Programmed cell death in the root cortex of soybean root necrosis mutants

The soybean root necrosis (rn) mutation causes a progressive browning of the root soon after germination that is associated with accumulation of phytoalexins and pathogenesis-related proteins and an increased tolerance to root-borne infection by the fungal pathogen, Phytophthora sojae. Grafting and decapitation experiments indicate that the rn phenotype is root-autonomous at the macroscopic level. However, the onset and severity of browning was modulated in intact plants by exposure to light, as was the extent of lateral root formation, suggesting that both lateral roots and the rn phenotype could be directly or indirectly controlled by similar shoot-derived factors. Browning first occurs in differentiated inner cortical cells adjacent to the stele and is preceded by a wave of autofluorescence that emanates from cortical cells opposite the xylem poles and spreads across the cortex. Before any visible changes in autofluorescence or browning, fragmented DNA was detected by TUNEL (Terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling) in small clusters of inner cortical cells that subsequently could be distinguished cytologically from neighboring cells throughout rn root development. Inner cortical cells overlying lateral root primordia in either Rn or rn plants also were stained by TUNEL. Features commonly observed in animal cell apoptosis were confirmed by electron microscopy but, surprisingly, cells with a necrotic morphology were detected alongside apoptotic cells in the cortex of rn roots when TUNEL-positive cells were first observed. The two morphologies may represent different stages of a common pathway for programmed cell death (pcd) in plant roots, or two separate pathways of pcd could be involved. The phenotype of rn plants suggests that the Rn gene could either negatively regulate cortical cell death or be required for cortical cell survival. The possibility of a mechanistic link between cortical cell death in rn plants and during lateral root emergence is discussed.

Role of the regulatory gene pl in the photocontrol of maize anthocyanin pigmentation

The pl gene encodes a regulatory protein that controls the transcription of a number of structural genes of the anthocyanin biosynthetic pathway in maize. pl alleles have been classified phenotypically into two categories: dominant (Pl) alleles lead to intense, light-independent pigmentation in vegetative and floral organs of the plant; recessive "sun-red" alleles (pl) lead to light-dependent red pigmentation in which only tissues exposed to light become pigmented. Based on these observations, two alternate pathways leading to anthocyanin synthesis in the plant have been proposed: one requiring light and the other bypassing the light requirement through the action of Pl. To evaluate this hypothesis, we have analyzed light-independent and light-dependent alleles of pl. Sequence analysis revealed that the two types of alleles have very distinct promoters but have the capacity to encode very similar proteins. The protein encoded by one recessive allele was shown to be functional in transient assays. Measurements of husk mRNA levels by quantitative polymerase chain reaction showed that sun-red pl alleles are expressed at much lower levels than a Pl allele, but their expression is increased approximately sixfold by exposure to light. These results lead to the conclusion that the sun-red pl alleles are not null; instead, they synthesize functional mRNA and protein. We propose that the light-dependent pigmentation observed in pl plants is the result of a threshold effect in which light exposure boosts pl mRNA expression past a crucial level necessary to generate sufficient PL protein molecules to activate transcription of the anthocyanin structural genes.

Electrical Energy Changes Conductivity and Determines Optimal Electrotransformation Frequency in Gram-Negative Bacteria

In many bacterial electrotransformation protocols, pulse time is related to the time constant for a capacitor discharging across a sample of fixed resistance. Using an electroporator which controls pulse time independently of the capacitor time constant, we found that the resistance of bacterial suspensions fluctuates widely during capacitor discharge. With three gram-negative species of bacteria, electrotransformation frequency and survival could be more simply related to the electrical energy delivered in each pulse than to component parameters, such as initial field strength, capacitance, and pulse time. In each case, the number of transformants per survivor increased exponentially and leveled off when more than 0.5 to 1.0 J of electrical energy was delivered. An inverse log-linear relationship between survival and energy delivered was also observed for all three species.

Factors affecting PEG-mediated stable transformation of maize protoplasts

Factors influencing the frequency of stable transformation and co-transformation of maize protoplasts utilizing a polyethylene glycol (PEG) mediated DNA uptake procedure have been investigated. Protoplast plating conditions, pre-treatment buffer composition, PEG concentration, and DNA concentration were all found to be important. Carrier DNA was not beneficial when transforming with circular plasmid DNA. The effect of linearizing plasmid DNA was inconsistent across experiments, and may be dependent on the presence of carrier DNA. Functional co-transformation of an unlinked marker gene (hygromycin phosphotransferase) was increased by increasing the ratio of nonselected:selected DNA, and varied from 39% at a 1∶1 ratio to 65% at a 100∶1 ratio. Under optimum conditions, up to 300 transformed calli were recovered per million input protoplasts. The protocol is simple, inexpensive, and effective, and is useful for studies in maize requiring large numbers of stably transformed or co-transformed cell lines.

Strain-Specific Inhibition of nod Gene Induction in Bradyrhizobium japonicum by Flavonoid Compounds

A broad-host-range plasmid, pEA2-21, containing a Bradyrhizobium japonicum nodABC'-'lacZ translational fusion was used to identify strain-specific inhibitors of the genes required for soybean nodulation, the common nod genes. The responses of type strains of B. japonicum serogroups USDA 110, USDA 123, USDA 127, USDA 129, USDA 122, and USDA 138 to nod gene inhibitors were compared. Few compounds inhibited nod gene expression in B. japonicum USDA 110. In contrast, nod gene expression in strains belonging to several other serogroups was inhibited by most of the flavonoids tested. However, the application of two of these strain-specific compounds, chrysin and naringenin, had little effect on the pattern of competition between indigenous and inoculum strains of B. japonicum in greenhouse and field trials. Preliminary studies with radiolabeled chrysin and naringenin suggest that the different responses to nod gene inhibitors may be partly due to the degree to which plant flavonoids can be metabolized by each strain.

The ribosomal DNA of Luzula pilosa (L.) Willd, a plant with holocentric chromosomes

The ribosomal DNA (rDNA) of Luzula pilosa (L.) Willd, a plant with holocentric chromosomes, has been cloned and characterized by restriction mapping. The major variant is present in about 730 tandemly arranged copies per haploid genome which occupy nearly an entire chromosome. We propose that much of the rDNA is flanked or interspersed by kinetochores, so that reciprocal interchromatid exchanges in this region would lead to chromosome breakage. Homogenization and amplification of rDNA spacer length variants may occur largely by intrachromatid exchanges and gene conversion. By trying to isolate rDNA junction fragments which might be closely linked to centromeric DNA, we have isolated three minor rDNA variants whose spacer regions do not cross-hybridize with one another or with the major variant. The possibility that these minor variants may be rRNA pseudogenes is discussed.Key words: centromere, holocentric, Luzula, rDNA, recombination.

The identification and high level expression of a protein encoded by the yeast Ty element

Transcription of the yeast Ty element, Ty1 -15, was placed under the control of the efficient PGK promoter on the yeast expression vector, pMA91 . In extracts of yeast transformants containing these constructions a new 52 K basic polypeptide was detected by one- and two-dimensional electrophoresis and was shown, by hybrid arrested translation, to be specifically encoded by the Ty element. The protein coding region was mapped to the first 1.45 kb of the transcribed region of Ty1 -15. These data show for the first time that Ty elements encode proteins and illustrate the general usefulness of high efficiency expression vectors for the detection of rare products.

Expression of Ty-lacZ fusions in Saccharomyces cerevisiae

We have determined the nucleotide sequence of about 520 bp spanning the 5' delta regions (Figure 1) of two Tyl elements. There is an open reading frame running out of the deltas for at least 180 nucleotides into the internal region of each element. The functional significance of these open reading frames has been tested by fusing them to a defective E.coli lacZ gene. Expression of B-galactosidase in yeast transformants containing these fusions shows that Tyl elements contain functional translation signals.

Referrals to social workers: a comparative study of a local authority intake team with a general practice attachment scheme

We studied clients seen by social workers in two settings, one a conventional intake team in a social services department and another where clients were referred to social workers attached to a primary health care team.In both groups a high proportion of clients were either physically ill or disabled and the attachment group had a high proportion of clients with mental ill health. A large proportion of both groups were elderly and in general they had similar characteristics.However, clients referred to intake teams were more likely to be unemployed, to be living on benefits in council or rented accommodation, and to have had some contact with social services before. The attachment group consisted of more women who were either housewives or working, living on either their own earnings or their husbands', and were more likely to own their own homes and not to have had previous contact with social services.Clients referred to attached social workers were more likely to have an emotional or relationship problem, and many had practical problems as well. The implication is that attachment schemes will tap a wider section of the community and that the additional clients will have as many and as severe problems as clients referred to intake teams.