Response to Anoxia in Rice and Wheat Seedlings

Abstract

ABSTRACT31P nuclear magnetic resonance spectroscopy was used to measure intracellular pH in living tissues. Oxygen deprivation caused fast cytoplasmic acidification from pH 7.4 to 7.0 in shoots of rice, Oryza sativa L. var arborio, a species highly resistant to anoxia. Acidification was complete after 10 minutes of anoxia. Alkalinization of both cytosplasm and vacuole followed thereafter. In the anoxia intolerant wheat shoots, Triticum aestivum L. var MEK, the same treatment caused a sharper cytoplasmic acidification, from pH 7.4 to 6.6, which occurred during a period of 2 hours. Cytoplasmic acidification continued with progress of anoxia and there was no vacuolar alkalinization comparable to the one observed in rice. In wheat oxygen, withdrawal also caused the reduction of both glucose-6-phosphate level and of metabolic rate. It also induced heavy losses of inorganic phosphate from tissues. Conversely, in rice, glucose-6-phosphate level and metabolic rate were increased and inorganic phosphate leakage from tissues was completely absent. These results are discussed in relation to the mechanisms of plant resistance to anoxia.According to studies on maize root tips, resistance to anoxia resides in the ability of some plants in exploiting the initial, lactate-based cytoplasmic acidification, to stop further lactate production and to activate at the same time alcoholic fermentation (22). The the synthesis of new isozymes and lasted for days, suggesting a long-term function for LDH in plants subjected to ROA. In the highly anoxia-tolerant rice shoots, alcoholic fermentation started in the absence of (21) or with limited lactate production (14). Instead, a prolonged though low succinate production was found (16).The response of plants to ROA has been shown to be accompanied by a revolution in the expression of genetic information. In particular, it results in the increase in several glycolytic and fermentative enzyme activities (24). Apparently, the success of resisting to anoxia is mediated by an increase in carbon flux through glycolytic and fermentative chains. Such an increase may be enhanced by acclimatization of plants through pretreatment in hypoxia (10).Anoxia caused acidification of cell sap in shoot tissues of sensitive plants like wheat and barley. In contrast, cell sap alkalinization has been observed in resistant species like rice and Echinochloa crus-galli (14). Metabolic proton consumption has been indicated as an important device used by plants to counteract or prevent cell sap acidosis (14). In the present study we evaluated whether and to what extent cytoplasmic acidification was still induced by ROA in a resistant plant like rice in spite of the previously reported alkalinization of cell sap in this species (14,15 RESPONSE TO ANOXIA IN RICE AND WHEAT SEEDLINGSand circulation of incubation media (6). The central glass tube of the airlift system for the upward flow of gas and medium had a diameter of 5 mm. Gases were delivered inside this tube, just above the signal detecting zone at the rate of 5 ...

Defining Core Metabolic and Transcriptomic Responses to Oxygen Availability in Rice Embryos and Young Seedlings

“…A number of the metabolite responses we observed also support previous reports in oxygendeprived rice seedlings. These include increases in the amino acids Ala, Val, Gly, Leu, Arg, Tyr, Phe, Pro, and 4-aminobutyrate (Bertani et al, 1981;Reggiani et al, 1988), the organic acids succinate and lactate (Menegus et al, 1988(Menegus et al, , 1989, and the hexose phosphate Fru-6-P (Menegus et al, 1991) as well as decreases in the amino acids Glu, Gln, Asp, and Asn (Bertani et al, 1981;Reggiani et al, 1988), the organic acid 2-oxoglutarate (Reggiani et al, 1988), and the sugars Glc and Fru (Menegus et al, 1991). The polyamine putrescine has been previously shown to accumulate approximately 2.5-fold in 3-d-old aerobically grown rice seedlings transferred to anoxia for 2 d (Reggiani et al, 1989).…”

Gibberellic Acid Induces Vacuolar Acidification in Barley Aleurone.

“…et al, 1990a, 19906). Stresses such as anoxia (Menegus et al, 1991), osmotic shock (Okazaki et al, 1996), and temperature shock (Yoshida, 1995) can affect the pH v . pH v also varies according to cell function.…”

“…pH, can also change during development; for example, during lemon fruit maturation, the pH, can drop from 6.2 to as low as 2.2 (Sinclair, 1984). Stresses, such as anoxia (Menegus et al, 1991) and chilling (Yoshida, 1995), can also alter pH,. Little is known, however, about the pH, in plant cells that respond to hormones.…”

Differential Molecular Responses of Rice and Wheat Coleoptiles to Anoxia Reveal Novel Metabolic Adaptations in Amino Acid Metabolism for Tissue Tolerance

“…Furthermore, the study of two species, as opposed to two cultivars of the same species, may be useful in highlighting mechanisms of anoxia adaptation in plants differing in the contexts of their domestication. Rice is an ideal model species for elucidating the mechanisms of anoxia tolerance in plants; its full genome sequence is available (Yu et al, 2002), it can survive under prolonged anoxia, and it can even display elongation of its coleoptiles under anoxic conditions (Menegus et al, 1991;Perata et al, 1997). A critical aspect of rice anoxia tolerance is the induction of the starch-degrading enzyme a-amylase under anoxia, providing a continuing supply of substrates for metabolism (Perata et al, 1992).…”