venerdì 1 dicembre 2006

PART 2 - 1. TAFKAV- What is a Plant?

Now, at last, we are ready to address the second part of our work – What is a plant?

Living beings are sentient, insofar as they have organs able to detect variations in the external environment and to render that useful for the inner environment.
There are living species that are able to interpret, as information, signals coming from the environment that man and other species do not recognize as significant.

The world would seem to be an aggregate of different worlds, which meet only on their border zones. Everyone lives in their own cognitive cage

(A longer version of this argument appears in Appendix IV)

Ted Turlings of the University of Neuchatel is working on the ménage-a-trois of a corn plant, the Spodotera exigua caterpillar and the Cotesia margini Hubner wasp.

fig. 4 corn plants

When the caterpillar attacks the corn plant, the latter communicates by emitting a mix of volatile substances, in large part engendering torpor, which tip the wasp off to the presence of the caterpillars on its leaves. The wasp dives down and attacks the caterpillars, turning them into food reserves for its larvae

(Turlings TCJ, Loughrin JH, McCall PJ, Röse USR, Lewis WJ, Tumlinson JH (1995) How caterpillar-wounded plants protect themselves by attracting parasitic wasps. Proc Natl Acad Sci USA 92: 4169–4174)

fig. 5 cotesia plutellae

Massimo Maffei, Simone Bossi, Dieter Spiteller, Axel Mithöfer and Wilhelm Boland of the Department of Plant Biology, University of Turin in Italy (M.M., S.B.); and Max Planck Institute for Chemical Ecology, Jena in Germany are working on the relation of the Lima bean plant Phaseolus lunatus and the Mediterranean climbing cutworm Spodoptera littoralis.

fig. 5 Phaseolus lunatus

When the cutworm attacks the beans plant, The results showed that the early events upon herbivore attack were: a) a strong Vm1 depolarization at the bite zone and an isotropic wave of Vm depolarization spreading throughout the entire attacked leaf; b) a Vm depolarization observed for the regurgitant but not with volicitin {N-(17-hydroxy-linolenoyl)-Gln} alone; c) an enhanced influx of Ca2+ at the very edge of the bite, which is halved, if the Ca2+ channel blocker Verapamil is used. Furthermore, the dose-dependence effects of N-acyl Gln conjugates-triggered influx of Ca2+ studied in transgenic aequorin-expressing soybean (Glycine max) cells, showed: a) a concentration-dependent influx of Ca2+; b) a configuration-independent effect concerning the stereochemistry of the amino acid moiety; c) a slightly reduced influx of Ca2+ after modification of the fatty acid backbone by functionalization with oxygen and; d) a comparable effect with the detergent SDS. Finally, the herbivore wounding causes a response in the plant cells that cannot be mimicked by mechanical wounding. The involvement of Ca2+ in signaling after herbivore wounding is discussed.

1 Membrane potentials (Vm)

fig. 6 Spodoptera littoralis

Plants are continuously interacting with the external world. The coordination of internal processes and their balance with the environment are connected with the excitability of plant cells.

Several plant species, including Lima bean Phaseolus lunatus, when attacked by herbivores emit volatiles that attract natural predators of the damaging insects. This signaling by the plant to higher trophic levels has been interpreted as the plant's cry for help.

(Dicke M, Sabelis MW (1992) Costs and benefits of chemical information conveyance: proximate and ultimate factors. In BD Roitberg, MB Isman, eds, Insect Chemical Ecology: An Evolutionary Approach. Chapman and Hall, New York, pp 122–155 and DeMoraes CM, Lewis WJ, Paré PW, Alborn HT, Tumlinson JH (1998) Herbivore-infested plants selectively attract parasitoids. Nature 393: 570–573)

The human nose can in fact detect the corn plant’s emission. So when an individual is aware of this dynamic and recognizes the odor, he will be able to decodify an abstract signal and insert it in a punctuation, a syntax and a dynamic communication with the corn plant. In short, he will be able to hear the plant’s alarm call and, if there are no wasps around, could intervene to save the harvest in some other way.

What matters here is that the understanding of the message transforms simple chemical information into an inter-species communication and defines the beginning of a communicative relationship between man and plants.

Science has also discovered that trees talk to each other, oak to oak, banana to banana and so on. Which means trees also listen.

The main conversation themes seem to be the risk of attack by insects, underground water levels and the quality of sunlight. Thomas Boller of the University of Basel has shown that plants can also communicate via their roots.

So, plants can communicate through odor, and they can also “smell odors “ and develop a kind of tactile sense. They can also “see.” Plants have many photosensitive organs that react specifically to certain frequencies of light, which help them know when it is day and when it is night, how much light is available, where it comes from, and how long the day will last. They can also detect where there is too much ultra-violet light around and react by producing pigments capable of filtering them outii.

iiFlorianne Koechlin, Biologist, Blueridge-Institute, membro del Board GENET e del Swiss Ethic Committee on Non-human Gene Technology – ECNH, Basilea, è l'autrice dell'articolo Concezioni moderne in biologia su cos'è una pianta, scritto per il 1° Congresso Internazionale “Cdg – Scienza e Società – La frontiera dell’invisibile: biomedicina, nutriceutical, nanobiotecnologie”, del 16 e 17 ottobre 2004 a Villa Caruso Bellosguardo, Lastra a Signa, Firenze . Articolo che ha dato spunto a questa parte dello scritto.

fig. 7 mimosa pudica

Plants also possess a tactile sense. Think of the mimosa pudica, whose leaves fold inward and drop when touched, earning it the nickname of the “touch-me-not” or, in Chinese, the “shy” plant. There are thousands of plants that react, in various ways, to tactile stimuli. Some react to mechanical stimuli that a human could never detect. The Bryonia dioica, for example, will react to a weigh of 0.00025 milligrams.

Plants are sensitive to at lest 17 environmental variables, they can perceive light, chemical substances, sounds, vibrations, gravity and temperature, and react to these variations by modifying their metabolic processes.

fig. 8 Bryonia dioica

Plants learn, remember and plan ahead:

Scientific research has shown that plants are able to learn, remember and plan in advance.

Many plants measure the amount of light reflected by neighboring plants, and in this way discover the position of the adjacent plants, which allows them protectively and pre-emptively to adapt to new situations before they actually come about.

Plants can plan ahead. They can carry out preventive actions through their metabolic processes, accelerating the growth of a stem, for example, or thickening a branch here and there, or bolstering key root networks. They can also produce defensive chemicals, all usually with the aim of placing themselves in the best possible position for the desired sunlight.

As plants must seek to avoid excessively intense competition with other plants, they must make decisions about how to grow and how extensively to use the available space. They must integrate signals of how hard the soil is, along with signals of acidity, nitrates, the distribution of water, temperature and light, the presence o insects, lichens, fungus and other microorganisms, and they must elaborate all these signals into a strategy to make the necessary decisions to grow.

Memory can be defined as the experience of an organ used to the advantage of others – in this sense, memory is also present in plants. By pre-exposing leafs to weak solar rays, a growing plant can survive later in conditions of weak light. Similar strategies are used by roots in relation to salt and water underground.

Cuscuta, dubbed “devil’s hair” or “strangleweed” as well as s “dodder,” is a parasitic perennial without leaves and with very low levels of chlorophyll. It attacks host plants with its scaly sucker extensions, wrapping around them and penetrating their vascular systems. Once germinated, the cuscuta’s root disappears and its stem lengthens, already hunting for a host. When it finds one, it wraps around it, but if the host is deemed unappealing, it will create only a few spiral stems to carry out its leeching of the other plant’s energy sources. It takes about four days to grow these spirals, so the cuscuta must decide four days beforehand if it has found a suitable host, indicating some forethought.

fig. 9 Cuscuta

But if plants are able to have experiences, to remember, learn and plan in advance, then it is natural to ask whether they also possess some form of intelligence. Some scientists are convinced they do, and note the amazing similarities between plants and animals on the cellular level. The paths followed by internal communication signs is quite similar in plants as to those in animals and humans.

The ancient communication system using hormones is present in animals as well as plants, and that is why our interaction with plants can be so beneficial or harmful.

The active principle for aspirin is a vegetable hormone produced by some plants in response to attack by viral pathogens. Humans, as well as some animals, have learned to use it for the same reason. The principle – salicylic acid – plays a central role in triggering immune systems of plants to control or weaken a certain pathogen. It is very interesting that it works just as well in animals – and that is because, indeed, many of the molecular mechanisms of mammals and insects are very similar to those of plants.

Like animals, plants have also developed a system of electrical communication. If touched, the mimosa pudica releases electric shocks that are created and spread across cellular membranes and can travel up to 20 centimeters a second, roughly the same speed as the nervous system of animals.

Many chemical substances that serve in the way communication occurs in animals’ nervous systems, such as amino acids and peptides, also occur in plant cells.

Plants and animals are also similar from a genetic point of view. Fred Meins, an epigenetic expert at the FMI in Basel, told Florianne Koechlin that, on the genetic level, the difference between plants and animals should be understood in terms of condition, not principlesi.

There is ample proof that the way plants learn can be compared to the way other organisms do, all based on molecular processes.

Animal organisms deploy neural learning, through the coordination of the way different muscles behave. For plants, the learning process results in the coordinated behavior of different tissues that produce an adaptive response in terms of phenotype plasticity.

Both plants and animals learn through trial and error, adapting to an environment that is constantly changing in a bid to survive.

Plants are not animals (I do not, however, want to propose that plants are animals1).

Modern biology teaches us that plants are sensitive living things. They are not simply molecular machines that can be patented like chemical compositions. There are, in fact, no patents for plants.)

1For a fuller discussion of the difference, see Appendix III.

iW.R. Ashby, Introduzione alla cibernetica, trad. it. Di M. nasti, Torino, Einaudi.

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