To study the response of non-mycorrhizal and mycorrhizal maize plants to drought, the changes in the pools of non-structural carbohydrates and amino acids were analysed in leaves and roots of two maize cvs. Plants well colonized by the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) (60% of root length infected) and comparable non-mycorrhizal plants were subjected to moderate drought stress by reducing the water supply. This stress induced a conspicuous increase in the trehalose pool in the mycorrhizal roots, probably because it was accumulated by the fungal symbiont. Furthermore, glucose and fructose were accumulated in leaves and roots of non-mycorrhizal plants but not in the mycorrhizal ones. Starch disappeared completely from the leaves of both mycorrhizal and non-mycorrhizal plants in response to drought. Activities of soluble acid invertase and trehalase were also measured. Acid invertase activity increased during drought in the leaves of both non-mycorrhizal and mycorrhizal plants whilst in the roots it was unaffected in non-mycorrhizal plants and decreased in the mycorrhizal ones. Without drought stress, trehalase activity was considerably higher in the leaves and roots of mycorrhizal plants than in those of non-mycorrhizal plants. It increased conspicuously during drought, primarily in the leaves of non-mycorrhizal plants. A drought-induced accumulation of amino acids as well as imino acids was found in roots and leaves of both mycorrhizal and non-mycorrhizal plants; leaves of mycorrhizal plants accumulated more imino acids than those of non-mycorrhizal ones. Our results show that drought stress and the presence of a mycorrhizal fungus have a considerable effect on carbon partitioning, imino acid and amino acid accumulation in maize plants.

Lincoln and Frisson varieties of endomycorrhiza-forming pea plants and isogenic mycorrhiza-resistant Frisson mutant (P2) plants were inoculated withGlomus mosseae. Nuclei released from inoculated and non-inoculated (control) roots were analysed for chromatin structure and activity using flow cytometric techniques. Chromatin accessibility to the specific DNA fluorochrome DAPI at saturating and non-saturating concentrations was measured. DNA fluorescence of nuclei of mycorrhizal Lincoln and wild genotype Frisson plants was significantly increased, compared to the controls, at saturating and, more strongly, at non-saturating DAPI concentrations. In contrast, the nuclei of inoculated P2 mutant roots showed a much lower increase in fluorescence, compared to uninoculated controls. Nuclei released from mycorrhiza-infected Lincoln roots were more sensitive to DNase I than those of uninfected ones. These results indicate a dramatic increase in that portion of the genome which can be transcribed in response to AM infection.

The aim of this study was to compare profiles of acid soluble proteins in roots of Pisum sativum L. cv. Frisson and non-mycorrhizal mutants (myc−) when infected by vesicular arbuscular mycorrhiza funghi. Quantitative and qualitative modifications were detected by native or SDS PAGE in the protein composition of acidic extracts of endomycorrhizal roots of myc+, nod+ wild type P. sativum and of a myc+, nod-mutant, as compared to uninoculated control plants or a myc−, nod− mutant, whether this was inoculated or not with Glomus mosseae. In native PAGE two proteins, already present in extracts of non-mycorrhizal pea roots, were enhanced in G. mosseae-infected myc+ plants (nod+ or nod−). One protein which appeared after inoculation with G. mosseae or G. fasciculatum in the roots of all pea plants, including the myc−, nod− mutants, may be associated with appressorium formation. Four new proteins were detected in root extracts of G. mosseae-infected myc− peas (nod+ or nod−), as compared to the myc−, nod− mutant or uninoculated controls. One of these was probably of fungal origin, since it was also found in G. mosseae-infected tobacco and leek roots. These plants showed protein modifications different to those in endomycorrhizal peas, suggesting host-specific responses. SDS PAGE revealed the presence of two polypeptides of about 25 and 35 kDa in endomycorrhizal roots of myc+ peas. None of the endomycorrhiza-related proteins detected in roots corresponded to those extracted from spores of different fungi. This study provides new evidence that different molecular modifications occur during successful (myc+ pea, leek, tobacco) and unsuccessful (myc− pea) endomycorrhiza infections, some of which are host-determined and others related to the expression of the fungal genome.

Morphological analysis, modelling and topological methods have been used to investigate the influence of a vesicular-arbuscular (VA) endomycorrhizal infection on the root system of Platanus acerifolia, a very common tree species in urban environments. Root systems of endomycorrhizal plants did not differ during the earliest growth period, but at five weeks' growth and onwards the overall effect of mycorrhiza formation was to increase lateral root frequency, giving rise to a more branched root system. During the earliest growth phase, root systems of P. acerifolia developed a herringbone pattern, which then tended towards a more dichotomous pattern in mycorrhizal plants after five weeks when infection was maximum and a mycorrhizal growth response occurred. This study shows for the first time that VA mycorrhizal infection can considerably affect root morphogenesis in a tree species.

The influence of vesicular-arbuscular (VA) endomycorrhizal infection on root morphology and architecture of a woody micropropagated plant, Vitis vinifera L., has been investigated using morphological analysis, modelling and topological methods. Endomycorrhiza formation caused increases in lateral root number and consequently total root length but did not alter the number of root axes. The rate of production of any order lateral roots was higher in mycorrhizal than non-mycorrhizal controls. The number of first- and second-order laterals increased linearly with time in mycorrhizal plants whilst in control plants both fitted a logistic function. Topological analysis indicated similar patterns of root branching in the early stages of growth, but the root system of non-mycorrhizal plants adopted a more herringbone pattern after 8 weeks, whereas that of mycorrhizal plants retained a more dichotomous pattern with repeated bifurcation. Although the root system pattern of non-mycorrhizal vines is more efficient in exploring soil, it is more expensive for the plant in terms of energy cost versus return benefit (nutrient acquisition). In contrast mycorrhizal plants develop a more economical root system which is rendered more efficient by the direct role of the mycorrhizal fungus in assisting nutrient absorption.

ABSTRACT The effects of phosphorus (P) applications combined with a Glomus species strain E 3 infection on the growth and root development in leeks ( Allium porrum L.) grown in sand culture were studied. Infected roots were more branched compared with controls at low P levels. The plants also had greater fresh weights and total root lengths, shorter and more numerous adventitious roots, as well as more secondary roots per centimetre of adventitious root. Progressive P additions did not markedly influence the level of root infection by the fungus in mycorrhizal plants and induced the same root developmental pattern in controls, leading to the disappearance of differences between mycorrhizal and control plants at higher P levels. It may be argued that, in our system, the fungal influence on root architecture is mediated by nutritional effects.