Distribution of the Products of Photosynthesis between Powdery Mildew and Barley

Abstract

'Sionnary. The photosynthetic assimilation of 1 CO., has been studied in healthy a,nd miiil(lew-infected barley. The parasite wvas separated from the host by removing the myceliumii with a camel's hai,r brugh. The ethanol soluble mentabolites of the parasite, infected host and healthy host were extracted, separated by paper chronmatography and individually i'den'tified. From this wvork it appears ithat there is a rapid movement of la)bel from host to parasite 'nainly in the form of sucrose which is then quickly metab-olized into many combpounds. Tihe majority is cionverted in'to mannitol, and lesser amounts are converted inlto trehailose, arabiltol, aspartic acid, and glutamic acid. In conidia the major cartbon reserve is arabitol instead of mannitol, with lesser amounts of trehalose and mannitol. Photosynthetic ulptake of 14CO2 by the complex decreases steadily after inoculation a's compared with healithy leaves. However, the ethanol soluble metabolites of the infected host tissue differ only slightly from those of healthy host tissue. The major differences are a sliglht decrease in thlie aimount of sucrose anid increases in mnalic acid and serine. Many investigationis have been reported in recent years on the metabolism of the obligate parasite-host complex in plants. Interpretation of the resulits of these studies has generally been difficult since separation of the host from ithe parasite had not been accomn.plished. This is particularly true in studies of rust infections. Hoowever, investigations of the comii-plex 'have revealed several changes which occur following infection. There is a considerable rise in the respiration rate of the complex (2, 16, 20), and a decrease in photosynthetic ability (1, 17, 18). There are also increases in several organicc consti,tuenits (9, 12, 19) as well as an increase in dry weight (28) of the comiiplex. These increases require thiat considler-able carbon be tbaken in by {the complex. There have been attemipts to determine what compounds play an inmpoltanit role in the accumulation;of carbon (8, 14), but ill none of these has a distinction been made between metabolites of the host and those of the parasite. The ectoparasite. powdery mildew, offers a distinct advanitage in this type of investigation. With a camel's hair brush the whole imycelium, except for the haustoria, may be removed from the infected host, thus accomplishing a separation. However, at present no attemipt to separate the miietabolites of the 2 organisms has been reported, thus very little is known about the metabolisnm of 'the parasite, nor of the IVersity of Wisconsin; actual chaniges whiich occur in the infected host. The wvork reponted 'in this paper presents the results of experiments conducted iby photosyn'thetically feeding 14CO. to the powdery mildew-barley complex. The ethanol soluble components of the hlokt were sep-araited from those of the parasite, and the indrividual metaboliltes of both fractions were analyzed using paper chromatographic technliques. The abiliity of the complex to fiix 14COO2 photosynthetically was compared with healthy host tissue. Material and Methods Planwt aterial. The barley seedling (var. Traill) was used exclusively as the host mnaterial. The powdery mildew, Ervsiphe gramninis hordei (race unidentified), was the parasite. Growth Coniditions. Barley was germinated and grown for 9 days 'in an environmenrtal control room with 14 hours of light and 10 hours of darkness. The light intensity at seedling level was 1000 ft-c., and the temperature of the room was held at 220 wiith a relative humidity of 50 %. At 9 davs the plants were transferred to a cool greenhouse (ca 150) and inoculated with conidia. It was found th-att under these conditions the resulting mildew my-celiurm could be readily separated from the host epi-dermis. Inoculation Procedutre. The following inoculation procedure was used to obbain den'se mycelial mats that could 'be easily removed: Primary leaves of 9-day-old seedlings were dusted with conidia usinc a camel's hair. brush. The inoculation wvas confined 683