A cheap chlorophyll (Chl) a fluorescence imaging system was developed for measuring leaf areas of 30×45 cm. Uniform saturating irradiances were created using CuSO4 filtered radiation from stroboscopes. The system was tested using maize leaves treated with diuron. Comparison was made with a small-area-measuring pulse amplified modulation Chl fluorometer. and P. Lootens, P. Vandecasteele.
A data base was generated for quantifying effects of thermal time (degree-days) on the appearance of new leaves, the expansion of such leaves to maximum area, their death, the appearance of new internodes below the node associated with such leaves, and the extension of these internodes to maximum length. The data base for a list of crop (agronomic and horticultural), weed, and native Tallgrass Prairie plants has been summarized, with equations for the above events as a function of degree days, with appropriate base temperatures and maximum cut-off temperatures, in a Java applet which is available at a website with the URL <http://th190-50.agn.uiuc.edu>. Associated graphical plots such as shown in this paper are also given. Branching behavior was accounted for. These events predict the effect of thermal time on leaf age and its height in the plant canopy, both important factors needed for upscaling functions for leaf behavior to those for behavior of the plant canopy. The data base is evolving to include coefficients for other species. Coefficients are used to predict the leaf area index of the canopy, which is important for predicting evapotranspiration from the crop and the protection of the soil from erosion. and X. Pan ... [et al,].
In order to study photosynthetic characteristics, phosphoenolpyruvate carboxylase (PEPC) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activities as well as soluble protein and chlorophyll contents were determined in leaf and fruit pericarp samples from diverse coffee genotypes (Coffea arabica cv. Colombia, Caturra, Caturra Erecta, San Pacho, Tipica, C. stenophylla, C. eugenioides, C. congensis, C. canephora, C. canephora cv. Arabusta, C. arabica cv. Caturra×C. canephora and Hibrido de Timor. We found a slightly higher PEPC activity in fruit pericarp than in leaves, while RuBPCO activity was much lower in pericarp than leaf tissue. Partial purification of PEPC and RuBPCO was carried out from leaves of C. arabica cv. Caturra and Michaelis-Menten kinetics for RuBPCO (Km CO2 = 5.34 µM), (Km RuBP = 9.09 µM) and PEPC (Km PEP = 19.5 µM) were determined. Leaf tissues of Colombia, Hibrido de Timor, and Caturra consistently showed higher content of protein [55.4-64.4 g kg-1 (f.m.)] than San Pacho, C. stenophylla, Tipica, Caturra Erecta, and Caturra×C. canephora [25.6-36.9 g kg-1 (f.m.)] and C. canephora cv. Arabusta, Borbon, C. congensis, C. eugenioides, and C. canephora [16.1-21.1 g kg-1 (f.m.)]. and Y. Lopez ... [et al.].
Two weeks-old maize (Zea mays cv. XL-72.3) plants were exposed to Al concentrations 0 (Al0), 9 (Al9), 27 (Al27) or 81 (Al81) g m-3 for 20 d in a growth medium with low ionic strength. Thereafter, the Al concentration-dependent interactions on root nitrate uptake, and its subsequent reduction to ammonia in the leaves were investigated. Al concentrations in the roots sharply increased with increasing Al concentrations while root elongation correspondingly decreased. Root fresh and dry masses, acidification capacity, and nitrate and nitrogen contents decreased from Al27 onwards, whereas leaf nitrogen, nitrate, nitrite, and ammonia concentrations decreased starting with Al9. Electrolytic conductance increased by 60 % in root tissues from Al0 to Al81 but it did not increase significantly in the leaves. In Al9, Al27, and Al81 plants a decrease in shoot fresh and dry masses was observed. Al concentrations between 0 and 27 g m-3 increased net photosynthetic rate, stomatal conductance, and the quantum yield of photosynthetic electron transport, whereas the intercellular CO2 concentration was minimum in Al27 plants. In the leaves, nitrate reductase (E.C. 1.6.6.1) activity increased until Al27, and nitrite reductase (E.C. 1.6.6.4) activity until Al81. Hence there may be an Al mediated extracellular and intracellular regulation of root net nitrate uptake. Nitrate accumulation in the roots affects the translocation rates and, therefore, the nitrate concentration in the leaves. The in vivo reducing power generated by the photosynthetic electron flow does not limit nitrate to ammonia reduction, and the increase of maximum nitrate and nitrite reductase activities parallels the decreasing nitrate, nitrite, and ammonia concentrations. and F. C. Lidon, J. C. Ramalho, M. G. Barreiro.
Elevated CO2 concentration (700 cm3 m-3, EC) inhibited chill-dependent (7 °C) depression of net photosynthetic rate of two maize hybrids with different sensitivity to low temperature. The rate of superoxide radical formation in leaves, leaf membrane injury, and the decrease in maximal quantum efficiency of photosystem 2 were successfully diminished by the treatment. The protective effect of EC toward stress conditions was prolonged at the recovery phase (20 °C). The genotypic impact on studied parameters was also notable. and R. Bączek-Kwinta, J. Kościelniak.
The effects of growth temperature on changes in net photosynthetic rate (PN) and the chlorophyll fluorescence induction parameter Fv/Fm were investigated after cold stress in inbred maize lines with different degrees of cold tolerance. There was no significant difference between lines grown at optimum temperatures of 25/23 and 20/18 °C as regards PN and Fv/Fm determined at the growth temperature, but these parameters were lower for plants grown at a suboptimum temperature of 15/13 °C. After cold treatment, the decrease in PN was more pronounced in chilling-sensitive lines. The higher the growth temperature was, the more pronounced decrease occurred in PN and Fv/Fm. Thus at low growth temperature both damaging and adaptive processes occur. and T. Janda ... [et al.].
Photosynthesis in iron-deficient soybean and maize leaves decreased drastically. The quantum yield of photosystem 2 (PS2) electron transport (ΦPS2), the efficiency of excitation energy capture by open PS2 reaction centres (Fv'/Fm'), and photochemical quenching coefficient (qP) under high irradiance were lowered significantly by iron deficiency, but non-photochemical quenching (NPQ) increased markedly. The analysis of the polyphasic rise of fluorescence transient showed that iron depletion induced a pronounced K step both in soybean and maize leaves. The maximal quantum yield of PS2 photochemistry (Φpo) decreased only slightly, however, the efficiency with which a trapped exciton can move an electron into the electron transport chain further than QA (Ψ0) and the quantum yield of electron transport beyond QA (ΨEo) in iron deficient leaves decreased more significantly compared with that in control. Thus not only the donor side but also the acceptor of PS2 was probably damaged in iron deficient soybean and maize leaves. and Chuang-Dao Jiang, Hui-Yuan Gao, Qi Zou.
Among various C4 plants we found a wide range in the level of inactivation of phosphoenolpyruvate carboxylase (PEPC) at low temperature (0 °C). The activity of the 2-fold diluted enzyme in crude leaf extracts after 60 min incubation (compared to zero time incubation) at pH 7.5, remained above 87 % at low temperatures for the species Setaria verticillata, Portulaca oleracea, and Saccharum officinarum, and between 11 and 17 % in the species Cynodon dactylon and Atriplex halimus. The enzyme exhibited intermediate levels of inactivation (42 to 58 %) for the species Amaranthus sp., Zea mays, Salsola kali, and Digitaria sanguinalis. The enzyme activity for S. verticillata was unaffected between pH 5.7 and 8.4 during incubation at room and low temperatures. Under similar conditions, the activity of the enzyme from C. dactylon was stable between pH 5.7 and 7.0 and decreased at pH above 7.0, but for Z. mays it was enhanced between pH 5.7 and 6.8 and decreased at pH above 7.0. and G. Zervoudakis ... [et al.].
Diurnal variation of gas exchange, chlorophyll (Chl) fluorescence, and xanthophyll cycle components of three maize (Zea mays L.) hybrids released in different years, i.e. Baimaya (1950s), Zhongdan2 (1970s), and Nongda108 (1990s), were compared. On cloudless days, the newer hybrids always had higher net photosynthetic rate (PN), especially at noon, than the older ones. At noon, all the hybrids decreased their maximal yield of photosystem 2 (PS2) photochemistry (Fv/Fm) and actual quantum yield of PS2 (ΦPS2), the newer ones always showing higher values. Generally, the newer hybrids displayed higher photochemical quenching of Chl (qP) and lower non-photochemical quenching (NPQ). The interhybrid differences in PN may be owing to their differential photochemical efficiency. A midday depression in P N occurred in all hybrids, which might be caused by serious photoinhibition or by decreased stomatal conductance. However, midday depression in PN was more obvious in the older hybrids, especially when leaves were senescent. The higher de-epoxidation state of the xanthophylls was noted in older hybrids, which was confirmed by their larger NPQ. The newer maize hybrids did not need a strong de-epoxidation state since they had a better photosynthetic quantum conversion rate and a lower NPQ. and L. Ding ... [et al.].
The effect of a short cold stress in combination with photoinhibition stress, similar to a low temperature and a high irradiance situation during early morning in the spring time, was examined on four maize cultivars common for Belgium, that differ in early vigour. After 1 h of 2 °C and 500 μmol(photon) m-2 s-1, quantum efficiency and maximum photosynthesis rate at saturating irradiance decreased on average by 11 and 8 %, respectively. For one cultivar, Magister, the decrease was the largest: by 23 and 10 %, respectively. For this cultivar it was combined with a decrease of the water vapour conductance after the stress. The decrease of Fv/F0 due to the cold/light stress was dependent on the cold tolerance (early vigour) of the cultivars. Fv/F0 changed with -45.5 and -40.2 % for the cultivars Ardiles and Banguy, respectively (cultivars with a less good early vigour) in comparison to -36.3 and -35.9 % for Fjord and Magister, which have a good early vigour. Also the ratio of total chlorophylls/total carotenoids changed in dependence on cold tolerance of the cultivars. For more cold tolerant cultivars, the relative amount of total carotenoids (x+c) was higher, indicating a higher protective state. Both the parameter Fv/F0 and the ratio of total chlorophylls to total carotenoids can be used to differentiate the cold tolerant cultivars from the cold non-tolerant ones. Fv/F0 has the advantage because its resolving power is larger and the measurement is less expensive than determination of the pigment ratio. and P. Lootens, J. van Waes, L. Carlier.