Although the beneficial role of Fe, Zn, and Mn on many physiological and biochemical processes is well established, effects of each of these elements on chlorophyll (Chl) a fluorescence and photosynthetic pigment contents is not well studied. The objective of this study was to evaluate effects of Fe, Zn, and Mn deficiency in two lettuce cultivars. The parameters investigated could serve also as physiological and biochemical markers in order to identify stress-tolerant cultivars. Our results indicated that microelement shortage significantly decreased contents of photosynthetic pigments in both lettuce cultivars. Chl a fluorescence parameters including maximal quantum yield of PSII photochemistry and performance index decreased under micronutrient deficiency, while relative variable fluorescence at J-step and minimal fluorescence yield of the dark-adapted state increased under such conditions in both cultivars. Micronutrient deficiency also reduced all parameters of quantum yield and specific energy fluxes excluding quantum yield of energy dissipation, quantum yield of reduction of end electron acceptors at the PSI, and total performance index for the photochemical activity. Osmoregulators, such as proline, soluble sugar, and total phenols were enhanced in plants grown under micronutrient deficiency. Fe, Zn, and Mn deficiency led to a lesser production of dry mass. The Fe deficiency was more destructive than that of Zn and Mn on the efficiency of PSII in both lettuce cultivars. Our results suggest that the leaf lettuce, which showed a higher efficiency of PSII, electron transport, quantum yield, specific energy fluxes, and osmoregulators under micronutrient deficiency, was more tolerant to stress conditions than crisphead lettuce., H. R. Roosta, A. Estaji, F. Niknam., and Obsahuje bibliografii
Hypobaria (low total atmospheric pressure) is essential in sustainable, energy-efficient plant production systems for long-term space exploration and human habitation on the Moon and Mars. There are also critical engineering, safety, and materials handling advantages of growing plants under hypobaria, including reduced atmospheric leakage from extraterrestrial base environments. The potential for producing crops under hypobaria and manipulating hypoxia (low oxygen stress) to increase health-promoting bioactive compounds is not well characterized. Here we showed that hypobaric-grown lettuce plants (25 kPa ≈ 25% of normal pressure) exposed to hypoxia (6 kPa pO2 ≈ 29% of normal pO2) during the final 3 d of the production cycle had enhanced antioxidant activity, increased synthesis of anthocyananins, phenolics, and carotenoids without reduction of photosynthesis or plant biomass. Net photosynthetic rate (PN) was not affected by total pressure. However, 10 d of hypoxia reduced PN, dark respiration rate (RD),
PN/RD ratio, and plant biomass. Growing plants under hypobaria and manipulating hypoxia during crop production to enhance health-promoting bioactive compounds is important for the health and well-being of astronauts exposed to space radiation and other stresses during long-term habitation. and C. He ... [et al.].
Photosynthetic utilization of radiant energy was studied by chlorophyll (Chl) fluorescence and maximum photosynthetic O2 evolution (Pmax) in temperate lettuce (Lactuca sativa L.) grown under natural tropical fluctuating ambient temperatures but with their roots exposed to two different root-zone temperatures (RZTs): a constant 20 °C-RZT (RZT20) and a fluctuating ambient RZT (RZTa) from 23 to 40 °C. On a sunny day, irrespective of RZT, ΔF/Fm' [ratio of the variable to maximal fluorescence under irradiation (the maximal photosystem 2 quantum yield with "actinic light")] decreased and non-photochemical quenching (NPQ) increased parallel to the increase of photosynthetic photon flux density (PPFD). However, RZTa plants showed lower ΔF/Fm' and higher NPQ than RZT20 plants. The electron transport rate (ETR) was much higher in RZT20 plants than in RZTa plants especially during moderately sunny days. There were no significant diurnal changes in Pmax although these values of RZT20 plants were much higher than those of RZTa plants. On cloudy days, no significant diurnal changes in ΔF/Fm' and NPQ occurred, but ΔF/Fm' was higher and NPQ was lower in RZT20 plants than in RZTa plants. Diurnal changes in ETR were also observed in all plants while Pmax values throughout the whole cloudy days in both RZT20 and RZTa plants were constant. Again, RZT20 plants had much higher values of Pmax than RZTa plants. During RZT transfer period, all Chl fluorescence parameters measured at midday fluctuated with PPFD. Impact of RZT on these parameters was observed 2-3 d after RZT transfer. ETR and Pmax measured with saturating PPFD in the laboratory did not vary with the fluctuating PPFD in the greenhouse but the effects of RZT on these two parameters were observed 3-4 d after RZT transfer. Thus RZT affects photosynthetic utilization of photon energy in temperate lettuce grown under natural tropical condition. and J. He, S. K. Lee.
Ozone is the major phytotoxic air pollutant that reduces the yield of several agricultural crops in the Spanish Mediterranean area. We studied four lettuce cultivars (Lactuca sativa L.) for the effects of different O3 concentrations during the winter on chlorophyll (Chl) a fluorescence, lipid peroxidation, and root length in outdoor open-top chambers. Under O3 the photosynthetic quantum conversion declined while heat emissions increased in all cultivars; these results provide more evidence of non-filtered air with additional ozone (NFA+O3) treatment compared with non-filtered air (NFA) and charcoal filtered ozone-free air (CFA). Changes in the Chl a fluorescence may be associated with an increase in membrane lipid peroxidation as well as with observed reduction of root length under O3 stress. and A. Calatayud, J. W. Alvarado, E. Barreno.
The aphid Uroleucon ambrosiae (Thomas) is one of the principal pests found on greenhouse lettuce crops, and there is no efficient biological control agent of this pest in Brazil. This work evaluates the aphid U. ambrosiae as a host for the parasitoid Praon volucre (Haliday), aimed at using P. volucre as a potential biological control agent of U. ambrosiae on lettuce. As Macrosiphum euphorbiae (Thomas) is a common host of P. volucre in the field, the development of the parasitoid was compared on these two aphid species. Twenty nymphs of the 2nd instar were kept with P. volucre for one hour at 22 ± 1°C, 70 ± 10% RH and a 12 h photophase. The size of the aphid's tibiae at the moment of oviposition indicated that there was no significant size difference between U. ambrosiae (0.6 ± 0.02 mm) and M. euphorbiae (0.7 ± 0.03 mm). When mummies were formed, M. euphorbiae had significantly longer tibia (1.5 ± 0.03 mm) than U. ambrosiae (1.4 ± 0.02 mm). No significant differences were detected in the percentage emergence (74.9 ± 7.92 and 87.5% ± 3.31 for U. ambrosiae and M. euphorbiae, respectively), or proportion of female offspring (56.2 ± 7.62 and 44.2 ± 7.14%). The development time from oviposition to adult and longevity of females and males of P. volucre reared on the two host species were not different. High parasitism levels were recorded for both host aphid species, but the percentage parasitism of M. euphorbiae (54.4 ± 4.40) was higher than of U. ambrosiae (35.6 ± 5.30). Female parasitoids reared on M. euphorbiae had longer tibiae (0.78 ± 0.01 mm) than those reared on U. ambrosiae (0.72 ± 0.01 mm). Our results demonstrate that the alternative host species U. ambrosiae, compared to the natural host species M. euphorbiae, affects the female's size, but did not affect parasitoid development time, longevity, emergence or sex ratio. The parasitoid P. volucre seems to be a good candidate for using as a biological control agent of U. ambrosiae on lettuce in Brazil.