Week Of Germination Research Articles

Aspects of Nitrogen Metabolism in the Rice Seedling

The effects of nitrogen source NO(3) (-) or NH(4) (+) on nitrogen metabolism during the first 2 weeks of germination of the rice seedling (Oryza sativa L., var. IR22) grown in nutrient solution containing 40 mug/ml N were studied. Total, soluble protein, and free amino N levels were higher in the NH(4) (+)-grown seedling, particularly during the 1st week of germination. Asparagine accounted for most of the difference in free amino acid level, in both the root and the shoot. Nitrate and nitrite reductase activities were present mainly in the shoot and were higher in the NO(3) (-)-grown seedling, whereas the activity of glutamate dehydrogenase and glutamine synthetase in the root tended to be lower than that of the NH(4) (+)-grown seedling during the 1st week of germination. Glycolate oxidase and catalase activities were present mainly in the shoot. Maximum activity of the above five enzymes occurred 7 to 10 days after germination. Differences in the zymograms of nitrate reductase, glutamate dehydrogenase, and catalase were mainly between shoot and root and not from N source. Nitrite reductase bands were observed only in plants grown in plants grown in NO(3) (-).Ten-day-old seedlings of three rices differing in level of grain protein did not differ in the level of N fractions and of enzyme activities, which were consistent with their differences in grain protein content.

Altered Development of Ribonuclease Activity and Formation of Polyribosomes in Chilled Cotton Cotyledons1

Sensitivity of cotton (Gossypium hirsutum L.) seedlings to 6 C chilling was measured by following the development of ribonuclease (RNase) activity in cotyledons during the first week of germination. Increases in RNase activity observed in control tissues were delayed during chilling. Development of RNase activity was most sensitive to chilling during the second day of germination.Both total and specific activities of RNase preparations were similarly affected by chilling. Alterations of protein synthesis were suggested by comparisons of free polyribosome profiles from control and chilled tissues.Chilled seedlings partially recovered RNase activity following return to warm temperature. Recovery was slowest in seedlings that were chilled during both the second and third days of germination.

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

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, beta-glucosidase, and alpha- and beta-galactosidase-closely followed the increase in protein content. Their peak activities occurred by the 5th to the 7th day. Some enzymes, such as beta-1, 3-glucanase and alpha-amylase, continued to increase in activity after the 7th day. Phytase, beta-1, 3-glucanase, and alpha-amylase followed a similar sequence of production in embryoless seed halves incubated in 0.12 muM gibberellin A(3), but the production of lipase was delayed.

Biochemical Changes in the Rice Grain during Germination

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.

Transport of Materials from the Cotyledons during Germination of Seeds of the Garden Pea (Pisum sativumL.)

The transport of total dry matter, nitrogen, phosphorus, sulphur, potassium, and calcium from the cotyledons into the developing axis of young pea (Pisum sativum L.) seedlings has been studied under a variety of growth conditions. It is shown that the duration of transport increased when the plants were grown in distilled water, or in the dark, or upon removal of the shoot ; all these treatments delayed senescence of the cotyledons. On the other hand, the rate of transport was increased by treatments, such as the supply of calcium and phosphate in the medium, or darkness, which stimulate growth of the axis. Treatment of the seeds before germination with gibberellic acid (GA3) did not affect the movement of materials from the cotyledons although it changed the pattern of growth of the axis. After the first week of germination the relationship between the amounts of total dry matter, nitrogen, phosphorus, sulphur, and potassium transferred to the axis from the cotyledons in the intact plant remained approximately constant irrespective of the conditions of growth. It is proposed that the ratio in which the individual elements are transported is determined by the proportions in which they are released by the storage cells. Deviation from this ratio during the first week of germination, and over a longer period in deshooted plants is attributed to competition for the available nutrients between actively metabolizing cells in the cotyledons and axis. It is demonstrated by steam-girdling that movement of materials from the cotyledons into the shoot probably occurs via the phloem. Calcium is mobile in the phloem during the early stages of germination, possibly because the amount of free calcium in the cotyledons is high.

Amino acids, soluble proteins, and isoenzyme patterns of peroxidase during the germination of jack pine

In germinating jack pine, changes in nitrogenous compounds were separated into two phases, the first, where through imbibition, seeds expanded but the prospective seedling remained enclosed by the haploid and nutritive female gametophyte (0 to 3 days), and second, when radicles emerged and only cotyledons remained in contact with the gametophyte (4 to 11 days).During imbibition, total soluble N in seeds dropped and the amino acid pool was dominated by high levels of free arginine. As levels of arginine N declined the greatest changes in percentage composition involved glutamic acid (gametophyte) and glutamine (embryo). Thereafter, arginine N accumulated. By 7 days, arginine N was recovered in seedlings primarily from cotyledons. High asparagine levels were observed in stems and roots as glutamine N in the emerging seedling declined.Protein reserves in the seedling were nearly depleted by 4 days. Total protein and, at later stages, the ratio of hexone bases to dicarboxylic acids was generally higher in the gametophyte than in the seedling. Soluble proteins of the embryo were separated into at least 18 bands by disc electrophoresis and contained peroxidase activity which increased strongly after the first week of germination. The increase of nine isoenzymes of peroxidase with mobilities towards the anode correlated with the histochemical localization of peroxidase at the emerging shoot and root tips and throughout the vascular tissues.

Pyrimidine Metabolism in Cotyledons of Germinating Alaska Peas

Cotyledons from Pisum sativum L. cv. Alaska seeds were excised 12, 36, 108, 132, and 156 hours after imbibition in aerated distilled water. They were then incubated under aseptic conditions for 6 hours in solutions containing either uridine-2-(14)C or orotic acid-6-(14)C. Uridine was more extensively degraded to (14)CO(2) at all germination stages than was orotate, and these rates remained essentially constant at each stage. Incorporation of each compound into RNA increased about 2-fold from the 12th to the 156th hour, although the total RNA present decreased slightly over this interval. Paper chromatography of soluble labeled metabolites produced from orotate showed that the capacity to metabolize this pyrimidine increased markedly as germination progressed. Radioactivity in uridine-5'-P, uridine diphosphate-hexoses, and uridine diphosphate increased most, while smaller or less consistent increases in uridine, uracil, uridine triphosphate, and an unidentified UDPX compound were also observed. The data suggest that orotate metabolism was initially limited by orotidine-5'-phosphate pyrophosphorylase or by 5-phosphoribosyl-1-pyrophosphate. Incorporation of uridine into RNA appeared to be limited at the earliest germination periods by conversion of uridine-5'-P to uridine diphosphate. Thus, during the 1st week of germination the orotic acid pathway and a salvage pathway converting uridine into RNA become activated.

ARGININE METABOLISM IN GERMINATING SEEDS OF SOME MEMBERS OF THE LEGUMINOSAE

SummaryEstimation of the arginine content of germinating seeds of Vicia faba, Canazalia ensiformis, Phaseolus vulgaris and Pisum sativum, showed a lowering in concentration during the first week of germination. When [14C] arginine was fed to cotyledon discs of Vicia faba, ornithine, proline, urea and carbon dioxide quickly became labelled and other amino acids became labelled after a longer period of incubation. Arginase was extracted from the V. faba and shown to be present in the roots, shoots and cotyledons during the first 6 days of germination. Urease was also extracted from V. faba and shown to have a pH optimum of 8.0 for extraction. The possible presence of an ornithine cycle is discussed.