The Nutrition of Excised Wheat Roots

From an investigation of the nutrient requirements of Hilgendorf wheat roots, glucose emerged as the only suitable source of carbon and energy, and thiamine as the only vitamin necessary. The roots had the ability to utilise nitrogen from calcium nitrate, urea, alanine, glutamine, allantoin, and hydrolyzed casein.     

小麦幼苗根系镉螯合素

从经Cd~(2+)处理的小麦幼苗根系中分离得到一种镉结合复合物(Cd-BC)。通过SephadexG75,DEAE-52柱层析纯化,鉴定了此复合物性质:(1)紫外吸收光谱在255～265 tim间有一个“肩”,A_(250)/A_(280)>1;(2)在Sephadex G75柱层析上的表观分子量约为10kD,但在SDS-聚丙烯酰胺凝胶电泳上呈现的条带紧接着前沿,分子量非常小;(3)氨基酸组分分析,约90％的氨基酸残基为Glu/Gln,Cys和Gly,三者比例约为4:4:1。结果说明小麦幼苗根系Cd-BC是寡聚肽,是植物镉螯合素(Cd-PCs)的聚合体。     

Phosphodiesterase Found in Young Wheat Roots

Phosphodiesterase has been found in the particulate and soluble fractions from young wheat roots. The intracellular distribution of this enzyme was studied by using RNA, oligo DNA and DNPP as the substrates. When oligo DNA was used, 50 to 60 per cent of PPDase activity was found in the soluble fraction and 30 to 40 per cent in the microsomal fraction. Besides magnesium ion, calcium, cobalt, manganese and nickel ions were effective for its activity. The pH optimum of the enzyme was found at 6.0. This PPDase produced 5′-nucleotides from RNA at pH 6.9 on addition of magnesium chloride.     

小麦根系生长对缺磷胁迫的反应

研究了缺磷诱导小麦（Ｔｒｉｔｉｃｕｍ ａｅｓｔｉｖｕｍＬ．）根系生长的反应,小麦根轴的生长与植株内外的磷浓度均呈显著的负线性关系。分根实验证明,随着低磷营养液中根比例的增加,在供磷水平不同的分根盒侧的根轴长度的均增加,这说明根轴生长是受体内磷浓度调控的。植株体内磷浓度的处理后１ｄ开始变化,而在不同供磷水平营养液中小麦根轴长度的差异达到显著水平的时间是处理后的第８天,说明植株体内磷浓度的变化可能是小     

DCPA Causes Cell Plate Disruption in Wheat Roots

Light and electron microscopy were used to investigate the effectsof the herbicide DCPA (dimethyl tetrachloroterephalate) on wheatroot meristems. Three different sorts of disruption are found.In the epidermal cells, the walls are incomplete and/or curved,as well as being oriented in directions other than perpendicularto the long axis of the root. In developing cell plates, phragmoplastmicrotubule arrays are oriented in many directions in this layer,probably accounting for the wall abnormalities. In the calyptrogenand cortical layers, no walls or incomplete walls are formedbetween the nuclei, so that these cell layers are essentiallyone large cell with multiple nuclei. This effect has not beenobserved for any other herbicide. Prometaphase figures witha few microtubules and multipolar mitosis are the predominantabnormalities in the meristematic zone. Aberrant cell wallsare also found in this tissue layer. These data indicate thatDCPA is effective at disrupting phragmoplast micTotubule arraysand cell wall formation. Herbicide, mitosis, cell plate, cell wall     

Orientation and Geotropic Reaction of Seminal Roots of Wheat

The geotropic orientation of seminal roots of wheat has been studied on seedlings grown in five different positions, stationary and on clinostats. The roots perceive a geoinduc-tion before they have emerged from the grain and perform curvatures inside the grain. These are very sharp and transient, the following root growth is straight in any direction unless the positions are shifted. The roots are insensitive to a static gravi-induction but react to a change in gravitation with a geotropic curvature in positive direction. The roots may not reach or reach, or even pass the plumb-line. The orientation of a root depends upon the direction of its initiation and the geotropic curvature attained before the reaction has ceased. There is no nastic component in the reactions. The ‘plagiotropic’ orientation is explained by the limited positive reaction followed by an ageotropic state. Main root and adventitious roots react in the same way. Reactions to later stimuli give likewise limited curvatures which are weaker but of longer duration. — The effect of temperatures from 10°C to 25°C has been studied and compared to the temperature effect on cell elongation. It is concluded that the whole reaction may be explained by the regular auxin effects on cell elongation. No other hormone should be required and no plagiotropic mechanism is necessary.     

Histopathology of Wheat Seedling Roots Infected with Pythium arrhenomanes

Two-day-old wheat seedlings were placed on the edge of a P. arrhenomanes culture for 3 h at 25°C, and transferred into test tubes (18 mm dia.) containing glass beads and 1 ml of sterile water. Roots were sampled every 6 or 12 h for 84 h, and observed with the scanning electron microscope, or serial sectioned for light microscopy. Roots were colonized extensively in the region of root hair formation near the tip within 30 h after inoculation. Extensive penetration occurred 0.1—2 mm behind the root tip, with hyphae breaching the endodermis and gaining entry into the stele. Behind this area, hyphae remained limited to the outer cortical cells, or did not penetrate at all. Hyphae grew intracellularly, and became irregularly inflated inside cells. In most cases, hyphae penetrated the roots directly through the epidermis with appressoria being formed, or through breaks on the surface. However, histological evidence suggested chemical action taking place both outside and inside the cells.     

小麦根系接受缺磷信号的部位（简报）

用局部供磷法研究小麦根系接受外界缺磷信号位点的结果表明,体内不缺磷的植株可以接受缺磷磷信号的刺激,根系局部缺磷有利于小麦的生长发育,小麦根的任何部位均可接受环境缺磷信号。     

Isolation and Identification of Actinobacteria from Surface-Sterilized Wheat Roots

This is the first report of filamentous actinobacteria isolated from surface-sterilized root tissues of healthy wheat plants (Triticum aestivum L.). Wheat roots from a range of sites across South Australia were used as the source material for the isolation of the endophytic actinobacteria. Roots were surface-sterilized by using ethanol and sodium hypochlorite prior to the isolation of the actinobacteria. Forty-nine of these isolates were identified by using 16S ribosomal DNA (rDNA) sequencing and found to belong to a small group of actinobacterial genera including Streptomyces, Microbispora, Micromonospora, and Nocardiodes spp. Many of the Streptomyces spp. were found to be similar, on the basis of their 16S rDNA gene sequence, to Streptomyces spp. that had been isolated from potato scabs. In particular, several isolates exhibited high 16S rDNA gene sequence homology to Streptomyces caviscabies and S. setonii. None of these isolates, nor the S. caviscabies and S. setonii type strains, were found to carry the nec1 pathogenicity-associated gene or to produce the toxin thaxtomin, indicating that they were nonpathogenic. These isolates were recovered from healthy plants over a range of geographically and temporally isolated sampling events and constitute an important plant-microbe interaction.     

Colonization of Wheat Root Hairs and Roots by Agrobacteria

Formation of extracellular structures in pure culture and in interaction with wheat root surface was studied by scanning and transmission electron microscopy. The effects of various factors (growth temperature as well as pretreatment of agrobacteria with kalanchoe extract, acetosyringone, and centrifugation) on formation of extracellular structures was tested. The data on Agrobacterium tumefaciens (wild-type strain C58 and mutants LBA2525 (virB2::lacZ) and LBA288 (without the Ti plasmid)) adhesion to wheat root surface and root hairs after pretreatment of agrobacteria with inducer of virulence genes (vir) acetosyringone were obtained. Formation of agrobacterial cell aggregates on wheat root hair tips was demonstrated. The proportion of root hairs with agrobacterial aggregates on the root hair tip insignificantly changed after pretreatment with acetosyringone but considerably increased after treatment of A. tumefaciens C58 and LBA2525 with kalanchoe leaf extract. The most active colonization of root hairs and formation of agrobacterial aggregates on hair root tips was observed at 22°C. The capacity of agrobacteria for adhesion on monocotyledon surface could be changed by pretreatment of bacteria with various surface-active substances. Bacterial cells subjected to centrifugation had a decreased capacity for attachment to both wheat root surface and root hairs. The relationship between the capacity for adhesion and pilus production in agrobacteria was considered.     

Effect of Preloading on Alanine Absorption by Wheat Roots

Studying the amino acid absorption by higher plants we observed a stimulation of ¹⁴C-alanine absorption by wheat roots preloaded with inactive alanine. Within the limits of concentration examined the increase of stimulation is more likely to depend on the free alanine content of the roots than on the alanine concentration of the solutions used for pretreatment. The stimulation is retained even after incubating the pretreated roots in diluted CaSO₄ solution before the uptake period. Besides the alanine only the glycine gave stimulation, while pretreatment with valine, arginine or aspartic acid gave an inhibition. (The aspartic acid is likely to cause a general rise in the permeability of cells.) We suppose that the phenomenon of flow driven by counterflow is likely to serve as an explanation to the stimulatory preloading effect observed in the alanine absorption by wheat roots.