Respiratory Properties of Mitochondria from Rice Seedlings Germinated under Water and Their Changes during Air Adaptation

Abstract

Respiratory activities were compared among rice seedlings germinated in air for 6 days (aerobic seedlings), those germinated under water for 5 days (submerged seedlings), and those grown in air for 1 day after 5 days' submerged germination (air-adapted seedlings). The respiratory activity of the submerged seedlings increased rapidly on transfer to air and reached a plateau at 16 hours in air. Respiration of the submerged seedlings was as sensitive to cyanide as those of aerobic and air-adapted seedlings. 2,4-Dinitrophenol had no effect on the respiration of the submerged seedlings, but stimulated those of the other two types of seedlings. Mitochondria from three types of seedlings did not differ in the ADP/O ratio and the respiratory control ratio (RCR) when succinate was oxidized. However, mitochondria from submerged seedln (submerged mitochondria) showed poor RCR of about unity when malate was oxidized. Both the rate of succinate oxidation and succinate dehydrogenase activity were low in submerged mitochondria, but increased during air adaptation. Although submerged mitochondria oxidized malate very slowly, this activity increased after exposure to air without any increase in malate dehydrogenase activity. When NADI was added to submerged mitochondria, oxidaton of malate was restored to the level of the aerobic controls. Addition of NADI enhanced the state 3 rate in submerged mitochondria, and RCR recovered to nearly the same value as that of the aerobic controls. Similar effects of NADI on 2-oxoglutarate oxidation were observed. All these defects in submerged mitochondria were repaired during air adaptation. These results suggest that NAD+-linked substrate oxidation was low in submerged mitochondria because of NADI deficiency, and that the oxidation increased with an increasing level of NADI during air adaptation.Rice seeds germinate in extremely anoxic environments (17,20,23). The seedlings show respiratory activity of a much lower rate than those of aerobically grown controls (20,22). This activity increases greatly after exposure to air (1,20) They were soaked in 60% ethanol solution for 3 min, then in Antiformin (1% active chlorine) for 20 min, after which they were washed thoroughly with sterilized distilled water. Stainless steel sieves 15 cm in diameter and 5 cm high were placed upside down and used as seedbeds. Seeds were sown on the screen and covered with a sheet of gauze, whose margin was fastened to the side of the sieve with a rubber band. This seedbed was put on the bottom of a container (Witt's filter jar 18 cm i.d.) containing sterilized distilled water 10 cm deep. The upper and side openings were plugged with a silicone sponge and stopper, respectively. All procedures for seeding were done in a Hitachi clean bench. The containers were placed in a dark room at 30°C. When the seeds germinated, roots and shoots were allowed to grow through the meshes of the steel screen and gauze, respectively. After 5 d of germination, water was drained off to the level just below the screen of the seed...

Effects of Anoxia on Mitochondrial Biogenesis in Rice Shoots

“…These promitochondria seem to be the precursors of functional mitochondria when anaerobically grown yeasts are returned to aerobic conditions (17). In contrast, the measurement of respiration in anaerobic tissues, in situ ultrastructural studies, and the isolation ofmitochondria from anoxia-treated tissues have shown that mitochondria are conserved in a potentially active configuration in the coleoptile of rice seedlings under anoxia (27,29,30).…”

Oxygen Initiation of Respiration and Mitochondrial Biogenesis in Rice

“…Historically, research into the effects of oxygen deprivation on mitochondria in plants has focused on ultrastructural changes to the appearance of these organelles and have shown that mitochondrial ultrastructure is maintained in anoxia-tolerant plant species, whereas a breakdown of the mitochondrial membrane structure is seen in cells of anoxia-intolerant species (12). Studies investigating the effect of oxygen deficit on mitochondrial function, in relatively mature rice tissues, have focused on changes in the abundance and activity of respiratory chain complexes and tricarboxylic acid cycle enzymes (11,(13)(14)(15)(16). Notably, a lack of heme-containing respiratory chain components in mitochondria isolated from tissue grown under anaerobic conditions and a rapid production of these components during reaeration has been shown (16), which appears to be analogous to the heme-linked oxygen response investigated in yeast and animals.…”

Changes in the Mitochondrial Proteome during the Anoxia to Air Transition in Rice Focus around Cytochrome-containing Respiratory Complexes

“…Some plant species exhibit extreme tolerance to prolonged anoxic conditions by maintaining an energy charge through increased glycolysis and redistributed energy allocation (9). Rice is one of the most anoxia-tolerant plant crop species (10), is able to germinate and sustain early seedling growth in strictly anoxic solutions (11,12) or even under a high vacuum (13), and can readily return to atmospheric or aerobic conditions without substantial damage (14,15). Under field conditions rice is often sown into anoxic mud in unstirred flooded land and germinates to meet aerobic conditions as it grows upward (16).…”

“…On the return of anoxically grown rice seedlings to air there are a number of well documented responses to sudden oxygen availability including increased respiratory rate (14), elevation of antioxidant enzymes such as catalase, ascorbate peroxidase, superoxide dismutase, dehydroascorbate/monohydroascorbate reductase, and glutathione reductase (15,17,18), and heightened levels of small molecule antioxidants such as glutathione, ascorbate, and ␣-tocopherol (15,17). Mitochondrial structures appear to proliferate in rice seedlings even when they are grown under anoxic conditions from dry seed.…”