In the seasonally flooded forest of the Mapire River, a tributary of the Orinoco, seedlings remain totally covered by flood water for over six months. In order to characterize the physiological response to flooding and submergence, seedlings of the tree Pouteria orinocoensis, an important component of the forest vegetation, were subjected experimentally to flooding. Flooding was imposed gradually, the maximum level of flood including submerged and emerged leaves. After 45 d a severe reduction of net photosynthetic rate (PN) and stomatal conductance (g s) was observed in emerged leaves, whereas leaf water potential remained constant. The decrease in PN of emerged leaves was associated to an increase in both relative stomatal and non-stomatal limitations, and the maintenance of the internal/air CO2 concentration (C i/C a) for at least 20 d of flooding. After this time, both PN and gs became almost zero. The decrease in photosynthetic capacity of emerged leaves with flooding was also evidenced by a decrease in carboxylation efficiency; photon-saturated photosynthetic rate, and apparent quantum yield of CO2 fixation. Oxygen evolution rate of submerged leaves measured after three days of treatment was 7 % of the photosynthetic rate of emerged leaves. Submersion determined a chronic photoinhibition of leaves, viewed as a reduction in maximum quantum yield in dark-adapted leaves, whereas the chlorophyll fluorescence analysis of emerged leaves pointed out at the occurrence of dynamic, rather than chronic, photoinhibition. This was evidenced by the absence of photochemical damage, i.e. the maintenance of maximum quantum yield in dark-adapted leaves. Nevertheless, the observed lack of complementarity between photochemical and non-photochemical quenching after 12 d of flooding implies that the capacity for photochemical quenching decreased in a non-co-ordinate manner with the increase in non-photochemical quenching.
Influence of drought (D) on changes of leaf water potential (Ψ) and parameters of gas exchange in D-resistant and D-sensitive genotypes of triticale and maize was compared. Soil D (from -0.01 to -2.45 MPa) was simulated by mannitol solutions. At -0.013 MPa significant differences in Ψ, net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), and internal CO2 concentration (Ci) of D-resistant and D-sensitive triticale and maize genotypes were not found. Together with the increase in concentration of the mannitol solution the impact of D on E and gs for D-sensitive genotypes (CHD-12, Ankora) became lower than for the D-resistant ones (CHD-247, Tina). Inversely, impact of D on Ψ was higher in D-sensitive than D-resistant genotypes. From 1 to 3 d of D, a higher decrease in PN was observed in D-resistant genotypes than in the D-sensitive ones. Under prolonged D (5-14 d) and simultaneous more severe D the decrease in PN was lower in D-resistant than in D-sensitive genotypes. Changes in Ψ, PN, E, and gs caused by D in genotypes differing in the drought susceptibility were similar for triticale and maize. Compared to control plants, increase of Ci was different for triticale and maize genotypes. Hence one of the physiological reasons of different susceptibility to D between sensitive and resistant genotypes is more efficient protection of tissue water status in resistant genotypes reflected in higher decrease in gs and limiting E compared to the sensitive ones. Other reason, observed in D-resistant genotypes during the recovery from D-stress, was more efficient removal of detrimental effects of D. and M. T. Grzesiak, S. Grzesiak, A. Skoczowski.
The effects of Cu, Cd, and Pb toxicity on photosynthesis in cucumber leaves (Cucumis sativus L.) were studied by the measurements of gas exchange characteristics, chlorophyll (Chl) fluorescence parameters, and Chl content. Concentrations of metals in sequence of 20 μM Cu, 20 and 50 μM Cd, and 1 000 μM Pb decreased the plant dry mass to 50-60 % after 10 d of treatment whereas 50 μM of Cu decreased it to 30 %. The content of Cd in leaves of plants treated with 50 μM Cd was three times higher than the contents of Cu and Pb after plant treatment with 50 μM Cu or 1 000 μM Pb. Hence Cd was transported to leaves much better than Cu and Pb. Nevertheless, the net photosynthetic rate and stomatal conductance in leaves treated with 50 μM Cu or Cd were similarly reduced. Thus, Cu was more toxic than Cd and Pb for photosynthesis in cucumber leaves. None of the investigated metals decreased internal CO2 concentrations. Also the effect of metals on potential efficiency of photosystem 2, PS2 (Fv/Fm) was negligible. The metal dependent reduction of PS2 quantum efficiency (ΦPS2) after plant adaptation in actinic irradiation was more noticeable. This could imply that reduced demand for ATP and NADPH in a dark phase of photosynthesis caused a down-regulation of PS2 photochemistry. Furthermore, in leaves of metal-treated plants the decrease in water percentage as well as lower contents of Chl and Fe were observed. Thus photosynthesis is not the main limiting factor for cucumber growth under Cu, Cd, or Pb stress. and M. Burzyński, G. Kłobus.
Tomato seeds exposed to space conditions for nearly six years on board the Long Duration Exposure Facility (LDEF) satellite were subsequently germinated and the resultant seedlings grown on earth under controlled conditions for analysis. Photosynthesis, biomass, and water relations were compared between mature plants grown from earth-based control seeds and space-exposed seeds under both well-watered and drought-stressed conditions. No consistent significant differences in photosynthesis and water relations were observed in the two sets of plants at any level of drought stress. Fruit production, however, though limited and variable, was significantly greater in plants grown from space-exposed seeds than in plants grown from earth-based seeds. Overall, exposure of seeds to space had only minor effects on the physiology and growth of plants grown from such seed. and M. S. Marmor, C. E. Martin.
Optical characteristics, contents of photosynthetic pigments, total soluble sugars, and starch, rates of gas exchange, chlorophyll (Chl) a fluorescence, and leaf water relations were analysed in three Vitis vinifera L. cultivars, Tinto Cão (TC), Touriga Nacional (TN), and Tinta Roriz (TR), grown in Mediterranean climate. Chl content was significantly lower in TC than in TN and TR leaves, while the Chl a/b ratio was higher. TR had the lowest net photosynthetic rate, stomatal conductance, and contents of soluble sugars and starch than TN and TC. In spite of low Chl content, TC showed the lowest photon absorbance and the highest photochemical efficiency of photosystem 2. TC had the lowest predawn and midday leaf water potential. The capability for osmotic adjustment was similar among cultivars and the calculated modulus of elasticity was higher in TC leaves. The typical lighter green leaves of TC seemed to be an adaptive strategy to high irradiance and air temperature associated to water stress. and J. Moutinho-Pereira ... [et al.].
High variability in leaf gas exchange and related traits were found in 30 genotypes of field grown finger millet. The variability in carbon exchange rate per unit leaf area (PN) can be partly attributed to the differences in the stomatal conductance (gs) and area leaf mass (ALM). The PN was positively correlated with total dry matter (TDM). However, no relationship between PN and seed yield was found. The leaf area showed a positive and significant correlation with total biomass. None of the other gas-exchange traits had significant relationship either with TDM or with seed yield. The ALM showed a strong positive association with PN. However, it was not correlated with either total biomass or seed yield. As a result, the use of ALM as surrogate for PN for identifying high biomass producing genotypes only had a limited value. Hence selection for high PN would result in higher biomass producing types.
Seedlings of chile ancho pepper were grown in pots containing a pasteurized mixture of sand and a low phosphorus (P) sandy loam soil, and either inoculated (VAM) or not inoculated (NVAM) with the endomycorrhizal fungus Glomus intraradices. Long Ashton nutrient solution (LANS) was modified to supply P to the seedlings at 0, 11, and 44 g(P) m-3 (P0, P11, P44, respectively). Low P depressed net photosynthetic rate (PN), stomatal conductance (gs), phosphorus use efficiency (PN/P), and internal CO2 concentration (Ci). The mycorrhiza alleviated low P effects by increasing PN, gs, PN/P, and decreasing Ci. At P0, Ci of NVAM plants was equal to or higher than that of VAM plants, suggesting nonstomatal inhibition of photosynthesis. Gas exchange of VAM plants at P0 was similar to that of NVAM plants at P11. Endomycorrhiza increased leaf number, leaf area, shoot, root and fruit mass at P0 and P11 compared to NVAM plants. Reproductive growth was enhanced by 450 % in mycorrhizal plants at P44. Root colonization (arbuscules, vesicles, internal and extraradical hyphae development) was higher at lower P concentrations, while sporulation was unaffected. The enhanced growth and gas exchange of mycorrhizal plants was in part due to greater uptake of P and greater extraradical hyphae development. and L. Aguilera-Gomez ... [et al.].
Wheat (Triticum aestivum L. cv. HD 2285) was grown in control (C) and heated (H) open top chambers (OTCs) for entire period of growth and development till maturity. The mean maximum temperature of the entire period was 3 °C higher in H-compared to C-OTCs. Net photosynthetic rate (P N) measured at different temperature (20-40 °C) of C-and H-grown plants showed greater sensitivity to high temperature in H-plants. PN measured at respective growth temperature was lower in H-compared to C-plants. The CO2 and irradiance response curves of photosynthesis also showed lesser response in H-compared to C-plants. The initial slope of PN versus internal CO2 concentration (PN/Ci) curve was lower in H-than C-plants indicating ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) limitation. In irradiance response curve, the plateau was lower in H-compared to C-plants which is interpreted as RuBPCO limitation. RuBPCO content in the leaves of C-and H-plants, however, was not significantly different. Ribulose-1,5-bisphosphate carboxylase (RuBPC) initial activity was lower in H-plants, whereas activity of fully activated enzyme was not affected, indicating a decrease in activation state of the enzyme. This was further substantiated by the observed decrease in RuBPCO activase activity in H-compared to C-plants. RuBPCO activase was thus sensitive even to moderate heat stress. The decrease in PN under moderate heat stress was mainly due to a decrease in activation state of RuBPCO catalysed by RuBPCO activase. and P. Pushpalatha, P. Sharma-Natu, M. C. Ghildiyal.
The effects of varying leaf temperature (T1) on some ecophysiological characteristics of photosynthesis for Quercus liaotungensis Koiz. under ambient radiation stress around midday on clear summer days were investigated using an IRGA equipped with a temperature-controlled cuvette. Net photosynthetic rate (PN) decreased as T1 increased from 30 to 35 °C as a result of stomatal closure, whereas non-stomatal limitation led to decreased PN in the T1 range of 35-45 °C. Decreased transpiration rate (E) and stomatal conductance (gs) at leaf temperatures above 30 °C were interpreted as a combined 'feedward' effect as a result of enhanced leaf-air vapour pressure deficit (VPD) and stomatal closure. Changes in E from T1 30 to 20 °C depended on VPD when gs was maintained constant. Water use efficiency (WUE) varied inversely with T1 by following a hyperbola. A decrease in intercellular CO2 concentration (Ci) occurred as a result of stomatal closure and a relatively high carboxylation capacity, whereas inactivation of mesophyll carboxylation in combination with photorespiration might be associated with the observed increase in Ci in the T1 range of 40 to 45 °C. and Shouren Zhang ... [et al.].