Activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) is an important parameter determining the rate of net photosynthesis (PN) in situ for which no information is available with reference to altitude. We analyzed activation state along with PN in three plant species and their cultivars grown at low (LA, 1 300 m) and high (HA, 4 200 m) altitudes. No significant change in PN and the initial activity of RuBPCO was obtained with reference to altitude. However, activation state of RuBPCO was reduced significantly in the HA plants as compared to the LA ones. Hence low partial pressure of CO2 prevailing at HA might be responsible for the lower activation state of RuBPCO. and Narinder Kumar, Sanjay Kumar, Paramvir Singh Ahuja.
In addition to other factors, high altitude (HA) environment is characterized by high photosynthetic photon flux density (PPFD). Photosynthetic characteristics of wild and cultivated plants were studied at different irradiances at Losar, India (altitude 4 200 m). Wild plants were tolerant to high PPFDs. Slopes of curve between net photosynthetic rate (PN) and intercellular CO2 concentration
(Ci) or stomatal conductance (gs) increased with increase in irradiance suggesting insensitivity or tolerance of these plants to higher PPFD. Cultivated plants, however, were sensitive to higher PPFD, their slopes of curves between PN and Ci or gs decreased with increased PPFD. Tolerance or insensitivity to higher PPFD was an important parameter affecting plant performance at HA. and N. Kumar, S. Kumar, P. S. Ahuja.
Leaf stomatal density (SD), net photosynthetic rates (PN), and stomatal conductance (gs) of Hordeum vulgare and Pisum sativum cultivars in Himalaya increased with altitude. Higher PN and leaf temperature under low CO2 partial pressure at high altitudes could evoke a higher gs and SD to allow sufficient influx of CO2 as well as more efficient leaf cooling through transpiration. and S. K. Vats, N. Kumar, S. Kumar.
Two types of photosystem 2-light-harvesting complex 2 (PS2-LHC2) supercomplexes with similar pigment and protein composition were isolated directly from thylakoid membranes by sucrose density gradient centrifugation. Electron microscopy and single particle image analysis revealed the first Type as single unpaired PS2-LHC2 supercomplexes, whereas the second Type was characterized as pairs of two PS2-LHC2 supercomplexes attached together by their stromal sides. Unstacking of thylakoid membranes resulted in a spontaneous disintegration of the paired supercomplexes into single unpaired particles. A model of the organisation of the pigment-protein complexes in grana region is proposed. and L. Bumba, M. Hušák, F. Vácha.
The thermo-sensitivity of two new pea (Pisum sativum L.) cultivars-Afila (mutant in the gene transforming leaves into mustaches) and Ranen (mutant for early ripening)-as compared to the control cultivar Pleven-4 to either low (4 °C, T4) or high temperature (38 °C, T38) was investigated by means of chlorophyll (Chl) fluorescence kinetics. The low temperature treatment decreased the photosynthetic activity, measured via a decline of the Chl fluorescence decrease ratios RFd690 and RFd735, and this was mainly due to a decline of the Chl fluorescence decrease parameter Fd and maximum Chl fluorescence Fm. In the new cv. Ranen the RFd ratios at first decreased and increased again after 24-h exposure to 4 °C, indicating its good acclimation ability to low temperature. The cold-induced changes in the photosynthetic performance of all cultivars were reversed after transferring plants back to 23 °C for 48 h. In the Chl and carotenoid (Car) contents no or little changes occurred during the T4 treatment, except for a slight but clear increase of the ratio Chl a/b and a decrease in the ratio Chl/Car. In contrast to this, the T38 treatment for 72 h decreased the RFd ratios more strongly than the T4 exposure did. In fact, an irreversible injury of the photosynthetic apparatus was caused in the control pea cv. Pleven-4 by a 48-h T38 exposure and for the new cv. Afila after a 72-h T38 exposure. In contrast, the cv. Ranen was less and little sensitive to the T38 exposure. In the heat-sensitive cvs. Pleven-4 and Afila, the decrease in RFd values at T38 was associated with a strong decline of the Chl a+b and total Car contents. The Chl a+b decline could also be followed via an increase of the Chl fluorescence ratio F690/F735. Parallel to this, a strong decline of Chl a/b from ca. 3.0 (range 2.85-3.15) to ca. 1.9 (range 1.85-1.95) occurred indicating a preferential decline of the Chl a-pigment proteins but not of the Chl a/b-pigment protein LHC2. In the relatively heat-tolerant cv. Ranen, however, the ratio Chl a/b declined only partially. After the T4 treatment the stress adaptation index Ap was higher in cv. Ranen than in controls and reached in heat-treated Ranen plants almost the starting value indicating a cold and heat stress hardening of the treated plants. The Chl fluorescence parameters and pigment contents were influenced by T38 and T4 treatments in various ways indicating that the mechanisms of low and high temperature injury of the photosynthetic apparatus are different. The new cv. Ranen exhibited a cross tolerance showing a fairly good acclimation ability to both T4 and T38, hence it is a very suitable plant for outdoor growth and for clarification of the accl, imation mechanisms to unfavourable temperatures., and K. Georgieva, H. K. Lichtenthaler.
In this historical review we summarize discoveries related to the flowering genes in controlling leaf area index (LAI, the leaf area per unit ground area) in sorghum, soybean, or pea crop stands. We also analyze similar work on Arabidopsis and dwarf and intermediate stem height genes in wheat and rice. and G. B. Begonia, M. T. Begonia.
Etiolated leaves of three different species, maize, wheat, and pea, as well as a pea mutant (lip1) were used to compare the excitation spectra of protochlorophyllide (Pchlide) in the red region. The species used have different composition of short-wavelength and long-wavelength Pchlide forms. The relation between different forms was furthermore changed through incubating the leaves in 5-aminolevulinic acid (ALA), which caused an accumulation of short-wavelength Pchlide forms, as shown by changes in absorption and fluorescence spectra. This is the first time a comprehensive comparison is made between excitation spectra from different species covering an emission wavelength range of 675-750 nm using fluorescence equipment with electronic compensation for the variations in excitation irradiance. The different forms of Pchlide having excitations peaks at 628, 632, 637, 650, and 672 nm could be best measured at 675, 700, 710, 725, and 750 nm, respectively. Measuring emission at wavelengths between 675-710 nm gave an exaggeration of the short-wavelength forms and measuring at longer wavelengths gave for the pea leaves an exaggeration of the 672 nm peak. In general, an energy transfer from short-wavelength Pchlide forms to long-wavelength Pchlide forms occurred, but such an energy transfer sometimes seemed to be limited as a result of a discrete location of the Pchlide spectral forms. The excitation spectra resembling the absorption spectrum most were measured at an emission wavelength of 740 nm. Measuring the excitation at 710 nm gave higher intensity of the spectra but the short-wavelength forms were accentuated. and M. R. Amirjani, C. Sundqvist.
The structural reorganization of pea thylakoid systems in response to osmotic shock in a wide range of temperatures (36-70°C) was studied. At temperatures 40-46°C, the configuration of thylakoid systems changed from a flattened to a nearly round, whereas thylakoids themselves remained compressed. The percentage of thylakoids stacked into grana at 44°C decreased from 71 % in the control to 40 % in experimental samples, reaching 59 % at 48°C. At 44°C and above, thylakoid systems ceased to respond to the osmotic shock by disordering, in contrast to what happened at lower temperatures (36-43°C) and in the control, and retained the configuration inherent in thylakoid systems at these temperatures. At 50°C and above, the packing of thylakoids in grana systems changed, and thylakoids formed extended strands of pseudograna. Simultaneously, single thylakoids formed a network of anastomoses through local fusions. At temperatures of 60-70°C, thylakoid systems appeared as spherical clusters of membrane vesicles with different degree of separation.
Measurement of the chlorophyll (Chl) a fluorescence rise (FR) under higher exciting irradiance (EI), the O-J-I-P transient, or under lower irradiance, the O-I-P transient, is a routinely used method to access photosystem 2 function in thylakoid membranes of chloroplasts. Our measurements with a suspension of pea thylakoid membranes showed that the relative heights of the J and I steps in the FR depended not only on EI but also on the concentration and thickness of the sample. We explain this effect as a consequence of the gradient of EI within the sample. We tested this suggestion by theoretical simulations of the FR based on the model that was previously used for simulation of the FR considering in addition the gradient of EI within the sample. Our theoretical results correspond well with the experiments. The irradiance gradient effect may influence measured FR significantly and this fact should be taken into consideration in the interpretation of measured FRs. and P. Sušila ... [et al.].