Margaret Holden

Changes in chlorophylls resulting from various chemical and physical treatments of leaves and leaf extracts

Abstract Chlorophylls a and b are easily altered chemically when leaves or leaf extracts are exposed to treatments which include heating and the action of organic solvents. Monitoring by thin-layer chromatography assists in the detection of the chlorophyll derivatives. In addition to loss of magnesium, formation of chlorophyllides and the a ′ and b ′ isomers, and loss of colour, chlorophylls a and b can each be converted into two other derivatives, with absorption spectra almost identical with those of the parent compounds. The conditions of formation, purification and some of the properties of these derivatives are described, and possible structures are discussed.

Lipoxidase activity of leaves.

Abstract The peroxidation of linoleic acid by leaf extracts is shown to be catalysed by a lipoxidase-type enzyme.

Chlorophyllase of sugar-beet leaves

Abstract The chlorophyllase of sugar-beet leaves was characterized and partly purified by gel-filtration and ion-exchange chromatography on various types of Sephadex. A rapid method was developed for determining the chlorophyllase activity of fractions from columns. Indications of more than one form of the enzyme may be explained by its tendency to associate or aggregate with itself or with other substances. Association is greater in 0·02 M citrate than in citrate containing 0·5 M NaCl. The enzyme is strongly adsorbed to negatively charged materials, which may explain its improved extractibility when the sodium chloride concentration of the medium is increased. Measurements of some properties of the enzyme are affected by insolubility of the substrate.

THE PURIFICATION AND PROPERTIES OF CHLOROPHYLLASE

CHLOROPHYLLASE, the enzyme which catalyses the removal of the phytyl group from chlorophyll, was discovered over fifty years ago by Willstatter and Stoll(25) but until recently has received little attention. It may be of considerable importance in the metabolism of the plant, and this paper reviews what is known about its occurrence and preparation, its properties in vitro and its function in vivo.

Methods of producing perithecia of Gaeumannomyces graminis and their application to related fungi

Fifty-seven isolates of fungi of the Gaeumannomyces-Phialophora complex that had been maintained in stock culture were tested by host-infection (in vivo) and agar plate, filterpaper and flask culture (in vitro) methods for production of perithecia. Most isolates of each of the three varieties of G. graminis produced perithecia in one test or another ( avenae (Gga) , 100%; tritici (Ggt) , 75%; graminis (Ggg) , 71%), but stock cultures of the two varieties of Phialophora radicicola did not form perithecia by any method. For G. graminis , in vivo methods (89, 56–75, 50% of isolates producing perithecia) were generally rather more effective than in vitro methods ( 33 , 69 and 43%). No one in vitro method was the best for all varieties of G. graminis : full-strength potato-dextrose agar was the least effective medium for perithecia, but at quarter-strength and supplemented with yeast extract it ranked with malt extract broth agar and a filter paper method as the most effective in vitro methods for Ggt , but not Gga or Ggg . In host-infection tests using stock isolates those host-parasite combinations that produced most disease or most colonized roots tended also to be those in which the fungus produced perithecia. Perithecia that formed on roots excised from wheat seedlings used to bioassay field soil with little infestation by Ggt were mostly on roots without take-all lesions. In soils with more infestation there was a positive association between lesioned roots and perithecia. G. cylin- drosporus perithecia also occurred on these excised roots, but not on the same plants as Ggt and concurrence of Ggt and P. radicicola var. radicicola was ≤£ 30% of isolates. These fungi seemed to have different seasonal occurrences. Some factors that influence the production of perithecia in vivo are discussed.

Treatments affecting the ultraviolet absorption spectrum of ribonucleic acid from three sources

Abstract The intensity of absorption in the 260 mμ region by three different types of ribonucleic acid and by the fraction of YNA that resists attack by pancreatic ribonuclease, is increased during several types of hydrolysis to an extent that parallels the extent of hydrolysis. Exposure to strong urea solutions has a small and irregular effect on the absorption by nucleic acid but diminishes the absorption by TMV.

Growth on oat-seedling agar of isolates of Gaeumannomyces graminis and some Phialophora species from cereal roots

Measurement of colony diameter on oat-leaf agar provides a quick and simple test for helping to distinguish between members of the Gaeumannomyces — Phialophora complex. Seventy two isolates were tested: all 19 European isolates of Phialophora radicicola var. radicicola , 18 of 20 Gaeumannomyces graminis var. tritici ( Ggt ) isolates and a Gaeumannomyces isolate from Deschampsia failed to grow out from the inoculum plug. Twelve isolates of G. graminis var. graminis spread over the agar at about the same rate as on potato dextrose agar (PDA) but three did not grow at all. Eight isolates of Phialophora graminicola , nine of G. graminis var. avenae and two oat-attacking isolates that had been identified as Ggt all showed some growth, although with most of the isolates this was retarded compared with that on PDA.