In wheat (Triticum aestivum I.) the level of seed dormancy expressed depends on the temperatures encountered during the grain‐filling period. Because of the significant role of seed dormancy in preharvest sprout damage of wheat cultivars, this study was undertaken to determine the levels of seed dormancy induced in wheat cultivars ‘Hyslop’, ‘Yamhill’, ‘P.I. 178211’, ‘Brevor’, and ‘Tom Thumb’ grown at controlled temperatures at 15 and 26°C in growth chambers during the grain‐filling period and in the field‐grown plants. The degree of dormancy was measured in terms of weighted germination percentage (WGP) that takes into account the rate and number of seeds that germinated at controlled germination temperatures of 15, 20, and 26°C. Yamhill and Hyslop exhibited the least potential for producing dormant seeds. Seeds of P.I. 17(1211, Brevor, and Tom Thumb acquire some dormancy when developed at 26°C, but the greatest degree of dormancy was measured in seeds developed at 15°C. It appears that the maximum potential a cultivar possesses for producing dormant seeds can be revealed by determining the germination of seeds developed at 15°C and germinated at 15, 20, and 26°C.

Rhizobium japonicum 122 DES bacteroids from soybean nodules possess an active H2-oxidizing system that recycles all of the H2 lost through nitrogenasedependent H2 evolution. The addition of 72 ,uM H2 to suspensions of bacteroids increased 02 uptake 300% and the rate of C2H2 reduction 300 to 500%. The optimal partial pressure of 02 was increased, and the partial pressure of 02 range for C2H2 reduction was extended by adding H2. A supply of succinate to bacteroids resulted in effects'similar to those obtained by adding H2. Both H2 and succinate provided respiratory protection for the N2-fixing system in bacteroids. The oxidation of H2 by bacteroids increased the steady-state pool of ATP by 20 to 40%. In the presence of 50 mM iodoacetate, which caused much greater inhibition of endogenous respiration than of H2 oxidation, the addition of H2 increased the steady-state pool of ATP in bacteroids by 500%. Inhibitor evidence and an absolute requirement for 02 indicated that the H2-stimulated ATP synthesis occurred through oxidative phosphorylation. In the presence of 50 mM iodoacetate, H2-dependent ATP synthesis occurred at a rate sufficient to support nitrogenase activity. The addition of H2 to H2 uptake-negative strains of R. japonicum had no effect on ATP formation or C2H2 reduction. It is concluded that the H2-oxidizing system in H2 uptake-positive bacteroids benefits the N2-fixing process by providing respiratory protection of the 02-labile nitrogenase proteins and generating ATP to support maximal rates of C2H2 reduction by oxidation of the H2 produced from the nitrogenase system.

Decoated ponderosa pine (Pinus ponderosa Laws) seeds contained 49%-lipids, whiclh were mainly stored in megagametophytic tissue and were utilized or converted to sugars via the glyoxylate cycle during germination. Mitochondria and glyoxysomes were isolated from the tissue by sucrose density gradient centrifugation at different stages of germination. It was found that isocitrate lyase, malate synthase, and catalase were mainly bound in glyoxysomes. Aconitase and fumarase were chiefly localized in mitochondria, whereas citrate synthase was common for both. Both organelles increased in quantity and specific activity of their respective marker enzymes witlh the advancement of germination.When the megagametophlyte was exhausted at the end of germination, the quantity of these organelles and the activity of their marker enzymes decreased abruptly. At (6) was followed for the estimation of total weight, lipids, sugars, and starch in megagametophytes and seedlings during germination. The total isocitrate lyase activity in tissue was completely solubilized and determined (20) in the soluble fraction extracted by grinding 10 megagametophytes or seedlings in 10 ml of tris-HCl buffer, 0.05 M, pH 7.5, which contained 10 mm mercaptoethanol and 1 mm disodium EDTA; centrifuging the slurry at 30,000g for 10 min; and treating the supernatant with charcoal (23).Isolation of Glyoxysomes. Using a constant weight of fresh material for isolation was found to be the key in obtaining reproducible results of organellar quantity and quality in the subsequent sucrose density gradient centrifugation, therefore, 7 g of megagametophyte tissue were used in all the experiments. The tissue was washed in 1 %0 sodium hypochlorite for 10 sec; chopped with a razor blade for 2 min in 10 ml of homogenizing medium which contained tris-HCl buffer (0.05 M, pH 7.5), 0.4 M sucrose, 10 mM mercaptoethanol or DTT,3 10 mm potassium chloride, 1 mm disodium EDTA, 0.5 mm magnesium chloride, and 0.1 % bovine serum albumin; and further homogenized in a mortar with a pestle for 30 sec with an additional 20 ml of medium. The homogenate was filtered through eight layers of cheesecloth and centrifuged at 5OOg in a Servall RC2 for 10 min. The supernatant was centrifuged at 10,OOOg for 10 min to sediment the crude pellet. The pellet was suspended in 2 ml of 32.5 c sucrose, layered over a discontinuous sucrose density gradient, and centrifuged for 4 hr in a SW 25.2 rotor, at 105,000g in a Spinco L2-HV ultracentrifuge. The gradient was composed of 15 ml of 60% (w/w) sucrose as a cushion in the bottom, then 8 ml each of 55, 50, 45, and 40%Y sucrose and S ml of 35%c sucrose. All the sucrose solutions contained 10 mm mercaptoethanol or DYT and 1 mM disodium EDTA. After centrifugation, 25 to 30 1-ml fractions were collected from the gradient in the density range from 1.17 to 1.27 with the aid of a Harvard Peti-pump which displaced a 63 %,, sucrose solution at a speed of 2 ml/min from the bottom of the gradient tube placed in an ISCO (Instrumentation Specialties Co.)...

An average of 540 picomoles of total adenosine phosphates was found in the embryo of mature seeds of ponderosa pine (Pinus ponderosa Laws.) and 1140 picomoles in the gametophyte. Adenylate energy charges were 0.44 and 0.26, respectively. After stratification, total adenosine phosphates increased 7-fold and 6-fold in embryo and gametophyte, respectively, and energy charges rose to 0.85 and 0.75. During germination, total adenosine phosphates increased to a 20-fold peak on the 9th day in gametophytic tissue, parallel with the peak of reserve regradation and organellar synthesis, and then decreased. In embryo and seedling, total adenosine phosphates elevated 80-fold with two distinct oscillating increases of AMP and ADP. (Table I). After the seedling length was measured, the seed coat was removed and the gametophyte was dissected. Fresh and dry weights (dried at 100 C for 24 hr) were determined on gametophytes and embryos or seedlings for each replication. Water content was calculated from the difference of fresh weight and dry weight.Determination of Adenosine Phosphates. Four seeds of the designated stage of germination were dissected into gametophyte and embryo or seedling in a moist chamber. The dissection of each seed took less than 10 sec in skilled hands. Each part was quickly extracted by 10 ml of boiling, glass-distilled water for 10 min at 100 C. The extract was cooled in an ice bath, and 0.8 ml of the original (early stages) or diluted (later stages) extract was incubated at 30 C for 15 min in each of the following mixtures (8).A. For ATP determination, 0.1 ml of reaction buffer containing 0.5 M N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), pH 7.5, and 0.5 M magnesium acetate and 0.1 ml of glass-distilled water. B. For ADP and ATP determination, 0.1 ml of the reaction buffer and 0.1 ml of solution containing 20 ,ug of pyruvate kinase (EC 2.7.1.40) (Sigma, crystalline), and 500 nmoles of trisodium phosphoenolpyruvate (Calbiochem).C. For TAP, 0.1 ml of the reaction buffer, and 0.1 ml of solution containing 20 ,ug of pyruvate kinase, 500 nmoles of trisodium phosphoenolpyruvate. and 20 ,.tg of dialyzed (against 1 mM phosphate buffer, pH 7.0) adenylate kinase (EC 2.7.4.3) (Sigma).After incubation, the extracts were either stored at 0 C overnight or assayed immediately by the luciferin-luciferase method using an Aminco Chem-Glow photometer (24