Salinity resistance in Zea mays: fluxes of potassium, sodium and chloride, cytoplasmic concentrations and microsomal membrane lipids

Cytoplasmic concentrations, fluxes of K+, Na+ and Cl and microsomal membrane lipids were investigated in a salt-sensitive and salt-resistant variety of Zea mays. The salt resistance of Protador relative to LGH (salt-sensitive) appears to be related to higher K+ fluxes and cytoplasmic concentrations, and lower Na+ and Cl fluxes and cytoplasmic concentrations, when grown in NaCl. There were no apparent differences in the simple chemical composition of root microsomal membrane lipids between the two varicties, neither were these affected by salt

Photosynthetic oxygen evolution in relation to ion contents in the chloroplasts of Suaeda maritima

The effects of sodium chloride on photosynthetic oxygen evolution by chloroplasts isolated from the leaves of the halophyte Suaeda maritima L. (Dum) are reported. When plants were grown in concentrations of salt increasing to 340 mol m−3 the rate of oxygen evolution by isolated chloro-plasts increased; beyond this concentration of salt it declined. Maximum rates of oxygen evolution (coupled and uncoupled) were found when the plants were grown in 340 mol m−3 NaCl. Under these conditions mean ion concentrations in the chloroplasts measured in vivo by X-ray microanalysis were Na+, 84–257 mol m−3; Cl−, 86–212 mol m−3; K+, 23–36 mol m−3. A comparative study was also made of the in vitro effects of sodium chloride on oxygen evolution. Here again maximum rates were found in the presence of 340 mol m−3 NaCl

Visualisation of human rad52 protein and its complexes with hRad51 and DNA.

The human Rad52 protein stimulates joint molecule formation by hRad51, a homologue of Escherichia coli RecA protein. Electron microscopic analysis of hRad52 shows that it self-associates to form ring structures with a diameter of approximately 10 nm. Each ring contains a hole at its centre. hRad52 binds to single and double-stranded DNA. In the ssDNA-hRad52 complexes, hRad52 was distributed along the length of the DNA, which exhibited a characteristic "beads on a string" appearance. At higher concentrations of hRad52, "super-rings" (approximately 30 nm) were observed and the ssDNA was collapsed upon itself. In contrast, in dsDNA-hRad52 complexes, some regions of the DNA remained protein-free while others, containing hRad52, interacted to form large protein-DNA networks. Saturating concentrations of hRad51 displaced hRad52 from ssDNA, whereas dsDNA-Rad52 complexes (networks) were more resistant to hRad51 invasion and nucleoprotein filament formation. When Rad52-Rad51-DNA complexes were probed with gold-conjugated hRad52 antibodies, the presence of globular hRad52 structures within the Rad51 nucleoprotein filament was observed. These data provide the first direct visualisation of protein-DNA complexes formed by the human Rad51 and Rad52 recombination/repair proteins

Estresse salino em plântulas de milho: parte I análise do crescimento Salt stress in maize seedlings: part I growth analysis

O trabalho foi conduzido em casa de vegetação, objetivando-se avaliar o efeito do estresse salino sobre o crescimento de cultivares de milho com tolerância diferenciada à salinidade. Foi utilizado um arranjo fatorial 2 x 5 com duas cultivares de milho (P-3051 e BR-5011) e cinco níveis de cloreto de sódio na solução nutritiva (0, 25, 50, 75 e 100 mol m-3). Avaliaram-se a matéria seca (MS) da parte aérea e raízes, razão parte aérea/raiz, área foliar (AF), taxas de crescimento absoluto (TCA), relativo (TCR) e de assimilação líquida (TAL) e razão de área foliar (RAF). Excetuando-se a RAF, o estresse salino afetou as demais variáveis estudadas. A MS da parte aérea e raízes, AF, TCA e TCR, sobressaíram-se como os indicadores que melhor representaram o efeito do estresse salino sobre as plantas. Por outro lado, a razão parte aérea/raiz, TAL e RAF foram as variáveis que melhor expressaram os caracteres de tolerância e sensibilidade nas cultivares analisadas.<br>The work was performed in the greenhouse, aiming to evaluate the effect of salt stress on maize cultivars differing in salinity tolerance. Data were carried out on 2 x 5 factorial arrangement with two maize cultivars (P-3051 and BR-5011) and five sodium chloride levels in nutritive solution (0, 25, 50, 75 or 100 mol m-3). The shoot dry matter, root dry matter, shoot to root ratio, leaf area (LA), absolute growth rate (AGR), relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) were analyzed. The salt stress affected all studied variables, except LAR. The shoot dry matter, root dry matter, LA, AGR and RGR were the best parameters to express the salt stress effect on maize plants. On the other hand, the shoot to root ratio, NAR and the LAR were the best parameters to express differences between cultivars regarding their tolerance or sensitivity to salt stress