Trichomes concentration

The action spectmm of positive and negative phototaxis of Anabaena variabilis was measured recently106). This species contains no C-phycoerythrin. Accordingly, maximum activity is found at around 615 nm (Fig. 7). In addition, in this form a second maximum occurs at around 675 nm, and a third small, but distinct, one at 440 nm, both indicating that chlorophyll a is also involved in the active light absorption (see above). The utilization via photosynthesis, however, could be excluded in this case, since the trichomes oriented themselves perfectly well to the light direction in the presence of photosynthetic inhibitors, such as DCMU and DBMIB, at concentrations in which the photosynthetic oxygen evolution was almost completely inhibited. 

It is clear from the above discussion that if we do not know about the localization of defense substances in specialized tissues like latex and glandular trichomes, adopt extraction methods disregarding the localization, and rely on average concentration, we may underestimate or may even overlook the biological effects and the existence of defense substances in defense tissues. On the contrary, the plant substances found in such defense-specialized tissues are very likely to have roles as defense substances. 

Therefore, it may be possible to increase the resistance of cultivated sunflower to Hj. electellum by breeding for increased concentrations of sesquiterpene lactone-containing glandular trichomes on the anther tips. The development of new cultivated lines with high densities of glandular trichomes may prove to be an... 

In contrast, Moutin et al. (2005) reported that natural populations of Trichodesmium, mostly as free trichomes, in the SW Pacific, had relatively high affinity for phosphate, with a Ks of 630 nM and a V ax of about 0.31 h (Table 4.2). They stated that these are the first accurate determinations of these parameters at environmentally relevant concentrations. They further asserted that the high Ks values presented in the text of McCarthy and Carpenter (1979) were due to a calculation which used an incorrect value for the colony specific rate of 1.2 pmol colony" h and which Moutin et al. (2005) state should have been 1.2 nmoR colony h This would result in values more in line with their observations. However, McCarthy (personal communication to DGC) stated that the original calculation and values given in the text of McCarthy and Carpenter (1979) are correct but that Fig. 4.4 in McCarthy and Carpenter (1979) had an incorrectly labeled y axis. 

Feverfew. Tanacetum parthenium (L.) Schultz Bip. is an herb that was used in antiquity to reduce fever and pain. The literature is replete with anecdotal evidence of the usefulness uf the herb, and recent clinical studies have added more support. Feverfew is a member of the aster/dai.sy family. The plant tissues have a pungent smell and very bitter taste. The medicinal principle of feverfew is concentrated in hairy trichomes on the chiysanthemum-like leaves.The plant displays clusters uf daisy-like flowers with yellow centers and radiating white florets. Recent uses uf feverfew are for migraine and arthritis, although the indication for arthritis is disputable. The anecdotal evidence that an herb could successfully treat a condition such as migraine headache naturally begged for some seientifle proof. 

B-caryophyllene, a major component of S. berthaultii trichomes and of S. tuberosum foliage. This effect of B-caryophyllene raises doubts about the claim of Gibson and Pickett (21) that E-B-farnesene of S. berthaultii trichomes is an important factor in resistance to aphids, because we found that trichomes of accessions studied by Gibson and Pickett (21) contain high concentrations of B-caryophyllene (22). 

Some very interesting results have been obtained by Henderson et al who have used micro-analytical techniques in conjunction with electron- and photomicroscopy to determine the sites of sesquiterpene accumulation in Pogostemon cablin (rich in guaiane-type sesquiterpene hydrocarbons). The results of this study indicate that there are specific sites of accumulation especially associated with the glandular trichomes of the second pair of primordial leaves, where the concentration of sesquiterpenes is twelve-fold relative to other parts of the plant. 

Many types of tobacco contain radioactive elements such as Ra and °Po at concentrations ranging from 0.1 to 0.47 pCi/g (1742, 2815, 3982, 3983). Phosphate fertilizers are the major source of these radioelements (3982, 3983) minor contributions come from airborne particles carrying °Pb and °Po. These particles are trapped by the trichomes on the undersides of the tobacco leaves (2467) and were first reported by Nystrom and Beilin (2815) in 1964. 

Browning and hardening of exudate on the insect s mouthparts and tarsi is due to the enzymatic activity of an O2- requiring oxidase (12), and has been associated with both peroxidase and polyphenol oxidase activities (2/14-fl2.). We recently showed that these enzymatic activities are due to a 59 kD polyphenol oxidase (PPO) which is present in the type A trichomes of S. berthaultii at approximately 1 ng/trichome head (a concentration of approximately 0.3 mM) (lA). The specialization of the glandular trichome is reflected in the fact that PPO comprises approximately 60% of the total soluble protein of the organ. 

Trichome PPO appears to be an example of an evolutionary modification of an existing plant enzyme for use as an insect defense mechanism. PPO enzymes, of molecular weight 45,000, are localized in the thylakoid and are nearly ubiquitous in tissues of plants (12,18.). Unlike other known nuclear encoded chloroplast proteins, the 45 kD thylakoid PPO, whose function is unknown, is translated at its mature size of 45 kD, and does not possess a transit peptide sequence (19). In contrast, the 5 9 kD trichome PPO is translated as a 67 kD precursor and localized in the leucoplasts of trichome and outer epidermal cells. Immunological and primary sequence similarities between the 59 kD trichome PPO and the 45 kD thylakoid PPO underscore the close evolutionary relationship between these two proteins. The apparent advantage of the very high concentration of PPO in the trichome is the high initial rate of catalysis which results upon trichome rupture, facilitating the entrapment of mobile insects. 

The negative tritrophic level effects associated with PI 134417 foliage are likely to be extreme relative to those associated with other plant defenses, because of the high acute toxicity of 2-tridecanone and 2 undecanone and their presence at biologically active concentrations in the tips of glandular trichomes on the leaf surfaces. Despite this, the tritrophic level interactions associated with PI 134417 provide some appreciation for the diversity and complexity of ecological effects of even relatively simple plant defenses. 

Fery, R, L. and G. G. Kennedy. 1987. Genetic analysis of 2-tridecanone concentration, leaf trichome characteristics, and tobacco hornworm resistance in tomato. J. Amer. Soc. Hort. Sci. 112 886-891. 

The external tissues of plants are usually the first to come into contact with herbivores. It is therefore not surprising that toxic secondary products are present in relatively high concentrations in these tissues, e.g., in the bark and in trichomes at the surface of leaves, stem etc. 

Secretion and accumulation of volatiles in specialized anatomical structures. These lead to higher concentrations of the essential oil in the plant. Such anatomical storage structures for essential oils can be secretory idioblasts (secretory cells), cavities/ducts, or glandular trichomes (Fahn, 1979, 1988 colorfully documented by Svoboda et al. [2000]). 

Terpenoids can be found in various plant organs. Concentrations of terpenoids in plant tissues are controlled by the availability of substrate and the activity and type of biosynthesis enzymes. Emission rates of volatile terpenoids from plant leaves are controlled by their synthesis rates and compound-specific physicochemical characteristics, mainly their solubility, volatility and diffusivity. These are affected by physicochemical constraints caused by temperature, stomatal conductance and leaf structure. Storage of terpenoids could be isolated from other plant tissues with specialized structures such as secretory cavities, resin canals (Fig. 94.1), latex canals (lactifers), and glandular trichomes. 

The phytochemical diversity of C. saliva is well illustrated by more than 500 com-potmds isolated from this plant, encompassing all major classes of phytochemicals (polyketides, terpenoids, alkaloids, flavonoids, stilbenoids, oxylipins). Undoubtedly, the most important and peculiar secondary metabolites of C. saliva are cannabinoids, a class of mono- to tetracyclic C21 (or C22) meroterpenoids encompassing more than 100 members. These compounds are synthesized in secretory cells of glandular trichomes, most concentrated in unfertilized female cannabis flowers prior to senescence. A number of detailed accounts on the cannabinoid chemistry have been reported in the literature [6-8], also recently by Appendino et al. [9]. In this paragraph, we will provide an updated, although not comprehensive, account of the chemistry of this fascinating class of secondary metabolites. 

A blue-green alga Phormidium was used by Noll and Bauer (1973) to detect a range of 22 herbicides including triazines, phenylureas, carbamates, dipyridylium derivatives, naphthoquinones, and phenoxy-carboxylic acid herbicides. They observed trichome migration to be markedly affected by most herbicides, and concentrations as low as 0.3 to 15.0 ppm could be detected in as httle as three hr. 

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