AOBPreview originally published online on September 4, 2002
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Annals of Botany 90: 453-460, 2002
© 2002 Annals of Botany Company
UV-B is Required for Normal Development of Oil Glands in Ocimum basilicum L. (Sweet Basil)
1 Department of Natural Products and Biotechnology, Mediterranean Agronomic Institute of Chania, PO Box 85, Alsyllion Agrokepion, 73100 Chania, Greece and 2 Department of Botany, The University of Reading, Whiteknights PO Box 221, Reading RG6 6AS, UK
* For correspondence. Department of Natural Products and Biotechnology, Mediterranean Agronomic Institute of Chania, PO Box 85, Alsyllion Agrokepion, 73100 Chania, Greece. E-mail cjohnson{at}maich.gr
Received: 22 March 2002; Returned for revision: 27 May 2002; Accepted: 19 June 2002 Published electronically: 4 September 2002
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Plants of Ocimum basilicum L. grown under glass were exposed to short treatments with supplementary UV-B. The effect of UV-B on volatile essential oil content was analysed and compared with morphological effects on the peltate and capitate glandular trichomes. In the absence of UV-B, both peltate and capitate glands were incompletely developed in both mature and developing leaves, the oil sacs being wrinkled and only partially filled. UV-B was found to have two main effects on the glandular trichomes. During the first 4 d of treatment, both peltate and capitate glands filled and their morphology reflected their ‘normal’ mature development as reported in the literature. During the following days there was a large increase in the number of broken oil sacs among the peltate glands as the mature glands broke open, releasing volatiles. Neither the number of glands nor the qualitative or quantitative composition of the volatiles was affected by UV-B. There seems to be a requirement for UV-B for the filling of the glandular trichomes of basil.
Key words: Ocimum basilicum L., sweet basil, glandular trichomes, UV-B, morphology, terpenes, essential oil.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
The many species of the genus Ocimum are characterized by their rich essential oil content. Commercially, the most significant of the genus is O. basilicum, sweet basil, a major herb and essential oil crop. Numerous different chemotypes exist in both wild and cultivated basil (Lawrence, 1988; Grayer et al., 1996; Lachowicz et al., 1997). Such is the variety of commercially exploited chemotypes (or chemocultivars) that no single compound can be said to provide the ‘characteristic’ basil aroma and taste. As well as terpenoids, many cultivars contain significant amounts of one or more phenyl-propanoids (usually eugenol, chavicol, methyl eugenol, methyl chavicol, methyl cinnamate), but varieties almost lacking phenyl-propanoids are also common. These are usually linalool-rich. The other major terpenoid constituent sometimes found is 1,8-cineole.
Interest in the effects of UV-B on plants has increased considerably in recent years as evidence for ozone depletion continues to accumulate (Houghton et al., 2001). UV-A (320–400 nm) is present in significant amounts in natural daylight and is relatively little affected by changes in the ozone layer. UV-C (200–280 nm) is extremely active photochemically and biologically lethal, but it is completely excluded by the ozone layer. It is the UV-B region (280–320 nm) that is the part of ultraviolet radiation which is not only biologically active, but also most vulnerable to significant changes resulting from differences in the extent of blocking by the ozone layer. For this reason, levels of UV-B perceived by plants are strongly dependent on latitude and hours of direct sunlight, as well as any changes that may occur in the thickness of the ozone layer. Plants that grow in Mediterranean and tropical environments, as well as those adapted to high altitudes, have developed a number of mechanisms to protect themselves from UV-B. Amongst these, there is now a substantial body of evidence indicating significant effects of UV-B on secondary compounds of the phenyl-propanoid pathway and the enzymes responsible for their synthesis (Cuadra et al., 1997; Olsson et al., 1999; Burchard et al., 2000; Tattini et al., 2000; Bieza and Lois, 2001; Liakoura et al., 2001), and there is good evidence that these compounds can act as sun-screens, providing protection against UV radiation (Mazza et al., 2000; Bieza and Lois, 2001; Kolb et al., 2001).
Monoterpenes may also play a role in UV-protection (Bosabalidis and Skoula, 1998) and recently there have been several reports of UV-B promotion of terpenoid production in aromatic plants, particularly members of the Labiatae. Many of these plants have their centres of origin in the Mediterranean, North Africa or Asia and their normal environments are characterized by high levels of UV-B. Significant induction of both terpenoids and phenyl-propanoids have been demonstrated in basil (Johnson et al., 1999; Raki
and Johnson, 2001), and positive effects of UV-B have also been reported in Mentha (Karousou et al., 1998; Maffei and Scannerini, 2000). In the case of aromatic plants, the possible involvement of UV-B in volatile production is also significant in relation to the increasing production of fresh herbs to meet market demand for such products. Much of this production is carried out under glass or plastic and therefore almost entirely in the absence of natural levels of UV-B. Many of the herbs produced in this way lack the aroma of the naturally grown herbs and, in the case of O. basilicum, the lack of UV-B appears to be the main cause of this.
The volatiles produced in Ocimum are synthesized in specialized oil glands and this paper examines the morphological events that occur as UV-B stimulation of volatiles is occurring in the glands. Experiments were carried out using a commercial linalool-rich cultivar largely lacking phenyl-propanoids in the essential oil.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Plant material and radiation source
Plants of Ocimum basilicum L. (seeds from Franchi Sementi S. P. A. Bergamo Italy, lot 163/XS) were grown in a mixture of compost (Levington Compost B2) and perlite (3 : 2) under glasshouse conditions at the Mediterranean Agro nomic Institute of Chania (MAICh) in January 2001 and at the University of Reading (UK) in June 2001. Plants were exposed to UV-B radiation for 1 h before dawn each day for up to 15 d. Radiation was supplied by two UV-B fluorescent Philips 20 W/12 tubes, placed 1 m apart and 1 m above the bench. The dose in the spectral region from 290–300 nm was calculated, from a comparison of spectral measurements of the emission of the lamps with daylight, to be approximately equivalent to a normal daily dose on a summer’s day in the Mediterranean.
Head space gas chromatography and mass spectrometer analysis
After treatments, leaves were collected, separated according to size into developing (1–5 cm long) or mature leaves (more than 5 cm long), and dried to constant weight at room temperature. One hundred milligrams of dried material was randomly selected and placed in a 20 ml glass vial for headspace GC analysis. A Hewlett Packard 5890 II gas chromatograph with coupled headspace analyser and equipped with flame ionization detector was used for the analysis. Each sample was retained in the headspace oven for 30 min at 90 °C, extracted with a carrier gas (He) at 38 cm s–1 and finally retained in the loop at 100 °C for 1 min before transfer to the GC at 100 °C. The column used was a DB5 (30 m long and 0·25 mm in diameter) and the split ratio was 1 : 50. The temperatures of the injector and detector were 230 and 260 °C, respectively. The initial oven temperature was 45 °C, increasing at 1·5 °C min–1 until 150 °C, then at 40 °C min–1 until 220 °C, being held at this temperature for the last 10 min.
For gas chromatography analysis, 0·25 ml of essential oil from the distillation of 80 mg of dried plant material was analysed in a GC/MS (HP8980 II GC coupled to a VGTRIO 2000 mass spectrometer with MASS LYNX software) to identify the different compounds, comparing their retention times with those of known standards. Mass spectra were taken at 70 eV, and the scanning speed was 1 scan s–1 from 40 to 230 m/z. Peaks of the different compounds were identified by considering their retention time and by comparison with mass spectra in two libraries (Wiley and Adams).
Anatomical study
For the anatomical study, upper and lower surfaces of developing and mature (as defined above) basil leaves were prepared for observation in the scanning electron microscope (SEM). After a preliminary examination of both confirmed generally similar gland morphology, upper (adaxial) surfaces were selected for further examination. Daily sampling took place during the 15 d of UV-B irradiation. Leaves were cut into approx. 5 mm squares, placed in 20 ml glass vials and fixed in 2 % glutaraldehyde in 0·1 M potassium phosphate buffer (pH 7) for 3 h at room temperature. The samples were dried in an Emitech K850 critical point drier. They were mounted on aluminium re-entrant stubs using double-sided adhesive tape, and gold coated (approx. 40 nm) in an Emscope SC500 sputter coater. SEM images were obtained using an LEO 1450 variable pressure scanning electron microscope. The SEM operated at 8·32 kV, with a spot size of 261 and a beam current of 60 µA. The collector bias was 300 V and the aperture used was 30 µm.
The numbers of both peltate and capitate glands were recorded and their size measured in at least ten images per sample, with 12 samples per treatment.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Essential oil composition
Forty-one compounds, accounting for more than 99 % of the total volatiles in most samples, were detected and identified. The average contents of the major constituents (accounting for approx. 90 % of the total) of developing and mature leaves, with or without UV-B treatment, are shown in Table 1. There were only small, largely insignificant, differences in the composition as affected by either leaf age or light treatment. The predominant compounds present were the monoterpenes linalool (approx. 50 %) and 1,8-cineole (approx. 22 %). Eugenol was the only phenyl-propanoid present in significant amounts (approx. 0·5 %).
|
Essential oil content
Essential oil content was very much dependent on the leaves examined, being strongly affected by leaf age and by UV-B treatment. The amount was much greater in developing leaves, and UV-B treatment led to an increased content in both developing and mature leaves, but this was more significant in mature leaves in which the volatile content more than doubled as a result of UV-B treatment (Table 2). Experiments carried out under the very different climatic conditions of the UK and Greece (especially concerning day length) yielded similar results.
|
Effects of leaf age on oil glands
Mature leaves contained far fewer glands per unit surface area than developing leaves (Fig. 1). Also noteworthy was the fact that the difference in gland number was much greater for the smaller capitate glands (nearly six-fold more in developing leaves) than for the larger peltate glands (less than two-fold) (Table 3). The difference in total oil content between developing and mature leaves per gram dry weight was 8·7 times in UV-B-treated plants and 4·4 times in control plants indicating that, as might have been expected, the amount of oil produced was strongly correlated with the number of glands present. It also suggests that the contribution of the capitate glands to the total amount of essential oil must have been rather more than their much smaller size warranted.
|
|
Effects of UV-B on oil glands
Peltate glands in basil plants growing without supplementary UV-B were characterized by the presence of only partially filled oil sacs: in both developing and mature leaves the membranes could be seen to be wrinkled and creased along the fissures between the apices of the secretory cells. Figure 2A and F, illustrating developing and mature leaves, respectively, is typical of 100s observed during the course of this investigation. By the second or third day of UV-B treatment (1 h each day, before dawn), the sac membranes had become distended and smooth. The response appeared to be more rapid in developing leaves (Fig. 2B–E), but more marked in mature leaves, in which the creasing was lost altogether (Fig. 2G–J). After the fourth or fifth day of the 15 d treatment no further differences were observed; glands are not shown here after the seventh day.
|
There was no significant effect of UV-B treatment on the number of glands, as might have been expected given the shortness of the experimental treatment period (Table 3). Estimates of the volumes of the oil sacs from the diameters observed under the SEM (Table 4) underestimate the difference between the volumes of control and UV-treated plants because of the very indented structures in the former. Even so, the calculated volume was 35 % greater in mature leaves of UV-treated plants and 20 % greater in developing leaves than in their corresponding controls. In comparison, in developing leaves this difference in volume was quite similar to the effect of UV-B on oil content (approx. 17 %) but the much larger increase in oil content of UV-B-treated mature leaves (approx. 135 %) was much greater than the apparent increase in volume of the peltate glands.
|
There was also a clear effect of UV-B on the size and shape of capitate glands. In UV-B-treated plants they appeared to be spherical and taut (Fig. 3A and B), like peltate glands, but in the absence of UV they appeared to be wrinkled and not fully expanded (Fig. 3C and D). The non UV-treated capitate glands of mature leaves were particularly affected and were typically very shrivelled (Fig. 3D), but even in these glands this effect could apparently be overcome by UV-B treatment since very few of the UV-treated glands had this appearance. Mature leaves also appeared to contain a significant number of just visible, presumably partially ‘degraded’ glands, which may explain the large reduction in the number of capitate glands in mature leaves. These were found in UV-treated and untreated plants alike (Fig. 3E–G).
|
UV-B and broken oil sacs
One of the immediately obvious consequences of UV-B treatment was a strong increase in the fragrance of the plants, obvious even before measurements were made. Indeed, subjectively, the difference in odour seemed to be rather more than was accounted for by the measured volatile content. Since the evidence clearly shows that the glands were much fuller under UV, the possibility was examined that part of the increase in odour was due to the rupture of glands, leading to release of volatiles into the air. Inspection of a large number of leaf samples in the SEM for broken oil sacs did indeed reveal a significantly increased number in UV-B-treated plants (Fig. 4). From an initial rate of about 17 %, the number rose to around 40–45 %. The increase was more noticeable after the fourth day and thus seemed to occur following the phase of increase in volume of the gland cells, an increase that was virtually complete after 4 d. The significant contribution to the odour of the plants caused by disruption of the gland sacs was, of course, lost before GC analysis of the material, leading to an underestimate of the effect of UV-B. It cannot be excluded that some of the glands do not break open naturally: increased susceptibility to mild abrasion of the UV-B-treated plants compared with control plants might also have led to a UV-B-mediated increase in breakage during preparation for microscopy.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Effect of UV-B on oil content and composition
It has previously been shown that short daily treatments with supplementary UV-B lead to a substantial induction (up to three-fold) of essential oils in developing plants of a eugenol variety of sweet basil grown in UV-B-deficient conditions in a glasshouse (Johnson et al., 1999). Maffei and Scannerini (2000) have also reported a small positive effect of UV-B on essential oil content in Mentha piperita, grown in controlled environments (i.e. lacking UV-B). Both of these reports indicate changes not only in total content, but also in quantitative (but not qualitative) composition. Interestingly, an enhancing effect of UV-B has also been obtained (over a much longer growing period) in Mentha spicata for plants growing in natural conditions in a Mediterranean climate: apparently, even under these conditions, supplementary UV-B (given for an entire season) can lead to enhanced levels of volatiles in the plants, but in this case with no significant effects on volatile composition (Karousou et al., 1998). Only one of two chemotypes investigated showed a significant response. In basil, too, previous work (Rakiæ and Johnson, 2001) has shown that different varieties respond to UV-B to markedly different extents. The results obtained here with mature plants of a linalool chemotype of basil confirm a strong positive effect of UV-B on volatile content, but show very little, if any, effect on volatile composition.
In the present investigation, quantitative measurements were made on the larger peltate glands. It was clearly seen that these glands first filled, then burst (or became vulnerable to breaking) in response to added UV-B. Gang et al. (2001) reported that the creased and wrinkled folds of the peltate glands, observed here in the absence of UV-B, are characteristic of immature developing glands, which normally become expanded on maturity. Thus, it seems that UV-B is required for the development of these glands to maturity in Ocimum basilicum, even in fully developed leaves, and at least part of the UV-B-mediated increase in oil content accompanies this developmental change. The data shown here demonstrate two temporally separated phases of UV-B response. The first, the filling of the glands, seems to be part of the normal development of the glands described by Gang et al. (2001), which does not occur in the unnatural absence of UV-B. The second phase, the ‘excess’ filling that leads to an increased propensity of the glands for bursting may be a defence response of the plant to excess UV-B. The daily doses of UV-B applied here correspond approximately to those of Mediterranean summer days and so would be experienced by unshaded ‘stressed’ plants in such an environment. It is possible that this release of volatiles under high UV-B conditions contributes to the formation of a ‘shield’ preventing penetration of UV to the upper leaf surfaces of the plant, as suggested by Bosabalidis and Skoula (1998).
The capitate glands are too small and irregular in shape for equivalent measurements to be reliable. Nevertheless, SEM photographs (Fig. 3) clearly indicate that these, like the peltate glands, are also far from full in the UV-depleted plants but become expanded in response to UV-B. This in turn suggests that capitate glands may also require UV-B to complete their full development and also that they, too, may contribute to the total oil produced.
Capitate and peltate glands
To what extent do capitate glands contribute to volatile oil production? Werker et al. (1993) reported that both peltate and capitate glands of Ocimum basilicum were stained with Sudan IV and Ruthenium Red, indicating that they contained both lipophilic and polysaccharidic substances. In later work, Gang et al. (2001) showed that only the peltate glands and not the capitate glands contained the enzymes coding for the phenyl-propanoid components of the basil essential oil (in a eugenol chemotype). They did not, however, examine the enzymes of terpenoid metabolism and were able to extract volatiles directly only from individual peltate glands; extraction from the capitate glands was not technically feasible. Although indirect, evidence from the present experiments suggests that the capitate glands contribute significantly to the essential oil content. The five- to eight-fold reduction in content of mature compared with developing leaves is not readily correlated with the less than 2·5-fold decrease in the number of peltate glands per unit area (of similar size in mature and developing leaves). However, it would be much more readily explicable in terms of the five-fold decrease in the number of capitate glands, assuming that these contribute significantly to the total oil content. Furthermore the obvious ‘filling’ of the capitate glands after UV-B treatment is suggestive of an active role for these glands. The lack of a role for the capitate glands in phenyl-propanoid production (Gang et al., 2001) does not necessarily indicate that the same holds for terpenoids. Indeed it has been shown (Bisio et al., 1999) that in Salvia blepharophylla only the peltate glands contain phenyl-propanoids, but both peltate and capitate glands contain terpenes. The variety of basil used in this investigation was of a chemotype that does not contain significant concentrations of phenyl-propanoids, but it is worth noting that in previous investigations of a eugenol-chemotype, the effects of UV-B were quantitatively different for the phenyl-propanoids compared with the terpenoids (Johnson et al., 1999; Raki and Johnson, 2001). In any event, the lack of effect of UV-B or age on the composition of volatiles and, in particular, the negligible differences between the composition of mature and developing leaves, suggest that if the capitate glands do contribute to the total volatiles of basil, their terpenoid composition must be quite similar to that of the peltate glands.
Considerations for horticultural practice
The effects of UV-B reported here have significant implications for production of basil plants under glass or plastic. Treatment of such plants with supplementary UV-B for 3 or 4 d would result in increased essential oil in the glands. Further increases in treatment dose, leading to bursting of some glands, would have the further effect of increasing the aroma of the plants, an effect obvious even to the untrained observer, and which would perhaps increase the attractiveness of the plants to consumers.
Clearly, the role and composition of the oil sacs of the capitate glands in basil warrant further investigation, including a comparison with different chemotypes of basil, and studies on the extent of filling of the glands under a range of different seasonal and environmental conditions. Similarly, the effects of UV-B demonstrated here on both capitate and peltate glands of basil plants need to be examined in other aromatic species.
|
ACKNOWLEDGEMENTS |
|---|
We thank Melpo Skoula and John Barnett for helpful discussions, George Naxakis for assistance with mass spectroscopy and the European Union for financial support to D.I. via the SOCRATES–ERASMUS programme.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
-
Bieza K, Lois R. 2001. An Arabidopsis mutant tolerant to lethal ultraviolet-B levels shows constitutively elevated accumulation of flavonoids and other phenolics. Plant Physiology 126: 1105–1115.
Bisio A, Corallo A, Gastaldo P, Romussi G, Ciarallo G, Fontana N, De Tommasi N, Profumo P. 1999. Glandular hairs and secreted material in Salvia blepharophylla Brandegee ex Epling grown in Italy. Annals of Botany 83: 441–452.
Bosabalidis AM, Skoula M. 1998. A comparative study of the glandular trichomes on the upper and lower leaf surfaces of Origanum x intercedens Rech. Journal of Essential Oil Research 10: 277–286.
Burchard P, Bilger W, Weissenbock G. 2000. Contribution of hydroxycinnamates and flavonoids to epidermal shielding of UV-A and UV-B radiation in developing rye primary leaves as assessed by ultraviolet-induced chlorophyll fluorescence measurements. Plant, Cell and Environment 23: 1373–1380.[CrossRef]
Cuadra P, Harbone JB, Waterman PG. 1997. Increases in surface flavonols and photosynthetic pigments in Gnaphalium luteo-album in response to UV-B radiation. Phytochemistry 45: 1377–1383.[CrossRef]
Houghton JT, Ding Y, Griggs DJ, Noguer M, van der Linden PJ, Dai X, Maskell K, Johnson CA, eds. 2001. Climate change 2001. Report of the Intergovernmental Panel on Climate Change (IPCC). New York: Cambridge University Press.
Gang DR, Wang J, Dudareva N, Nam KH, Simon JE, Lewinsohn E, Pichersky E. 2001. An investigation of the storage and biosynthesis of phenylpropenes in sweet basil. Plant Physiology 125: 539–555.
Grayer RJ, Kite GC, Goldstone FJ, Bryan SE, Paton A, Putievsky E. 1996. Infraspecific taxonomy and essential oil chemotypes in sweet basil, Ocimum basilicum. Phytochemistry 43: 1033–1039.[CrossRef][ISI][Medline]
Johnson CB, Kirby J, Naxakis G, Pearson S. 1999. Substantial UV-B-mediated induction of essential oils in sweet basil (Ocimum basilicum L.). Phytochemistry 51: 507–510.
Karousou R, Grammatikopoulos G, Lanaras T, Manetas Y, Kokkini S. 1998. Effects of enhanced UV-B radiation on Mentha spicata essential oil. Phytochemistry 49: 2273–2277.[CrossRef]
Kolb CA, Kaser MA, Kopecky J, Zotz G, Riederer M, Pfundel EE. 2001. Effects of natural intensities of visible and ultraviolet radiation on epidermal ultraviolet screening and photosynthesis in grape leaves. Plant Physiology 127: 863–875.
Lachowicz KJ, Jones GP, Briggs DR, Bienvenu FE, Palmer MV, Mishra V, Hunter MM. 1997. Characteristics of plants and plant extracts from five varieties of basil (Ocimum basilicum) grown in Australia. Journal of Agricultural and Food Chemistry 45: 2660–2665.[CrossRef]
Lawrence BM. 1988. A further examination of the variation of Ocimum basilicum L. In: Lawrence BM, Mookherjee BD, Willis BJ, eds. Flavors and fragrances: a world perspective. Proceedings of the 10th International Congress of Essential Oils, Washington, DC, USA, 16–20 November 1986. Amsterdam: Elsevier Science Publishers B.V.
Liakoura V, Manetas Y, Karabourniotis G. 2001. Seasonal fluctuations in the concentration of UV-absorbing compounds in the leaves of some Mediterranean plants under field conditions. Physiologia Planarum 111: 491–500.[CrossRef][Medline]
Maffei M, Scannerini S. 2000. UV-B effect on photomorphogenesis and essential oil composition in peppermint (Mentha piperita L.). Journal of Essential Oil Research 12: 523–529.
Mazza CA, Boccalandro HE, Giordano CV, Battista D, Scopel AL, Ballare CL. 2000. Functional significance and induction by solar radiation of ultraviolet-absorbing sunscreens in field-grown soybean crops. Plant Physiology 122: 117–125.
Olsson LC, Veit M, Bornman JF. 1999. Epidermal transmittance and phenolic composition in leaves of atrazine-tolerant and atrazine-sensitive cultivars of Brassica napus grown under enhanced UV-B radiation. Physiologia Plantarum 107: 259–266.[CrossRef]
Raki Z, Johnson CB. 2001. Influence of environmental factors (including UV-B radiation) on the composition of essential oil of Ocimum basilicum – sweet basil. Journal of Herbs, Spices and Medicinal Plants 9 (in press).
Tattini M, Gravano E, Pinelli P, Mulinacci N, Romani A. 2000. Flavonoids accumulate in leaves and glandular trichomes of Phillyrea latifolia exposed to excess solar radiation. New Phytologist 148: 69–77.[CrossRef]
Werker E, Putievsky E, Ravid U, Dudai, N, Katzir I. 1993. Glandular hairs and essential oil in developing leaves of Ocimum basilicum L. (Lamiaceae). Annals of Botany 71: 43–50.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  S. Combrinck, G. W. Du Plooy, R. I. McCrindle, and B. M. Botha Morphology and Histochemistry of the Glandular Trichomes of Lippia scaberrima (Verbenaceae) Ann. Bot., June 1, 2007; 99(6): 1111 - 1119. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||