Many plants are subjected to temporary anoxia or hypoxia as a result of flooding, waterlogging, or ice encasement. Among crop plants, rice (Oryza sativa L.) is the most tolerant of anoxic conditions (Mocquot et al., 1981), and corn (Zea mays L.) is also moderately tolerant (Johnson et al., 1989). In seedlings of these species, a number of metabolic changes have been observed in response to hypoxia, and evidence has been presented that at least some of these responses are adaptive, i.e. they increase the ability of the plant to survive the stress (Johnson et al., 1989). In anoxic conditions, cessation of oxidative phosphorylation typically results in a marked decrease in ATP levels (Raymond et al., 1985). This can be alleviated in tolerant species by an increase in alcoholic, lactic, and other fermentation pathways (Kennedy et al., 1992; Menegus et al., 19931, and many of the proteins induced by hypoxia are enzymes of these glycolytic pathways (Bailey-Serres et al., 1988). Chilling likewise creates energy stress (Stewart and Guinn, 1969) due to mitochondrial dysfunction (Lyons and Raison, 1970), and like hypoxia chilling induces alcohol dehydrogenase in corn and rice seedlings (Christie et al., 1991). 1-514-398-5069. 1As an additional adaptation to energy stress, glycolytic enzyme reactions consuming ATP can be at least partially replaced by reactions utilizing PPi as an energy source. In rice, anoxia induces an increase in SUC synthase (Ricard et al., 1991) as well as an increase in PPi:Fru-6-P l-phosphotransferase but not phosphofructokinase (Mertens et al., 1990). Since anoxia also induces an increase in Fru-2,6-bisphosphate (Mertens et al., 1990), which activates PPi: Fru-6-P 1-phosphotransferase in the glycolytic rather than the reverse direction (Enomoto et al., 1992), these effects of anoxia favor glycolytic pathways utilizing PPi over those consuming ATP. In corn, it has been noted that, although many glycolytic enzymes are induced by hypoxia, none of these are kinases (Bailey-Serres et al., 1988). Cytosolic PPi levels seem to be independent of those of ATP (Dancer et al., 1990) and unaffected by anoxic stress (Dancer and ap Rees, 1989). Moreover, the cytoplasmic acidification that commonly results from anaerobic metabolism tends to increase the free energy of hydrolysis of PPi but has the opposite effect on the free energy of ATP hydrolysis (Davies et al., 1993). It appears therefore that PPi metabolism may play an important role in plant adaptation to anoxia.The V-PPase (Rea and Poole, 1993) represents another enzyme that might advantageously replace an ATP-consuming one (the V-ATPase) in anoxia or chilling stress. These parallel proton pumps are ubiquitous in the plant kingdom, although present in differing proportions in various tissues and species. The reaction stoichiometries of the two enzymes (Davies et al., 1992;Schmidt and Briskin, 1993) permit them to generate approximately equal proton gradients (Hedrich et al., 1989) across the vacuolar membrane, and calculations of free energy changes (Davie...

In the United States, the two-stage theory of blood coagulation is widely accepted. This theory recently reviewed by Quick (1) and Eagle (2) suggests that in the first stage prothrombin, calcium ion and thromboplastin interact to form thrombin. Thrombin, in the second stage, converts fibrinogen to fibrin. Plasma thromboplastin has been considered to be of platelet origin. The phenomenon of the initiation of coagulation when blood is shed has been considered by many investigators to be due to the disintegration of platelets with the release of thromboplastin.It has been known for many years that the coagulation time of blood taken in paraffin tubes is much longer than that of blood taken in glass tubes. The explanation usually offered for this phenomenon is that the glass, acting as a foreign surface, destroys the platelets at a more rapid rate than occurs in the presence of paraffin. The increased amount of thromboplastin so liberated is then considered to be responsible for the shorter coagulation time in glass vessels. Nolf (3) has criticized this explanation. He states that his experimental data indicate that cell-and platelet-free plasma already contains all of the factors necessary for blood coagulation. He believes that the initiation of coagulation is the result of the direct modification of one or more of the constituents of cellfree plasma by contact with a foreign surface such as glass.In view of this difference of opinion, it seemed advisable to reinvestigate the role which foreign surfaces play in the blood coagulation reaction.

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