Effects of 22 herbicides on the synthesis of RNA and protein were investigated in excised tissues. The assays measured ATP and orotate incorporation into RNA, leucine incorporation into protein, and the gibberellin-controlled induction of a-amylase Statistical analysis of the average responses measured in the four assays suggested that 14 of the herbicides inhibited RNA and protein biosynthesesin vivo.The most inhibitory chemicals were 4-hydroxy-3,5-diiodobenzonitrile (ioxynil), 2-sec-butyl-4,6-dinitrophenol (dinoseb), 3',4'-dichloropropionanilide (propanil), 2,3,5-trichloro-4-pyridinol (pyriclor), and isopropylm-chlorocarbanilate (chlorpropham). The activity of an RNA polymerase isolated from corn(Zea maysL.) tissue was inhibited maximally at approximately 20% by ioxynil, dinoseb, and pyriclor. Hence, interference with RNA polymerase, which performs a pivotal role in RNA and protein biosyntheses, does not fully account for all inhibitions.

SUMMARY Biochemical effects of sulphur dioxide arise from its unique ability to act as an oxidizing or a reducing agent. Among some of the important metabolic effects are direct interference with photosynthetic CO2 fixation (competitive inhibition of ribulose diphosphate carboxylase by SO3−) and with energy metabolism (inhibition of mitochondrial ATP production by SO3=). Many indirect effects result from formation of sulphites and organic sulphonates with other cell constituents. These compounds can cause inhibition of a variety of metabolic enzyme systems. All these factors are probably instrumental in the gross disruption of chloroplast and mitochondrial ultrastructure. Injurious effects result when sulphur dioxide is taken up in excess of the capacity of the tissue to incorporate sulphur into the normal metabolic activities. The ubiquitous presence of small amounts of SO, and the subtle and varied nature of its biochemical effects suggest that crop losses to SO, pollution may be more widespread and serious than is generally suspected.

Integrated studies comprising biochemical and electron microscopic analysis suggested that the increase in respiratory activity of pea cotyledon mitochondria during germination results from further development of the original mitochondria present in dormant seeds. Electron microscopy of isolated mitochondria as well as mitochondria in situ has revealed that membranes are scarce in the mitochondria present in dormant seeds. Mitochondrial cristae become well developed during the initial stages of germination. Crude mitochondrial preparations from pea cotyledons were fractionated by sucrose density gradient centrifugation and analyzed through electron microscopy. These studies showed that, at all stages of germination, "peroxisome"-like structures were present in the fractions of higher sucrose densities than that containing mitochondria. Biochemical studies revealed that the activities of catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6) and peroxidase (guaicol:H2O2 oxidoreductase, EC 1.11.1.7) were associated mainly with these fractions and their activities increased during germination.

Treatment of jack pine (Pinus banksiana Lamb.) seedlings with gaseous SO2 resulted in a shift between the reducing and non‐reducing sugars. Increasing concentrations of gaseous SO2 caused an increase in reducing sugars and a decline in the non‐reducing sugars, suggesting a conversion from the latter to the former at high SO2 concentrations. The total amino acid content of the intact tissues also increased with increasing concentrations of gaseous SO2. Gas‐liquid chromatographic analyses of the amino acids indicated that SO2 (1. 34 mg · m‐3 for 96 h) resulted in an increase in the content of alanine, valine, glycine, isoleucine, leucine, threonine, aspartic acid tyrosine, lysine, and arginine, and a decrease in the content of serine and glutamic acid. The enzymatic and other implications of such changes are discussed.

Our laboratory has been investigating membranelinked functions of plant mitochondria which might help explain active ion transport. Corn mitochondria will actively accumulate calcium + phosphate in a process very like that of animal mitochondria (9); i.e., a high energy intermediate derived from substrate oxidation or ATP furnishes the energy.'With the substrate-powered system, there appears to be a competition between uptake and ATP formation, for the addition of ADP + hexokinase trap diminished calcium uptake. However, unlike animal mitochondria, the corn mitochondria proved to require phosphate for calcium uptake. Furthermore, the accumulation of magniesium and phosphate could not be demonstrated unless some calcium was present.These experiments were done with low concentrations of calcium (0.1-0.2 mm) in order to avoid uncoupling the mitochondria. We had observed that concentrations of calcium of 1 mM and higher reduced P/O ratios, and we assumed that calcium was acting as an uncoupling agent, a view commonly expressed on the basis of experiments with mammalian mitochondria. Calcium has been long known to stimulate acceptorless respiration of animal mitochondria (16,17) and to induce adenosine triphosphatase activity (13), thus mimicking the action of the uncoupling agent, 2,4-dinitrophenol (DNP). Calcium also accelerates the swelling of animal mitochondria, which is thought to reflect a calcium-stimulated release of fatty acids, or U-factor (10).More recent work suggests that the action of calcium is more complex than initially visualized. Chance (2)