Rhizoid Production Research Articles

The attachment of zygotes and germlings of Halidrys siliquosa (L.) Lyngb. (Phaeophyceae, Fucales)

There is a lapse of several days before rhizoids are produced from the zygote of Halidrys siliquosa (L.) Lyngb. In order to remain attached to the substratum until this time, the zygote rapidly secretes a rigid adhesive zygote wall with associated adhesive mucilages. The cell wall proper is laid down inside this zygote wall. A multicellular spherical germling develops and once the rhizoid system has formed, the zygote wall is shed from the thallus in the form of a cap. Four primary rhizoids are followed by the production of more rhizoids throughout the life of the plant and in this way the hold fast of the adult is built up. These events have been followed using the techniques of light, scanning and transmission electron microscopy.

The use of Stigeoclonium subsecundum (chlorophycae) as a bioassay organism—I. Attachment of the algal cells to glass slides

A technique was developed for the use of Stigeoclonium subsecundum Kutz., an attached, filamentous, green alga, as a bioassay organism. The procedure involved the settling of a freshly blended suspension of algal cells onto the surface of glass slides. The production, release, and attachment of zoospores as well as the production of rhizoids from the blended filaments produced an attached algal mat on a glass surface. The pigment extract absorbance and the dry weight of the algae attached to each glass slide were normally distributed about a mean.

Mammalian Safety of the Aphid-Attacking Fungus Entomophthora nr. thaxteriana12

A strain of the entomogenous fungus, Entomophthoza nr. thaxteriana (Petch), isolated from the green peach aphid, Myzus persicae (Sulzer) shows promise as a biological control agent for aphids. This isolate is intermediate in its morphology between E. thaxteriana and E. virulenta Hall and Dunn. The spore sizes, i.e. conidia 24 × 19μ, resting spores 22μ, more closely approximate E. virulenta . Lack of rhizoid production, however, has caused us to call this strain E. thaxteriana . The resting spores produced by this isolate can be stored for long periods of time and when properly treated will give up to 98% germination. Greenhouse and field studies have shown this species to be both pathogenic and virulent, giving 100% control in 3 days. The resting spores of this fungus are currently under production in the laboratory and will be field tested against the potato aphid complex in Northern Maine. Effectiveness, however, is not the only criteria which determines an insect pathogen as a good candidate for biological control. It must also be demonstrated that it is safe for man.

Effect of X rays on the growth of the first rhizoid in spores of Osmunda regalis

Spores of the fern Osmunda regalis were germinated and X irradiated at different stages of their growth. It was found that in sporelings which later died from radiation damage, irradiation at first metaphase or earlier inhibited the production of the first rhizoid, which normally is formed by the elongation of one of the daughters of the first division. Irradiation at first ana-telophase or later did not inhibit first rhizoid production, even at doses which killed the sister (prothallial) cells in the large majority of sporelings. The first rhizoids of radiation survivors had the same growth rate and reached the same length at 21 days as those of unirradiated prothalli.

Rhizoid Formation in Megagametophytes of Marsilea in Response to Growth Substances

In an earlier paper by Bloom (1962), dealing with rhizoid formation in unfertilized megagametophytes of Marsilea, it was suggested that rhizoid formation is a geotropic response involving an endogenous auxin. It was suggested that the auxin becomes concentrated in the ventral region of the gametophyte plant as a result of gravitational force. As a result of a series of experiments conducted in our laboratories, further evidence has been gathered to confirm the roles of auxins and gravitational forces in determining rhizoid formation. Maravolo and Voth (1966) have reported that gemmalings of Marchantia normally form ventral rhizoids on new tissue, but that when exogenous auxins are applied and reach a threshold concentration on the dorsal surface, rhizoids form there as well. The number of rhizoids formed was reported to be proportional to the concentration of the exogenous auxin. Miller and Miller (1964) reported effects of auxins on cell enlargement in fern gametophytes of Onoclea sensibilis, but did not report any observations of unusual effects on rhizoid formation. Kelley and Postlethwait (1962) studied the effects of the plant growth substance 2-chloroethyltrimethyl-ammonium chloride on gametophytes of Pteridium aquilinum and noted an effect on the time sequence of rhizoid production, but did not report any unusual effect on the position of the rhizoids formed. If auxins are indeed involved in rhizoid formation in the megagametophytes of Marsilea and if a higher concentration of auxin at the ventral sites is a response to gravitational force, certain predictions can be made concerning the effect of the application of exogenous auxins to the megagametophytes. In diverse processes auxins are generally stimulatory at certain concentrations and inhibitory at higher concentrations (Leopold, 1964). It could be predicted that rhizoid formation would be inhibited at high concentrations of exogenous auxins and stimulated at low concentrations. An additive effect could be expected if exogenous auxins are applied at very low concentrations. To test the above hypotheses the following experiments were conducted. Mineral nutrient solutions were prepared using Hoagland's No. 2 solution as given by Hoagland and Arnon (1938), with appropriate micronutrients added. Separate solutions were prepared by adding indole-3-acetic acid, napthalene acetic acid, or gibberellic acid in amounts to provide concentrations by weight of one part in 10,000 (10-4), 100,000 (10-5), 1,000,000 (10-6), and 10,000,000 (10-7). Plain agar was added at a concentration of 1.5% to each solution and the solutions were autoclaved and poured into sterile 100 X 15 mm plastic Petri dishes. Sporocarps of Marsilea mucronata were hydrated in deionized water. As soon as the megaspores were free they were transferred to the surface of the agar plates. Organic materials other than agar were not included in the media since the mega-

Rhizoid production in excisedDictyota dichotoma

Excised segments of fronds of Dictyota dichotoma (Huds.) Lamour. show a marked basipetal increase in rhizoid production when grown in culture. Rhizoid production is inhibited by bright light and apparently enhanced by red light (λ 600–690 mμ).

Morphogenic Effects of Three Growth Substances on Marchantia gemmalings

Sterile gemmae of Marchantia polymorpha were grown on an agar substrate prepared with inorganic mineral nutrients. Various concentrations of indoleacetic acid, naphthaleneacetic acid, and maleic hydrazide were added, and the progressive morphogenic responses of the developing gemmalings were measured. The two auxins promoted similar responses, many interpretable in terms of those noted in higher plants. Rhizoids elongated on the dorsal surface; the growing region became quiescent, and cells elongated very markedly. A winged thallus was the characteristic response to inhibition of apical growth. The degree of response followed a normal distribution curve. Maleic hydrazide induced pronounced effects at a concentration of 10-1 g/liter, slight ones at 10-2 g/liter, and none on lesser concentrations. Observed responses, similar to those in higher plants, included inactivation of meristematic regions, deterioration of chloroplasts, hyperplasia, and inhibition of rhizoid production.

EFFECT OF 2‐CHLOROETHYLTRIMETHYLAMMONIUM CHLORIDE ON FERN GAMETOPHYTES

Kelley, A. G., and S. N. Postlethwait. (Purdue U., Lafayette, Ind.) Effect of 2‐chloroethyltrimethylammonium chloride on fern gametophytes. Amer. Jour. Bot. 49(7): 778–786. Illus. 1962.—2‐chloroethyltrimethylammonium chloride (CCC) promotes growth of fern gametophytes by stimulating the rate of cell division. The transition from filamentous to biplanar to triplanar cell division is hastened, resulting in earlier and more numerous gametangia on treated prothalli. Growth is stimulated in the range of 10‐4 m–10‐2 m CCC, with the optimal effect at 10‐3 m CCC. The time sequence of rhizoid production is altered by 10‐2 m CCC; the resultant production of rhizoids by prothalli treated with 10‐2 m CCC does not exceed that of controls.

Experimental Control of Zoid Discharge and Rhizoid Formation in the Green Alga Enteromorpha

1. An isolate of Enteromorpha growing in the Shedd Aquarium, Chicago, was tested for zoid discharge under various environmental conditions, for the distribution of zoid-producing areas, and for polar and position effects of rhizoid production. 2. Discharge of zoids occurred almost predictably in 2-5 days in excised sections removed from the stock culture. 3. A wounding effect was tested by comparing discharge in similar lengths of thalli, half of which were cut and half left entire. No differences in discharge were noted. 4. Other changes encountered in transfer from stock culture to new media were discounted as factors inducing discharge. 5. Discharge in sections transferred to water from the stock culture lagged initially in comparison with discharge in sections transferred to fresh sea water, but final discharge indexes were equal. When the stock-culture water was autoclaved before plants were transferred into it, there was no lag period. This indicated that an unstable inhibitor was possibly present in crowded cultures. 6. When thalli were crowded into smaller volumes of water, discharge was less. 7. The effect of gross nutrient deficiency in the culture medium was tested by observing discharge in parallel graded concentration series of sea water and artificial sea water. Nutrient deficiency had no effect, while dilution reduced the discharge of zoids. 8. Addition of inorganic nutrients and soil solution enhanced discharge markedly. 9. No discharge response was evident in sections exposed to continuous light of less than 10 ft-c., or in sections exposed to 250 ft-c. for 1 hour or less per day. Above 100 ft-c. or 5 hours of light there was little change in response. 10. Discharge was affected by changes in pH, with greatest response in the range 6.5-7.5. 11. In sections discharging completely, two sequences of events were found: a leisurely emergence of zoids from scattered cells, or a fast, explosive discharge, beginning near the middle and spreading outward toward each end, with release of zoids only from the periphery of the expanding belt of empty cells. 12. Distribution of zoid-producing areas, both in random excised sections and in sections from known portions on branches, was more frequent at distal and proximal ends and much less in intermediate areas. 13. IAA supplied exogenously in the sea water (10-3-10-10 M) suppressed zoid liberation moderately at the higher concentrations, but there was no apparent effect at lower concentrations. 14. A single thallus, exposed simultaneously to two different culture media-a discharge stimulant and a discharge suppressor-released zoids only in the former. This was evidence against a mobile endogenous stimulant. 15. Polarity was noted in rhizoid production. Rhizoids formed only at the proximal ends of sections of Enteromorpha sp., E. clathrata, E. intestinalis, and E. linza. The distal end either remained open, closed up, or became swollen and lumpy. 16. In sections from known portions of thalli, rhizoids formed first, and most vigorously, from apical ones. There was a noticeable decrease in size in rhizoids of E. intestinalis from apical to basal sections, and also as the size of the section was decreased from 4.0 to 0.25 mm. in length.