The structure and expression of a senescence-associated gene (SPG31) encoding a cysteine proteinase precursor of sweet potato have been characterized. The coding region of the gene consists of two exons encoding an enzyme precursor of 341 amino acids with conserved catalytic amino acids of papain. Examination of the expression patterns of the SPG31 gene in sweet potato by Northern blot analyses reveals that the transcripts of SPG31 are specifically induced in the senescing leaves but not in other organs. The differential accumulation of the mature SPG31 protein in the senescing leaves was further identified by two-dimensional electrophoresis of leaf proteins and N-terminal sequencing. This result suggests the important role played by SPG31 in proteolysis and nitrogen remobilization during the leaf senescence process. Furthermore, treatment of mature green leaves with ethylene for 3 d resulted in a high-level induction of SPG31 transcripts. Ethylene-regulated expression of SPG31 is consistent with the presence of a number of putative ethylene-responsive elements in the 899-bp SPG31 promoter region.

Genes that are expressed during leaf senescence in sweet potato (Ipomoea batatas, cv. Tainong 57) were identified by the isolation of cDNA fragments with the mRNA differential display method. Eight senescence-associated cDNA clones for mRNAs differentially expressed during leaf senescence were obtained and characterized. Northern blot analysis indicated that all these clones represented genes that are up-regulated during natural leaf senescence. Among them, five cDNA clones have been obtained in full length by screening a senescing leaf cDNA library or by performing rapid amplification of cDNA ends. DNA and protein database searches revealed that clones SPA15 and SPC9 encode proteins of unknown function. The other six clones SPG31, SPC20, SPG27, SPC25, SPC15 and SPC1 showed significant sequence homology to known genes encoding a cysteine proteinase, isocitrate lyase, S-adenosylmethionine decarboxylase, cysteine proteinase inhibitor and metallothionein-like type I protein. The gene expression patterns represented by SPG31, SPG27 and SPA15 were found to be highly specific in senescing leaves. The corresponding transcripts for SPG31, SPG27 and SPA15 were below detectable levels in other organs such as flowers, stems, roots and tubers. The possible physiological roles of these gene products in the leaf senescence process are discussed.

The structure and expression of a novel senescence-associated gene (SPA15) of sweet potato were characterized. The protein coding region of the gene consists of 13 exons encoding 420 amino acids. Apparent homologues of this sweet potato gene are found in a variety of dicot and monocot plants, but not in animals or microorganisms. Examination of the expression patterns of the SPA15 gene in sweet potato reveals that the transcripts of SPA15 are specifically induced in the senescing leaves, and the temporal profile of SPA15 protein accumulation is correlated with that of SPA15 transcripts. Studies on the distribution of SPA15 homologue in rice plants also indicate that SPA15 homologue is up-regulated specifically in senescing rice leaves. Treatment of detached sweet potato leaves with phytohormones including ethylene, methyl jasmonate, salicylic acid and abscisic acid resulted in a high-level induction of SPA15. Immunoelectron microscopic analysis demonstrates that SPA15 is specifically associated with the cell wall. The potential role for SPA15 during leaf senescence is discussed.

This paper proposes a three-dimensional model for combinative analysis of the illuminative and thermal properties of organic light-emitting diodes (OLED). By means of the energy conversion ratio and energy conservation theory, two individual optical and thermal sub-models are integrated to form a single model constructed in a multi-physics platform. According to the measured luminous performance and temperature distribution of the fabricated OLED samples, the proposed model demonstrates sufficient accuracy. Moreover, the temperature distribution on the cross-section of the OLED can be derived from the proposed model and used as a valuable reference for manufacturers to select appropriate organic materials.