icon

CHARACTERISTICS OF JUVENILE PLANTS

There are numerous substantive phenotypic traits associated with juvenility, but they vary onsiderably among species.  Commonly, the leaves on young plants are of a different shape than those on mature parts and may be simple rather than compound (or occasionally the reverse); juvenile leaves may also have a special type of cuticle and be arranged with a distinct phyllotaxy. Compared to their adult counterparts, young plants may have a modified resistance to pests and diseases.  Juvenility in woody plants is often manifested by prolonged vigorous shoot growth.  With Citrus and Gleditsia triacanthos, juvenile forms are thorny, whereas adult forms lack the thorniness and with some tree species, such as those of  Quercus and  Fagus, juvenile forms and older, more juvenile parts of the trees, hold their senesced leaves throughout the winter.

1.1.1.      Vegetative propagation

            To the plant propagator, the most important attribute of juvenile shoots is their ability to rovide cuttings that readily form adventitious roots or explants that respond and grow well  in vitro. Cuttings taken from adult shoots of plants can be rooted, but the frequency of success is often low, especially with woody plants.  Likewise, researchers have had great challenges when attempting to micropropagate adult forms of many woody species. The change from the juvenile to adult phase is the most serious constraint to rooting in shrubs and trees (Howard, 1990).  Most of the difficulty experienced in rooting mature shoots seems to be caused by their altered physiology, but can also be related to greater contamination with microorganisms and viruses.

            Hedera helix has been used widely to study juvenility because it has a distinctively different morphology between the juvenile and adult phases. Juvenile plants have a different growth habit, leaf shape, and an enhanced ability to form adventitious roots.  When petioles from the juvenile form were excised and treated with auxin  in vitro, cortical parenchyma cells adjacent to the vascular bundles divided and formed root primordia (Geneve  et al., 1988).  However, when  petioles from adult leaves were treated in a similar manner, callus formed and some callus cells divided to form root primordia.  The juvenile form had pre-existing competent cells that were able to respond to auxin and become determined to form roots.  However, the adult form appeared to lack cells with pre-existing competence to form roots, but competence was acquired by some callus cells once they had been initiated.

            Explants taken from mature shoots are frequently more liable than juvenile material to uffer necrosis, especially when surface disinfested and placed in culture (Hanus and Rohr, 1987).  For example, shoot tip explant death can occur within a few hours for adult  Juglans nigra whereas healthy growth was evident on seedling explants when both sources were compared in different vessels containing the same medium (Preece and Van Sambeek unpublished).  It was only by changing the medium and culture conditions that adult J. nigra shoot cultures have been maintained for years  (Pearson and Preece un-published). However, adult origin  J. nigra micro-shoots still cannot be rooted.

For tissue culture, juvenile explants are usually more readily established  in vitro and grow and proliferate at a more rapid rate than adult material. This is particularly true with tree species where micropropagation of adult material is often difficult.

1.1.2.      Plant propagation dilemma 

            It is well known that it is easier to propagate vegetatively, juvenile forms of plants than adult forms of plants.  When breeding and selecting new, superior plants for clonal propagation, it is sually necessary to wait until the plant reaches maturity.  This allows for evaluation of important features, such as ultimate form and size, flowering and fruiting characteristics, autumnal coloration, and other traits.  At the point that the mature phenotype is known, the plant is an adult and often becomes difficult to propagate clonally.  Libby and Hood (1976) showed that juvenility can be maintained by hedging radiata pine. They rooted cuttings of many juvenile selections and  by allowing some individuals to grow to maturity for evaluation, other, hedged members of the same clone could be maintained as juvenile plants for propagation.  This technique also has potential for micropropagation.

PHASES OF GROWTH

The sequence of stages through which a higher plant has passed in its development from a ertilized egg to an adult organism, is known as its ontogeny or ontogenesis.

In the juvenile phase, a young seedling plant displays one or more distinctive characteristics of both a morphological and physiological nature. These distinguish a juvenile plant from an adult.  The juvenile phenotype gradually disappears during subsequent growth, and under natural conditions it is replaced by the adult (mature) phase in those parts of capable of changing from vegetative to flowering meristems under “normal” inductive conditions.  In some plants, a transitional phase of development can be distinguished between the juvenile and adult phases during which the potential to flower gradually increases. the plant in which maturation has occurred. Maturation occurs when the apical meristems become capable of changing from vegetative to flowering meristems under “normal” inductive conditions.  In some plants, a transitional phase of development can be distinguished between the juvenile and adult phases during which the potential to flower gradually increases.

When a plant is induced to flower, the shoot apical meristem changes from forming vegetative structures to forming reproductive organs (Hackett and Murray, 1997).  Typically, it is an external environmental stimulus, such as day length or chilling that will trigger this change.  Under such a normal environmental stimulus the apical meristem of a juvenile plant is not capable of perceiving or responding to the signal and remains vegetative. Under certain circumstances,  juvenile plants can be induced to initiate flowers but will revert to the non-flowering juvenile state for several years (Hackett, 1987).  However, it is often difficult to devise methods to promote flowering that will not also advance maturation (Hackett, 1985).  In many conifers, flowering can be induced on juvenile shoots by gibberellins or auxin/gibberellin combinations (Pharis and King, 1985; Pharis and Kuo, 1977; Pharis et al., 1976, 1980; Ross et al., 1981).

In general, the duration of the juvenile phase is proportional to the potential ultimate size of the plant, being shortest in annual herbaceous species and progressively longer and more noticeable in perennial and woody plants.  In trees it may sometimes persist for many years.

Phase change from juvenile to adult is an epigenetic change, in that there are phenotypical changes that are the result of changing gene expression, not mutation.  When an adult plant is regenerated from an embryo (either zygotic or somatic), juvenile traits are again expressed.  Gene expression for dihydroflavonol reductase (DFR) was studied in adult and juvenile leaf lamina tissue of English Ivy (Hackett and Murray, 1997).   DFR activity was detected in juvenile leaves treated with sucrose and light, but not in mature phase discs.  It was determined that the lack of DFR activity was because there was no accumulation of DFR mRNA because of a lack of transcription of the DFR gene in mature phase discs.  Lack of expression of this gene was also reported for adult phase stem tissue.  This gene was expressed in juvenile leaves and stems. The specific reason why the  DFR locus was not transcribed was unknown.  In Arabidopsis, both light and temperature independently regulate the floral promoter (FT) gene (Poethig, 2003).  However, there are other genes that also regulate temperature sensitivity of flowering time.  These genes (FCA and FVE) act upstream from the FT gene and seem to be involved in phase change.

EPIGENETIC EXPRESSION AND CELL DETERMINATION

Plants cells have an amazing ability to respond to a signal, which almost invariably is a plant growth substance.  When the cells can respond, they can change from a previously determined developmental pathway.  For example, a leaf cell can change so that it will begin to divide and a root or shoot will form.

            In tissue culture and plant propagation, the ratio of cytokinin : auxin is important (Chapter 6).  When cytokinin is in excess, adventitious shoots will form, when auxin is in excess, adventitious roots or somatic embryos will form, and when there are moderate to high levels of both, callus will develop.  This is the normal wound healing process in plants.  Many plant species have the remarkable ability to replace wounded or lost organs.  Following wounding, the endogenous hormone levels change and callus formation and organogenesis are often the result.  Similarly, with some species, because of high auxin levels associated with sexual fertilization in the seed, adjacent somatic cells change and produce embryos through the process of apomixis.  In plant propagation and plant tissue culture, we exploit this healing process and the apomictic ability of cells.

            Different cells within a tissue will not all respond the same way to a change in the cytokinin : auxin ratio.  Understanding what distinguishes certain cells from others in their ability to respond to the plant growth substance is important.  As our knowledge of the molecular biology of cells increases we may understand why there are these cellular differences.  With such knowledge, we may gain the ability to regenerate recalcitrant genotypes, such as adult forms of many plants.

Christianson (1987) and Christianson and Warnick (1983, 1988) stated that there are competent cells in a plant or explant (see Chapter 10).  These are the cells that are capable  of recognizing the plant growth regulator signal  and changing, or becoming determined.  When the plant growth regulator signal is removed, the determined cells will continue to respond.  They will dedifferentiate (become meristematic again), and their daughter cells will differentiate into the new shoot, root, or somatic embryo.

Not all cells in a tissue  are competent.  Exactly what makes one cell competent to perceive a plant growth regulator signal and its adjacent cell not to be competent is not well understood.  It is known that applied plant growth regulators elicit specific mRNA molecules (Christianson and Warnick, 1988).  This is evidence of specific genes being expressed in response to the exogenous plant growth substances.  However, this specific gene expression is more clearly related to changes in determined cells than to what makes cells competent.

A problem with trying to understand what makes a cell competent is that it is difficult to ascertain that a specific cell is competent until after it responds to the plant growth substances and becomes determined.  Once determined, the cell changes and its gene expression can be studied.  However, it is difficult to know which cell is competent and which one is not before the cell becomes determined.

            It is likely that epigenetic expression is the reason that a cell is competent.  Perhaps there is a gene or genes expressed for the receptor molecule of the elicitor plant growth regulator, which would allow that competent cell to recognize the plant growth substance.  However, there are other possibilities that could lead to competence, such as a expression of an important gene in the signal transduction pathway in a competent cell.

The predetermination of cells and tissues can often be changed in culture by cell differentiation and cell division, leading to the direct formation of organogenic or embryogenic meristems or callus. But if the tissue is not competent to undergo these changes, or the growth regulators in the medium are not suitable, previously predicated developmental pathways may not be interrupted.  Some aspects of determination may nevertheless survive in newly-established cultures and can occasionally persist for many callus transfers.

Results and Discussion

One of the most popular gateways is NowSMS since it can work very well with mobile phone that soon
will operate as a GSM modem where Sony Ericsson k800i had been preferred. Configuration process is
important to make sure that SMS gateway can work well with the mobile phone. 
Alert system will be activated only if the normal parameter range is exceeded. Normally, the temperature
and humidity of tissue culture did not change rapidly. In many cases, the next reading will be more or less
than previous reading. It is quite troublesome  since monitoring process is done manually by using
thermometer and hydrometer. The problem typically occurred during weekend or holidays since there is no
one available to do the monitoring process. Worst case scenario is electrical supply failure when its blackout,
the tissue culture will definitely contaminate be due to the inconsistency of temperature and humidity. Fig. 3
shows the data of temperature and humidity in tissue culture growth room at MPOB.

The suitable parameter for temperature is between 25°C to 30°C while for humidity is between 45% until
90%. If the parameter range is exceeded, alert system will notify the user by sending SMS and email
notification. Fig. 4 shows the temperature and humidity graphs of tissue culture in growth room.

SMS and email notifications display shows in Fig. 5. The SMS information are including the subject,
parameters range, date and time as well as the current value of parameters. The email notification shows the
sender’s address, date and time, recipient’s address, subject, the parameters range as well as the current value
of temperature and humidity that had been triggered by alert system.

Methodology

Besides expanding the range of applications in wireless technology, this development also focusing on
alert system that provide a new application of SMS in order to quickly provide urgent information to the user.
A mobile phone used to connect with the computer and act as GSM modems to replace a common modem
that requires a higher cost. Fig. 1 shows the process involved in monitoring the oil palm tissue culture which
is begin with hardware development to collect the data, data monitoring and acquisition and finally, an alert
system. In addition to the SMS service, the user also will receive an email notification about the parameter
data that can be kept as the track record.

This alert system is connected with database that contains data of temperature and humidity in the tissue
culture vessel or in growth room. It begins with comparison of the current data and the parameters range. In
condition of current data is within normal range, the alert system will be in idle stage. Nevertheless, if the
current data is beyond the parameters range, the alert system will be activated where notification will be send
to user’s mobile phone via SMS and email to user’s email address. 
The intention of this implementation alert system into the technology of oil palm tissue culture is to
provide efficient monitoring methods. The combination between Apache, PHP and MySQL is the most
important tools to develop the alert system. Apache is used as a web server that is connected with MySQL
database and PHP scripting language.
SMS alert system is developed by using SMS Gateway software called NowSMS. NowSMS is a scalable
solution that is affordable for development and testing, with scalability to support mobile operator systems.
The configurations for email and SMS are including the recipient’s address, sender’s address, present date
and time, parameters range and also current value of temperature and humidity that triggered the alert system.
Fig. 2 shows a diagram on how SMS and emails are sent from PHP scripting command through the MySQL
database manager.