Effects of O₂ Concentration on Rice Seedlings

Abstract

The ability of rice, wheat, and oat seedlngs to germinate and grow as the 02 concentration was lowered to zero was compared. The germination of rice was completely unaffected by 02 supply, whereas that of oats and wheat was strongly retarded at levels below 5% 02. In contrast to the coleopties of oats and wheat and to roots of all three species where growth was progressively diminished as the 02 concentration was lowered, that of the rice coleoptile was progressively increased. However, the dry weight and content of protein, sugars, and cellulose were all depressed In the rice coleoptile in anoxia, and the levels of several respiratory enzymes, particularly those of mitochondria, were also much lower than those of the coleoptiles grown in air. In 1% 02, the growth of the rice coleoptile was similar to that in air. The effect of ethanol concentration on germination and growth of rice was measured. Coleoptile growth was reduced when the ethanol concentration exceeded 40 mfllimolarity, and root growth was somewhat more sensitive. Coleoptiles of all three species grown in air were transferred to N2, and ethanol accumulation was measured over 24 hours. The rate of ethanol accumulation in oats was close to that in rice, and in all three species the amounts of ethanol lost to the surrounding medium were those expected from simple diffusion from the tissue. The ability of the rice coleoptile to grow in anoxia is apparently not due to a particularly low rate of ethanol formation or to unusual ethanol tolerance. Any explanation of the success of rice in anoxia must encompass the much lower rate of ATP synthesis than that in air and account for the biochemical deficiencies of the coleoptile.When deprived of 02, the seeds of most higher plant species fail to germinate, and for plants growing in air the imposition of anaerobic conditions prevents their further growth. Rice is one of the few species whose seeds can germinate in anaerobic conditions. Although there is now an extensive literature on some aspects of growth and anaerobic metabolism in rice, the biochemical basis for its unusual adaptation to anoxia is not known (8). It is frequently inferred that rice germinates better in the absence of 02, although several authors have emphasized that only the coleoptile elongates and no roots are produced under these conditions (4,11,17,22,31,33,34). In this paper, we present data on the growth and some biochemical features of rice seeds exposed to different levels of 02 Seeds sterilized in 1% NaOCl were germinated in darkness in 250-ml flasks containing five Whatman No. 1 filter papers and 7 ml H20. A moistened gas stream of air, 5% 02, 1% 02 or N2 (99.998% purity) was passed through the flasks at 3 ml/min throughout the experiment period.Growth Measurements. Increases in fresh and dry weights of roots, coleoptiles, and primary leaves were recorded over a 7-d period.Effect of Ethanol on Germination. Seeds were germinated in air in darkness in the presence of a graded series of ethanol concentrations from 0.08% (14 mM...

Effects of Seed Hydropriming on Germination and Seedling Vigor during Emergence of Rice under Different Soil Moisture Conditions

“…At these soil moisture contents particularly at 20%, standing water was observed and anaerobic conditions probably developed. Under anaerobic condition, rice seeds germinate by coleoptile elongation [34,35]. However, in some rice genotypes, germination time is longer under anaerobic than aerobic conditions [36][37][38].…”

Distribution of Starch-degrading Enzymes in Rice Grains of Different Cultivars and Elution Behavior during Cooking

“…These isoforms are classified into two groups based on their optimal temperatures: α-amylase I (70℃) and α-amylase II (37℃) (Mitsui et al, 1996). These α-amylase isoforms are strongly induced during germination (Alpi and Beevers, 1983;Perata et al, 1992;Perata et al, 1993) and play a major role in degrading native starch to oligosaccharides during rice seed development. The β-amylases reagents were purchased from Wako Pure Chemicals (Osaka, Japan), unless otherwise noted.…”

Anaerobic Stress in Germinating Castor Bean, Ethanol Metabolism, and Effects on Subcellular Organelles

“…In the earlier investigation of anoxic castor bean endosperm, Kobr and Beevers (1 1) followed ethanol accumulation for 2 h in endosperms after 5 d germination. However, plant tissues are often capable of producing ethanol for longer periods of time (1,4).One purpose of this study was to determine the extent and regulation ofethanol production in castor bean during prolonged anoxia as a function of seedling age. Also, we examined the possibility that other alcohols might be produced and metabolized during anoxia.…”

“…In the earlier investigation of anoxic castor bean endosperm, Kobr and Beevers (1 1) followed ethanol accumulation for 2 h in endosperms after 5 d germination. However, plant tissues are often capable of producing ethanol for longer periods of time (1,4).…”

“…Ethanol is produced by flooded seedlings (1,18,19), ice encased leaves (2), root nodules (20), and tissues exposed to S02 and 03 (10). The endosperm of germinating castor bean endosperm is an appropriate model to study anaerobic stress and alcohol metabolism.…”