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Senescence, a sequence of biochemical and physiological events, constitutes the final stage of development in higher plants and is modulated by a variety of environmental factors and internal factors. PPF1 possesses an important biological function in plant development by controlling the Ca2+ storage capacity within chloroplasts. Here we show that the expression of PPF1 might play a pivotal role in negatively regulating plant senescence as revealed by the regulation of overexpression and suppression of PPF1 on plant development. Moreover, TFL1, a key regulator in the floral repression pathway, was screened out as one of the downstream targets for PPF1 in the senescence-signaling pathway. Investigation of the senescence-related phenotypes in PPF1(−) tfl1-1 and PPF1(+) tfl1-1 double mutants confirmed and further highlighted the relation of PPF1 with TFL1 in transgenic plants. The activation of TFL1 expression by PPF1 defines an important pathway possibly essential for the negative regulation of plant senescence in transgenic Arabidopsis. [ABSTRACT FROM AUTHOR]

Germination is the first and maybe the foremost growth stage in the life cycle of a plant. Herein, we report that initiation of germination in the Arabidopsis Columbia ecotype was accompanied by a sharp decrease in the amount of extractable total RNA. At the beginning of our germination experiment, we were usually able to obtain 35–40 μg total RNA from 100 mg dry seeds. However, after 3 d of cold stratification, we could only obtain less than 5 μg total RNA from the same amount of starting material. Young seedlings contained approximately 100 μg total RNA per 100 mg fresh tissue. Further studies showed that inhibition of de novo RNA synthesis by actinomycin D prevented the degradation of parental RNA and, in the meantime, significantly delayed the germination process. Several ribonuclease-like genes that were highly expressed in dry seeds, and especially during the cold stratification period, were discovered. We propose that these enzymes are involved in the regulation of parental RNA degradation. These results indicate that parental RNA metabolism may be an important process for Arabidopsis seed germination. (Managing editor: Ya-Qin Han) [ABSTRACT FROM AUTHOR]

Proteomic analysis was performed on seedlings after different light treatments. A total of (1 350±31) protein spots was separated and visualized on each silver nitrate-stained two-dimensional gel using protein samples prepared from light-grown or etiolated seedlings with or without 6–9 h light treatment. Twenty-five protein spots (encoded by 19 genes) that were significantly accumulated upon light treatment were identified using the matrix-assisted laser desorption ionization time-of-flight mass spectrometry method. Functional proteomics indicated that these proteins involved mainly in chloroplast development, energy metabolism, cell cycle progression and membrane electron transport. For 18 of the protein-coding genes we identified through an internet search, the transcript levels of 17 genes matched roughly with their protein content in etiolated and green seedlings, suggesting that these genes were regulated by light mainly at the transcriptional level. Despite a very significant increase in the amount of proteins upon light treatment, similar RNA levels were found in dark-grown or green seedlings for the carbonic anhydrase gene At3g05100, indicating a possible post-transcriptional regulatory mechanism. Elucidation of light-induced protein accumulation will undoubtedly enhance our understanding of plant photomorphogenesis. (Managing editor: Ya-Qin Han) [ABSTRACT FROM AUTHOR]

Using a degenerative probe designed according to the most conservative region of a known Lys- and His-specific amino acid transporter (LHT1) fromArabidopsis, we isolated a full-length cDNA namedOxHT(histidine transporter ofOryza sativaL.) by screening the rice cDNA library. The cDNA is 1.3 kb in length and the open reading frame encodes for a 441 amino acid protein with a calculated molecular mass of 49 kDa. Multiple sequence alignments showed thatOsHTshares a high degree of sequence conservation at the deduced amino acid level with theArabidopsisLHT1 and six putative lysine and histidine transporters. Computational analysis indicated thatOsHTis an integral membrane protein with 11 putative transmembrane helices. This was confirmed by the transient expression assay because theOsHT-GFPfusion protein was, indeed, localized mainly in the plasma membrane of onion epidermal cells. Functional complementation experiments demonstrated thatOsHT wasable to work as a histidine transporter inSaccharomyces cerevisiae, suggesting thatOsHTis a gene that encodes for a histidine transporter from rice. This is the first time that an LHT-type amino acid transporter gene has been cloned from higher plants other thanArabidopsis. [ABSTRACT FROM AUTHOR]