A rapid, simple test, complementary to the test for amylose content, was developed based on the consistency of a cold 4.4% milled-rice paste in 0.20 N-KOH. Consistency is measured by the length in a test tube of the cold gel held horizontally for 0.5 or 1 h. The consistency values are correlated with amylograph setback viscosity and can differentiate into three consistency types–low, medium, and high–even rice samples of similar amylose contents as long as they are between 24 to 30%.

A gel consistency test for eating quality of rice.

The influence of varied supply of phosphorus (10 and 250 mmol P m -3 ), potassium (50 and 2010 mmol K m -3 ) and magnesium (20 and 1000 mmol Mg m -3 ) on the partitioning of dry matter and carbohydrates (reducing sugars, sucrose and starch) between shoots and roots was studied in bean (Phaseolus vulgaris) plants grown in nutrient solution over a 12 d period. Shoot and root growth were quite differently affected by low supply of P, K, and Mg. The shoot/root dry weight ratios were 4.9 in the control (sufficient plants), 1.8 in P-deficient, 6.9 in K-deficient and 10.2 in Mg-deficient plants. In primary (source) leaves, but not in trifoliate leaves, concentrations of reducing sugars, sucrose and starch were also differently affected by low nutrient supply

Partitioning of shoot and root dry matter and carbohydrates in bean plants suffering from phosphorus, potassium and magnesium deficiency

Article de synthese a propos de la signification des enzymes, de la comparaison de la degradation de l'amidon de reserve et de l'amidon transitoire et de la localisation des enzymes degradant l'amidon dans la feuille vegetal

Biosynthesis and Degradation of Starch in Higher Plants

Publisher Summary This chapter reviews nonmutant starch granule composition and development, and focuses on genetic mutants and how they have been useful in understanding the complexity of polysaccharide biosynthesis and development. Plant species, which are important sources of commercial starch production are focused on, especially maize, because of the many known endosperm mutants of maize, which affect polysaccharide biosynthesis. The information gained applies to other species, and these effects are illustrated in the chapter. General trends in the genetics and physiology of starch development have been illustrated with examples. Starch is a common constituent of higher plants and a source of carbohydrates. Starch in chloroplasts is transitory and accumulates during the light period and is utilized during the dark. Storage starch accumulates in reserve organs during one phase of the plant's lifecycle and is utilized at another time. Starches from reserve organs of many plants are important in commerce. Although considerable effort has been directed at characterizing the enzymes involved in starch synthesis, the role of these enzymes and other factors in determining subtle variations in starch granule structure and starch fine structure remain largely unknown. Variations in granule structure can be associated with plant species, cultivars of a species, the environment in which a cultivar is grown, and genetic mutations.

Genetics and Physiology of Starch Development

Drought is the major environmental factor limiting crop productivity worldwide. We hypothesized that it is possible to enhance drought tolerance by delaying stress-induced senescence through the stress-induced synthesis of cytokinins in crop-plants. We generated transgenic rice (Oryza sativa) plants expressing an isopentenyltransferase (IPT) gene driven by P(SARK) , a stress- and maturation-induced promoter. Plants were tested for drought tolerance at two yield-sensitive developmental stages: pre- and post-anthesis. Under both treatments, the transgenic rice plants exhibited delayed response to stress with significantly higher grain yield (GY) when compared to wild-type plants. Gene expression analysis revealed a significant shift in expression of hormone-associated genes in the transgenic plants. During water-stress (WS), P(SARK)::IPT plants displayed increased expression of brassinosteroid-related genes and repression of jasmonate-related genes. Changes in hormone homeostasis were associated with resource(s) mobilization during stress. The transgenic plants displayed differential expression of genes encoding enzymes associated with hormone synthesis and hormone-regulated pathways. These changes and associated hormonal crosstalk resulted in the modification of source/sink relationships and a stronger sink capacity of the P(SARK)::IPT plants during WS. As a result, the transgenic plants had higher GY with improved quality (nutrients and starch content).

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Cytokinin‐mediated source/sink modifications improve drought tolerance and increase grain yield in rice under water‐stress

Changes in the content of starch, protein, and RNA and in the activity of their hydrolases in the rice endosperm (Oryza sativa L., variety IR8) were determined during the first week of germination without added nutrient both in the dark and in the light. Changes were generally more rapid in the dark than in the light. Oxygen uptake and RNase activity started to increase and the root protruded on the second day, followed by the coleoptile on the third day, and the primary leaf on the fourth day. ATP level was at a maximum on the fourth day. The activity of amylases and R enzyme increased progressively, but that of phosphorylase tended to decrease during starch degradation. A new alpha amylase isozyme band appeared during germination. Glucose was the major product of starch degradation. Sucrose, maltose, maltotriose, raffinose, and fructose were also detected. Protease activity reached a maximum on the fifth or sixth day and closely paralleled the increase in soluble amino N and soluble protein.In embryoless seed halves with 0.12 muM gibberellin As, peak protease activity occurred in 2.5 days and peak alpha amylase activity on the fifth day of incubation. The production of alpha amylase, protease, and R enzyme was inhibited by 40 muM cycloheximide, but only alpha amylase and R enzyme were inhibited by 20 mug/ml actinomycin D.

Biochemical Changes in the Rice Grain during Germination

The levels of starch, soluble sugars, protein, and enzymes involved in starch metabolism-alpha-amylase, beta-amylase, phosphorylase, Q-enzyme, R-enzyme, and starch synthetase -were assayed in dehulled developing rice grains (Oryzasativa L., variety IR8). Phosphorylase, Q-enzyme, and R-enzyme had peak activities 10 days after flowering, whereas alpha- and beta-amylases had maximal activities 14 days after flowering. Starch synthetase bound to the starch granule increased in activity up to 21 days after flowering. These enzymes (except the starch synthetases) were also detected by polyacrylamide gel electrophoresis. Their activity in grains at the midmilky stage (8-10 days after flowering) was determined in five pairs of lines with low and high amylose content from different crosses. The samples had similar levels of amylases, phosphorylase, R-enzyme, and Q-enzyme. The samples consistently differed in their levels of starch synthetase bound to the starch granule, which was proportional to amylose content. Granule-bound starch synthetase may be responsible for the integrity of amylose in the developing starch granule.

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Enzymes of starch metabolism in the developing rice grain.

The levels of starch and dextrin, free sugars, soluble protein, and enzymes involved in starch metabolism-alpha-amylase, beta-amylase, phosphorylase, Q-enzyme, R-enzyme, and ADP-glucose starch synthetases-were assayed in the leaf sheaths and culm of the rice plant (Oryza sativa L., variety IR8) during growth.Starch accumulation in the leaf sheaths reached a maximum 10 to 11 weeks after transplanting, the time of development of the rice panicle. Maximal concentration of free sugars occurred earlier. Starch and sugars in the leaf sheaths and culm decreased rapidly during grain development.During starch accumulation, the starch granules of the leaf sheaths increased slightly in size and its gelatinization temperature decreased. The molecular size of amylose and amylopectin and amylose content of the starch were similar in both culm and leaf sheaths.Changes in the level of soluble protein paralleled changes in starch level in the leaf sheaths. Among the enzymes, only synthetase bound to the starch granule paralleled the level of starch in the leaf sheaths and in the culm. ADP-glucose, but not UDP-glucose, was utilized as a glucosyl donor by these starch synthetases. Zymograms of these extracts showed only one alpha-amylase band, one beta-amylase band, two phosphorylase bands, and one Q-enzyme band.

Starch Metabolism in the Leaf Sheaths and Culm of Rice

A study was made of the changes in activity of enzymes involved in the breakdown of stored phytin, lipid, and hemicellulose in the aleurone layer of rice seed (Oryza sativa L., variety IR8) during the 1st week of germination in the light. Enzyme assays were made on crude extracts from degermed seed, and activities were expressed on a per seed basis. Phytase activity increased within the 1st day of germination. The increase in activity of most other enzymes—phosphomonoesterase, phosphodiesterase, esterase, lipase, peroxidase, catalase, β-glucosidase, and α- and β-galactosidase—closely followed the increase in protein content. Their peak activities occurred by the 5th to the 7th day. Some enzymes, such as β-1, 3-glucanase and α-amylase, continued to increase in activity after the 7th day. Phytase, β-1, 3-glucanase, and α-amylase followed a similar sequence of production in embryoless seed halves incubated in 0.12 μM gibberellin A3, but the production of lipase was delayed.

Evelyn P. Palmiano

Papers

Biochemical Changes in the Rice Grain during Germination

Enzymes of starch metabolism in the developing rice grain.

Starch Metabolism in the Leaf Sheaths and Culm of Rice

Changes in the Activity of Some Hydrolases, Peroxidase, and Catalase in the Rice Seed during Germination

Physicochemical Properties of Niigata Waxy Rices