Characterization of β-amylase and its deficiency in various rice cultivars

 β-Amylase deficiency in various cultivars of rice was examined at the molecular level. Using an antibody against β-amylase purified from germinating seeds of rice, we were able to demonstrate the expression and organization of the β-amylase gene in normal and deficient cultivars. Although β-amylase is a starch-hydrolyzing enzyme, as is α-amylase, the β-amylase protein/gene is expressed differently from the α-amylase protein/gene; i.e. (1) β-amylase is synthesized only in aleurone cells, (2) the enzyme production in the embryo-less half-seeds is not under hormonal control. We identified some cultivars of rice that are deficient for β-amylase activity. We present new evidence that synthesis is blocked at the level of mRNA synthesis in the deficient cultivars. The usefulness of β-amylase as a crop trait is also discussed. Received: 8 May 1998 / Accepted: 5 June 1998     

Release of Fe,Mn and P in a calcareous vertisol and yield of upland rice as influenced by presowing soil water treatments

Summary A field experiment was conducted on a calcareous vertisol at Mahatma Phule Agricultural University, Rahuri to study the release of Fe, Mn and P in soil and yield of two rice cultivars due to different soil water treatments for 15 days prior to sowing. Soil saturation (daily two irrigations) for 15 days prior to sowing increased the supply of Fe, Mn and P in soil at sowing as a result of reduction in pH and Eh. Dry matter yield at different growth stages as well as grain yields of Karjat 184 (dwarf) and Tuljapur 1 (tall) also increased due to presowing soil saturation treatment. Tuljapur 1 yielded more than Karjat 184 when grown under upland conditions. Laboratory incubation studies showed reduction in soil pH (from 8.6 to 7.5) and Eh (from +501 to +362 mv) at the end of 15 days under soil submergence treatment. Availability of Fe, Mn and P was also found to be increased.     

Changes in DTPA-iron and management of iron chlorosis in rice nurseries

Summary On a Typic Ustochrept soil incorporation of 10 tons/ha of a green manure plus submergence for 10 days followed by raising upland nursery checked iron chlorosis. In contrast, presubmergence with and without FYM and iron sulfate or pyrite were a failure. Nor weekly sprays with 3.0% iron sulfate were found very effective. The success of green manure plus submergence was associated with the mobilization of soil iron as a result of intense reduction and its subsequent retention in available form at a sufficient high level during the growth of upland nursery.     

Genetic mapping identifies a rice naringenin O-glucosyltransferase that influences insect resistance

Naringenin, the biochemical precursor for predominant flavonoids in grasses, provides protection against UV damage, pathogen infection and insect feeding. To identify previously unknown loci influencing naringenin accumulation in rice (Oryza sativa), recombinant inbred lines derived from the Nipponbare and IR64 cultivars were used to map a quantitative trait locus (QTL) for naringenin abundance to a region of 50 genes on rice chromosome 7. Examination of candidate genes in the QTL confidence interval identified four predicted uridine diphosphate-dependent glucosyltransferases (Os07g31960, Os07g32010, Os07g32020 and Os07g32060). In vitro assays demonstrated that one of these genes, Os07g32020 (UGT707A3), encodes a glucosyltransferase that converts naringenin and uridine diphosphate-glucose to naringenin-7-O-β-d -glucoside. The function of Os07g32020 was verified with CRISPR/Cas9 mutant lines, which accumulated more naringenin and less naringenin-7-O-β-d -glucoside and apigenin-7-O-β-d -glucoside than wild-type Nipponbare. Expression of Os12g13800, which encodes a naringenin 7-O-methyltransferase that produces sakuranetin, was elevated in the mutant lines after treatment with methyl jasmonate and insect pests, Spodoptera litura (cotton leafworm), Oxya hyla intricata (rice grasshopper) and Nilaparvata lugens (brown planthopper), leading to a higher accumulation of sakuranetin. Feeding damage from O. hyla intricata and N. lugens was reduced on the Os07g32020 mutant lines relative to Nipponbare. Modification of the Os07g32020 gene could be used to increase the production of naringenin and sakuranetin rice flavonoids in a more targeted manner. These findings may open up new opportunities for selective breeding of this important rice metabolic trait.     

Studies on a Quantitative Analysis of Oryzalides and Oryzalic Acids in Rice Plants by GC-SIM

A procedure for the quantitative analysis of oryzalides and oryzalic acids in leaves of rice cultivars was established by using GC-MS-selective ion monitoring (GC-SIM), 17-deuterated oryzalide B being used as an internal reference. The total contents of four compounds of oryzalides and oryzalic acids in the leaves at three different growth stages of Norin-27, i.e., seedling, tillering, and ripening, showed values of 5.3, 17.9, and 37.9 μg/g, respectively. The contents of oryzalides and oryzalic acids in each organ, i.e., leaf, stem, ear, and root, showed values of 35.0 and 1.7 μg/g for the former two, respectively, and were not detectable for the latter two. A preliminary analysis of Norin-27 and Rantai emas leaves inoculated with an incompatible and compatible strain of Xanthomonas campestris pv. oryzae showed a greater accumulation of oryzalides and oryzalic acids, especially in the lesion area, than the figures for healthy leaves. Mechanical injury by a needle-bundle also increased the total amounts.     

The Action of Rice Branching Enzyme I (BEI) on Starches

The rice branching enzyme I (BEI) overproduced in Escherichia coli cells was investigated with respect to action on starches. BEI treatment decreased the turbidity of starch suspensions with distinct pasting behaviors from a native starch. This result suggests the great potential of BEI as a molecular tool for the production of a novel glucan polymer.     

Proteomic Characterization of Tissue Expansion of Rice Scutellum Stimulated by Abscisic Acid

We found that appropriate treatment with a highly potent and long-lasting abscisic acid analog enhanced the tissue expansion of scutellum during early seedling development of rice, accompanied by increases of protein and starch accumulation in the tissue. A comparative display of the protein expression patterns in the abscisic acid analog-treated and non-treated tissues on two dimensional gel electrophoretogram indicated that approximately 30% of the scutellar proteins were induced by abscisic acid. The abscisic acid-induced proteins included sucrose metabolizing, glycolytic, and ATP-producing enzymes. Most of these enzyme proteins also increased during the seedling growth. In addition, the expression of some isoforms of UDP-glucose pyrophosphorylase, 3-phosphoglycerate kinase, and mitochondrial ATP synthase beta chain was stimulated in the scutellum, with suppressed expression of α-amylase. We concluded that abscisic acid directly and indirectly stimulates the expression of numerous proteins, including carbohydrate metabolic enzymes, in scutellar tissues.