Comparison of rates of natural senescence of the root cortex of wheat (with and without mildew infection), barley,oats and rye

Summary In comparative tests in a glasshouse, the cortex of oat and rye roots senesced more slowly than the cortex of wheat and barley roots. Of the cereals tested, wheat showed the most rapid rate of root cortical senescence, and the rate was unaffected by inoculation of leaves withErysiphe graminis. The results are discussed in relation to infection by root pathogens.     

Ultrastructural analysis ofErysiphe graminis haustoria and subcuticular stroma ofVenturia inaequalis using cryosubstitution

Summary Cryosubstitution provides an improved ultrastructural preservation of the two plant pathogensVenturia inaequalis andErysiphe graminis when compared to conventional preparation methods. Further, freezing the infected whole leaf material on a copper block cooled with liquid helium gave better results than those observed with the propane plunging method. Novel observations concerning the fungal stroma and haustoria were made which showed ribosomes organized into groups that were evenly distributed throughout the cytoplasm of both fungi. Stretches of rough endoplasmic reticulum were present, and microtubules were seen, sometimes associated with mitochondria. A large number of darkly staining vacuoles were observed in both fungi. The polarity of organelles and microtubules along the longitudinal axis of the haustorial body ofE. gramnis and along the growing direction of subcuticular stroma and runner hypha ofV. inaequalis was evident. InE. graminis filasomes were observed, as were Golgi-like bodies. These new observations, together with the advantages of the cryosubstitution technique, can serve as a basis for further studies in understanding host-parasite interactions.     

受白粉菌诱导大麦抗感等基因系蛋白质变化的双向电泳分析

分别对接种与否的大麦抗—感白粉病等基因系—叶期幼苗取材进行蛋白质双向电泳分析。结果表明,病原的侵入使抗—感两系在30Kd以下的低分子量区域的蛋白质发生了明显变化。接种48小时之后,抗病系在pH5.5、6.0、6.8及8.8附近出现了对照中所没有的蛋白质,而在pH6.0和8.8附近的蛋白质则较对照有减小的趋势;感病系在pH6.0附近蛋白质明显增多,在pH8.8处不仅在量上有大幅度提高,而且种类也有增加。结果还表明,抗—感系间在未接种的情况下双向电泳图谱也有差异,接种之后由于感病系在pH8.8处蛋白质的特异性合成,使抗—感两系间的差异缩小。     

白粉菌属一新种

本文报道了寄生在白花菜科醉蝶花属上的一个白粉菌属新种醉蝶花白粉菌Erysiphecleomes白花菜科是白粉菌在我国的寄主科新记录。新种有中文和拉丁文描述。     

Effects of sowing date and vernalisation on the growth of winter barley and its resistance to powdery mildew (Erysiphe graminis f.sp. hordei)

Detailed studies on the production of individual leaves, and the development of powdery mildew on them, were made in field plots of winter barley sown on different dates. The greater severity of the disease on early-sown than on later-sown seedlings during the autumn and winter can probably be explained mainly by changes in the abundance of inoculum and the suitability of the weather for infection. Results from glasshouse experiments suggest that the differences may be reinforced by direct effects of vernalisation on the susceptibility of seedlings to the disease. Contrary effects of sowing date on mildew severity during summer are probably due to the progressively greater resistance to mildew of the later-formed than of seedling leaves, and the earlier appearance of corresponding leaves on early-sown than on later-sown plants. Early sowing can also increase the total number of leaves produced per stem. Therefore, because resistance of the leaves increases progressively, the maximum degree of resistance expressed by the later-formed (e.g. flag) leaves will often be greater on early-sown than on later-sown plants.     

Ultrastructural comparison of incompatible and compatible interactions in the barley powdery mildew disease

Summary In the powdery mildew disease of barley,Erysiphe graminis f. sp.hordei forms an intimate relationship with compatible hosts, in which haustoria form in epidermal cells with no obvious detrimental effects on the host until late in the infection sequence. In incompatible interactions, by contrast, the deposition of papillae and localized host cell death have been correlated with the cessation of growth byE. g. hordei. With the advent of improved, low temperature methods of sample preparation, we felt that it was useful to reevaluate the structural details of interactions between barley andE. g. hordei by transmission electron microscopy. The haustoria that develop in susceptible barley lines appear highly metabolically active based on the occurrrence of abundant endoplasmic reticulum, Golgi-like cisternae, and vesicles. In comparison, haustoria found in the resistant barley line exhibited varying signs of degradation. A striking clearing of the matrix and loss of cristae were typical early changes in the haustorial mitochondria in incompatible interactions. The absence of distinct endoplasmic reticulum and Golgi-like cisternae, the formation of vacuoles, and the occurrence of a distended sheath were characteristic of intermediate stages of haustorial degeneration. At more advanced stages of degeneration, haustoria were dominated by large vacuoles containing membrane fragments. This process of degeneration was not observed in haustoria ofE. g. hordei developing in the susceptible barley line.Abbreviations b endoplasmic reticulum extension, blebbing - er endoplasmic reticulum - f fibrillar material - g Golgi-like structure - h haustorium - hb haustorial body - hcw haustorial cell wall - hcy haustorial cytoplasm - hf haustorial finger - hocw host cell wall - hocy host cytoplasm - 1 lipid-like droplet - m mitochondrion - mt microtubule - mve multivesicular body - n nucleus - p papilla - ph penetration site of an infection peg - pl plasma membrane - s sheath - sm extrahaustorial membrane - v vacuole - ve vesicle