AU668141B2 - A method of environmental control - Google Patents

Description

668 14 1

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT o o .o coa ae a cooo ao Applicant(s): NEW ZEALAND FOREST RESEARCH INSTITUTE LIMITED Invention Title: A METHOD OF ENVIRONMENTAL CONTROL The following statement is a full description of this invention, including the best method of performing it known to me/us:

IA'

BACKGROUND TO THE INVENTION This invention relates to a method of environmental control.

In particular, but not exclusively, this invention relates to a method of environmental control for plant material grown on solid medium.

Reference throughout the specificati u will be made to the plant material as being somatic embryos, although it should be appreciated that the present invention can be applied to other plant material.

The growing of somatic embryos on a solid medium is still a relatively new science. Typically, the solid medium is a gelatinous/solid mixture with various ingredients such as minerals, sugars and amino acids which are required by the growing embryos. The medium in its liquid form is usually poured into containers such as Petri dishes. Once the medium has solidified, the embryos are placed onto the medium and the dish is 'covered with a plastic or glass lid or closure. The margins where the closure and dish overlap is sealed with a clear cling film. Cling film is used as it provides a seal against possible microbial infection which could be fatal to the embryos.

II Cling film of the sort presently used is gas and vapour impermeable.

While such cling film can effectively seal dishes against microbial infection, there are other problems associated with the use of this film.

One problem is that the use of vapour and gas impervious enclosure may result in build-up of condensation on the underside of the closure. This condensation not only causes viewing problems but it also causes more significant physiological problems: namely, condensate (generally water) may form which can drop back onto the medium.

The medium has certain properties including a defined concentration of solutes which govern the rate at which water can be taken up by the growing embryos. It is important that the concentration of the various ingredients of the medium are at an optimum value for successful embryogenic development. Free water dropping onto the medium from the film can therefore cause the effective concentration of essential ingredients as received by the embryos to alter and can adversely affect the growth of the embryos.

There are believed to be additional problems to those described above caused by the use of traditional cling film.

l..i While it was known in the past that fully developed plants have a gaseous exchange with the atmosphere, it was thought that this did not apply to plant embryos which were considered to be totally dependent on their S, internal environment. The basis of this belief was the understanding that embryos do not have a requirement for fixing carbon dioxide, as embryos do not photosynthesise unlike fully developed plants.

0000 It is now believed by the applicant that embryos do have a gaseous exchange with the atmosphere. In the case of embryos grown under typical closure, there are strong indications that under the closure there is a build-up of ethylene and a possible depletion of carbon dioxide and oxygen. Ethylene is a bioactive substance and is thought to cause elongation of the cells in the embryos, perhaps to such an extent that the cells revert to non-embryogenic types. Auxins cause a similar undesirable effect on embryogenic tissues. The effect of the changing concentrations of oxygen and carbon dioxide is also thought to be harmful to the tissue.

It is an object of the present invention to address the above problems, or at least to provide the public with a useful choice.

Further objects and advantages of the present invention will become apparent from the following description which is given by way of example only.

SUMMARY OF THE INVENTION According to one aspect of the present invention there is provided a method of growing plant material on a medium characterised by the step of placing a filter over a vessel containing the plant material and medium,

I

said filter being gas and vapour permeable, and impermeable to micro- Sorganisms.

GENERAL DESCRIPTION OF THE INVENTION Reference throughout this specification will now be made to the filter being a film, although it should be appreciated that other gas permeable filters

U

s may be used, for instance filters based on clay, charcoal and the like.

,,In preferred uses of the present invention, the plant material will be embryogenic in nature and the medium will be a solid medium, however it should be appreciated that the present invention could apply to situations different from those described herein, such as a liquid medium.

In a preferred embodiment, the film may be differentially permeable to the different gases and vapour such as oxygen, carbon dioxide, ethylene anac water vapour. That is, the film may let through different gases and vapours at different rates to each other and therefore there can be provided a distinctive transmission ratio for these gases. Preferably, the transmission ratio for the gases and vapours through the film will correspond to the ratios of emission and absorption of the same gases by naturally growing plant material and in particular embryos if this is the material being grown.

In preferred embodiments of the present invention, the film allows a controlled rate of water loss. A preferred range of water loss for embryogenic tissue is between 90 to 150 grams/square metres/day. The unit grams refers to the weight of the water, the unit square metres refers to the surface area of the culture medium being covered by the film. A preferred rate which is particularly suitable for Pinus radiata embryos is 118 grams/square metre/day.

i In preferred embodiments, a filter which allows a controlled rate of exchange of oxygen is desired. In particular, it has been found that a range of between 7200 and 32000 cubic centimetres/square metres/day works particularly well. A optimum rate of oxygen exchange for Pinus radiata embryo has been found to be in the order of 16700 cubic centimetres/square metres/day.

Many types of film may be used for the present invention provided they *i have the desired qualities of being able to seal against microbial infection and are sufficiently permeable to the appropriate gases and vapours. For instance, the film may be made from plastics material such as polyvinyl chloride (PVC). Alternatively the film may achieve an appropriate filtering effect by being microporous with pores small enough to let gases through but not bacteria.

4 _L ~l Table 1 on the following page illustrates properties of films which are suitable for use with the present invention. These films are sold under the trade mark VITAFILM by the Goodyear Tyre and Rubber Company (Australia) Limited. Of those films listed, the films listed under the names OMNI, VW, MWT and F10 V/S have provided the most promising i results so far. In particular, the OMNI film has shown itself to be i4 particularly suitable for use in pine embryogenesis.

I It should be appreciated that films and filters may be used other than the Sselection described above.

In a further aspect of tbe present invention, there is provided a method of growing plant material on a medium as described previously characterised by the further step of controlling the atmosphere outside of i the film. For instance, a certain mixture of gases considered to be most Ssuitable to the growth of embryogenic tissue may be supplied outside of the f film ensuring that the growing embryos receive the appropriate mixture through the film.

i:! ii Lh. i Zllc -aaa aa~-p~ 01 r o o~ o so~ ~or oo oo PROPERTY UNITS Ow OMNI-FILM PWGS VW MW MWT FIOVIS Water vapour g m 2 1m 2 /124 hrs 50 510 400 340 461 475 410 transmission rate 95% r lhunm 88c Gas trans rat 02 emlm/m/24 hra 15700 1 16700 8835 12900 14871 9500 7200 Gas trans rate CO 2 emlmm 2 /24 hrs 145000 164300 8906 116200 168704 83000 62000 Tensile strength '310 360 281 290 308 645 470 longitudinal kg/clm 2 800o 825 263 235 265 290 440 transverse Elongation 270 250 270 250 224 180 250.

longitudinal 835 275 850 275 276 450 280 transverse 100% modulus 190 220 200 165 190 480 330 longitudinal kg/em 140 155 140 125 140 120 255 transverse Tear initiation 48 75 65 78 46 123 (graves) N/mm 83 60 65 65 00 74 78 longitudinal transverse Tear propogation (elemendorf) N/mm25 12 24 25 25 25 12 longitudinal 45 26 45 45 44 44 28 transverse Drop height Metres RIT. 1.4 1.1 1.2 1.8 1.2 1.8 Sealng *0 160 10 150 172 150 165 150 temperature Flammability self Self self self Belf self Self I y_ extinguishing extinguishing extinguishing extinguishing extinguishing extinguishing extingulaihing Light %9 39 39 39 transmission I 1 92 Hnze 0.5 0.8 I 1 0.7 1 0.8 1 Resistance to grease, oils, acids, Good Good Good Good Good Good Good alkalis Specific Gravity 1.26 1.26 1.24 1.26 1.26 1.27 1.27

'-A

en L 1 7 It can be seen that the present invention has a number of advantages over the methods previously used. As the film is permeable to water vapour, there is now no build-up of condensation. Thus, problems such as those relating to the changing concentration of minerals due to free water on the medium, have been avoided. As well, oxygen and carbon dioxide levels are now free to fluctuate in accordance with the physiological demands of the embryogenic tissue.

Further, with the present invention there is no build-up of ethylene with its potentially harmful effects on embryonic tissues. Accompanying the tissue multiplication stage in dishes with lids is an accumulation of fruity, volatile substances that are readily evident when a lid is removed.

Included in this emission among other substances, is a build up of ethylene. However, with the present invention there is no detectable accumulation of fruity, volatile substances.

The present invention also provides an advantage beyond solving the problems previously discussed. The applicant has found that embryogenic tissue passes through two development stages.

The first development stage is the formation of the embryo axis which requires a lower concentration of certain ingredients in the medium.

The second development stage is the formation of the cotyledon primordia which requires a higher concentration of certain ingredients in the medium, and desiccation of the medium accompanied by maturation of the embryo including physiological changes that prepare it for desiccation.

Previously it was necessary to transfer the embryos from the lower concentration medium to the higher concentration medium to promote 7

L.

embryo development. Not only is this time consuming but it greatly increases the risk of damage and/or contamination of the embryogenic tissue. With the present invention, transf--ence of tissue between media is now not necessary as the loss of water vapour through the permeable film naturally increases the concentration of ingredients in the medium sufficient to encourage embryo development. Simultaneous with this is an increase in the matrix potential the ability of the medium to withhold water from the embryos during development. The progressive withholding of free water from the somatic embryos mimics the desiccation that occurs during natural embryo development, and is achieved as a continuous process, rather than as a step-wise gradient such as would be obtained by serial transfer of tissue across media with i 3'o, different physical properties.

*0 DETAILED DESCRIPTION OF THE INVENTION :0,40, Some examples whereby the use of the present invention are given below.

Example 1 The effect of filters on pine somatic embryo production "".Tissue of a plant forming Pinus radiata embryogenic cell line was distributed in equal amounts at random over a number of petri dishes containing a solid medium that favours development and maturation of somatic embryos. Some of the dishes retained plastic lids which were sealed at the margins with impermeable cling film. Other dishes were covered with one of four different plastic films. After a period of ten days, cotyledonary stage embryos were harvested. The results are shown in Table 2 below. Each treatment had four dishes of embryo-forming tissue.

TABLE 1 Film/Closure Total number of somatic embryos Plastic lid 28 Vitafilm F10 V/S 51 Vitafilm VW 62 Vitafilm Omni-film 97 Vitafilm MWT The use of Vitafilm Omni-film produced the greatest yield of somatic embryos.

See previous Table 1 for film properties.

Example 2 The determination of the effect of filters on water loss from growth 9 a a St a i o ro t t o t i lt t S I

I

Ii1 medium in petri dishes.

Petri dishes containing solid somatic embryo development medium were covered with plastic lids, sealed on with cling film, or with one of four different gas permeable plastic films. Initial weights of the dishes were recorded, and weight loss noted at intervals of 2-3 days. There were four replicates of each treatment, and dishes were maintained in a 24°C incubator under the same conditions as used for somatic embryo development.

The mean water loss from dishes after 9 days when covered with lids of different films was determined. Water loss was correlated with the i L II I.;p~-n.~DeS31 somatic embryo counts from identical dishes of medium cultured under the same conditions. A correlation between embryo formation and water loss of 0.994 was determined statistically for the film covered dishes.

Experimental results are shown in Table 3.

TABLE 2 Embryo formatinn and wat.cr Ine fr nm morlin Embro frmaton nd wteross from medAia 0 0 0~~ Lid/Film Number of Embryos Water Loss (gm per 9 days) Lid 28 0 Vitafilm F10 V/S 51 4.88 Vitafilm VW 62 5.14 Vitafilm Omni-film 97 6.73 Vitafilm MWT 50 4.60 The water loss from dishes giving the highest yield of somatic embryos, that is those covered with Vitafilm Omni-film, was determined to be 118 g/m 2 dish area/day.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the appended claims.

Claims (9)

1. A method of r 'turing cotyledonary stage embryos on a medium comprising (a) distributing embryogenic l .naterial onto a solid medium in a vessel, and placing a filter over the vessel containing the embryogenic plant material wherein said filter allows a controlled rate of water loss and a controlled rate of exchange of oxygen and is impermeable to microorganisms.

2. A method as claimed in claim I wherein the filter is a film.

3. A method as claimed in claim 1 wherein the filter allows the transmission of water vapour at the rate of between 90 to 150 grams/square metre/day.

4. A method as claimed in claim 4 wherein the filter has a water vapour transmission rate of 118 gramns/square metre/day.

A method as claimed in any one of claims 1 to 4 wherein the filter allows oxygen to be exchanged at the rate of between 7200 and 32000 cubic centimetres/square metre/day.

6. A method as claimed in claim 5 wherein the filter allows the rate of oxygen exchange of about 16700 cubic centimetres/square metre/day.

7. A method as claimed in claim 1 wherein said embryos are pine embryos.

A method as claimed in claim 7 wherein said embryos are Pinus radiata embryos. 12

9. A method substantially as described herein with reference to and as illustrated by Examples 1 and 2. A method of growing plant material on a medium as claimed in any one of claims 1 to 9 characterised by the further step of controlling the atmosphere outside of the filter. DATED THIS 26TH DAY OF FEBRUARY 1996 NEW ZEALAND FOREST RESEARCH INSTITUTE LIMITED By its Patent Attorneys: GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia sec* s o 4 o a o o 0 o e o Q 0o 0 0o 0 0 o a De a so o o Afl51RACT The present invention relates -to a method of growing plant material on a medium, characterised by the step of placing a filter over a vessel containing the plant material and medium, said filter being gas and vapour perm~eable and impermeable to mnicro-organisnms. 4