A bifurcation problem for the equation ∆u + λu − αu+ + βu− + g(λ,u)=0 in a bounded domain in N with mixed boundary conditions, given nonnegative functions α, β ∈ L∞ and a small perturbation g is considered. The existence of a global bifurcation between two given simple eigenvalues λ(1), λ(2) of the Laplacian is proved under some assumptions about the supports of the functions α, β. These assumptions are given by the character of the eigenfunctions of the Laplacian corresponding to λ(1), λ(2).
Most organisms inhabiting earth feed directly or indirectly on the products synthesized by the reaction of photosynthesis, which at the current atmospheric CO2 levels operates only at two thirds of its peak efficiency. Restricting the photorespiratory loss of carbon and thereby improving the efficiency of photosynthesis is seen by many as a good option to enhance productivity of food crops. Research during last half a century has shown that several plant species developed CO2-concentrating mechanism (CCM) to restrict photorespiration under lower concentration of available CO2. CCMs are now known to be operative in several terrestrial and aquatic plants, ranging from most advanced higher plants to algae, cyanobacteria and diatoms. Plants with C4 pathway of photosynthesis (where four-carbon compound is the first product of photosynthesis) or crassulacean acid metabolism (CAM) may consistently operate CCM. Some plants however can undergo a shift in photosynthetic metabolism only with change in environmental variables. More recently, a shift in plant photosynthetic metabolism is reported at high altitude where improved efficiency of CO2 uptake is related to the recapture of photorespiratory loss of carbon. Of the divergent CO2 assimilation strategies operative in different oraganisms, the capacity to recapture photorespiratory CO2 could be an important approach to develop plants with efficient photosynthetic capacity. and S. K. Vats, S. Kumar, P. S. Ahuja
Translational efficiency of wheat ribosomes was studied as a function of an in vivo temperature pretreatment of wheat seedlings. The ribosomes were isolated from 41 oř 36 oC-adapted and non-adapted (20 oQ wheat seedlings. The poly-U-dependent translational efficiency, measured as ^H phenylalanine incorporation into poly-Phe, was enhanced up to 3-fold in the heat-adapted ribosomes. The adaptive enhancement was due to the large ribosomal subunit, as demonstrated earlier by heterologous recombination of ribosomal subímits, obtained from the plants pretreated by different temperatures. According to this, the pattem of ribosomal proteins of the large subunit exhibited pronounced differences as a function of preadaptation temperature: one spot increased markedly in the protein staining intensity on the two-dimensional polyacrylamide gels, while another almost disappeared. Two minor protein spots disappeared at high preadaptation temperatures. An evaluation of the protein phosphorylation of ribosomal proteins yielded a decreased ^zp-iabel degree in čase of the smáli subunit of heat-adapted ribosomes. These results are considered to be an important molecular correlation to phenotypical temperature adaptatíon of in vivo protein synthesis in wheat, where the optimum temperature of ^‘♦C-leucine incorporation into the total protein fraction, as a measure of in vivo protein synthesis, shifts to higher grades with increasing preadaptation temperature of the wheat seedlings. Besides Triticum aestivum L. (spring wheat; cv. Kolibri), heat adaptatíon potentíals of T. dicoccoides (tetraploid), T. longissimum (2n), T. monococcum (2n), T speltoides (2«) and T. tauschii (2n) were investígated. The temperature coefficient p (apparent actívation energy) also underwent adaptive alteratíons, although these changes were not unidirectíonal. T. tauschii proved to be the species with the most pronounced adaptive potentíal in the high temperature range, surpassed only by the heat adaptability of 14 d-postanthesis caryopses: its optimum temperature of in vivo protein synthesis rose by more than 20 «€ after a 38 oC-preadaptation period (2 d).
Two different pathways for protochlorophyllide a (Pchlide) reduction in photosynthetic organisms have been proved: one is strictly light-dependent whereas the second is light-independent. Both pathways occur in all photosynthetic cells except in angiosperms which form chlorophyll only through the light-dependent pathway. Most cells belonging to Eubacteria (i.e., the anoxygenic photosynthetic bacteria) synthesize bacteriochlorophyll through the light-independent pathway. This review deals with the physiological, biochemical, and molecular biological features of molecules involved in both pathways of Pchlide reduction.