Molecular aspects of leaf senescence.

Senescence is the last stage of leaf development and one type of programmed cell death that occurs in plants. The relationships among senescence programs that are induced by a variety of factors have been addressed at a molecular level in recent studies. Furthermore, an overlap between the pathogen-response and senescence programs is beginning to be characterized. The complexity of the senescence program is also evident in studies of senescence-specific gene regulation and the role of photosynthesis and plant hormones in senescence regulation. New molecular-genetic approaches are expected to be useful in unraveling the molecular mechanisms of the leaf senescence program.

Identification of a promoter region responsible for the senescence-specific expression of SAG12.

SAG12, an Arabidopsis gene encoding a cysteine protease, is expressed only in senescent tissues. Studies of the expression patterns of a variety of genes showing senescence-specific or senescence-preferential expression indicate that plant senescence involves multiple regulatory pathways. In this study it is shown that the expression of SAG12 is specifically activated by developmentally controlled senescence pathways but not by stress- or hormone-controlled pathways. Using SAG12 as a molecular marker for the study of developmental senescence, we show that cytokinin, auxin, and sugars can repress developmental senescence at the molecular level. Studies using promoter deletions and recombination of promoter fragments indicate that a highly conserved region of the SAG12 promoter is responsible for senescence-specific regulation, while at least two other regions of the SAG12 promoter are important for full promoter activity. Extracts from young and senescent Arabidopsis leaves contain factors that exhibit differential binding to the senescence-responsive promoter element.

Regulation of developmental senescence is conserved between Arabidopsis and Brassica napus.

SAG12 is a developmentally controlled, senescence-specific gene from Arabidopsis which encodes a cysteine protease. Using SAG12 as a probe, we isolated two SAG12 homologues (BnSAG12-1 and BnSAG12-2) from Brassica napus. Structural comparisons and expression studies indicate that these two genes are orthologues of SAG12. The expression patterns of BnSAG12-1 and BnSAG12-2 in Arabidopsis demonstrate that the senescence-specific regulation of this class of cysteine proteases is conserved across these species. Gel-shift assays using the essential promoter regions of SAG12, BnSAG12-1, and BnSAG12-2 show that the extent of binding of a senescence-specific, DNA-binding protein from Arabidopsis is proportional to the expression levels of these genes in Arabidopsis. Therefore, the expression levels of these genes may reflect the affinities of the senescence-specific DNA-binding protein for the promoter element.

A new backbone of artificial enzymes obtained by cross-linkage of poly(ethylenimine).

Cross-linkage of the branches of poly(ethylenimine) (PEI) suppresses flexibility of the polymer as revealed by decreased affinity of the amino groups on PEI backbone towards proton or Ni(II) ion. The cross-linkage improves ability of the PEI derivative equipped with beta-cyclodextrin to deacylate an ester containing t-butylphenyl moiety.

Toward clinical end-user computing: programmable order protocols for efficient human computer interaction.

We have developed and implemented an efficient method of managing routine patient care information as a programmable group order protocol. The purpose of protocol is to minimize a labor-intensive manual computer interaction by grouping clinically related routine orders as a single entity, thus to greatly speed up the time taken for manual entry such as keyboard stroke and/or mouse clicking. User programmability is added to facilitate insertion, deletion and update of order items to be a locally independent operation. A sequence of menu screen is also programmable when a change of standard operation is needed. Department specific order protocols are classified into four categories to improve user convenience. The degree of efficiency is measured by a number of key strokes and entry time. In most cases the time to enter order protocol with correction is found to take less than one minute with less than five key strokes. The method of order protocol entry clearly demonstrates end-user computing capability so that department specific requirements are resolved without resorting to computer department personnel. Flexibility of managing individual physician specific protocols is also beneficial enough to enhance the morale toward a hospital information system currently in use.

Phenotypic alterations of petal and sepal by ectopic expression of a rice MADS box gene in tobacco.

Floral organ development is controlled by a group of regulatory factors containing the MADS domain. In this study, we have isolated and characterized a cDNA clone from rice, OsMADS3, which encodes a MADS-domain containing protein. The OsMADS3 amino acid sequence shows over 60% identity to AG of Arabidopsis, PLE of Antirrhinum majus, and AG/PLE homologues of petunia, tobacco, tomato, Brassica napus, and maize. Homology in the MADS box region is most conserved. RNA blot analysis indicated that the rice MADS gene was preferentially expressed in reproductive organs, especially in stamen and carpel. In situ localization studies showed that the transcript was present primarily in stamen and carpel. The function of the rice OsMADS3 was elucidated by ectopic expression of the gene under the control of the CaMV 35S promoter in a heterologous tobacco plant system. Transgenic plants exhibited an altered morphology and coloration of the perianth organs. Sepals were pale green and elongated. Limbs of the corolla were split into sections which in some plants became antheroid structures attached to tubes that resembled filaments. The phenotypes mimic the results of ectopic expression of dicot AG gene or AG homologues. These results indicate that the OsMADS3 gene is possibly an AG homologue and that the AG genes appear to be structurally and functionally conserved between dicot and monocot.