J.H. Visser

Germination stimulants of Alectra vogeliiBenth seed

Summary Root exudates of host plants of A. vogelii contain substances which stimulate the germination of the sensitised parasite seed. These stimulants could be resolved in a high pressure liquid chromatography system into a number of stimulatory zones, at least two of which were apparently common to all the investigated hosts.

The Effect of Arachidonic Acid, Prostaglandins and Inhibitors of Prostaglandin Synthetase, on the Flowering of Excised Pharbitis nil Shoot Apices under Different Photoperiods

Summary Arachidonic acid and PGE 1 (10 -4 M) hastened the time to flowering of Pharbitis nil plantlets which developed from excised shoot apices under inductive conditions (short days). Gentisic acid, acetylsalicylic acid, salicylic acid and oleic acid, all known inhibitors of prostaglandin synthetase, inhibited flowering of plantlets under inductive conditions. Arachidonic acid and PGE 1 , PGE 2 , PGF 1 a , PGF 2 a , PGA 1 , PGA 2 , PGB 1 , and PGB 2 , (10 -4 M, 10 -5 M and 10 -6 M) did not induce flowering in plantlets which were kept under long days. However, leaf blade growth was reduced by the treatments. A hypothetical scheme is presented for the possible regulation of flowering by prostaglandins and phenolic acids (salicylic acid).

Chromatographic investigation of the Striga seed germination stimulant

Summary The highly efficient technique of high speed liquid chromatography has been applied to the separation of stimulants involved in the germination of the seed of Striga lutea, a root parasite on gramineous plants. Nine apparently different compounds were resolved. Plants that induce germination of S. lutea seed possibly produce at least one common substance.

On the parasitism of Alectra vogeliiBenth. (Scrophulariaceae) I. Early development of the primary haustorium and initiation of the stem

Summary The development of the primary haustorium of the hemiparasite, Alectra vogelii , on the roots of one of its hosts, Voandzeia subterranea (Fabaceae), has been studied morphologically and anatomically. A simple method for cultivation was used in order to observe the different stages of parasite development. Upon contact between parasite seedling and host, localized swelling of host root tissue ensues. The front cells of the advancing primary haustorium are densely structured and directed towards the stele of the host root. Several lateral roots originate in the swollen area of contact. That part of the formerly rather thin root of the parasite that remains outside the host root thickens. The apical meristem of the stem then grows out of the seed coat. The nature of the connecting tissue within the haustorium is presently being investigated.

On the Parasitism of Alectra vogelii BENTH. (Scrophulariaceae) III. The Occurrence of Phloem between Host and Parasite

Summary The presence of sieve tube elements in the primary haustorium of the root parasitic Alectra vogelii as well as in the contact zone of the host, Voandzeia subterranea , could be demonstrated by bright field and fluorescence microscopy as well as electronoptically. Pprotein in the sieve elements of the fabacean host exhibited typical paracrystalline inclusions, thus making it possible to distinguish between host and parasite sieve elements. Although the host and parasite phloem systems came very close together, they were always separated by a parenchymatic bridge consisting of at least eight cells.

The effect of certain inhibitors of prostaglandin biosynthesis on flowering of Pharbitis nil

Summary Certain inhibitors of prostaglandin biosynthesis in mammalian systems, namely, aspirin, phenylbutazone, indomethacin and niflumic acid inhibit flowering of Pharbitis nil to a greater or lesser extent.

The occurrence of prostaglandin (PG) F2α in Pharbitis nil seedlings grown under short days or long days

The concentration of PGF 2 α present in Pharbitis nil kept under short days is about 20 times higher than in plants kept under long days.

The chlorophyll concentration and photosynthetic activity of some parasitic flowering plants.

Summary Fifteen species (7 stem and 8 root parasites) were investigated. Their chlorophyll concentration ranged from 0 (1 species) to 11.7 mg per dry leaf or shoot mass and their chlorophyll a : b ratio varied between 1.0 and 2.3. The relative rates of 14CO2 assimilation varied from 3 to 4 226 d.p.m. g-1 dry aerial material.

Photosynthesis of certain South African parasitic flowering plants.

Summary The rate of apparent photosynthesis, the C0 2 compensation point and the chlorophyll concentration of a number of holo- and hemiparasitic plants were studied in order to establish the degree of their dependence on their hosts. The hemiparasitic stem-parasites exhibited an exceptionally high C0 2 compensation point and the low rate of apparent photosynthesis possibly indicating a high degree of dependence on their hosts for photosynthate.

On the Parasitism of Alectra vogelii BENTH. (Scrophulariaceae) II. Origin of Lateral Roots in the Contact Area of the Haustorium

Summary The angiosperm root parasite Alectra vogelii induces the formation of lateral roots of the host plant. This is shown by histological-, physiological-, and karyological proof. The lateral roots arise within the haustorial region, where parasite and host tissue form a heterogenous complex. Besides the formation of lateral roots the haustorium causes a general dilatation of the cortex cells and a proliferation of cells of the host stele. These effects are discussed as a result of growth stimulating substances.