Five decades ago, a novel mode of CO2 assimilation that was later described as C4-photosynthesis was discovered on mature leaves of maize (Zea mays L.) plants. Here we show that 3- to 5-day-old developing maize leaves recapitulate the evolutionary advance from the ancient, inefficient C3 mode of photosynthesis to the C4 pathway, a mechanism for overcoming the wasteful process of photorespiration. Chlorophyll fluorescence measurements documented that photorespiration was high in 3-day-old juvenile primary leaves with non-specialized C3-like leaf anatomy and low in 5-day-old organs with the typical "Kranz-anatomy" of C4 leaves. Photosynthetic gas (CO2)-exchange measurements on 5-day-old leaves revealed the characteristic features of C4 photosynthesis, with a CO2 compensation point close to zero and little inhibition of photosynthesis by the normal oxygen concentration in the air. This indicates a very low photorespiratory activity in contrast to control experiments conducted with mature C3 sunflower (Helianthus annuus L.) leaves, which display a high rate of photorespiration. and U. Kutschera ... [et al.].
Upland cotton (Gossypium hirsutum L.) can move leaves to track the sun throughout the day, so-called leaf diaheliotropic movement. This paper reports an experimental test of the hypothesis that leaf diaheliotropic movement in upland cotton can enhance carbon assimilation and not increase the risk of stress from high energy load. In this experiment, cotton leaves were divided into two groups: one was that leaves could track the sun freely; another was that leaves were retained to the horizontal position. The diaheliotropic leaves recorded higher incident irradiance than the restrained ones, especially in the morning and late afternoon. Compared with restrained leaves, diaheliotropic leaves were generally warmer throughout the day. As expected, diaheliotropic leaves had significantly higher diurnal time courses of net photosynthetic rate (PN) than restrained leaves, except during 14:00-18:00 of the local time. Higher instantaneous water-use efficiency (WUE) was observed in diaheliotropic leaves in the early morning and late afternoon than in the restrained leaves. During the given day, diaheliotropic and restrained leaves had similar diurnal time courses of recovery of maximal quantum yield of PSII photochemistry (Fv/Fm). Diaheliotropic leaves recorded lower or similar photochemical quenching coefficient (qp) than restrained leaves did throughout the day. These results suggest that cotton leaf diaheliotropic movement can improve carbon gain and water use efficiency and not intensify photoinhibition. and Y.-L. Zhang ... [et al.].
The effects of N and P deficiency, isolated or in combination, on leaf gas exchange and fast chlorophyll (Chl) fluorescence emission were studied in common bean cv. Negrito. 10-d-old plants grown in aerated nutrient solution were supplied with high N (HN, 7.5 mol m-3) or low N (LN, 0.5 mol m-3), and also with high P (HP, 0.5 mol m-3) or low P (LP, 0.005 mol m-3). Regardless of the external P supply, in LN plants the initial fluorescence (F0) increased 12 % in parallel to a quenching of about 14 % in maximum fluorescence (Fm). As a consequence, the variable to maximum fluorescence ratio (Fv/Fm) decreased by about 7 %, and the variable to initial fluorescence ratio (Fv/F0) was lowered by 25 % in relation to control plants. In LP plants, Fv/Fm remained unchanged whilst Fv/F0 decreased slightly as a result of 5 % decline in Fm. Under N deficiency, the net photosynthetic rate (P N) halved at 6 d after imposition of treatment and so remained afterwards. As compared to LN plants, P N declined in LP plants latter and to a less extent. From 12 d of P deprivation onwards. P N fell down progressively to display rates similar to those of LN plants only at the end of the experiment. The greater P N in LP plants was not reflected in larger biomass accumulation in relation to LN beans. In general, P and N limitation affected photosynthesis parameters and growth without showing any synergistic or additive effect between deficiency of both nutrients. and J. D. Lima, P. R. Mosquim, F. M. da Matta.
Three prevalent aliphatic polyamines (PAs) include putrescine, spermidine, and spermine; they are low-molecular-mass polycations involved in many physiological processes in plants, especially, under stressful conditions. In this experiment, three bean (Phaseolus vulgaris L.) genotypes were subjected to well-watered conditions and two moderate and severe water-stressed conditions with and without spermidine foliar application. Water stress reduced leaf relative water content (RWC), chlorophyll contents, stomatal conductance (gs), intercellular CO2 concentration (Ci), transpiration rate, maximal quantum yield of PSII (Fv/Fm), net photosynthetic rate (PN), and finally grain yield of bean plants. However, spermidine application elevated RWC, gs, Ci, Fv/Fm, and PN, which caused an increase in the grain yield and harvest index of bean plants under water stress. Overall, exogenous spermidine could be utilized to alleviate water stress through protection of photosynthetic pigments, increase of proline and carotenoid contents, and reduction of malondialdehyde content., S. Torabian, M. R. Shakiba, A. Dabbagh Mohammadi Nasab, M. Toorchi., and Obsahuje bibliografii
Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-line formation at a global scale. We studied gas exchange and water relations of Polylepis tarapacana in the field, considering the possible effects of water stress limitations imposed on net photosynthetic rate (PN). Daily courses of microclimatic variables, gas exchange, and leaf water potential were measured in both dry-cold and wet-warm seasons at an altitude of 4 300 m. Marked differences in environmental conditions between seasons resulted in differences for the dry-cold and wet-warm seasons in mean leaf water potentials (-1.67 and -1.02 MPa, respectively) and mean leaf conductances (33.5 and 58.9 mmol m-2 s-1, respectively), while differences in mean PN (2.5 and 2.8 μmol m-2 s-1, respectively) were not as evident. This may be related to limitations imposed by water deficit and lower photon flux densities during dry and wet seasons, respectively. Hence P. tarapacana has coupled its gas exchange characteristics to the extreme daily and seasonal variations in temperature and water availability of high elevations. and C. García-Núñez ... [et al.].
Diurnal and seasonal changes in the leaf water potential (Ψ), stomatal conductance (gs), net CO2 assimilation rate (PN), transpiration rate (E), internal CO2 concentration (Ci), and intrinsic water use efficiency (PN/gs) were studied in grapevines (Vitis vinifera L. cv. Touriga Nacional) growing in low, moderate, and severe summer stress at Vila Real (VR), Pinhão (PI), and Almendra (AL) experimental sites, respectively. In VR and PI site the limitation to photosynthesis was caused more by stomatal limitations, while in AL mesophyll limitations were also responsible for the summer decline in PN. and J. M. Moutinho-Pereira ... [et al.].
The effects of soil flooding on gas exchange and photosystem 2 (PS2) activity were analyzed in leaves of Phragmites australis, Carex cinerascens, and Hemarthria altissima. Pronounced decrease in net photosynthetic rate and stomatal conductance with flooding was found only in C. cinerascens. No significant changes in PS2 activity were observed in all three species which suggests that the photosynthetic apparatus was not damaged. Among the three species, H. altissima is better adapted to flooding than P. australis and C. cinerascens. and M. Li, D. Yang, W. Li.
Species of the Theobroma genus are primarily known by their commercially valuable seeds, especially, T. cacao is one of the most important tropical perennial crops. Beside T. grandiflorum, T. bicolor, and T. angustifolium, T. cacao is the only species of the genus that has been better studied to obtain physiologically relevant information. The main objective of this work was to evaluate the leaf gas exchange in seedlings of seven species of the Theobroma genus, seeking to identify characteristics that could be used in T. cacao breeding programmes. The study was realized under greenhouse conditions using six-month-old seedlings, in which net photosynthetic rate (PN), stomatal conductance (gs), transpiration (E), as well as parameters derived from light curves (PN vs. photosynthetically active radiation) were evaluated. T. cacao, along with T. microcarpum, showed the lowest values of PN, gs, and E, while the highest values were presented by T. speciosum, which showed higher saturation irradiance and lower intrinsic and instantaneous water-use efficiencies, being considered the species less conservative in water use. Therefore, the parameters shown by the different evaluated species could serve to design T. cacao genotypes, through introgression of genes for specific environments such as the cabruca system widespread in southern Bahia, Brazil., A.-A. F. Almeida, F. P. Gomes, R. P. Araujo, R. C. Santos, R. R. Valle., and Obsahuje bibliografii
Gas exchange, water relations, and leaf traits were studied in the tuberous-root producing legumes ahipa (Pachyrhizus ahipa) and yambean (P. erosus) under different environmental conditions. Differences in leaf traits (hairiness, leaf area, areal leaf mass, stomatal density) and paraheliotropism were found between ahipa and yambean. Under sufficient water supply, the increase in air temperature and decrease in air humidity increased stomatal conductance (gs) and net photosynthetic rate (PN) in yambean but reduced them in ahipa. In a drying soil (14 d after irrigation), inter-specific variation in gas exchange was only observed in the early morning, and yambean showed a greater sensitivity to water restriction than ahipa. High gs at low humidity increased PN of P. erosus but resulted in lower water-use efficiency (WUE). However, long-term WUE, estimated by leaf carbon isotope discrimination, showed little variation between species. Daily-irrigated ahipa and yambean grown in the greenhouse did not show significant differences in gas exchange. However, leaf temperature was significantly greater in yambean than in ahipa while a steepper relationship between E and PN and gs was observed in ahipa.
Periodic flooding of trees in tropical floodplains and reservoirs where water levels fluctuate is a common phenomenon. The effects of flooding and subsequent recovery on gas exchange, chlorophyll fluorescence and growth responses of Melaleuca alternifolia seedlings, a tall shrub species used in floodplain and reservoir forest restoration in southern China, were studied during a grow season (from March to December in 2007). M. alternifolia seedlings were flooded for 180 days, drained and left to recover for another 60 days. Survival rates of the seedlings were 100% during the 180-day flooding period. Chlorophyll (Chl) content, net photosynthetic rate
(PN), stomatal conductance (gs), and transpiration rate (E) of the flooded seedlings were all significantly lower than those of the control. Significant reductions of photochemical quenching coefficient (qp) and increases of nonphotochemical quenching (NPQ) in the flooded seedlings were observed. However, there were no significant differences in the maximal quantum yield of PSII photochemistry (Fv/Fm) between treatments. All seedlings survived during the two-month recovery period after the flooded treatment was drained, and the biomass and height of the recovered seedlings approached those of the control at the end of the experiment. During the first-month recovery period, Chl content, PN, gs and E in the recovered seedlings were all obviously low, then increased gradually and rose to the levels similar to the control by the end of the experiment. Quenching analysis revealed significant reductions of qp and increments of NPQ in the recovered seedlings at the beginning of draining, and a nearly complete recovery for both parameters by the end of the experiment. However, Fv/Fm of the recovered seedlings did not differ significantly from the control during the recovery period. Our study demonstrated that M. alternifolia seedlings can survive and grow through 180 days of flooding with a subsequent 60-day recovery period in drained conditions, indicating that seedlings of this species would be suitable for afforestation in areas exposed to intermittent flooding. and Y. X. Ying ... [et al.].