New Phytologist

doi: 10.1111/j.1469-8137.1989.tb04210.xpmid: N/A

THOMAS, HOWARD; BORTLIK, KARLHEINZ; RENTSCH, DORIS; SCHELLENBERG, MAYA; MATILE, PHILIPPE

doi: 10.1111/j.1469-8137.1989.tb04211.xpmid: N/A

During dark incubation of excised leaf tissue from Bf 993, a senescence mutant of Festuca pratensis Huds., a highly polar green pigment fraction (PC) increased from negligible amounts at day 0 to maximal concentrations at days 4–6 and declined thereafter. Over the same time‐scale, chlorophyll (chl) was lost from leaves of the normal genotype Rossa without any detectable accumulation of PC. Chromatographic analysis established that PCs are a group of dephytylated derivatives of chl a. Chl‐ protein complexes from 4–day‐senesced Bf 993 tissue were isolated by sucrose gradient centrifugation and PCs identified by thin‐layer chromatography. High levels of PC were associated with the light‐harvesting complex of Photosystem II; Photosystem I yielded none. Cycloheximide, at a concentration sufficient to inhibit yellowing in the normal genotype, completely abolished the appearance of PC in Bf 993. Accumulation of PC‐like pigments in Rossa leaf tissue could be induced by anoxia. It is proposed that PCs are normal intermediates in chl catabolism, which begins with a protein synthesis‐dependent dephytylation, followed by oxidation leading ultimately to open‐chain pyrrole derivatives. The first steps in the breakdown sequence take place while the pigment is associated with proteins in the thylakoid membrane. The metabolic lesion in the Festuca mutant appears to be located downstream of the dephytylation step, leading to an abnormal accumulation of PCs in this genotype.

ATKINSON, C. J.; MANSFIELD, T. A.; KEAN, A. M.; DAVIES, W. J.

doi: 10.1111/j.1469-8137.1989.tb04212.xpmid: N/A

Plants of Commelina communis L. were grown in media containing different concentrations of calcium from 1 to 8 mol m −3. After 4 weeks' growth stomatal behaviour was studied both on the intact plants and on isolated abaxial epidermis. The effect of Ca nutrition on stomatal opening was apparently different according to these two methods of observation. The apertures measured in light and in absence of CO2 were smaller on abaxial epidermal strips from plants grown at larger Ca concentrations than those grown at smaller concentrations. The inhibition of opening was thought to be due to the presence of free Ca2+ ions because inhibition was not found when EGTA was included in the medium used for incubating the isolated epidermis, and significant quantities of Ca were lost to the medium by epidermal tissue from plants grown on high concentrations of Ca.

CLOWES, F. A. L.; WADEKAR, R.

doi: 10.1111/j.1469-8137.1989.tb04213.xpmid: N/A

Primary roots of Zea mays L., when grown to 100 mm long, may display instability in the architecture of their meristems. This occurs over the whole temperature range from 15 to 35 °C, but most frequently at the two extremes of the range and is associated with abnormally low ratios between rates of mitosis in the proximal tier of the cap cells and rates in the cells of the Quiescent centre. Anomalous meristems show either proliferation of the number of cell layers between stelar pole and cap boundary or protrusions of cells derived from the quiescent centre into the cap where they can spread to form new sets of cap initials. The process can be repeated, but there is no evidence to suggest that the originally closed meristem ever operates as an open meristem with only transiently quiescent cells distal to the stelar pole.

BURGGRAAF, A. J. P.; BERINGER, J. E.

doi: 10.1111/j.1469-8137.1989.tb04214.xpmid: N/A

A study of the in vitro viability of VA mycorrhizal propagules [Glomus caledonium (Nicol. & Gerd.), Gigaspora margarita (Becher & Hall)], indicated that none could be used for continuous in vitro cultivation. Large numbers of nuclei (at least 20000 for G. margarita) were found in the chlamydospores. Nuclear division could not be demonstrated in vitro, during or after spore germination using various cell cycle inhibitors, or by direct isotope labelling of nuclear DNA. Manipulation of secondary messengers (cAMP, calcium) and the microtubule or micro‐filament system did not increase the in vitro growth of the tested VA mycorrhizal strains.

KOIDE, ROGER T.; LI, MINGGUANG

doi: 10.1111/j.1469-8137.1989.tb04215.xpmid: N/A

Sunflower (Helianthus animus L.) and mustard (Brassica hirta Moench.) plants were grown in autoclaved soil to which was added various components of soil inoculum. Use of inocula containing mycorrhizal propagules ultimately resulted in growth promotions which were related to improved phosphorus nutrition. Inoculation with soil containing mycorrhizal propagules caused an initial growth depression in comparison with plants receiving no inoculation, but inoculation with washed spores did not. For several reasons, the growth depression caused by inoculation with soil was not attributable to mycorrhizal infection. First, the growth depression was evident before mycorrhizal infections had become established. Second, the growth depression was also evident when either soil or soil sievings, both lacking mycorrhizal propagules, were used. Third, similar growth depressions were observed in mustard. The results suggest that careful selection of appropriate controls for mycorrhizal plants must be made, particularly if the emphasis is on early phases of plant growth. Use of non‐sterile soil reduced the extent of mycorrhizal infection.

ALLEN, MICHAEL F.; ALLEN, EDITH B.; FRIESE, CARL F.

doi: 10.1111/j.1469-8137.1989.tb04216.xpmid: N/A

Vesicular–arbuscular mycorrhizal fungi reduced the growth and survival of the non‐mycotrophic weed, Salsola kali (Chenopodiaceae) in field and greenhouse experiments. To determine the mechanisms by which mycorrhizal fungi can affect a non‐mycotrophic plant, we mapped the root responses of S. kali and the mycotrophic grass Agropyron dasystachyum to invasion by a mixture of Glomus spp. and by Gigaspora margarita. The fungi invaded the roots of both species within 10 days following seed germination. In A. dasystachyum normal mycorrhizal development occurred and no root browning or autofluorescence was observed, indicating a compatible reaction. In S. kali, the fungi initially invaded the roots and formed arbuscules and peletons. The roots reacted to invasion by autofluorescing bright yellow, suggesting lignification. With 1 or 2 days following root penetration by the fungus, the invaded root segment turned brown and, with the exception of some vesicles, the fungus disappeared from the root. The fungus sometimes then reinvaded new root segments farther down the root.

DOUD MILLER, DIANE; BODMER, MAJA; SCHÜEPP, HANNES

doi: 10.1111/j.1469-8137.1989.tb04217.xpmid: N/A

An experiment to determine the short‐term characteristics of root colonization by two vesicular‐arbuscular (VA) mycorrhizal fungi with apple (Malus × domestica Borkh.) was initiated concurrently with an experiment to determine longer‐term effects of colonization by these fungi on the growth of apple seedlings. Short‐term characteristics of colonization were determined by sequential harvesting of a cuvette system which also allowed monitoring of hyphal spread from inoculated ‘spreader’ plants, through a root‐free soil region, to non‐inoculated ‘receiver’ plants. Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe exceeded Glomus macrocarpum Tul. & Tul. in rate of initial colonization, amount of maximum colonization, and persistence of arbuscules and external hyphae. Colonization by either fungus reduced shoot fresh weight 11 days after inoculation but increased shoot and total fresh weight by day 38. Hyphae of G. mosseae had traversed through 2 and 3 cm of root‐free soil to colonize non‐inoculated ‘receiver’ roots by 29 days, and hyphae of G. macrocarpum by 38 days. G. mosseae colonized ‘receiver’ roots more intensely than did G. macrocarpum at 2 and 3 cm, and 3 and 4 cm distance, at subsequent harvests. The fungi were effective, singly and in combination, in increasing apple plant biomass, as compared to non‐mycorrhizal controls. Relative height growth rate, and colonization at harvest, of G. macrocarpum‐inoculated plants were less than those of G. mosseae‐inoculated or G. mosseae + G. macrocarpum‐ inoculated plants, but greater than those of the non‐mycorrhizal control trees.

PRICE, N. S.; RONCADORI, R. W.; HUSSEY, R. S.

doi: 10.1111/j.1469-8137.1989.tb04218.xpmid: N/A

Cotton, Gossypium hirsutum L., was grown in the greenhouse in sand‐nutrient culture at five phosphorus (P) concentrations, and root systems were examined after 10 and 20 days. Extension rates of primary laterals and numbers of secondary laterals increased with increasing P. Cotton was grown for 6 weeks in environment cabinets in soils of three P concentrations with and without mycorrhizas. Increased P and mycorrhizas both stimulated plant growth (f. wt shoot d. wt), but however specific root length (cm root g' root f. wt) of mycorrhizal plants was reduced.

Ames, R. N.; Mihara, K. L.; Bayne, H. G.

doi: 10.1111/j.1469-8137.1989.tb04219.xpmid: N/A

Spores of Glomus macrocarpum Tul. & Tul. were sieved from a calcareous, silty clay loam soil, washed in sterile water, and plated on chit in agar for the isolation of actinomycetes. Of the 190 spores examined, 100 were colonized by one or more chitin‐decomposing microorganisms: 82% were colonized by actinomycetes, 17% by bacteria, and 1 % by fungi. Fifty‐one actinomycete isolates were classified on the basis of morphological, cultural and biochemical criteria. Tentative identifications to genera and numbers of different isolates are as follows: Streptomyces (29); Nocardia (3); Streptosporangium (1); Streptoverticillium (1); Intrasporangium (1); Nocardiodes (1); and unidentified (15). This is the first study to report the prevalence and diversity of chitin‐decomposing actinomycetes associated with spores of a vesicular‐arbuscular mycorrhizal fungus in field soil.