Zenzaburo Kasai

FORMATION OF PHYTIC ACID IN CEREAL GRAINS

The ripening process of plants is characterized by the accumulation of substances in the seeds. The important mineral nutrient phosphorus is no exception to this accumulation process. The active transport of phosphorus to seeds from leaves and roots is an important part of the ripening. In the rice plant, at the end of the ripening, about 60% of the phosphorus in the whole plant is found in the grains.l Most of the phosphorus thus transported to the seeds exists in the form of phytic acid, inositol hexaphosphate. In cereal grains, 60-80% of the total phosphorus is found in phytic acid. It has been generally supposed that phytic acid functions as a storage form of phosphorus and is utilized as a source of phosphorus at germination. Recently, the occurrence of transphosphorylation between phytic acid and adenosine diphosphate has been suggested.2 Further, the occurrence of an enzyme catalyzing the transphosphorylation between phytic acid and guanosine diphosphate was established in mung bean.3 These findings show a more active participation of phytic acid as a phosphagen, rather than as a source of phosphorus at germination. We do not have much information regarding the formation of phytic acid, but the enzyme catalyzing the formation of inositol monophosphate has been fo~nd .4 -~ However, the phosphorylation mechanism in the biosynthesis of more highly phosphorylated inositol is unknown. Phytic acid is unique in having six phosphate ester linkages in one molecule of small molecular weight; hitherto, a highly phosphorylated compound such as phytic acid has not been known. From this point of view, it is supposed that phosphorylation of inositol is carried out through a mechanism different from the usual kinase reaction. A hypothesis for the mechanism of inositol phosphorylation, based on experiments on ripening grains of rice and wheat, is presented in this paper. According to this hypothesis, the phosphorylation of inositol in the formation of phytic acid does not occur in a sequential fashion through phosphorylated inositol, but occurs through a hypothetical phosphorylated inositol derivative. The occurrence of a new kind of polyphosphorylated inositol derivative in the ripening grains is postulated as a possible candidate.

Tartaric acid synthesis from l-ascorbic acid-1-14C in grape berries

Abstract Young grape berries were exposed to 14CO2 for 10 min under light and dark conditions, and changes of 14C-assimilation products was surveyed during a short period. In the light, radioactivity was found in tartaric acid immediately after 14CO2-fixation, while in the dark, radioactivity was not detected in tartaric acid until 480 min after 14CO2-fixation. d -Glucurono-γ-lactone-6-14C, l -ascorbate-1-14C, d -glucuronate-6-14C and sucrose-U-14C were fed to young grape berries, and the incorporation into tartaric acid was investigated. A considerable amount of radioactivity was incorporated into tartaric acid from d -glucurono-γ-lactone-6-14C and l -ascorbic acid-1-14C, and, in the case of l -ascorbic acid-1-14C, 72 per cent of the total radioactivity was found in tartaric acid. The tartaric acid synthesized was partly degraded; when sucrose-U-14C was fed, uniformly labeled tartaric acid was obtained, but when d -glucurono-γ-lactone-6-14C or l -ascorbic acid-1-14C was used, most of radioactivity was localized in the carboxyl groups.

Purification and characterization of acid phosphatase in aleurone particles of rice grains

The major acid phosphatase (EC 3.1.3.2) associated with aleurone particles of rice grains (Oryza sativa L. Japonica cv. Koshihikari) was purified to homogeneous state by polyacrylamide gel electrophoresis. Its molecular weight was 72,000 when determined by gel filtration and 68,000 when found by polyacrylamide gradient gel electrophoresis in the presence of sodium dodecyl sulfate and β-mercaptoethanol. The purified enzyme had a violet color and an absorption peak at 530 nm. Triton X-100 and lysolecithin stabilized the purified enzyme. The optimum pH for hydrolysis of p-nitrophenyl phosphate was 4.8. The enzyme hydrolyzed all inositol phosphates, several other phosphomonoesters and pyrophosphate. However, α,β-glycerol phosphate, glucose-6-phosphate, adenosine monophosphate and inosine monophosphate were not hydrolyzed. The Km for myo-inositol hexaphosphate was 0.43 mm, which was the lowest among myo-inositol phosphates. The Km value increased as the number of phosphate linkages on myo-inositol decreased. No correlation between the maximum initial velocity (Vmax) and Km was observed. Among the myo-inositol phosphates, the Vmax for myo-inositol triphosphate was the highest. The Km for p-nitrophenyl phosphate was 1.74 mm and that for ATP was 5.26 mm. l-Tartrate, orthophosphate, molybdate and arsenate were competitive inhibitors, and F(-) was a noncompetitive inhibitor. Ag(+), Zn(2+), Hg(2+), Cu(2+) and Fe(2+) were inhibitory and the enzyme was also inactivated by preincubation with EDTA.

Distribution of mineral elements in the outer layer of rice and wheat grains, using electron microprobe X-Ray analysis

Abstract Electron microprobe X-ray analysis was used to determine the transversal microdistribution of P, K, Mg, Ca, Fe, and Mn, with special attention to the outer layers of rice and wheat grains. P, K, Mg, Fe, and Mn were concentrated in the aleurone layer in each case. In particular, P, Mg, and K were highly concentrated in the subcellular particles of the aleurone layer, and had very similar distribution patterns in the outer layers of the matured grain of rice and wheat. By contrast, Ca was abundant in the pericarp.

Energy-dispersive x-ray analysis of phytin globoids in aleurone particles of developing rice grains

Abstract In this study energy-dispersive X-ray analysis was used to discover changes in the composition of phytin globoids in aleurone particles of developing rice grains. At early milky stage (the 7th to 10th day after flowering) many aleurone particles were observed as electron lucent vacuole-like particles in aleurone cells, some of which contained a small electron-dense inclusion (phytin globoid). The major mineral elements present in phytin globoids were phosphorus (P) and magnesium (Mg). Potassium (K) was also detectable but its concentration was extremely low relative to these two. Calcium (Ca) and zinc (Zn) were found as minor components. At early dough stage (the 17th to 19th day after ftowering) P, Mg and K were observed as the major mineral elements. The composition of mineral elements in phytin globoids tend to be constant in the late staae of ripening. On the other hand, minor elements, i.e. Ca and Zn, were only detectable in the early stage of ripening, suuesting that these elements accumula...

Ethylene Formation from Ethyl Moiety of Ethionine

In plants, ethylene is formed in the presence of light and flavin mononucleotide from ethionine and S-ethylcysteine. The ethylene is formed from the ethyl moiety of ethionine.

Conversion of tartrate to malate and monoethyl tartrate in grape leaves

Abstract 14 CO 2 evolution from l (+)-tartrate-[U- 14 C] in grape leaves was observed confirming the dissimilation of tartrate. 30 sec after the administration of l (+)-tartrate-[U- 14 C], 3 compounds were found to contain 14 C. Two of them were identified as monethyl tartrate and malate by chromatographic and MS studies. It is suggested that the 14 CO 2 evolved is derived from malate-[U- 14 C] which is metabolically formed from l (+)-tartrate-[U- 14 C], and that monoethyl tartrate is not an intermediate for the conversion to malate.

Diurnal change of tartrate dissimilation during the ripening of grapes

Abstract l (+)-tartrate-[U- 14 C] or sucrose-[U- 14 C] was fed into grape berries and 14 CO 2 evolution was determined. 14 CO 2 evolution front l (+)-tartrate-[U- 14 C] was slightly higher in mature than immature berries, and that from sucrose-[U- 14 C] was higher in immature than mature ones. 14 CO 2 evolution from l (+)-tartrate-[U- 14 C] was irregular throughout the day until 2 or 3 weeks after flowering. This stage shifted to regular 14 CO 2 evolution until 6 or 7 weeks after flowering, and the mode of 14 CO 2 evolution showed diurnal variation; higher in the day than at night. Then the stage without variation of 14 CO 2 evolution followed 10 weeks after flowering. These observations indicate that tartrate is not biochemically inert in grape berries, while the amount of 14 CO 2 evolution from sucrose-[U- 14 C] was higher at night than in the day through the whole ripening process, except in the early stage.

Growth of fruit-bodies inFavolus arcularius

The fruiting ofFavolus arcularius in culture is described. When the cultures, which have been pre-incubated in darkness to allow the inoculum mycelia to become thick and white wooly in texture, are exposed to light, fruit-body primordia, 1 mm in height, are formed about 4 days after the start of illumination. The primordium develops into a cylindrical stipe, the growth of which mainly occurs in the final 1 mm of the terminal region. Hyphal elongation in the region within 3 mm of the apex is predominant in the growth of the pileate stipe. With maturation of the stipe, changes in hyphal orientation occur on the periphery of the subapical region, and then the pileus-primordium is formed. The differentiation into the inner layer and the outer layer (pre-hymenial layer) in the pileus tissue is completed at this stage. The early growth of the pileus may be due to rapid elongation of the hyphae on the margin in addition to gradual expansion of the hyphae in the preformed pseudo-tissue. When the pileus has grown to about 3 mm in diameter, the subsequent three to four fold increase in size may be due to parallel expansion of the hyphae constituting the young pileus tissue.

ACID-SOLUBLE NUCLEOTIDES OF RIPENING RICE GRAINS.

Abstract Accumulation of starch, protein and other components in the grains of rice plant during the ripening process is one of the prominent features characterizing the change to the reproductive grOwth from the vegetative growth. Despite the fact that it has been assumed that in these processes nucleotides play a role, especially in the energy transformation and as a co-factor of enzymic action, no survey on the nucleotides in the ripening rice grains was performed. But several studies are found on the other phosphorus containing compounds. Fractionation of phosphorus compounds in the ripening rice grains was studied by Aimi and Konno 1), and ASADA and Kasai 2). Kurasawa et al 3) identified glucose-1-phosphate from the ripening rice grains.