Grain Filling Characteristics and Their Relations with Endogenous Hormones in Large- and Small-Grain Mutants of Rice.

This study determined if the variation in grain filling parameters between two different spikelet types of rice (Oryza sativa L.) is regulated by the hormonal levels in the grains. Two rice mutants, namely, a large-grain mutant (AZU-M) and a small-grain mutant (ZF802-M), and their respective wild types (AZU-WT and ZF802-WT) were grown in the field. The endosperm cell division rate, filling rate, and hormonal levels: zeatin + zeatin riboside (Z+ZR), indo-3-acetic acid (IAA), polyamines (PAs), and abscisic acid (ABA) were determined. The results showed that there was no significant difference between the filling and endosperm cell division rates. These rates were synchronous between the superior and inferior spikelets for both mutants. However, the abovementioned parameters were significantly different between the two spikelet types for the two wild types. The superior spikelets filled faster and their filling rate was higher compared to the inferior ones. Changes in the concentrations of plant hormones were consistent with the observed endosperm cell division rate and the filling rate for both types of spikelets of mutant and wild type plants. Regression analysis showed a significant positive correlation between cell division and filling rates with the concentrations of the investigated hormones. Exogenous chemical application verified the role of ABA, IAA, and PAs in grain filling. The results indicate that poor filling of inferior spikelets in rice occurs primarily due to the reduced hormone concentrations therein, leading to lower division rate of endosperm cells, fewer endosperm cells, slower filling rate, and smaller grain weight.

Cytokinin metabolism in maize: Novel evidence of cytokinin abundance, interconversions and formation of a new trans-zeatin metabolic product with a weak anticytokinin activity.

Cytokinins (CKs) are an important group of phytohormones. Their tightly regulated and balanced levels are essential for proper cell division and plant organ development. Here we report precise quantification of CK metabolites and other phytohormones in maize reproductive organs in the course of pollination and kernel maturation. A novel enzymatic activity dependent on NADP(+) converting trans-zeatin (tZ) to 6-(3-methylpyrrol-1-yl)purine (MPP) was detected. MPP shows weak anticytokinin properties and inhibition of CK dehydrogenases due to their ability to bind to an active site in the opposite orientation than substrates. Although the physiological significance of tZ side-chain cyclization is not anticipated as the MPP occurrence in maize tissue is very low, properties of the novel CK metabolite indicate its potential for utilization in plant in vitro tissue culture. Furthermore, feeding experiments with different isoprenoid CKs revealed distinct preferences in glycosylation of tZ and cis-zeatin (cZ). While tZ is preferentially glucosylated at the N9 position, cZ forms mainly O-glucosides. Since O-glucosides, in contrast to N9-glucosides, are resistant to irreversible cleavage catalyzed by CK dehydrogenases, the observed preference of maize CK glycosyltransferases to O-glycosylate zeatin in the cis-position might be a reason why cZ derivatives are over-accumulated in different maize tissues and organs.

Inhibitory effect of zeatin, isolated from Fiatoua villosa, on acetylcholinesterase activity from PC12 cells.

Acetylcholinesterase (AChE) inhibitors, which enhance cholinergic transmission by reducing the enzymatic degradation of acetylcholine, are the only source of the compound that is currently approved for the treatment of Alzheimer's disease (AD). The methanol extract from Fiatoua villosa among 100 traditional edible plants that were tested, showed the most potent inhibitory effect (51%) on acetylcholinesterase in vitro. After the sequential solvent fractionation of the methanol extract of Fiatoua villosa, the active fraction was repeatedly subjected to open-column chromatography on silica gel. From the highest inhibitory fraction, the chloroform fraction (75%) on AChE, the single compound, was obtained by the Sep-Pak Cartridge (C18: reverse phase column). This compound was finally purified by HPLC (micro-bondapack C18 reverse phase column: 19 x 300 mm). According to the electron impact mass spectrometry (EI-MS), we confirmed that the molecular mass was 219 m/z. The structure of this compound was identified as zeatin [2-methyl-4-(1H-purine-6-ylamino)-2-buten-1-ol], one of the derivatives of purine adenine. The concentration that was required for 50% enzyme inhibition (IC50 value) was 1.09 x 10(-4) M. This study demonstrated that the zeatin from Fiatoua villosa appeared to be the most potent AChE inhibitor in AD.

Cell-division factors from Vinca rosca L. crown gall tumor tissue.

A cell-division factor has been precipitated from extracts of cultured Vinca rosea L. crown gall tumor tissue by using the mercuric acetate procedure previously employed by Wood and colleagues to obtain their "cytokinesin I." On the basis of its mass spectrum, ultraviolet light absorbancy spectra, solubilities, chromatographic migration values, and growth activity, the factor is ribosyl-trans-zeatin, that is, 6-(4-hydroxy-3-methyl-trans-2-butenylamino)-9-beta-D-ribofuranosylpurine. Ribosylzeatin has now been isolated from tumor tissue by four experimental techniques; any possibility that it is an artifact seems to have been eliminated. Contrary to the report by Wood and colleagues, synthetic ribosylzeatin is precipitated from an aqueous solution by mercuric acetate, provided the complete precipitation procedure is utilized. These facts and others discussed strongly support our suggestion that ribosylzeatin was present in the preparation ("cytokinesin I") examined by Wood and colleagues in several biological assays. The reasons advanced by Wood and others for rejecting this suggestion have been found either not to be pertinent to the question or to have insufficient experimental bases.