Two gramineous species among wild plants, Echinochloa oryzicola Vasing and Setaria viridis (L.) Beauv., and Oryza sativa L. cv. Nipponbare were subjected to salt stress. The relative growth rate (RGR), Na content, photosynthetic rate, antioxidant enzymes activity (superoxide disumutase (SOD), catalase (CAT), ascorbate peroxidase (APx) and glutathione reductase (GR)), and malondialdehyde (MDA) content in leaves after NaCl treatment were studied. RGR significantly decreased in O. sativa more than in E. oryzicola and S. viridis. Comparatively salt-tolerant S. viridis showed higher growth rate, lower Na accumulation rate in leaves, higher photosynthetic rate, and induced more SOD, CAT, APx, and GR activity and lower increase of MDA content as compared to the salt-sensitive O. sativa. At the same time, the comparatively salt-tolerant E. oryzicola also showed higher growth rate, much lower Na accumulation and no observable increase of MDA content, even though the CAT and APx activities were not induced by salinity. These results suggested that the scavenging system induced by H 2 O 2 -mediated oxidative damage might, at least in part, play an important role in the mechanism of salt tolerance against cell toxicity of NaCl in some gramineous plants

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Brachiaria species are widely cultivated and the low nitrogen (N) fertility of soils is one of the limiting factors for grass production in the Brazilian savannas (Cerrados). In the present study, we compared the characteristics of N utilization in Brachiaria brizantha (BB), B. decumbens (BD), and B. humidicola (BH), which are common species in these areas. In a soil culture experiment, BB, BD, and BH were grown under 3 levels of N, equivalent to 0 application (ON), 0 . 1 (lN), and 0.3 (2N) g N pot-', with N as ammonium sulfate. The plant dry weight of BB and BD increased with the increase of N levels, whereas BH showed a weaker growth response to N application and the plant dry weight of BH was lower than that of BB and BD. The amount of N accumulated in plant increased with the increase of N levels in BB and BD. The amount of N accumulated in plant in BH was slightly lower than or almost comparable to that in BB and BD. The plant N concentration was higher in BH than in BB and BD. The stronger growth response of BB and BD resulted in a higher fertilizer use efliciency (FUE) and a N use efficiency in fertilizer application (NUEF). The N absorption efficiency (NAE) of BH was higher than that of the other two grasses for 1N and 2N. In the absence of N treatment (hereafter refferred to as "ON treatment"), the specific N absorption rate in the roots (SAR) was higher in BH than in BB and BD throughout the growth period. These data suggested that the N absorption ability in roots would be higher in BH than in the other 2 tested grasses, as confirmed by the Michaelis-Menten kinetic analysis. In a nitrate absorption experiment, the K,,, value of BH was lower than that of BB and BD. As BH showed a higher affinity for nitrate absorption, it could maintain a higher N absorption rate. Therefore, it was considered that the perfop mance of N accumulation of BH would be slightly lower than or almost comparable to that of BB and BD because of the high ability of BH to absorb N, although dry matter production of BH was lower than that of BB and BD.

Abstract:Two gramineous weeds, early watergrass (Echinochloa wyzicola Vasing) and foxtail (Setaria viridis (L.) Beauv.), and rice (Oryza sativa L. cv. Nipponbare) were exposed to salinity stress. The leaf water status, levels of amino acid, proline, and glycinebetaine of seedlings during the 7 days following root treatment of 50 and 100mMNaCI were measured. Foxtail and early watergrass were able to maintain a high turgor and high relative water content under the salinity condition. Proline content in leaves was also increased by salt stress in these plants, but this was lower in rice than in foxtail or early watergrass. Glycinebetaine content was also increased by salinity in the two weeds. However, glycinebetaine was not

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