Light and electron microscopic studies of corn plants (Zea mays I.) exposed to Pb in hydroponic solution showed that the roots generally accumulated a surface Pb precipitate and slowly accumulated Pb crystals in the cell walls. The root surface precipitate formed without the apparent influence of any cell organelles. In contrast, Pb taken up by roots was concentrated in dictyosome vesicles. Dictyosome vesicles containing cell wall material fused with one another to encase the Pb deposit. This encased deposit which was surrounded by a membrane migrated toward the outside of the cell where the membrane surrounding the deposit fused with the plasmalemma. The material surrounding the deposit then fused with the cell wall. The result of this process was a concentration of Pb deposits in the cell wall outside the plasmalemma. Similar deposits were observed in stems and leaves suggesting that Pb was transported and deposited in a similar manner.Many researchers have shown that plants will accumulate Pb either from soil, stem, or foliar application (1,3,8,9,13,14,16,25). However, the reports conflict as to the amounts accumulated and the amounts that can be translocated. Little has been done to localize the Pb accumulated within an organ, although Hammett (5-7) indicated that much of the Pb was associated with cell walls and nuclei, and Suchodoller (24) found that it was concentrated in the root cortex.It was the purpose of this research to study the localization of accumulated Pb and characterize the method of accumulation as specifically as possible. MATEIUALS AND METHODSCorn (Zea mays L. Wf9 X M14) was grown by a standard hydroponic procedure (19) in a greenhouse or was grown on paper toweling in a moist chamber.

Mitochondria isolated from etiolated Texas male-sterile (TMS) cytoplasm maize (Zea mays L.) seedlings were adversely affected by methomyl (Lannate, 90 wettable powder), while those isolated from normal-fertile seedlings were not. In a manner analogous to that reported for Bipolaris (Helminthosporium) maydis (race T) toxin, experiments with TMS mitochondria showed that 1 to 3 millimolar methomyl inhibited the state 4 oxidation rate of combined malate and pyruvate while stimulating that of succinate or exogenous reduced nicotinamide adenine dinucleotide. Similar concentrations of methomyl effected an inhibition of phosphorylation, an increase in the percentage of transmittance of light through mitochondrial suspensions, and a decrease in the density of the mitochondrial matrix. Methomyl (15 millimolar) had little effect on the physiological activity or ultrastructure of isolated normal-fertile mitochondria. These observations provide the opportunity to specifically assess the homogeneity, or lack of it, of a cytoplasmic heritable characteristic in a widely divergent group of higher plants.

A cytochemical study has been made on the localization of ATPase activity in corn (Zea mays L.) roots. Light microscopy shows washing for 4 hours to increase the general ATPase activity in the peripheral layers of the root cortex; oligomycin and N,N-dicyclohexylcarbodiimide inhibit this activity, oligomycin being more effective. Ultrastructural studies of ATPase Histochemical localization of ATPase activity was based on the widely used technique of precipitating the phosphate released by the dephosphorylation of ATP as an insoluble metal phosphate (5, 11-13, 24, 25). Several variations in the technique were used and the procedures are compared in Table I. The small segments used in methods 2, 3, and 5 were cut after washing (and pretreatment with oligomycin or DCCD) and stained as thin sections rather than as 1-cm segments. Washing and pretreatment were the same for all roots in methods 1 through 5. If the insoluble metal phosphate was Ca3(PO4)2 then it was converted to Pb3(PO4)2 by incubating the specimen in 1 mM Pb(NO3)2 for 10 min. If the specimens were to be observed by light microscopy, Pb3(PO4)2 was converted to PbS by incubating specimens in 4% ammonium sulfide for 10 min. Specimens were rinsed in distilled H20 (if not done previously, 250-,um free hand sections were cut at this time) and photographed. If the specimens were to be observed by electron microscopy, specimens were rinsed twice in buffer (see Table I) then postfixed in 2% OS04 in buffer for 1 hr. Specimens were rinsed three times in buffer and dehydrated in a graded ethyl alcohol series. Propylene oxide was used as a solvent for the Epon embedment.Controls were maintained by incubating specimens in glucose-6-P or f8-glycero-P at pH 7 in place of ATP, by completely omitting any phosphorous containing compound, or by omitting the capture agent.

This study examines the previously reported inhibitory effects of Cd on root growth. In hydroponic experiments, 100 μg Cd/ℓ effected a 33% inhibition of lateral root initiation of corn. The growth of corn and soybean primary roots was not reduced at Cd concentrations of 1 mg/ℓ, and the number of lateral root initials in soybeans was not reduced at 2 mg Cd/ℓ. The toxic effects of Cd were ameliorated by additions of Zn or by additions of Fe citrate to nutrient growth solutions. While both Zn and Fe additions did result in increased lateral root initiation, the number of initials was significantly lower than the controls. Lead had no effect on the initiation of soybean lateral roots at a concentration of 100 μg Pb/ℓ. However, 5 mg Pb/ℓ did effect a 21% decrease in corn lateral root initials, but this decrease could not be demonstrated with higher Pb concentrations.

The addition of 2‐deoxyglucose to tissue elicits an in vivo mitochondrial conformation response (contraction) that can be viewed ultrastructurally and is indicative of the phosphorylative capability of mitochondria. Utilizing this technique toxin from Bipolaris (Helminthosporium) maydis race T was found to penetrate leaf and root tissue of Texas male‐sterile cytoplasm corn (Zea mays L. W64A) only slowly, but once in cells the toxin had a rapid deleterious effect on mitochondrial function. It is concluded that B. maydis (race T) toxin has effects on in vivo mitochondria similar to those reported after in vitro experimentation and that mitochondria are a primary site of toxin action. These observations are followed by the suggestion that susceptibility or resistance to B. maydis (race T) is conferred in corn by a cytoplasmically inheritable character associated with mitochondria.