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Entry of the divalent cations Ni2+, Co2+ and Zn2+ into cells of maize (Zea mays L. cv. Dekalb XL 85) root tissue is accompanied by an acidification of the incubation medium, a decrease in both the pH of the cell sap and the level of malate in the cells, and by an inhibition of dark fixation of CO2. K+, on the contrary, induces only a very low acidification of the incubation medium, does not change either the pH of the cell sap or the malate level in the cells, and induces an increase in CO2 dark fixation. Different mechanisms are postulated for the stimulation of proton extrusion by divalent cations and K+. [ABSTRACT FROM AUTHOR]

The presence of Ni2+ in the incubation medium of maize rout segments (Zea mays L. cv. Dekalb XL 640) induces an early and significant enhancement of the rate of proton extrusion both in the absence and presence of fusicoccin; with time, an inhibition of proton extrusion and a leakage of K+ appear. The inhibition of proton extrusion is accompanied by a decrease in the dark CO2 fixation and by a decrease in the level of malate in the cells, Ni2+ inhibits in vitro phosphoenolpyruvate carboxylase activity of maize roots. The data indicate a correlation between the operativity of the proton pump and that of the malate-pH stat mechanism for the homeostasis of cytoplasmic pH. [ABSTRACT FROM AUTHOR]

A low-molecular-mass protein able to bind GTP in both native and SDS-denaturating conditions was detected in the cytosol of embryos from wheat (Triticum aestivum L.) seeds germinated for 40 h. The protein fulfilled most of the distinguishing criteria common to eukaryotic small GTP-binding proteins. It retained the ability to bind GTP after SDS/PAGE and nitrocellulose blotting. The protein eluted from Sephadex G-200 gel filtration with a Ve/Vo value corresponding to a molecular mass of 18 kDa, whereas on SDS/PAGE the molecular mass was 20 kDa. The native protein, which showed an intrinsic GTPase activity highly sensitive to NaF, bound the guanine nucleotide with high specificity and with a relatively high affinity (Kd ≈ 85 nM). The GTP-binding protein was not detectable in other subcellular fractions; in the microsomal fraction, two other peptides of low molecular mass (23.5 and 21.5 kDa) with GTP-binding activity were detected. These results indicate that in the cytosolic fraction of germinating wheat embryos there is a 20-kDa protein which is biochemically similar to the known small GTP-binding proteins that currently have been detected almost exclusively in the membrane fraction of plant material. [ABSTRACT FROM AUTHOR]

Two forms of EF-1 are present in the high-speed supernatant fraction from wheat embryo homogenate. In embryos from dry seeds EF-1H is 55% of the total amount of EF-1, while alter 40 h of germination this form completely disappears. When germination and protein synthesis are accelerated by means of 6-benzyladenine, the rate of conversion of EF-1H is increased. On the other hand, the block of germination and of the evolution of protein synthesis by abscisic acid, block this conversion; the block of water uptake, that stops germination and causes a decrease m protein synthesis, reverses the conversion of EF-1H to EF-1L, increasing EF-1H from 15% to 40% of the total. [ABSTRACT FROM AUTHOR]

A poly(U)-binding activity is present in the high-speed supernatant fraction of embryo homogenates from wheat seeds. The factor responsible for such activity was found to have a stimulatory effect on the elongation factor 1 (EF-1). It copurifies with EF-1L, the lighter form of EF-1. through Sephadex G-200, DEAE-cellulose, hvdroxvapatiw and poly(U )-Sepharose 4B column chromatography. The two factors could be separated only through a heating step which destroyed EF-l activity whilst leaving most of the poly(U)-binding activity unaltered. [ABSTRACT FROM AUTHOR]