WO2000051414A1

WO2000051414A1 - Plant treatment method

Info

Publication number: WO2000051414A1
Application number: PCT/GB2000/000746
Authority: WO
Inventors: Christopher Brian Johnson
Original assignee: Plant Bioscience Limited
Priority date: 1999-03-02
Filing date: 2000-03-02
Publication date: 2000-09-08
Also published as: AU2924400A; GB9904765D0

Abstract

Aromatic plants such as herbs have reduced aromaticity when they are grown under cover in green houses and the like, compared to the same plants grown outdoors. This reduced aromaticity correlates with a reduction in the essential oil content of the plant. The essential oil content and therefore the aromaticity of plants grown under cover may be raised by treating the growing plant with UV-B light (280 nm - 320 nm).

Description

PLANT TREATMENT METHOD

The present invention relates to a method for growing and/or maintaining plants under cover. In particular, the invention relates to a method for growing or maintaining plants under glass or plastic.

Traditionally, dried herbs have been used in the form of condiments or as simple additives to food for the enhancement of flavour. Relatively recently there has been a growing trend towards using fresh leaf or flower material derived from herbs. Food outlets, such as supermarkets, have responded to this trend by offering for sale fresh herbs in pots, packed fresh-cut sprigs of herbs, and herb flowers.

The fresh herbs offered for sale by such outlets are available year round. The herbs are generally grown under cover in glass greenhouses or under plastic covers such as cloches or sheets and the like. Although herbs grown under cover are available all year round such herbs generally lack the aromaticity generally associated with fresh herbs grown in season and outdoors, that is to say, not under cover.

'Essential oils' are responsible in large part for the aromaticity associated with plants, such as plants comprising perfumed flowers and herbs, such as culinary herbs. Essential oils consist mainly of terpenoids and can include such compounds as 1,8-cineole, limonene, linalool and β- ocimene. Other compounds which may be found in essential oils, that is, oils which are not terpenoids, can include phenyl-propanoid-derived compounds such as methyl chavicol, methyl cinnamate, eugenol, and methyl eugenol . Thus, the skilled addressee will appreciate that the term 'essential oils' is used in a qualitative sense to encompass compounds as indicated herein which contribute to the aromaticity of plants such as perfumed ornamentals and culinary herbs.

Ultraviolet light (and specifically UV-B) is known to have effects on secondary compounds of the phenyl-propanoid pathway of plants via action on key regulatory enzymes such as phenylalaline ammonia-lyase (Kuhn, D.N. et al (1984) Proc . Natl . Acad. Sci . , USA, 81, 1102-1106) and chalcone synthase (Batschauer, A. et al (1996) The Plant Journal 9, 63-69 and Christie, J. . and Jenkins, G.I. (1996) The Plant Cell 8, 1555-1567) . There are many published reports of UV- B stimulation of phenolic compounds, including surface flavonols and flavonoids (Cuadra, P. and Harborne, J.B. (1996) Zei tschrift fur Faturforschung 51c, 671-680 and Cuadra, P. et al (1997) Phyto chemistry 45, 1377-1383), anthocyanins (Yatsuhashi, H. et al (1982) Plant Physiology 70, 735-741 and Oelmϋller, R. and Mohr, H. (1985) . Proc . Natl . Acad. Sci . , USA 82, 6124-6128) and betacyanins (Rudat, A. and Goring, H. (1995) . J. Ex.pl . Bot . 46, 129-134) and these compounds have been implicated both in plant defence (Chappell, J. and Hahlbrock, K. (1984) Nature 311, 76-78 and Guevara, P. et al (1997) Phyton 60, 137-140) and as protection against UV-light (Lois, R. (1994) Planta 194,

498-503; Ziska, L.H. et al (1992) Am . Jnl . Bot . 79, 863- 871 and Fiusello, N. et al (1985) Allionia (Turin) 26, 79- 88) .

The present inventor has discovered that UV-B light irradiation of plants grown or maintained under cover, such as plants grown in the greenhouse, can contribute to the elevation of the amounts of many of the essential oils found in the said plants. As a consequence, the aromaticity of plants grown under cover, for example, greenhouse produced plants, such as greenhouse produced herbs, may be enhanced to a level more commonly associated with that of plants grown in season and outdoors .

According to the present invention there is provided a method of growing and/or maintaining live plants in a UV-B light deficient environment by irradiating the said plants with UV- B light from an artificial light source. In a preferment, the said plants are located under cover.

In a further embodiment, there is provided a method of raising the essential oil content in live plants in a UV-B light deficient environment by irradiating the said plants with UV-B light from an artificial light source. In a preferment, the said plants are located under cover.

In a further embodiment, there is provided a method of growing plants under cover wherein the said plants are irradiated with UV-B light from an artificial light source.

Plants grown or maintained under cover are exposed to reduced levels of UV-B light because the penetration of light of the wavelength of UV-B (280nm to 320nm) through the cover is limited. This creates a UV-B light deficient environment under the cover. Covers may be made of glass or plastic, and may be generally translucent to light of other wavelengths. Examples of covers include greenhouses, glasshouses, cloches and sheets. Generally, the UV-B light wavelength lies between 280-320 nm, preferably between 290 - 320nm, and most preferably between 290 - 300nm, for example 290nm.

"Plants" include those plants and/or plant parts which display an aromaticity which is detectable by the human olfactory senses. Such plants may display the aromaticity naturally, for example via the flowers and/or when cut for display, for example, in the case of cut herbs. The plants include ornamentals such as roses, freesias, carnations, lilies, jasmines, hyacinths, stocks and scented-leaf geraniums, and members of the Labiatae, such as the broad- leafed herbs. Suitable examples of broad-leafed herbs include basil, oregano, sage, coriander, dill, marjoram and thyme. Naturally, the skilled addressee will appreciate that the said plants are alive and may be located or planted in any suitable medium capable of sustaining growth and/or maintaining life of whole plants or indeed plant parts, such as cut plant parts. Suitable media include soils, peats, potting composts, agars, peat-perlite mixtures, compost- perlite mixtures, hydroponic media, water and the like commonly used in the art .

The plants may be irradiated with UV-B light during the nocturnal and/or diurnal periods of the 24 hour day. The plants may be irradiated with UV-B for any length of time, such as up to 240 minutes, more generally up to 180 minutes, more usually from about 100 - 150 minutes, for example 150 minutes or 120 minutes. In the case of UV-B irradiation of basil, it has been found that about 150 minutes for any one day over a suitable period of days is sufficient to elevate the levels of essential oils within the leaves. UV-B irradiation may be applied to the plants during the diurnal hours, nocturnal hours or for a period running from the nocturnal phase to the diurnal phase or vice versa on any given day. For ease of maintenance however, UV-B irradiation may be applied at similar set periods of any one day over a course of many days, for example, for basil, for 150 minutes per day over the time period from 04.30 to 07.00 each day for 14 days. Naturally, the skilled addressee will appreciate that the length of time of daily UV-B irradiation over the course of many days may vary from plant species to plant species, and indeed, from plant variety to plant variety in any one given species. The skilled addressee will also appreciate that other factors such as the natural day length (ie photoperiod) , supply of artificially generated light, distance of the irradiating light source from the plants, heating, availability of water and respiratory gases, such as, carbon dioxide and oxygen, may affect the length of time UV-B irradiation may be employed in order to have an elevating effect on the essential oils content of plants of interest.

Plants may be UV-B irradiated at or from any stage of growth, for example, from the 2-leaf, 3-4 leaf, and 5-leaf stages or later. In a preferment, plants are UV-B irradiated from the 3 to 4 leaf stage and most preferably in the case of culinary herbs such as basil, the 5-leaf stage. It is envisaged that plants such as culinary herbs are most usefully irradiated as hereindescribed for upto 14 days from market, more preferably from about 7 - 10 days from market, that is to say the harvesting of cuttings from such plants and/or the provision of young plants for market. Plants treated with UV-B light, for a period of time, particularly those measured at the 5- leaf stage, display elevated levels of essential oils relative to control plants which are not exposed to a UV-B light treatment. The level of increase of the total essential oils content in plants subjected to UV-B irradiation as described herein may be raised relative to controls by up to 4-fold or more depending on the 'leaf- stage' of the plant, the age of the plant (mature age), length and dose of irradiation, and the plant type. For example, using basil it has been shown that the essential oils content of plants analysed at the 5-leaf stage, after being irradiated under the conditions described in the examples, had a total essential oils content of about 4x the amount of that of control plants. Thus, the skilled addressee will appreciate that the optimum amount of UV-B irradiation will vary from plant to plant.

Naturally, the skilled addressee will appreciate that in the case of the UV-B irradiation of plants comprising perfumed flowers, the irradiation may be carried out when the flower heads are present on the plant, preferably in the opening phase thereof.

The artificial light source is any source which does not include the sun or even moon. Some artificial UV-B generating light sources are known and come in the form of light bulbs or fluorescent tubes, such as Philips 20 W/12 UV- B fluorescent tubes. The light source may be placed at any distance from the plants, however it is preferable to locate it in a position which affords the greatest amounts of irradiation per square metre of the growing plants. Suitably, depending on the size of the covered area, for example that of a greenhouse, the number of UV-B light sources may be as little as one to a whole 'battery' of light sources arranged in series and/or in parallel, each light source being suitably distanced one from the other at appropriate intervals. It has been found that when used on basil, that light sources positioned at 1 m apart and at 1 m above the plants proved to be adequate for raising the levels of essential oils in such plants.

In a further embodiment of the invention there is provided use of an artificial UV-B light source in a method of growing plants under cover.

In a further embodiment, there is provided use of an artificial UV-B light source in a UV-B light deficient environment in a method for increasing the essential oils content in live plants. In a preferment, the said plants are located under cover.

In a further embodiment of the invention there is provided the use of plant parts derived from UV-B irradiated herbs grown under cover in the manufacture of human foodstuffs, such as bottled or canned condiments, for example sauces for meat, fish and poultry dishes, flavourings, for example tapenade, salad dressings, cooking oils such as olive oil, sunflower oil and the like, soups, pasta and cheeses.

In a further embodiment of the invention there is provided an animal feed supplement, comprising one or more artificially UV-B irradiated herb species . An example of such an animal feed supplement is an equine herb supplement comprising at least one UV-B irradiated broad-leafed herb. The invention will now be described with reference to the following examples section and Figure 1. It is to be understood that the examples are not to be viewed as limiting the scope of the invention in any way.

Figure 1. Ratio of content of selected essential oils and total content in UV-B irradiated plants compared to Controls .Symbols : closed bars: 2 -leaf stage; open bars: 3- leaf stage; hatched bars: 5-leaf stage. A value of 0 indicates equal level in both; a value of +1 indicates double the level in UV-V treated plants etc.

EXPERIMENTAL

Plant Material . Broad leafed sweet basil ( Ocimum basilicum L.) seeds (Vilmorin, La Verpilliere Cedex, France) were sown either in 1% agar at 25°C and transferred to a mixture of peat and perlite (1:3) after 5 days, or else sown directly in the same peat-perlite mixture. The seedlings were grown in a cool glasshouse (mean temperature 15°C) until the start of the experimental light treatment, a period of four to six weeks in March and April 1998 in Chania, Crete. Care was taken to ensure that none of the plants received significant doses of UV-B prior to the onset of the experimental treatment.

Light Treatments . Plants for UV-B irradiation and the control plants were placed on parallel benches in the glasshouse separated by a transparent plastic screen, opaque to UV-B, in a glasshouse with ambient daylight. The experimental period for the UV-treatment was 2 weeks commencing 22 April. The UV-B light was provided by two Philips 20W/12 UV-B fluorescent tubes placed 1 m apart and 1 m above the bench. The UV-B treatments were given between 0430 and 0700 each day, i.e, commencing ca, 1.5 h before dawn.

Analysis of Plant Material . Leaves were harvested and dried to constant weight for gas chromatographic analysis. At the start of the experimental treatments indicated above, plants were divided into groups, the first typically having 3 leaf pairs, the second 3 or 4 leaf pairs and the third, 5 leaf pairs. Headspace sampling for GC analysis was carried out using 100 mg dry leaf material, randomly selected from the plants of the indicated developmental stage. Analysis was carried out using a Hewlett Packard 5890 II gas chromatograph with coupled headspace analyser and equipped with FID. For analysis, the dried leaves were placed in a 20 ml vial. Each sample was retained in the headspace oven for 30 min at 90°C, then it was extracted with carrier gas, retained in the loop at 100°C for 1 min and transferred to the GC at 100°C. The column was a DB5 (length 30 m, 0.25 mm diameter) and the carrier gas He at a velocity of 38 cm/sec. The split ratio was 1:28. Injector and detector temperatures were 230°C and 260°C respectively. The initial oven temperature was 45°C, rising at 1.5°C/min to 150°C, then at 40°C/min to 220°C and then held for the final 10 min at 220°C. Compounds were identified by comparison of retention times with known standards, and by GC/MS (HP5980 II GC coupled to a VG-TRIO 2000 mass spectrometer with MASS LYNX software) . Mass spectra were taken at 70 eV. Scanning speed was 1 scan/sec from 35 to 320 m/z . Peaks were identified from retention times (Adams, R.P. (1995) Identification of Essential Oil Compounds by Gas Chromatography / Mass Spectroscopy. 2^nd Ed. Allured Publishing Crop. Carol Stream, Illinois, USA) and by comparison with mass spectra in two libraries (Wiley, Adams) .

Table 1. Effect of UV-B treatment on essential oil content in Ocimum basilicum . DB5 values from Adams, R.P. (1995) supra, and our own observed retention times are shown. Content is expressed as integrated peak FID readings for each compound, and for the total. Since most compounds were affected by UV-B treatment, these values are more informative than % composition.

Legend a- = α- g- = γ-

Claims

1. A method of raising the essential oil content of live plants grown or maintained under cover comprising irradiating said live plants with UV-B light from an artificial light source.

2. A method of claim 1 wherein the UV-B light has a wavelength of from 290nm to 320nm

3. A method of claim 1 wherein the UV-B light has a wavelength of from 290nm to 300nm

4. A method of any one of claims 1 to 3 wherein the live plants are irradiated for up to 240 minutes per day.

5. A method of any one of the preceding claims wherein the live plant is at the 2-leaf stage of growth or later.

6. A method of claim 5 wherein the live plant is at the 3-4 leaf stage of growth or later.

7. A method of claim 6 wherein the live plant is at the 5 leaf stage of growth or later.

8. A method of any one of the preceding claims wherein the live plant is a perfumed ornamental plant.

9. A method of claim 8 wherein the perfumed ornamental plant comprises a perfumed flower and said plant is irradiated when a flower head is present and in the opening phase.

10. A method of any one of claims 1 to 7 wherein the live plant is a member of the Labiatiae genus.

11. A method of claim 10 wherein the live plant is a broad- leafed herb.

12. A method of any one of the preceding claims wherein the live plant is a cut plant part .

13. A method of any one of the preceding claims wherein the live plant is located in a medium capable of sustaining growth .

14. A method according any one of the preceding claims including incorporating plant parts derived from said live plants in human foodstuffs.

15. A method according any one of the preceding claims including incorporating plant parts derived from said live plants in animal feed supplements.

16. Use of UV-B treatment for increasing the essential oil content of a live plant growing under cover.

17. Use of an artificial UV-B light source in a method of increasing the essential oils in live plants growing under cover.

18. Use according to claim 16 wherein said method is according to any one of claims 2 to 13.