Sequence diversity in the coat protein coding region of the genome RNA of Johnsongrass mosaic virus in Australia.

Sequence diversity in the coat protein coding region of Australian strains of Johnsongrass mosaic virus (JGMV) was investigated. Field isolates were sampled during a seven year period from Johnsongrass, sorghum and corn across the northern grain growing region. The 23 isolates were found to have greater than 94% nucleotide and amino acid sequence identity. The Australian isolates and two strains from the U.S.A. had about 90% nucleotide sequence identity and were between 19 and 30% different in the N-terminus of the coat protein. Two amino acid residues were found in the core region of the coat protein in isolates obtained from sorghum having the Krish gene for JGMV resistance that differed from those found in isolates from other hosts which did not have this single dominant resistance gene. These amino acid changes may have been responsible for overcoming the resistance conferred by the Krish gene for JGMV resistance in sorghum. The identification of these variable regions was essential for the development of durable pathogen-derived resistance to JGMV in sorghum.

Infectivity of in vitro transcripts of Johnsongrass mosaic potyvirus full-length cDNA clones in maize and sorghum.

In vitro transcripts of full-length cDNA clones of the Johnsongrass strain of Johnsongrass mosaic potyvirus (JGMV-Jg) were infectious on maize and sorghum when inoculated by mechanical or by biolistic bombardment. Two of the cDNA clones with spontaneous mutations in the coat protein were not infectious. Sequence differences between infectious and non-infectious transcripts revealed that alteration of inferred amino sequences, near or in the N-terminus of the coat protein, profoundly affected the infectivity of transcripts. Transcripts of chimeric full-length cDNA of JGMV-Jg, containing coat protein sequences from the Krish-infecting strain of JGMV, were infectious in Krish resistant sorghums.

Coat protein sequence of Krish-infecting strain of Johnsongrass mosaic potyvirus.

The morphology of an Australian strain of Johnsongrass mosaic potyvirus (JGMV Krish-infecting strain), capable of infecting sorghums carrying the Krish potyvirus resistance gene, was investigated and the base sequence of the coat protein region determined. Under the electron microscope the virus was indistinguishable from the wild type prevalent in Australia, JGMV-Jg. However, there were some significant changes in the inferred amino acid sequence in both the N-terminus and the core regions of the coat protein. Some of these amino acid changes may be responsible for breaking the resistance of sorghums carrying the Krish virus resistance gene. In the discussion mention is made of a preliminary result with a mutated in vitro transcript which supports this suggestion.

Replication of maize streak virus mutants in maize protoplasts: evidence for a movement protein.

We have used protoplasts derived from a maize (Black Mexican Sweet) suspension culture to study the replication of maize streak virus (MSV) wild-type (wt) and mutant DNA genomes. Following inoculation with plasmids containing multimeric copies of MSV, both single-stranded (ss) and double-stranded MSV DNA forms were produced, in proportions relative to those seen in infected plants. The immunodetection of coat protein (PV2) and geminate particles confirmed that the protoplasts were able to support the entire multiplication cycle of MSV and therefore were suitable for the study of MSV gene function. Inoculation of protoplasts with V1 gene mutants which are unable to produce systemic infections in plants resulted in DNA replication and encapsidation indistinguishable from that obtained with wt constructs implicating the protein in virus movement. Computer analysis of the V1 protein (PV1) indicated a potential trans-membrane or membrane-embedded domain. Following inoculation of protoplasts with V2 mutants, ssDNA was not detected; the inability of these mutants to spread in plants may be due to a lack of ssDNA, PV2, or a combination of the two. The requirements for systemic infection of MSV are discussed.

Microautoradiographic investigations of sulfate uptake by glands and epidermal cells of water lily (Nymphaea) leaves with special reference to the effect of poly-L-lysine.

The uptake of(35)S-labelled sulfate ions into hydropote cells (densely cytoplasmic gland cells) and into epidermal cells (highly vacuolated cells) ofNymphaea leaves is dependent on metabolic energy. Only a very small fraction of the accumulated(35)S is incorporated into organic macromolecules during the experimental period. Both cell types exhibit a hyperbolic isotherm for(35)S uptake from labelled K2SO4 solutions over an external concentration range of 0 to 0.5MM. Although the gland and epidermal cells behave qualitatively similarly, the glands generally absorb about twice as much(35)S per unit area of sections of the cells as do the epidermal cells. At 3 °C, poly-L-lysine concentrations of 10(-8) M and up to 10(-7) M enhance(35)S uptake by the epidermal and gland cells for the first 7.5 hr after application of the poly-L-lysine. Samples treated with 5×10(-7) M poly-L-lysine are indistinguishable from the controls over the same period. After longer periods of treatment with poly-L-lysine (7.5 to 24 hr), the rates of(35)S uptake were reduced by all poly-L-lysine concentrations between the range 10(-8) to 5×10(-7) M. After 7.5 hr of(35)S uptake, the control samples contained the smallest amount of label, but after an uptake period of 24 hr the amount of label in the controls is considerably larger than in samples treated with poly-L-lysine. The results suggest that poly-L-lysine increases the membrane permeability and alters the metabolic uptake of sulfate in both hydropotes and epidermal cells.

Stomatal movement and potassium transport in epidermal strips of Zea mays: The effect of CO2.

The correlation between stomatal action and potassium movement in the epidermis of Zea mays was examined in isolated epidermal strips floated on distilled water. Stomatal opening in the isolated epidermis is reversible in response to alternate periods of light or darkness, and is always correlated with a shift in the potassium content of the guard cells. K accumulates in guard cells during stomatal opening, and moves from the guard cells into the subsidiary cells during rapid stomatal closure. When epidermal strips are illuminated in normal air, as against CO2-free air, the stomata do not open and there is a virtually complete depletion of K from the stomatal apparatus. In darkness CO2-containing air inhibits stomatal opening and K accumulation in guard cells, but does not lead to a depletion of K from the stomata as observed in the light.

Coupling of ion transport in green cells ofAtriplex spongiosa leaves to energy sources in the light and in the dark.

The coupling of ion transport to energy sources in the light and in the dark in green cells ofAtriplex spongiosa leaves was investigated using light of different qualities, an inhibitor of electron transport (dichlorophenyl dimethyl urea), and an uncoupler (p-CF3O-carbonyl cyanide phenylhydrazone). Two different mechanisms of ion uptake were, distinguished. (1) A light-dependent Cl(-) pump which is linked to light-dependent K(+) uptake. The energy for this pump is probably derived from photosynthetic electron transport or from nicotinamide adenine dinucleotide phosphate, reduced form. This mechanism is dichlorophenyl dimethyl urea-sensitive and enhanced by uncouplers. (2) A mechanism independent of light, which operates at the same rate in the light and in the dark. This mechanism is sensitive to uncouplers. It is probably aK-Na exchange mechanism since K(+) and Cl(-) uptake and a small net uptake of H(+) are balanced by Na(+) loss.