Influence of x-rays on the fresh weight and the chlorophyll synthesis of spruce seedlings

Abstract

Since a few years, many X-ray techniques have been used for the control of forest tree seeds. The influence of high quantities of X-rays and the enduring character of these irradiations have been examined. After an imbibition time of 24 h selected seeds of Picea abies KARST. (provenance Bodensee) were irradiated during different periods, corresponding with 0 r, 690 r, 1.380 r, 2.590 r, 3.880 r, 5.175 r and 10.350 r. Determinations of the fresh weight and the chlorophyll content in different levels of the primary shoot have been done on nine weeks old seedlings. 1. Influence of X-rays on the fresh weight a. An irradiation time of 30 min (2.590 r) has a positive influence on the fresh weight of each considered primary shoot level. b. The irradiation effect disappears as the seedlings grow up and the slightest influence has been observed in the lowest levels of the primary shoot. c. The influence of the irradiation is not so strongly marked in the cotyledons because these needles are already present in the seed at the moment of the applied irradiations. 2. Influence of X-rays on the chlorophyll synthesis a. An irradiation time of 30 min (2.950 r) has a negative influence on the chlorophyll synthesis. This quantity of X-rays probably brakes high energetic reactions, necessary for the formation of chlorophyll. Irradiation times of 8 min (690 r) and 120 min (10.350 r) have a positive influence. b. This X-ray effect is lost as the needles become older and is replaced by a 'formation' effect. This influence is nothing else than a chlorophyll synthesis taking place in proportion to the fresh weight. c. The cotyledons must be considered separately. They are only liable to the 'formation' effect because a great part of the precursors, necessary for the formation of chlorophyll, exists before the X-ray treatment. The influence of the used irradiations (0 r ~ 10.350 r) is in the beginning of the development of the seedling very high, but disappears when the plant grows up. It can be expected that on one year old seedlings the consequences of a X-ray treatment can hardly be discovered anymore. On the other hand it must be mentioned that an irradiation time of 120 min (10.350 r) brings on a reduction of the germination percentage. Probably 10.000 r is the lethal limit dose.