5.3 Growth-Promotion of Plants by Using Radiation Induced Depolymerized Natural Polysaccharides


Fig. 5-3 Changes in molecular weight by gamma-ray irradiation

This figure shows the degree of decrease in molecular weight of alginate irradiated in the 4% aqueous solution and the solid state (powdery). The molecular weight decreases in the liquid state with 1/10 of the dose required in the solid state. However, from the viewpoint of practical utilization, irradiation in solid state can be presumed to have a higher effectiveness than that of aqueous irradiation.


Fig. 5-6 Effect of irradiated oligo-alginate

The degree of growth promotion of rice in hydroponic solution with alginates irradiated at 0, 50 and 100 kGy are shown in this photograph. Marked growth promotion of the root is clearly observed when using irradiated alginate. A qualitative promotion effect was defined by measuring the weight of the dried specimens after 9 days grown in a greenhouse. By adding oligo-alginate prepared by irradiation with 100 kGy, a promotion effect of 20% was observed for a concentration of 20 to 50 ppm.


Fig. 5-7 Effect of oligo-alginate on photosynthesis

Effect of oligo-alginate on photosynthesis was measured on the basis of CO2 consumption (mM/m2/s) for peanuts foliar after spraying oligo-alginate. It can be seen CO2 consumption increases in the plant sprayed with oligo-alginate and photosynthesis is promoted.



Natural polysaccharides with high molecular weight like alginate and chitosan, which are found in seaweed and crustaceans, are widely utilized in food, pharmaceutical and bioengineering industries. Recently, oligo-saccharides derived from the depolymer-ization of polysaccharides by enzyme
reaction were shown to have novel features such as the enhancement of antibiosis, promotion of germination and root elongation of plants. We have studied radiation-induced depolymerization caused by chain scission, which is one of the characteristics
of the effect of radiation on organic materials, and clarified that the oligo-saccharides obtained by this radiation method have excellent functions.
When organic materials are irradiated by ionizing radiation, they are divided to two types, i.e., degradation (chain scission) type and chain link (crosslinking) type. Alginate is classified as a degradation type (Fig. 5-5). To confirm the plant growth promotion effect, the oligo-alginate prepared by radiation-induced depolymerization was supplied to rice through a hydroponic solution. A clear promotion effect can be seen (Fig. 5-6). In the case of peanuts, the effect was examined by using the method of spraying oligo-alginate to the foliar after 30 days of cultivation. By the spraying of the solution, which contained with 100 ppm of the oligo-alginate obtained by 100 kGy gamma-ray irradiation, 60% of growth promotion was confirmed after 15 days of spraying. Figure 5-7 is the result of the promotion of photosynthesis. The increases in biochemical and physiological function are confirmed. Moreover, it has been confirmed in field tests for peanut, tea, carrot and cabbage, that productivity increases 15-40% by using a solution with 20-100 ppm of oligo-alginate. Chitosan is also depolymerized by gamma-ray irradiation and growth promotion of the plant has been confirmed.


Reference
N.Q. Hien et al., Growth-Promotion of Plants with Depolymerized Alginates by Irradiation, Radiat. Phys. Chem., 59, 97 (2000).

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