David B. Dickinson

Germination of Lily Pollen: Respiration and Tube Growth

Germinating pollen of Lilium longiflorum (cv. Ace) briefly exhibited a high rate of respiration before pollen tubes began to grow. A second period of high respiration occurred while tubes were growing. Between these periods respiration proceeded at a lower rate. Respiration was stimulated by 2,4-dinitrophenol to occur at approximately the same rate in all three periods.

Dimethyl sulfoxide protects tightly coupled mitochondria from freezing damage.

Dimethyl sulfoxide prevented loss of respiratory control and decrease in efficiency of oxidative phosphorylation when plant mitochondria were stored in liquid nitrogen. Respiration was severely inhibited and was not stimulated by adenosine diphosphate when mitochondria were frozen in liquid nitrogen without dimethyl sulfoxide. Thus, isolated mitochondria provide a model system for the study of the effects of freezing on biological membranes and of the prevention, by dimethyl sulfoxide, of freezing damage.

Partial purification and sugar nucleotide inhibition of UDP-glucose pyrophosphorylase from Lilium longiflorum pollen

Abstract Uridine diphosphate glucose pyrophosphorylase was purified 34-fold from ungerminated pollen of Lilium longiflorum using ammonium sulfate fractionation, sephadex G-200 gel filtration, and DEAE-cellulose ion exchange column chromatography. Its kinetic properties and inhibition by uridine diphosphate sugars were determined using an isotopic assay which employs retention of the product, UDP-[ 14 C] glucose, on DEAE cellulose discs. The Michaelis-Menten constants for the substrates UTP and glucose-1- P were 0.14 m m and 0.46 m m , respectively. Inhibitor studies showed UDP-glucose, UDP-glucuronic acid, UDP-galacturonic acid, UDP-xylose, UDP-galactose, and UDP-mannose to be noncompetitive with the substrate glucose-1- P (only V max decreased), and mixed competitive and noncompetitive ( K m increased, and V max decreased) with the substrate UTP. The apparent inhibition constants ( K i ) were determined to be; UDP-glucose, 0.13 m m ; UDP-glucuronic acid, 0.75 m m ; UDP-galacturonic acid, 0.93 m m ; UDP-xylose, 1.6 m m ; UDP-galactose, 4.8 m m ; and UDP-mannose, 9.6 m m . In various combinations tested these inhibitors showed simple additive inhibition when present at low individual concentrations (0.4 m m for UDP-galactose, and 0.1 m m for the others) in the presence of low substrate concentrations (UTP at 0.32 m m and glucose-1- P at 0.58 m m ). The results of these in vitro studies indicate the possibility that the uridine diphosphate sugars and uridine diphosphate sugar acids, which are the last soluble precursors for cell wall polysaccharide biosynthesis, participate in vivo in a cumulative feedback manner at the UDP-glucose pyrophosphorylase reaction. Such feedback could, in turn, modulate the flow of carbon into pathways leading to cell wall polysaccharides.

Properties of uridine diphosphoglucose dehydrogenase from pollen of Lilium longiflorum

UDP-glucose dehydrogenase was partially purified from germinating lily pollen (Lilium longiflorum). The enzyme was associated with the particulate fraction in extracts of nongerminated pollen but could be solubilized when this fraction was treated with the detergent Tween 80. The enzyme was inhibited by UDP-galacturonic acid, UDP-glucuronic acid, and UDP-xylose. The latter was a powerful inhibitor when concentration of the substrate UDP-glucose was low and caused the normally hyperbolic UDP-glucose saturation curve to become sigmoid. These data were interpreted as indicating cooperative effects, UDP-glucose dehydrogenase being viewed as a regulatory enzyme.

Antigen E content of pollen from individual plants of short ragweed (Ambrosia artemisiifolia)

A study was conducted to ascertain how much variation in allergenic potency of ragweed pollen occurs among individual plants and different plant populations in a restricted geographic area. Seeds of the short ragweed (Ambrosia artemisiifolia) were collected from 38 different sites in Champaign County, Ill. Plants from these seeds were grown under similar conditions, and antigen E (AgE) was determined on pollen samples harvested from individual plants. The populations from various sites in Champaign County differed by as much as severalfold with respect to mean AgE values. There were statistically significant differences among population means, although large variations occurred among plants within populations. Further research was conducted to learn whether the level of AgE was determined by genetic factors within the plants. Genetic regulation was indicated by the finding that 3 plants which had unusually low levels of pollen AgE all produced offspring with significantly lower mean AgE levels than those of control plants.

Hexokinase from maize endosperm

Abstract Hexokinase was detected in the endosperm of developing and germinating maize seeds. Hexokinase activities in the endosperm of germinating dent, flint, and floury genotypes were quite similar, but were only one-fifth of the activity of shrunken-2 (sugary) genotype. A reduced enzyme level in endosperm of germinating compared to developing seeds, and a continual decline in enzyme during germination suggest that hexokinase in the endosperm of germinating maize is residual and has no major metabolic role. In the endosperm of developing seed the enzyme would be important as a first step in the metabolism of translocated sugars.

Reserve carbohydrates from kernels of sugary and sugary enhancer maize

Abstract Mature seeds of ‘sugary’ (su) and ‘sugary-sugary enhancer’ (su-se) maize inbreds were compared with respect to amount and properties of starch and glycogen. Sugars and sorbitol were also determined. Sucrose and maltose were elevated in the su-se seeds, starch was reduced and phytoglycogen was within the range expected for an su line. The se trait did not result in altered structure of the starch or phytoglycogen. Hence, it is unlikely that the observed increase in maltose resulted from premature action of amylases on starch and phytoglycogen during seed maturation.

Sugar characteristics of sweet corn populations from a sugary enhancer breeding program

SummaryEndosperm sugars and sorbitol were determined on 18 sweet corn (Zea mays L.) populations from a breeding program undertaken to transfer the sugary enhacer (se) gene into diverse sugary (su) backgrounds. Three subpopulations of IL677a, the source of se, and six su Se inbreds were included for comparison. Mature dry kernels of between two and four successive generations of these populations were analyzed. Immature kernels at two developmental stages (21 and 35 days after pollination) were also analyzed for one generation.Eleven of the breeding populations closely resemble IL677a, with high sucrose at the edible stage (21 days after pollination) and maltose accumulating as the seeds matured. In most instances, the distinctive sugar profiles were observed consistently in dry seeds of various generations. Hence, it appears that the se trait can be transferred successfully into su cultivars having various genetic backgrounds. The remaining seven breeding populations possessed elevated sucrose and glucose compared to most of the standard su Se inbreds, but maltose did not accumulate during seed maturation. It is not clear whether se was transferred to these populations and its expression modified or whether another trait was responsible. There were also marked differences in glucose levels among the su Se populations examined.

Metabolism of Germinating Lily Pollen: Pollen Enzymes*

Publisher Summary This chapter discusses a study conducted to learn whether enzymes that produce carbon skeletons and energy for polysaccharide biosynthesis occur in mature lily pollen or appear during germination. Pollen of Lilium longiflorum cv. Ace was incubated in pentaerythritol +3 mM KPO4. Pyrophosphorylases were assayed by the adsorption of radioactive product to DEAE-cellulose paper and counting in a Packard scintillation counter. UDP-glucose pyrophosphorylase is present in an apparent 80-fold excess, and it is not yet known whether pollen starch synthetase reacts with UDP-glucose. As UDP-glucose is thought to be the precursor for callose, cellulose, pectin, and at least part of the hemicelluloses, UDP-glucose pyrophosphorylase probably catalyzes a vital step in pollen wall synthesis.

Nucleotide stimulation of the uncoupler-initiated inhibition of mitochondrial succinate oxidation

Abstract Tomato fruit mitochondria depended upon adenine nucleotide to relieve the inhibition of succinate oxidation initiated by uncouplers of oxidative phosphorylation. Both ADP and ATP were effective. Magnesium and other divalent cations enhanced this effectiveness. Oligomycin, sufficient to repress state 3 respiration in coupled mitochondria, slightly diminished but did not eliminate the effect of ADP. Relief by ADP depended on orthophosphate, negating the possibility that ATP, synthesized by adenylate kinase, was the basis of relief. The stimulation by the nucleotides thus did not appear to require the energy of ATP or to function through a reversible reaction involving ATP and ADP plus Pi. Stimulation may, therefore, result from a binding by nucleotide which effects a favorable conformation for respiration and/or an unfavorable condition for binding by an inhibitor. Pyruvate prevented the inhibition, indicating that oxaloacetate was the immediate cause of the inhibition.