Fatty acid alteration of plastidic and extra-plastidic membrane lipids in metribuzin-resistant photoautotrophic Chenopodium rubrum cells as compared to wild-type cells.

The fatty acid compositions of plastidic and extra-plastidic membrane lipids of two metribuzin-resistant cell lines L4 and L7 of Chenopodium rubrum were determined after growth in the absence and in the presence of the herbicide and compared with those of wild type cells. Fatty acid biosynthesis was markedly affected in all cell lines by metribuzin treatment. In the absence and in the presence of metribuzin alterations of the fatty acid composition of the various lipid classes were, as compared to wild type cells, generally lower in the highly resistant L4 cells than in the less resistant L7 cells. The two resistant cell lines demonstrated a higher degree of unsaturation within the plastidic monogalactosyldiacylglycerols (L4 cells also within plastidic digalactosyldiacylglycerols) and, particularly, within the predominantly extra-plastidic phosphatidylcholines (L7 cells also within the predominantly extra-plastidic phosphatidylethanolamines), whereas the degree of unsaturation was slightly altered in the plastidic phosphatidylglycerols. Within the two metribuzin-resistant cell lines, the highly resistant L4 cells differed from the less resistant L7 cells by increased alpha-linolenic acid/palmitic acid ratios in both the plastidic and extra-plastidic membrane lipids suggesting that particularly in L4 cells higher proportions of linolenate are formed as a result of selection pressure. On the other hand, the proportion of linoleate was increased predominantly in extra-plastidic membrane lipids of both L4 and L7 cells which explains a raise in linoleic acid/palmitic acid ratios in both cell lines as compared to wild-type cells. Moreover, in the absence of metribuzin decreased proportions of trans-3-hexadecenoic acid were found in phosphatidylglycerols of L4 and, particularly, of L7 cells as compared to the wild type cells. It is suggested that L4 and L7 cells--having multiple mutations in the psbA gene as observed earlier--are additionally characterized by increased degree of unsaturation of acyl moieties in various polar lipids, e.g. linoleoyl moieties in L4 and L7 cells as well as linolenoyl moieties particularly in highly resistant L4 cells. This increase gives rise to a change in membrane fluidity and may finally lead to increased metribuzin resistance.

Genes expressed in Ascochyta rabiei-inoculated chickpea plants and elicited cell cultures as detected by differential cDNA-hybridization.

In response to the exogenous application of elicitors and attempted invasion by pathogens, plants exhibit a wide range of defense reactions. To understand the defense mechanisms at the level of gene activation and deactivation, differential screenings were performed to isolate cDNA clones which are differentially expressed in pathogen-inoculated resistant chickpea plants and elicitor-treated cell cultures. A plenty of genes were isolated and arranged in 5 groups, namely defense-related pathways, signal transduction pathways, regulation of gene expression, catabolic pathways and primary metabolism. Most of these genes were activated although several genes were also found to be suppressed. We discuss the plausible functions of cDNA products in plant defense responses. The cDNAs provide a variety of tools to investigate molecular mechanisms of defense responses and clearly reflect the massive genomic and metabolic changes which occur during manifestation of antimicrobial defense.

A new psbA mutation yielding an amino-acid exchange at the lumen-exposed site of the D1 protein.

In eight metribuzin-resistant photoautotrophic cell cultures of Chenopodium rubrum (Thiemann and Barz, 1994 a, b) sequence analyses of a part of the psbA gene coding for the photosystem-II D1 protein had revealed different double and triple mutations within the herbicide binding niche of the protein (Schwenger-Erger et al., 1993). Two pairs of the examined cell lines carried identical mutations within this part of the protein, although their growth performance and their herbicide resistance patterns were different, both at the cellular and the thylakoid level. Starting from the known part of the psbA gene we have amplified the remaining psbA sequences using inverse polymerase chain reaction. Thus the complete sequence of the coding part of the gene was elucidated. After sequence analyses we found an additional amino acid exchange at the position 184 (ile-->asn) of the D1 protein in cell line L1. Metabolic consequences of this mutation are discussed. Partial sequence analyses of the psbD gene of the herbicide resistant cell culture lines revealed no mutation within that part of the D2 protein, which is in direct contact with the D1 protein.

Metribuzin resistance in photoautotrophic Chenopodium rubrum cell cultures. Characterization of double and triple mutations in the psbA gene.

Sequence analysis of eight metribuzin-resistant mutants of photoautotrophic Chenopodium rubrum cell cultures revealed new mutations in the psbA gene coding for the 32 kDa herbicide binding protein. Mutants were found to possess either two or three changes in the amino acid sequence of the D1-protein between positions 219 and 272.