Plant Growth Substances Produced by Micro‐organisms of Soil and Rhizosphere

Abstract

Summary: Micro‐organisms isolated from rhizospheres and rhizoplanes of wheat plants, and from root‐free soil, produced growth regulating substances with the properties of gibberellins and indolyl‐3‐acetic acid (IAA). Substances inhibiting extensions of pea plant internodes and lettuce hypocotyls were also produced, especially by bacteria from the root region of seedlings 6 days old. Bacteria producing growth promoting substances were most abundant on roots of older plants. Seedlings grown aseptically with added gibberellic acid (GA3) and IAA, or grown with a soil inoculum, developed similarly and differed in their morphology from those grown aseptically without additives.

Growth Enhancement and Developmental Modifications of in Vitro Grown Potato (Solanum tuberosum spp. tuberosum) as Affected by a Nonfluorescent Pseudomonas sp.

“…Hormone production, primarily cytokinin and IAA, has been demonstrated in extracts ofculture media ofnumerous PGPR (6,9,14,23). In experiments to ascertain how different concentrations of these two hormones affect development of bacterized and control axillary buds, we noted statistically significant alterations due to hormone and bacterial treatments, as well as interactions between them (our unpublished observations).…”

“…Our approach for studying growth promotion is to produce nonpromoting mutants (isogenic to the parental strain) by Tn5 transposon mutagenesis. This course of action has been suggested by a number of investigators (3,6,7). We have now obtained five mutant strains with altered growth promoting capabilities and are in the process of characterizing the DNA regions responsible for encoding growth stimulation.…”

“…contrast, there are numerous reports describing strains fluorescent Pseudomonas sp. with this characteristic (2,6,9,10,19,20,23 (17) and is a mechanism ro of disease resistance (30). Pathological symptoms, however, (11), poor epicuticular and cuticular wax formation (11), reduced trichome number, altered trichome and stomatal distribution (13), and other foliar anatomical defects (13,18).…”

“…The mechanisms involved in growth stimulation by these PGPR3 have not been fully explained. In the genus Pseudomonas, site competition (2,7,10), increased phosphate uptake (19), synthesis of plant growth promoting substances (6,14), and antagonisms through production of antibiotics and siderophores (7,9) have been shown to be involved. In most 'This study was partially supported by grants from the National Science and Engineering Research Council of Canada (STRIN039) and the Ontario Ministry of Agriculture and Food.…”

Microbial-faunal interactions in the rhizosphere and effects on plant growth

“…Thus, there is increasing evidence that microbial grazers, particularly protozoa, are able to alter the composition and the functioning of the rhizosphere microbial community ( figure 3). Roots support a community of bacteria in which some populations are able to produce trace amounts of growth regulators which can markedly affect plant growth either positively or negatively [12,13,86]. Hence, grazing by protozoa may alter the composition of the rhizosphere microflora from unfavourable micro-organisms towards a plant growth-promoting rhizosphere community [15].…”