Tolerance of Grasses to Calcium Chloride, Magnesium Chloride and Sodium Chloride

The tolerance of six cool-season grasses and six warm-season grasses to three kinds of salt was examined in solution culture. Among the cool-season grasses, tall fescue (Festuca arundinacea Schreb.) was the most tolerant to all three salts. Among the warm-season grasses, bermudagrass (Cynodon dactylon (L.) Pers.) was the most tolerant to excess calcium chloride and sodium chloride, while bahiagrass (Paspalum notatum Flugge) was the most tolerant to excess magnesium chloride. A positive and significant correlation was found between estimates of the concentration at which plant growth decreases by 50% (C50) in the presence of excess CaCl2 and those in the presence of excess NaCl. The C50 estimates in excess MgCl2, however, were not correlated with those in the other two salts. The results suggest that common physiological mechanism confers tolerance to both excess CaCl2 and excess NaCl, but a different mechanism to excess MgCl2

Effects of Excess Magnesium on the Growth and Mineral Content of Rice and Echinochloa

The tolerance of three cultivars of rice (Oryza sativa L.) and three species of the genus Echinochloa to excess magnesium was examined in solution culture. In Echinochloa species, excess MgCl2 or MgSO4 in the culture solution (30 mM) reduced the growth to 33-42% of that in the control plants and caused symptoms resembling those of calcium deficiency. In rice cultivars, however, excess Mg in the culture solution reduced the growth only to 54-67% of that in the control and did not cause the symptoms like those of Ca deficiency. The effect of excess Mg on the mineral contents of plants differed between rice (Nipponbare) and Echinochloa oryzicola. The Mg content of the whole plants in rice increased in proportion to MgCl2 concentration in the culture solution up to 30 mM, while that in E. oryzicola leveled off when MgCl2 concentration exceeded 10 mM. The excess MgCl2 treatment greatly reduced the calcium content of the whole plants in E. oryzicola and slightly in rice. In rice, the excess Mg treatment increased the Mg content of shoots and roots, and the potassium and chloride contents of roots, but slightly decreased the Ca and K contents of shoots. In E. oryzicola, the excess Mg treatment increased the K and Cl contents of shoots and the Mg and K contents of roots, and slightly increased the Mg content of shoots, but greatly decreased the Ca content of shoots. These results indicate that rice is more tolerant than Echinochloa to excess Mg and that the tolerance is related to Ca deficiency

Cytoplasmic destruction of p53 by the endoplasmic reticulum-resident ubiquitin ligase ‘Synoviolin'

Synoviolin, also called HRD1, is an E3 ubiquitin ligase and is implicated in endoplasmic reticulum -associated degradation. In mammals, Synoviolin plays crucial roles in various physiological and pathological processes, including embryogenesis and the pathogenesis of arthropathy. However, little is known about the molecular mechanisms of Synoviolin in these actions. To clarify these issues, we analyzed the profile of protein expression in synoviolin-null cells. Here, we report that Synoviolin targets tumor suppressor gene p53 for ubiquitination. Synoviolin sequestrated and metabolized p53 in the cytoplasm and negatively regulated its cellular level and biological functions, including transcription, cell cycle regulation and apoptosis. Furthermore, these p53 regulatory functions of Synoviolin were irrelevant to other E3 ubiquitin ligases for p53, such as MDM2, Pirh2 and Cop1, which form autoregulatory feedback loops. Our results provide novel insights into p53 signaling mediated by Synoviolin