Acid Soluble Nucleotides in Rice Plants at Ripening Stage and Effect of Removal of Ears on the Nucleotide Pool

[摘要] In the previous work, a survey of acid soluble nucleotides in whole rice plants was carried out at their different growth-stages, and only adenosine nucleotides were found to show the remarkable change at the ripening stage. The present study was done to make clear which part of the rice plant is attributable to these changes. Rice plants were harvested at one month after heading and divided into grains and leaved including culms. Nucleotides were extracted from each sample and fractionated. Furthermore, nuclectides were surveyed on the plant whose ears were cut off at the flowering stage, and the pattern of nucleotides was compared to that of the non-treated plant. Seventy-two grams of each plant part were homogenized with 0.6 N cold perchloric acid in a cold room. The extract was concentrated in vacuo and fractionated with Dowex-1 anion exchange column chromatography. Stepwise elution of "HC1-NaC1" system was carried out. Outline of the method was illustrated in fig.1. The ion exchange chromatograms of the extracts from rice plants were shown in fig. 2. In this figure, the following materials were used :(a); grains, (b); leaves and culms, and (c) ;leaves and culms of the plant whose ears were cut off at the early flowering stage. The nucleotides in each peak were identified by the following measurements; the position of the peaks on the ion exchange chromatogram, absorption spectra (210-310mμ), absorbance ratios (250mμ/260 mμ, 280 mμ/260 mμ, and 290 mμ/26Q mμ) and paper chromatography. As shown in fig. 4, each peak-VI from the samples (a) and (c) contains ADP-glucose (adenosine diphosphate glucose). As shown in fig. 2, grains contained ADP-glucose (peak-VI) but leaves and culms little. By the cutting off of the ear, ADP-glucose was accumulated in the leaves and culms. The appearance of peak-VIII, which contains ATP (adenosine triphosphate), was also similar to that of ADP-glucose. But, the accumulation of ATP by the cutting off of the ear was not clear as compared to ADP-glucose. Peak- VII, which contailns UDP-glucose (uridine diphosphate glucose), appeared in all samples. Peak-V appeared typically in leaves and culms, but the substance responsible for this peak may not be the nucleotide. Localization of these nuclectides between each sample was summarized in table 3. As shown in this table, UDP-glucose and UTP (uridine triphosphate) uniformly existed in every part. Adenosine nucleotides such as AMP (adenosine monophosphdte), ADP-glucose and ATP, and uridine nucleotides such as UMP (uridine monophosphate) and UDP (uridine diphosphate) existed a small amount in the part of leaves and culms, but there were large amounts of these nucleotides in the part of grains. By the removal of the ear, AMP, ADP-glucose, ATP and UMP accumulated in the part of leaves and culms. From the results of the present experiments, adenosine and uridine derivatives were found to be rich in the ripening rice plant. But other nucleotides such as cytidine mono-, di-, and tri-phosphate were little. These results were also observed by Asada and Kasai. They reported that the rather high content of uridine derivatives in the ripening ricd grains is of interest for their special role in the metabolism of sugars. But the present auther wants to point out that ADP-glucose may take a role in the biosynthesis of starch in the ripening rice plant as indicated by Murata et al. Because ADP-glucose was present only in grains but UDP-glucose was uniformly present in the ripening rice plant.

[学科分类] 农业科学（综合）