Effects of salt stress on plant growth characteristics and mineral content in diverse rice genotypes

ABSTRACT

When rice is grown under moderate salinity (6?dS m^?1), yields are reduced by up to 50%. The development of salt-tolerant varieties is a key strategy for increasing yields. We conducted an experiment using a hydroponic system with ion components similar to seawater to determine useful parameters for assessing salt tolerance. Two-week-old seedlings were grown for 7 days on Yoshida hydroponic solution. The treatment group then additionally received an artificial seawater solution (electrical conductivity, 12 dS m^?1). After a 2-week period of salt stress, standard evaluation scores (SES) of visual salt injuries were assessed. The K, Na, Mg, and Ca contents were then determined in the roots, sheaths, and leaves of each plant. Following the SES results, we divided the 37 genotypes into four groups: salt-tolerant groups (STGs), moderately salt-tolerant groups, salt-sensitive groups (HSSGs), and highly salt-sensitive groups (HSSGs). In the control, STGs had the highest sheath K content (30.1 mg g^?1 dried weight [DW]), whereas HSSGs had the lowest (21.4 mg g^?1 DW). Sheath K was also highly and negatively correlated with SES. This suggests that sheath K may be useful for identifying salt-tolerant varieties under non-saline conditions. Plant growth was significantly affected under salt stress, but STGs had the smallest decrease in sheath DW. SES was significantly correlated with sheath and leaf Na, sheath K and Mg, and sheath and leaf Na/K and Na/Mg ratios. The results suggested that sheath K, Na/K, and Na/Mg may be useful indicators for genetic analyses of salt-tolerant varieties under salt-stress conditions. The salt-tolerant cultivars, KCR20, KCR124, and KCR136, are possible candidates for such studies because they had high sheath K content (31.19, 31.21, 29.44 mg g^?1 DW, respectively) under non-saline conditions and low SES (3.3, 3.6, 3.9, respectively), and low sheath Na/K (0.64, 0.52, 0.92, respectively) and Na/Mg ratios (2.96, 2.27, 3.03, respectively) under salt-stress conditions.     

Factors affecting methane production and mitigation in ruminants

Methane (CH₄) is the second most important greenhouse gas (GHG) and that emitted from enteric fermentation in livestock is the single largest source of emissions in Japan. Many factors influence ruminant CH₄ production, including level of intake, type and quality of feeds and environmental temperature. The objectives of this review are to identify the factors affecting CH₄ production in ruminants, to examine technologies for the mitigation of CH₄ emissions from ruminants, and to identify areas requiring further research. The following equation for CH₄ prediction was formulated using only dry matter intake (DMI) and has been adopted in Japan to estimate emissions from ruminant livestock for the National GHG Inventory Report: Y = −17.766 + 42.793X − 0.849X², where Y is CH₄ production (L/day) and X is DMI (kg/day). Technologies for the mitigation of CH₄ emissions from ruminants include increasing productivity by improving nutritional management, the manipulation of ruminal fermentation by changing feed composition, the addition of CH₄ inhibitors, and defaunation. Considering the importance of ruminant livestock, it is essential to establish economically feasible ways of reducing ruminant CH₄ production while improving productivity; it is therefore critical to conduct a full system analysis to select the best combination of approaches or new technologies to be applied under long-term field conditions.     

Non-steroidal inhibitors of Drosophila melanogaster steroidogenic glutathione S-transferase Noppera-bo

Insect growth regulators (IGRs) can be developed by elucidating the molecular mechanisms of insect-specific biological events. Because insect molting, and metamorphosis are controlled by ecdysteroids, their biosynthetic pathways can serve as targets for IGR development. The glutathione S-transferase Noppera-bo (Nobo), which is conserved in dipteran and lepidopteran species, plays an essential role in ecdysteroid biosynthesis. Our previous study using 17β-estradiol as a molecular probe revealed that Asp113 of Drosophila melanogaster Nobo (DmNobo) is essential for its biological function. However, to develop IGRs with a greater Nobo inhibitory activity than 17β-estradiol, further structural information is warranted. Here, we report five novel non-steroidal DmNobo inhibitors. Analysis of crystal structures of complexes revealed that DmNobo binds these inhibitors in an Asp113-independent manner. Among amino acid residues at the substrate-recognition site, conformation of conserved Phe39 was dynamically altered upon inhibitor binding. Therefore, these inhibitors can serve as seed compounds for IGR development.     

Relationships between tropomyosin and myosin heavy chain isoforms in bovine skeletal muscle

The composition of tropomyosin (TPM) and myosin heavy chain (MyHC) isoforms was analyzed in 10 physiologically different bovine muscles ( masseter , diaphragm, tongue, semispinalis, pectoralis profundus , biceps femoris, psoas major , semimembranosus, longissimus thoracis and semitendinosus ) to clarify the relationships between TPM and MyHC isoforms in different muscle fiber types. The content of TPM1 and TPM3 was different in muscles according to their function in muscle contraction, although the content of TPM2 was constantly about 50% of the total TPM in all muscles. The content of TPM1 was higher in semimembranosus , longissimus thoracis and semitendinosus, while that of TPM3 was higher in masseter and diaphragm. The high positive correlation between MyHC-slow content and TPM3 content ( r  = 0.92) suggested a coexpression of TPM3 and MyHC-slow isoforms in a muscle fiber. MyHC-slow and TPM3 were expressed at the same level in masseter and diaphragm, whereas there was more TPM3 than MyHC-slow in tongue and semispinalis , so it appears that the excess TPM3 in tongue and semispinalis is expressed with other MyHC isoforms. MyHC-2a was the only fast type isoform expressed in tongue and semispinalis . Therefore, the excess TPM3 was composed of myofibrils with MyHC-2a. The results suggested that a fiber expressing MyHC-2a would be regulated delicately by changing the TPM isoform types.     

Hydrogeochemical Conditions Affecting Acidification of Stream Water in Mountainous Watersheds

Acid deposition in eastern Asia will increase and freshwaters in Japan are likely to become acidified in future. In order to make long-term predictions about freshwater acidification, it is necessary to evaluate acid neutralization mechanisms in Japanese watersheds. Ikeda and Miyanaga (1999) earlier proposed a method of separating acid-neutralization capacity into chemical weathering and cation exchange. By this means, we were able to assess the effect of hydrogeochemical properties on chemical weathering and stream water chemistry for three watersheds in Japan. On the basis of this assessment, acid-neutralization stream water chemistry was predicted using the ILWAS (Integrated Lake-Watershed Acidification Study) model. The main factors determining acidification are the thickness of weatherd profile and chemical weathering rates. The principal results are: (1) for non-acidified watersheds in Japan, acid deposition is neutralized by chemical weathering of primary minerals; (2) freshwaters in Japanese watersheds will not acidify even if acid deposition increases to the extent found in an acidified watershed in the U.S.A.     

Arterial supply to the rat colon

Rats are often used as animal models in studies such as on intestinal transplantation and anastomosis healing, which require colectomy. Although detailed information regarding arterial supply is important to establish accurate and reproducible experimental procedures, this has not been studied in the rat colon. Therefore, we analysed the detailed arterial distribution pattern and its individual variations in the colon of 34 rats. The rat colon received colic branches of the ileocolic artery, and the right, middle and left colic arteries. The single left colic artery constantly arose from the caudal mesenteric artery and was distributed to the descending colon, whereas the others showed variations in number and distribution. The ileocolic artery gave rise to one (12%) or two (88%) colic branches supplying the proximal ascending colon, and these branches formed rich, mesh-like anastomoses along the initial portion of the ascending colon. One (74%) or two (26%) right colic arteries originated from the cranial mesenteric artery and supplied the ascending colon and right colic flexure. Moreover, one (38%), two (56%) or three (6%) middle colic arteries emerged from the cranial mesenteric artery and were distributed to the transverse colon, left colic flexure and proximal descending colon. In total, we categorized the individual variations in arterial branching and anastomosis into 11 patterns. Arterial supply to the rat colon showed a specific pattern and frequent individual variations. These findings thus provide essential information for establishing reproducible models of rat colic surgery.     

水稻叶蝉抗性基因回交转育和CAPS标记辅助选择

 以综合性状好但对黑尾叶蝉 (NephotettixcincticepsUhler)敏感的品种台中 6 5作为轮回亲本 ,与抗性品种DV85连续回交 ,得到回交高代BC6F2 群体 ,进行抗叶蝉性状的回交转育。将抗黑尾叶蝉基因Grh2两侧的RFLP标记C189和G14 6 5成功地转换为在亲本间具有多态的CAPS标记。在进行表型选择的同时 ,利用CAPS标记对BC6F2 进行了标记辅助选择 ,分析了CAPS标记与Grh2间的遗传距离和标记辅助选择的效果。所选出的个体具有台中 6 5的遗传背景且携带纯合Grh2基因 ,可作为聚合抗叶蝉基因培育新品种的重要中间材料。