Phytohormones Hormones

Plant hormones (phytohormones) see plant growth substances. 

In plants, a plan hormone or "phytohormone" is an organa compound produced by the plant, controlling growth and other functions at sites... 

Salicylic acid at 25 pM strongly inhibited ethylene formation from ACC in cell suspension cultures, and a number of other benzoic acid derivatives suppress ethylene production at higher concentrations.44 The complex interrelationship of phenolic acids with phytohormones deserves further investigation. The early stage of seedling growth is very sensitive to phenolic acids, and this is a prime time in hormone-mediated growth responses. 

The adventitious root cultures of Datura innoxia, Duboisia hybrid M-II-8-14 (a cross-bred between D. myoporoides and D. leichhardtii), and Scopolia tangutica were established from the axenic shoot cultures or intact plants (in the case of Duboisia) on MS solid medium containing 0.1 mg/1 NAA or 1.0 mg/1 lAA. The adventitious roots were maintained in MS liquid medium containing the same phytohormones (0.1 mg/1 NAA or 0.5 mg/1 lAA) in the dark. Addition of auxin in the culture medium has been employed for the maintenance of adventitious root cultures [14], however, the adventitious roots of H. albus and H. niger were induced and maintained in hormone-free 1/2 MS medium [15]. 

Like all steroids, brassinosteroids derive from a single common precursor mevalonic acid. Some phytohormones are synthesized totally or in part via the isoprenoid pathway, such as absdsic acid, gibberellins and cytokinins. The importance of this biosynthetic pathway in processes involved with cell cycle regulation and tumorigenesis in mammals is well documented. Having in mind the similarities between certain regulatory systems in plants and animals the question arose whether brassinosteroids as putative plant steroid hormones would show a specific effect on plant tumor cells. 

Flowers of Morita navel oranges were treated with brassinolide solution at anthesis. Fruit set of trees treated with 0.1 and 0.01 ppm brassinolide increased by ca. 5 and 2.5 times respectively, when surveyed 50 days after treatment. At harvest there were no differences in quality between treated and untreated fruits. Since brassinolide-treated squash segments only showed slight changes in hormone content, brassinolide may have a direct action on stimulating fruit set without marked changes in the levels of other endogenous phytohormones. 

These variations in behavior indicate that harvesting melons at different stages of maturity causes subsequent biochemical events involved in amino acid accumulation to follow markedly different pathways. Recent work shows that melon fhiit harvested up to ten days before commercial maturity exhibits climacteric behavior with respect to ethylene production showing that at least this aspect of ripening is not completely inhibited by premature separation from the plant(P). However, the amount of ethylene produced is dependent on maturity at harvest and fruit harvested five days prematurely generated only about half of the amount of ethylene produced by fruit harvested two days before maturity. Also the lag time required to initiate ethylene production after harvest depended on maturity and was longer for prematurely harvested fruit. Changes in the content of the phytohormone abscisic acid were also correlated with that of ethylene. However whether the different maturity related metabolic responses observed above result from the action of these or other plant hormones awaits further study. 

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