Intracellular Localization of Jasmonate-Induced Proteins in Barley Leaves

Type 1 ribosome-inactivating proteins from Phytolacca dioica L. leaves: differential seasonal and age expression, and cellular localization

The expression of type 1 ribosome-inactivating proteins (RIPs) in Phytolacca dioica L. leaves was investigated. Fully expanded leaves of young P. dioica plants (up to 3 years old) expressed two novel RIPs, dioicin 1 and dioicin 2. The former was also found in developing leaves from adult P. dioica within about two and a half weeks after leaf development, and the latter continuously synthesized, with no seasonal or ontogenetic constraint. Fully expanded leaves from adult P. dioica expressed four RIPs (PD-Ls1-4) exhibiting seasonal variation. RIPs were localized in the extracellular space, in the vacuole and in the Golgi apparatus of mesophyll cells. Dioicin 1 and dioicin 2 showed rRNA N-beta-glycosidase activity and displayed the following properties, respectively: (1) Mr values of 30,047.00 and 29,910.00, (2) pIs of 8.74 and 9.37, and (3) IC(50) values of 19.74 (0.658 nM) and 6.85 ng/mL (0.229 nM). Furthermore, they showed adenine polynucleotide glycosylase activity and nicked pBR322 dsDNA. The amino acid sequence of dioicin 2 had 266 amino acid residues, and the highest percentage identity (81.6%) and similarity (84.6%) with PAP-II from Phytolacca americana, while its identity with other RIPs from Phytolaccaceae was around 40%.

Cloning and characterization of a coronatine-regulated tyrosine aminotransferase from Arabidopsis

In plants, the phytotoxin coronatine, which is an analog of the octadecanoids 12-oxo-phytodienoic acid and/or jasmonic acid, gives rise to a number of physiological responses similar to those of octadecanoids. To further elucidate the physiological role of these compounds, the differential RNA display technique was used to isolate a number of novel octadecanoid-inducible genes expressed in coronatine-treated Arabidopsis. Among these, a cDNA clone was identified that was similar to known tyrosine aminotransferases (TATs). The function was verified with the expressed recombinant protein. In Arabidopsis, the protein is present as a multimer of 98 kD, with a monomer of an apparent molecular mass of 47 kD. TAT mRNA could be induced within 2 h by various octadecanoids and by wounding of the plants. Accumulation of the TAT protein and a 5- to 7-fold increase in its enzymatic activity was observed 7 to 9 h after application of octadecanoids, coronatine, or wounding. The potential role of TAT in the defense response to herbivores and pathogens is discussed.

The jasmonate-induced 60 kDa protein of barley exhibits N-glycosidase activity in vivo

Upon jasmonate treatment barley leaf segments express a putative ribosome-inactivating protein (JIP60). The influence of this protein on translation in planta has been analysed by using barley plants and tobacco plants transformed with a barley cDNA encoding JIP60. In both plant systems JIP60 exhibited N-glycosidase activity in vivo. The depurination of the 25S rRNA of tobacco and barley ribosomes led to accumulation of translationally inactive polysomes.

Formation of lipoxygenase-pathway-derived aldehydes in barley leaves upon methyl jasmonate treatment

In barley leaves, the application of jasmonates leads to dramatic alterations of gene expression. Among the up-regulated gene products lipoxygenases occur abundantly. Here, at least four of them were identified as 13-lipoxygenases exhibiting acidic pH optima between pH 5.0 and 6.5. (13S,9Z,11E,15Z)-13-hydroxy-9,11,15-octadecatrienoic acid was found to be the main endogenous lipoxygenase-derived polyenoic fatty acid derivative indicating 13-lipoxygenase activity in vivo. Moreover, upon methyl jasmonate treatment > 78% of the fatty acid hydroperoxides are metabolized by hydroperoxide lyase activity resulting in the endogenous occurrence of volatile aldehydes. (2E)-4-Hydroxy-2-hexenal, hexanal and (3Z)- plus (2E)-hexenal were identified as 2,4-dinitro-phenylhydrazones using HPLC and identification was confirmed by GC/MS analysis. This is the first proof that (2E)-4-hydroxy-2-hexenal is formed in plants under physiological conditions. Quantification of (2E)-4-hydroxy-2-hexenal, hexanal and hexenals upon methyl jasmonate treatment of barley leaf segments revealed that hexenals were the major aldehydes peaking at 24 h after methyl jasmonate treatment. Their endogenous content increased from 1.6 nmol.g-1 fresh weight to 45 nmol.g-1 fresh weight in methyl-jasmonate-treated leaf segments, whereas (2E)-4-hydroxy-2-hexenal, peaking at 48 h of methyl jasmonate treatment increased from 9 to 15 nmol.g-1 fresh weight. Similar to the hexenals, hexanal reached its maximal amount 24 h after methyl jasmonate treatment, but increased from 0.6 to 3.0 nmol.g-1 fresh weight. In addition to the classical leaf aldehydes, (2E)-4-hydroxy-2-hexenal was detected, thereby raising the question of whether it functions in the degradation of chloroplast membrane constituents, which takes place after methyl jasmonate treatment.

Overexpression of the jasmonate-inducible 23 kDa protein (JIP 23) from barley in transgenic tobacco leads to the repression of leaf proteins

We investigated transgenic tobacco lines which express different amounts of the barley JIP 23. In these plants the amount of several proteins decreased proportionally to increasing amounts of JIP 23 whereas the transcript levels were constant as determined for the small and the large subunit of RuBPCase. However, the translation initiation of the rbcS transcript was found to be less efficient than in the wild type. In contrast, the jip 23 transcript was efficiently initiated, indicating that no unspecific impairment of initiation occurred. The data suggest that the barley JIP 23 leads to discrimination among certain tobacco transcripts during translation initiation.