, the importance of electrochemistry in Po and Pn flotation has been demonstrated and a comprehensive study was conducted on two different feed streams (i.e., magnetic concentrate and scavenger cleaner streams, containing magnetic and nonmagnetic forms of Po, respectively), from Vale’s Clarabelle Mill in Sudbury, Ontario, with an objective to determine if improvements in Po rejection and Pn recovery could be achieved by controlling pulp electrochemistry. By conducting a series of flotation tests under different Eh conditions and reagent usage schemes, it was revealed that higher Po content in the magnetic stream may protect Pn from being oxidized, improving Pn recovery. The results indicated that at low oxidizing pulp chemistry, the rest potential for the Pn is still high enough to allow the formation of dixanthogen to promote its flotation. Using a Pt electrode, it was found that by controlling pulp potential at −50<Eh< +50 mV, the Pn recovery and Po depression would be satisfactory. The results, using mineral electrodes (Outotec Chena analyzer), indicated that selective separation can be achieved if low-to-moderate oxidation potentials (0 to 100 mV) or reduction (0 to −100 mV) potentials are monitored using Pn and Po electrodes. Mixing two streams at 50:50 wt % would be possibly beneficial in selective separation.

Effects of Duration and Temperature in Simulated Dark Shipping on the Subsequent Performance of the Nobile-type Dendrobiums

The popularity of the nobile-type dendrobium (Dendrobium nobile hybrids) has been increasing globally. More information regarding the effects of long-distance shipping, from producing countries to destination market countries, on the post-shipping plant performance is needed. In this study, two nobile-type dendrobium cultivars were subjected to simulated dark shipping (SDS) at various temperatures and durations. Changes in net CO2 uptake rate (Pn), chlorophyll fluorescence, and leaf relative water content after plants had been treated with SDS were investigated. Furthermore, shipped plants were vernalized to investigate the effect of dark shipping on the subsequent flowering quality. Dark shipping for 7 days at 15 °C did not affect the post-shipping photosynthetic performance of D. Lan Tarn Beauty. Increasing the shipping duration from 7 to 21 days increased the time required for Pn recovery from 1 to 12 days. Dendrobium Lan Tarn Beauty recovered its Pn within 4 days when shipped for 21 days at 10 °C, and this was prolonged to 11 days when the plants were shipped at 20 °C. Changes in Fv/Fm indicated that there was no marked damage to either cultivars, and the leaf relative water content was little affected by SDS. Dendrobium Lan Tarn Beauty and D. Lucky Girl shipped at 10 °C flowered 5 and 8 days earlier, respectively, compared with unshipped plants. Regardless of the shipping conditions, shipped D. Lucky Girl had a lower flower diameter and higher total flower count than unshipped plants. No differences were found in the number of nodes with flowers or the total flower count between shipped and unshipped D. Lan Tarn Beauty. Our study suggested that dark shipping for up to 21 days is possible for nobile-type dendrobiums. We recommend shipping temperatures of 10 to 15 °C to reduce the detrimental effects caused by long-term dark shipping.

Nerium oleander indirect leaf photosynthesis and light harvesting reductions after clipping injury or Spodoptera eridania herbivory: High sensitivity to injury

Variable indirect photosynthetic rate (Pn) responses occur on injured leaves after insect herbivory. It is important to understand factors that influence indirect Pn reductions after injury. The current study examines the relationship between gas exchange and chlorophyll a fluorescence parameters with injury intensity (% single leaf tissue removal) from clipping or Spodoptera eridania Stoll (Noctuidae) herbivory on Nerium oleander L. (Apocynaceae). Two experiments showed intercellular [CO2] increases but Pn and stomatal conductance reductions with increasing injury intensity, suggesting non-stomatal Pn limitation. Also, Pn recovery was incomplete at 3d post-injury. This is the first report of a negative exponential Pn impairment function with leaf injury intensity to suggest high N. oleander leaf sensitivity to indirect Pn impairment. Negative linear functions occurred between most other gas exchange and chlorophyll a fluorescence parameters with injury intensity. The degree of light harvesting impairment increased with injury intensity via lower (1) photochemical efficiency indicated lower energy transfer efficiency from reaction centers to PSII, (2) photochemical quenching indicated reaction center closure, and (3) electron transport rates indicated less energy traveling through PSII. Future studies can examine additional mechanisms (mesophyll conductance, carbon fixation, and cardenolide induction) to cause N. oleander indirect leaf Pn reductions after injury.

Effects of exogenous abscisic acid pre-treatment of cucumber (Cucumis sativus) seeds on seedling growth and water-stress tolerance

The effect of treating cucumber seeds (Cucumis sativus ‘Zhongnong 12’) with exogenous abscisic acid (ABA) on seedling growth and various plant characteristics, including chlorophyll a fluorescence, net photosynthesis, antioxidant enzyme activity and water-stress tolerance under dehydration was investigated. The results showed that the photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and the apparent quantum yield of photosynthesis (AQY) all declined gradually, but the decline in ABA seed pre-treated seedlings (ASPS) was less than in non-ABA seed pre-treated seedlings (NASPS), especially for Pn during dehydration. Water use efficiency (WUE) was observed in ASPS, which was three times greater than that in NASPS, implying that the corresponding increase in WUE, calculated on the basis of water uptake, was the result of increased Pn and a reduction in transpiration in ASPS. During dehydration, the levels of electron transport rate (ETR), photochemical efficiency of PSII (Fv/Fm), photochemical quenching (qP), quantum efficiency of PSII photochemistry (ΦPSII) and the ratio of photochemicals (Pc) all decreased; in particular, the decline in NASPS was more than that in ASPS. The levels of non-photochemical quench (NPQ), ratio of antenna heat dissipation (Hd) and ratio of heat dissipation in PSII (Ex) all increased more in NASPS than in ASPS, suggesting that ABA could protect cucumber seedlings from the damage of photoinhibition by improved heat dissipation. Dehydration caused an increase in antioxidant enzyme activities in the first two days, especially in ASPS, and then declined slightly. In comparison with NASPS, ASPS showed a marked decrease in malondialdehyde (MDA) content during dehydration. On the other hand, rehydration resulted in nearly 100% recovery of Pn, Gs and Tr in ASPS, as well as chlorophyll fluorescence parameters, but only a small recovery in NASPS. These results suggest that imbibition of cucumber seeds with ABA protected cucumber seedlings from water-loss damage and increased their resistance or tolerance of dehydration, especially improving their WUE by improved Pn rather than by reduced water uptake under dehydration. The beneficial effect of exogenous ABA applications on reducing susceptibility to gradual dehydration of cucumber seedlings was confirmed in our study by applying ABA to imbibition cucumber seeds.

Salicylic acid alleviates decreases in photosynthesis under heat stress and accelerates recovery in grapevine leaves

BackgroundAlthough the effect of salicylic acid (SA) on photosynthesis of plants including grapevines has been investigated, very little is yet known about the effects of SA on carbon assimilation and several components of PSII electron transport (donor side, reaction center and acceptor side). In this study, the impact of SA pretreatment on photosynthesis was evaluated in the leaves of young grapevines before heat stress (25°C), during heat stress (43°C for 5 h), and through the following recovery period (25°C). Photosynthetic measures included gas exchange parameters, PSII electron transport, energy dissipation, and Rubisco activation state. The levels of heat shock proteins (HSPs) in the chloroplast were also investigated.ResultsSA did not significantly (P < 0.05) influence the net photosynthesis rate (Pn) of leaves before heat stress. But, SA did alleviate declines in Pn and Rubisco activition state, and did not alter negative changes in PSII parameters (donor side, acceptor side and reaction center QA) under heat stress. Following heat treatment, the recovery of Pn in SA-treated leaves was accelerated compared with the control (H2O-treated) leaves, and, donor and acceptor parameters of PSII in SA-treated leaves recovered to normal levels more rapidly than in the controls. Rubisco, however, was not significantly (P < 0.05) influenced by SA. Before heat stress, SA did not affect level of HSP 21, but the HSP21 immune signal increased in both SA-treated and control leaves during heat stress. During the recovery period, HSP21 levels remained high through the end of the experiment in the SA-treated leaves, but decreased in controls.ConclusionSA pretreatment alleviated the heat stress induced decrease in Pn mainly through maintaining higher Rubisco activition state, and it accelerated the recovery of Pn mainly through effects on PSII function. These effects of SA may be related in part to enhanced levels of HSP21.

Photosynthetic performance and stomatal characteristics during ex vitro acclimatisation of true service tree (Sorbus domestica L.)

SummaryMortality rates of micropropagated plantlets after transfer to an ex vitro environment are often high. The temporal pattern of developmental changes was examined in a slow-growing true service tree (Sorbus domestica L.) in relation to its photosynthetic and stomatal characteristics. The rates of net photosynthesis (Pn), transpiration (E), and stomatal conductance (gs), the maximum photochemical efficiency of photosystem II (Fv/Fm), potential electron capacity (‘area’), maximum-to-initial fluorescence ratio (Fm/F0), as well as stomatal densities and sizes, were determined over the course of a 63-day acclimatisation period. In vitro-rooted plantlets were photosynthetically competent. A sudden decrease in Pn was observed 7 d after transfer. The recovery of Pn took place within the next 28 d, and the rate remained steady until the end of acclimatisation.The most prominent changes in the Fv/Fm and Fm/F0 ratios were found between days-7 and -35. Full acclimatisation was achieved 63 d after transfer. This stage was associated with the lowest values of E, gs, and stomatal density, as well as the highest values of Fv/Fm, ‘area’, Fm/F0, and stomatal size.

Impairment of Leaf Photosynthesis After Insect Herbivory or Mechanical Injury on Common Milkweed, &lt;I&gt;Asclepias syriaca&lt;/I&gt;

Insect herbivory has variable consequences on plant physiology, growth, and reproduction. In some plants, herbivory reduces photosynthetic rate (Pn) activity on remaining tissue of injured leaves. We sought to better understand the influence of leaf injury on Pn of common milkweed, Asclepias syriaca (Asclepiadaceae), leaves. Initially, we tested whether Pn reductions occurred after insect herbivory or mechanical injury. We also (1) examined the duration of photosynthetic recovery, (2) compared mechanical injury with insect herbivory, (3) studied the relationship between leaf Pn with leaf injury intensity, and (4) considered uninjured leaf compensatory Pn responses neighboring an injured leaf. Leaf Pn was significantly reduced on mechanically injured or insect-fed leaves in all reported experiments except one, so some factor(s) (cardiac glycoside induction, reproductive investment, and water stress) likely interacts with leaf injury to influence whether Pn impairment occurs. Milkweed tussock moth larval herbivory, Euchaetes egle L. (Arctiidae), impaired leaf Pn more severely than mechanical injury in one experiment. Duration of Pn impairment lasted > 5 d to indicate high leaf Pn sensitivity to injury, but Pn recovery occurred within 13 d in one experiment. The degree of Pn reduction was more severe from E. egle herbivory than similar levels of mechanical tissue removal. Negative linear relationships characterized leaf Pn with percentage tissue loss from single E. egle-fed leaves and mechanically injured leaves and suggested that the signal to trigger leaf Pn impairment on remaining tissue of an injured leaf was amplified by additional tissue loss. Finally, neighboring uninjured leaves to an E. egle-fed leaf had a small (approximately 10%) degree of compensatory Pn to partly offset tissue loss and injured leaf Pn impairment.

Impairment of Leaf Photosynthesis After Insect Herbivory or Mechanical Injury on Common Milkweed,Asclepias syriaca

Insect herbivory has variable consequences on plant physiology, growth, and reproduction. In some plants, herbivory reduces photosynthetic rate (Pn) activity on remaining tissue of injured leaves. We sought to better understand the influence of leaf injury on Pn of common milkweed, Asclepias syriaca (Asclepiadaceae), leaves. Initially, we tested whether Pn reductions occurred after insect herbivory or mechanical injury. We also (1) examined the duration of photosynthetic recovery, (2) compared mechanical injury with insect herbivory, (3) studied the relationship between leaf Pn with leaf injury intensity, and (4) considered uninjured leaf compensatory Pn responses neighboring an injured leaf. Leaf Pn was significantly reduced on mechanically injured or insect-fed leaves in all reported experiments except one, so some factor(s) (cardiac glycoside induction, reproductive investment, and water stress) likely interacts with leaf injury to influence whether Pn impairment occurs. Milkweed tussock moth larval herbivory, Euchaetes egle L. (Arctiidae), impaired leaf Pn more severely than mechanical injury in one experiment. Duration of Pn impairment lasted >5 d to indicate high leaf Pn sensitivity to injury, but Pn recovery occurred within 13 d in one experiment. The degree of Pn reduction was more severe from E. egle herbivory than similar levels of mechanical tissue removal. Negative linear relationships characterized leaf Pn with percentage tissue loss from single E. egle –fed leaves and mechanically injured leaves and suggested that the signal to trigger leaf Pn impairment on remaining tissue of an injured leaf was amplified by additional tissue loss. Finally, neighboring uninjured leaves to an E. egle –fed leaf had a small (≈10%) degree of compensatory Pn to partly offset tissue loss and injured leaf Pn impairment.

Overexpression of Sweet Pepper Glycerol‐3‐Phosphate Acyltransferase Gene Enhanced Thermotolerance of Photosynthetic Apparatus in Transgenic Tobacco

In order to investigate the relationship between the lipid composition in thylakoid membrane and thermostability of photosynthetic apparatus, tobacco transformed with sweet pepper sense glycerol-3-phosphate acyltransferase (GPAT) gene were used to analyze the lipid composition in thylakoid membrane, the net photosynthetic rate and chlorophyll fluorescence parameters under high temperature stress. The results showed that the saturated extent of monogalactosyldiacylglycerol (MGDG), sulfoquinovosyldiacylglycerol, digalactosyldiacylglycerol and phosphatidylglycerol in thylakoid membrane of transgenic tobacco T(1) lines increased generally. Particularly, the saturated extent in MGDG increased obviously by 16.2% and 12.0% in T(1)-2 and T(1)-1, respectively. With stress temperature elevating, the maximum efficiency of photosystem II (PSII) photochemistry (Fv/Fm), actual photochemical efficiency of PSII in the light (Phi(PSII)) and net photosynthetic rate (Pn) of the two lines and wild type tobacco plants decreased gradually, but those parameters decreased much less in transgenic plants. Even though the recovery process appeared differently in the donor and acceptor side of PSII in transgenic tobacco compared with wild-type plants, the entire capability of PSII recovered faster in transgenic tobacco, which was shown in the parameters of PI, Fv/Fm and Phi(PSII), as a result, the recovery of Pn was accelerated. Conclusively, we proposed that the increase in saturated extent of thylakoid membrane lipids in transgenic plants enhanced the stability of photosynthetic apparatus under high temperature stress.

Gas exchanges and yield responses of mungbean (Vigna radiata L. Wilczek) genotypes differing in flooding tolerance

Flooding-induced changes in leaf gas exchanges, grain yield, and yield-related parameters of mungbean were evaluated employing two flood-tolerant (GK48 and VC3945A) and one flood-susceptible (Vo1982A-G) genotypes. Three flooding regimes viz. 1, 3 and 7-day were imposed at vegetative, flowering, and pod-fill stages. Flooding caused a drastic reduction in photosynthesis rates (Pn), irrespective of flooding duration. However, the flooded plants recovered Pn to a large extent depending on genotypes. Used genotypes showed a significant variation in Pn during and after flooding. Post-flooding recovery in Pn of GK48 and VC3945A was more pronounced at the vegetative and flowering stages than the pod-fill stage. At the pod-fill stage, only plants of GK48 survived when flooding prolonged for 7 days. Flooded plants showed higher intercellular CO2 concentrations (Ci), and reduced stomatal conductance (gs). However, during recovery, Pn increased significantly along with reduced Ci in flood-tolerant GK48 and VC3945A genotypes. In contrast, Ci remained high and Pn recovery was minimal in flood-susceptible Vo1982A-G genotype. This implies that mesophyll tolerance rather than stomatal factor might be the major limitation of Pn recovery in a susceptible genotype. Very weak relationship between Pn and transpiration rate (Tr) indicated low water use efficiency (WUE) in flooded plants, but subsequent recovery of both the parameters, suggesting higher WUE, particularly in tolerant genotypes. Seed yield of mungbean was the product of number of pods per plant and seed size, and longer the flooding period, the lower were the pods per plant at the flowering and pod-fill stage. Flooding reduced seed yield in all the three genotypes, but the extent of reduction was much less in flood-tolerant GK48 and VC3945A. Higher yield of flood-tolerant genotypes may be attributed to the rapid recovery of leaf gas exchanges.