I've been experimenting with yeast/algae/fungi inoculants for a number years and have had some very good results .. Here is a small article i wrote to summarize some of the advantages of supplementation and the mutalistic/symbiotic activities of yeast in plants. There are various techniques that one may apply to cultivate reliable and prolific yeasts and algae that you simply wont find in a bottle. I will document these shortly.. It is also a very cost effective strategy and is good for the environment since is reduces the amount of additives required in the soil. In recent years active yeasts have also been shown to have some very important applications in hormone manipulation for prolonging blooming periods and slowing maturity to increase production.
Introduction - Abscisic acid (ABA)
Abscisic acid (ABA), also known as abscisin II or 'dormin' is a plant signalling hormone responsible for many plant developmental processes, including transpiration and bud maturation. ABA was originally believed to be involved exclusively in leaf abscission but it has been shown by Bastawisy, M. H and Sorial (1998) not to be the case.
In the natural setting, plants preparing for the fall, following a growing season produce high quantities of ABA in their terminal buds. This slows plant growth until a state of dormancy or suspended animation is reached. This induces abscission and directs leaf primordia to develop thickening of vascular tissues to protect the seeded buds during the winter season.
ABA degradation - Role of yeast in oxidoreductase bio-sythesis
ABA is degraded by the oxidoreductase enzyme (+)-abscisic acid 8'-hydroxylase produced by plants to inhibit the activity of abscisic acid at the termini of immature flowering tops. This induces periods of rapid blooming following the onset of pre-flowers and limits ethylene production. As the growing season draws to a close and floral density reaches a Plateau (full bloom), oxidoreductase levels plummet with a rapid decline and thereby raising levels of ABA activity and ethylene production - initiating the maturation process.
Oxidoreductases are also produced in abundance by various marine algae, pathogenic fungi and yeast cells. With regards to phenotypes supplemented with, or producing-directly an abundance of oxidoreductase enzymes, periods of prolonged blooming are clearly observed (Abd-El-Dayem and El –Deeb 2000). Flower development in these phenotypes is often accelerated and significantly more productive. Conversely, those phenotypes that display a sensitivity to ABA are often found to dramatically under-perform, and have poor stomatal regulation.
The application of active yeasts to induce ABA inhibition can be used suitably in the agricultural setting to prolong or sustain the development of crops to significantly improve commercial yields. By selective inoculation of early maturing crops with active yeasts and yeast extracts in the early stages of flowering, bloom times can be extended considerably .
Recent findings (Davis and Zhang, 1991/1998) suggest that the increased productivity and quality of yeilds may be related to the coupling of elevated levels of growth promoters (auxin/cytokinins) and ABA inhibition and the colony's ability to fix nitrogen as well as to dramatically increase the rhizome surface area enhancing the levels micronutrient (not P and K though..) absorption. Others studies provide similar findings (Marchner, 1995 and Nakhlla 1998)... They concluded that B-vitamins, Zn as well as an abundant cytokinin source is required for oxidoreductase bio-synthesis. These results indicate that the shoots characteristics were significantly improved by both bacterial and yeast culture inoculation or both in combination.
Azotobacter bacteria has the ability to release some chemical compounds that stimulate growth hormones like cytokinins, indoleacetic acid and gibberellins (Marha et al., 2000) and release siderophores compounds that serve as chelating agents for various minerals and cations that increase the availability of these elements in soil (Marin et al., 2001).
The advantages attributed to the application of yeast inoculants on enhancing vegetative and floral characteristics might be due to the direct or indirect effect of it's ability to change the environment of the root system to form a fine network of polysaccharide that behaves symbiotically with the rhizome, or because the development of the yeast after its saturation with groups of amino acids and vitamins. For example, Subba and Rao (1984) discuss that yeast induces the absorption of nutrient elements by buffering/stabilizing the soil pH near neutral. Ahmed et al. (1995) and Glick (1995) report that the yeast is capable of increasing the stimulative growth compounds like gibberellins, auxins and cytokinins that act in improving plant cell division and growth.
Furthermore, active yeast and yeast extracts are suggested to participate in the role of sugar accumulation in soils during vegetative and reproductive stages of development improving soil fertility (Barnett et al, 1990). Yeast is also an abundant source of cryoprotective agents, sugars and amino acids (Shady, 1978 and Mahmoued, 2001).
References and further reading
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