OXYGEN CONCENTRATION WITHIN THE NITROGEN-FIXING ROOT NODULES OF MYRICA GALE L.

Microelectrodes were used to study the oxygen concentration within Myrica gale L. nodules. Low oxygen concentrations were found only in the region of the mature, nitrogen-fixing endophyte, and appeared to correspond to clusters of infected host cells. The oxygen concentration in the remainder of the nodule was much higher. Interconnected intercellular air spaces were demonstrated by infiltration with India ink. Infiltration of the spaces with water greatly reduced oxygen concentration throughout the nodule, indicating that they function in supplying oxygen to the infected cells and remainder of the nodule. These results differ from those found previously for soybean nodules and provide evidence that legume and actinorhizal nodules have different mechanisms for protecting nitrogenase from oxygen.     

土壤水分胁迫对小麦根系与旗叶衰老的影响

随土壤水分胁迫加剧,旗叶,根中的超氧化物歧化酶,过氧化氢酶活性降低,腊脂过氧化产物丙二醛含量增加,花后１４ｄ为膜脂过氧化作用加重的转折点,此时受水分胁迫愈重,旗叶与根中ＳＯＤ,ＣＡＴ活性降低愈迅速,ＭＤＡ含量迅速升高,根系活力,旗叶与根中可溶性蛋白含量骤降,加重了膜脂过氧化程度,降低了清除了自由基能力,加速植株衰老。     

水分胁迫和氮素营养对小麦根苗生长及水分利用效率的效应

采用目前生产上广泛种植的小麦品种小偃６号,在一种特制木盒中土培,研究了水分胁迫和氮素营养对小麦根系和幼苗生长及水分利用效率（ＷＵＥ）的效应。小麦根系生长在双层尼龙网之间,土壤中的水分和养分可以被正常吸收,但主根和侧根不能穿过。结果表明：在土壤含水量为田间持水量的４０％－７０％范围内,随着土壤干旱程度的增加,小麦根长（ＲＬ）、根干重（ＲＤＷ）、叶面积（ＬＡ）和ＷＵＥ显著降低。氮肥的效应更为复杂。随着     

大豆根瘤中根瘤菌的电镜观察(简报)

在研究大豆根瘤的超微结构时,也常常描述一些有关细菌结构的变化,但一般比较简单,且多指寄主细胞中的幼龄细菌和成熟细菌,而对于侵入线中的细菌和寄主细胞中衰老细菌却很少有详细报道,即使在其他根瘤,特别是球形根瘤也是如此。显然这对研究根瘤中细菌的发育和衰老是很不够的。丰收11号大豆产量高,抗干旱,其根瘤在超微结构方面有许多特点。为了了解这种     

水分胁迫和胁迫后复水对玉米叶片生长速率的影响

玉米叶片延伸速率(LER)对水分状况的变化很敏感。快速干旱处理,水分消耗迅速,LER从最大到零需5h,叶水势改变0.5～0.6 MPa,缓慢干旱处理,水分消耗较慢,LER从最大到零需20h,叶水势改变1 MPa。缓慢干旱植株叶片成熟部位的渗透势,在任何LER下,均比快速干旱叶片更负。LER为零时,快速干旱叶渗透势为-1.3 MPa,缓慢干旱为一1.6MPa左右。短时间水分胁迫后复水,LER迅速增加,有部分补偿前期胁迫减少的生长量能力;长时间水分胁迫后复水,LER在6 h内不可能恢复到正常水平。     

DOES ARCTOSTAPHYLOS UVA-URSI (BEARBERRY) HAVE NITROGEN-FIXING ROOT NODULES?

An earlier report of the presence of Alnus-type nitrogen-fixation root nodules on Arctostaphylos uva-ursi (bearberry) has been re-examined. Nodular structures, externally resembling those of alder, were observed at four locations in eastern North America and in northern Scotland. No endophytes could be found in these structures and repeated assays by the acetylene reduction technique failed to demonstrate their ability to fix dinitrogen in North American material. The structures, in microscopic section, possessed typical bud morphology, could be sprouted in a moist chamber and produced shoots under stressed conditions in the field. The suspected 'nodules' are probably latent buds, serving to re-establish bearberry plants following damage.     

EFFECTS OF SOIL WATER DISTRIBUTION ON THE LATERAL ROOT DEVELOPMENT OF THREE SPECIES OF CALIFORNIA OAKS

The responses of seedling root systems of three species of oaks in California to two experimental soil moisture regimes were studied by comparing lateral root development, root and shoot weights, and root: shoot ratios. In the first soil moisture treatment the taproot was allowed to extend into moist soil throughout the duration of the experiment (control), while in the second treatment (shallow) the taproot grew into a dry substrate below 30 cm of moist soil. The treatments were intended to approximate soil moisture conditions experienced by oak seedlings in the field when deep soil water sources vary in their accessibility (control: accessible, shallow: inaccessible). Lateral root growth of Quercus agrifolia did not increase significantly when the primary root tip died in the shallow treatment, resulting in an overall decrease in the percent of the root system composed of lateral roots. Q. douglasii and Q. lobata increased lateral root weights by 80% and 70%, respectively, on the upper 30 cm of the primary root when the primary root tip died. Q. lobata was the only species that decreased in shoot and root weight (25% and 21%, respectively) with the loss of the root tip, indicating that, unlike the other species, it was dependent on the primary root for maximum growth. The morphological responses of these species correspond with their distributions and also may be a factor that influences their interactions with other species.     

水分胁迫对植物线粒体结构和脯氨酸氧化酶活性的影响

水分胁迫期间,小麦幼苗芽鞘和棉花幼苗胚轴细胞内游离脯氨酸浓度增加;但复水后又恢复正常。电镜观察发现线粒体肿大,嵴消失。胞质中出现脂肪滴。气相层析技术分析,发现水分胁迫使线粒体脂肪酸组成及含量有明显变化;不饱和脂肪酸含量增加。随着水分胁迫时间的延长,脯氨酸氧化酶活性也明显下降。设想水分胁迫使线粒体结构和组分发生了不利于脯氨酸氧化酶活性表达的变化,因而抑制了酶活性。     

水分胁迫对小麦叶绿素a荧光诱导动力学的影响

利用调制式荧光动力学分光光度计研究了水分胁迫对小麦叶片及叶绿体的叶绿素α荧光诱导动力学的影响.结果表明,水分胁迫对小麦光合作用的损伤是多部位的,它影响了PSⅠ活性、PSⅡ活性以及CO_2同化.对于PSⅡ的损伤部位除了它的氧化侧处,还可能损伤了PSⅡ反应中心.     

箭舌豌豆根瘤中根瘤菌的形态变化观察

箭舌豌豆(Vicia sativa)是一种抗性强、适应性广、产量高、营养丰富的优质饲料和绿肥作物,能大最结瘤固氮,有效提高土地肥力,因此全国各地广为种植。人们对箭舌豌豆的栽培技术、生长条件、遗传规律和有毒成份已有不少研究,但至今国内外对该种根瘤中根     

调控活性氧代谢对渗透胁迫时杨树光合作用光抑制的影响

根系受渗透胁迫时杨树(Populus×euramericana     

翅果油树根瘤超微结构及其内生菌的观察

作者用光学显微镜,透射电镜和扫描电镜对翅果油树(Eldaeagnus mollis D.)根瘤侵染细胞的超微结构及其内生菌的形态进行了观察研究。翅果油树根瘤中的内生菌具有五种不同的发育形态:菌丝、固氮泡囊、孢囊、孢囊孢子和拟类菌体。内生菌的这些不同形态以及它们在共生固氮中的作用,本文也作了讨论。