A gene encoding a chloroplast-targeted lipoxygenase in tomato leaves is transiently induced by wounding, systemin, and methyl jasmonate.

We investigated the relationship between the expression of lipoxygenase (LOX) genes and the systemin-dependent wound response in tomato (Lycopersicon esculentum) leaves. A polymerase chain reaction-based approach was used to isolate two tomato Lox cDNAs, called TomLoxC and TomLoxD. Both TomLOXC and TomLOXD amino acid sequences possess an N-terminal extension of about 60 residues that were shown by in vitro uptake to function as transit peptides, targeting these proteins into the chloroplast. Within 30 to 50 min following wounding or systemin or methyl jasmonate treatments, the TomLoxD mRNA level increased and reached a maximum between 1 and 2 h. TomLoxC mRNA was not detectable in leaves and was not found following wounding, but it was found in ripening fruits, indicating that the two tomato Lox genes are regulated in different tissues by different processes. The results suggest that the TomLoxD gene is up-regulated in leaves in response to wounding and encodes a chloroplast LOX that may play a role as a component of the octadecanoid defense-signaling pathway.     

In Situ Hybridization of Biotinylated Dna Probes to Cotton Meiotic Chromosomes

A modified procedure for in situ hybridization of biotinylated probes to meiotic chromosomes of cotton has been developed with high retention of squashed cells on slides, preservation of acid-fixed chromosome morphology, exceptionally low levels of background precipitate at nonspecific hybridization sites and improved photomicrographic recording. Salient features of the techniques include pretreatment of slides before squashing, cold storage of squash preparations, and use of interference Biters for distinguishing precipitate from chromatin. A cloned 18S/28S ribosomal DNA fragment from soybean was biotinylated via nick-translation and hybridized to microsporocyte meiotic chromosomes 6f cotton (Gostypium hirsutum L. and G. hirsutum L. X G. barbadense L.). Enzymatically formed precipitate from streptavidin-bound peroxidase marked the in situ hybridization.

In situ hybridization of biotinylated probes to cotton meiotic chromosomes adds the specificity and resolution of in situ hybridization to the chromosomal and genomic perspectives provided by meiotic cytogenetic analyses. Molecular cytogenetic analyses of meiotic cells offer certain inherent analytical advantages over analyses of somatic cells, e.g., in terms of mapping, and for studying fundamental biological and genetic problems, particularly for organisms that are not amenable to somatic karyotypic analysis.     

Substrate characteristics affect colonization by the bloom-forming diatom <Emphasis Type="Italic">Didymosphenia geminata</Emphasis>

The long-stalked Didymosphenia is capable of forming large blooms and is expanding its range. To better understand the colonization dynamics of this species, we investigated the role of substrate characteristics—rock roughness and biofilm condition—on Didymosphenia colonization in a montane Colorado stream. Rocks differing in roughness (shale and sandstone) were treated to manipulate the diatom-dominated biofilm by scrubbing or submersion in 30% hydrogen peroxide. Initial chlorophyll concentration differed among rock types (sandstone > shale) and biofilm treatments (untreated > scrubbed > hydrogen peroxide-treated). Rocks were placed in a Didymosphenia bloom area for 8 days. More Didymosphenia colonized the rougher sandstone than the smoother shale, and more colonized stones with intact biofilms than stones with reduced biofilms (intact > scrubbed > hydrogen peroxide). These results suggest that rougher stones may be targeted for surveillance for new populations and that the colonization of intact biofilms is consistent with Didymosphenia’s habitat in regulated rivers, where biofilm-scouring spates may be suppressed.