Allelochemicals, terpenoids

Experiment 2. Effects of terpenoid allelochemicals on pollen germination The effects of the terpenoids found in many allelopathically active plants are dependent on the concentration of the active matter (Fig. 4). Linalool, cymol, citral, gaillardine and austricine excreted by many flowers, stimulated the pollen germination upto 10 7-1()" M concentrations and depress in higher ones. Rodriguez et.al (1976) described the biological effects of some sesquiterpene lactones, which are allelochemicals. 

Victoria Roshchina s group elucidated and identified the mechanisms of pollen allelochemicals. At this stage, it remains to be tested whether terpenoid allelochemicals require pollen rehydration and exudation, which would make them likely to occur in trinucleate pollen and then function by binding on plasmalemma and perhaps are then transformed in a growing heterospecific pollen tube into free radicals that affect membranes or key enzymes. 

Terpenoids are the most diverse class of organic compounds in plants and the largest group of allelochemicals. The word is derived from terpentin ... 

Higher plants produce a great variety of terpenoids (78) but only a few of these have been implicated in allelopathy. The monoterpenoids are the major components of essential oils of plants and they are the predominant terpenoid inhibitors that have been identified from higher plants. Many fungi (82) and algae (83) produce terpenoid allelochemicals also. 

Terpenoids are one of the many classes of allelochemicals known to play an important role in such Interactions (13). Of particular interest are the diterpenoids. These are widely distributed in plants, and are also present in fungi and marine organisms, and as such provide a ready source for the isolation of new compounds (13-15). 

There are a number of allelochemicals among the mono-, sesqui-, and diterpenoids. In particular, plants in arid and semiarid regions produce diverse volatile terpenoids with allelopathic activity.5 Among the volatile monoterpenes, 1,8-cineole (4) and camphor (5) exhibit strong growth inhibitory effects on plants and are considered to be involved in plant competition. 1,4-Cineole (6), a minor isomer of 1,8-cineole, is a potent inhibitor of asparagine synthetase.6 -Menthane-3,8-diols (fir 7 and frw .r8), -menth-2-en-l-ols (cis 9 and trans 10), thymol (11), carvacrol (12), 1,8-cineole, cr-pinene (13), and /3-pinene (14) were isolated as allelopathic monoterpenes from Eucalyptus species.7 Eucalyptus trees also produce allelopathic sesquiterpenes including spathulenol (15), and a-, (3-, and 7-eudesmols (16-18).7... 

Hydrolases are also induced by xenobiotics in insects, but to a lesser extent, by juvenile hormone, juvenoids, triazine herbicides (e.g., atrazine and ametryn), and allelochemicals (e.g., terpenoids, indoles, and flavonoids) (Yu and Hsu, 1985 Yu, 2004). 

The exact identity of allelochemics in BPH-resistant varieties is not yet known. However, a large group of low molecular weight compounds, such as essential oils, particularly terpenoids, alcohols, aldehydes, fatty acids, esters, waxes, etc., would be obtained by steam distillation (34, 35). Obata et al. (32) have identified a... 

The volatility of the lower terpenoids makes them particularly suitable for signaling between living organisms, as they can be carried through the air from the donor to the recipient of the signal. Such materials (semiochemicals) can carry messages between organisms of the same species (pheromones) or of different species (allelochemic als). 

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