ABSTRACT
Systems already exist and operate on the grand scale in nature. Rhizobium root nodules in leguminous plants, which fix nitrogen from the atmosphere, are not far from our specification except with respect to size. These nodules are complex structures in which atmospheric nitrogen can flow through the walls of the nodule and combine with the hydrogen generated by the splitting of sugars through a set of enzymes. Oxygen is trapped by a form of haemoglobin, leg-haemoglobin, which then releases it to the bacterium, which is an obligate aerobi. The reason for this side-loop is that the central enzymes for nitrogen fixation, hydrogenase and nitrogenase, are very sensitive to oxygen poisoning. Rhizobia sequester a sizeable amount of the photosynthate produced by their host, perhaps 30%, without, however, overdrawing it presumably via regulatory feedback process. They obviously possess all other feedbacks necessary for a harmonious symbiosis. Presumably because of the open nodule structure needed for nitrogen to diffuse into it, the nodules leak hydrogen into the atmosphere. The fundamental issue is whether an artificial gall could modify a tree cell structure locally to induce this chemical alteration. This may appear as a tall order, but in nature numerous brilliant, if sometimes extravagant, sets of solutions have already been found to this kind of problem and operate right before our eyes. Many insects are capable of inducing the formation of bodies in plants-the galls-that may be related to tumours but are profoundly different in that they grow according to a precise functional architecture, as does any other organ or a plant. These galls are engineered to provide protection and food for the larvae of the insect, and are perfectly adjusted to their needs and timed to their state of development. Not only insects but also bacteria and fungi have found their way to induce gall formation. They number in tens of thousands of different kinds. Oaks host a few hundred types of galls. Their structural and functional variety is astonishing: they range in size from a pinhead to a rugby ball, and appear as spongy nests or complex structures with precisely machined doors opening at the proper time for the mature insect to come out. How information is transferred between parasite or symboint and host for the generation of galls and nodules has been the subject of extensive speculation for many years, but the obvious suspicion-that a transfer of DNA is at work-has been proven, at least in some cases, only recently. Without DNA or RNA, however, the extreme structural and functional sophistication of the galls would be unthinkable. Marchetti notes that a tree has a metabolic power of the order of 1 KW. World forests produce an amount of carbohydrates of the order of 100TW. Man uses about 8TW mostly in the form of fossil fuels. He also observes that in nature plants give off hydrogen and cites the case of the US Soybean crop leaking 30 billion m3 of hydrogen per annum.
