Low light intensity causes poor flower pigmentation possibly by two mechanisms: 1) the reaction mediated by photoreceptors located in the petal, 2) the reaction mediated by the sugar supply from leaves or stems. We investigated which mechanism is more important in the pigmentation of the oriental hybrid lily, 'Acapulco' and stock, 'Pigmy Rose'. Shading flowers by cheesecloth (PPFD<17umo\om～2osec1) or by aluminum foil (0umo\om～2osec1) reduced anthocyanin concentration in both species, suggesting that anthocyanin production is a photoreceptor-mediated reaction. When whole plants were shaded by cheesecloth (<17umolom～2osec1) in lily, anthocyanin concentration became lower than that of flower-shaded plants. This treatment reduced total sugar concentration from 3% to 1.6%, suggesting that limited sugar supply caused poor anthocyanin production in lily. In contrast, in stock, whole plant shading did not reduce anthocyanin concentration as compared with flower-shaded plants, suggesting that the amount of available sugar is not a limiting factor for anthocyanin production. Although this treatment reduced total sugar concentration from 4.7% to 3.7%, it was still higher than that of the control l i ly plants. When detached florets of stock were placed on sucrose solutions, the anthocyanin concentration declined as hexose concentration in the petal decreased, especially under 2%. These results indicate that, although soluble sugars in petals affected anthocyanin production, their high concentration prevented fading of flower color, even under low light conditions in stock.

The effects of light intensity perceived by the fruit surface on anthocyanin biosynthesis were compared between 'Nyoho' and 'Toyonoka' strawberries. Fruit of 'Toyonoka' was collected at green fruit stage (G; 2 weeks after anthesis), white fruit stage (W; about 3 weeks after anthesis), onset of pigmentation (OP; 1-2 days after white fruit stage), pink fruit stage (P; 3-4 days after white fruit stage), and full pigmentation stage (FP; 8 days after white fruit stage). The expression of chalcone synthase (CHS) gene was highest at G stage, but remained present during pigmentation. The expression of dihyroflavonol 4-reductase (DFR) gene was low at OP stage and then increased as fruit pigmented. This suggested that DFR but not CHS is involved in developmental regulation of anthocyanin biosynthesis. When fruit of 'Toyonoka' were shaded by wrapping with aluminum foil after W stage, the accumulation of anthocyanin was remarkably reduced. In contrast shading of 'Nyoho' fruits after\\stage did not reduce anthocyanin accumulation. Northern blot analysis showed that the expression of both genes was not affected by fruit shading, suggesting that both CHS and DFR are not involved in light dependent biosynthesis of anthocyanin in 'Toyonoka' strawberry fruits.

The expression of anthocyanin biosynthesis pathway genes was investigated in 'Nyoho' strawberry fruits during fruit development. Fruit color changed from pale-green to white about 3 weeks after anthesis (white-mature stage). At this stage, anthocyanins rapidly accumulated until the full ripe. Total soluble sugar content also increased after white-mature stage. This includes sucrose but not glucose and fructose levels that remained constant during ripening. The transcript level of phenylalanine ammonialyase (PAL) and chalcone synthase (CHS) genes did not change markedly throughout the fruit development. The transcript level of chalcone isomerase (CHI) and dihydroflavonol 4-reductase (DFR) gene was high in the young fruit, decreased to an almost undetectable level at the white-mature stage, and then increased again until the fully ripe stage paralleling mostly the accumulation of anthocyanin. The latter corelation suggests the involvement of CHI and DFR in the regulation of anthocyanin biosynthesis during fruit ripening.

Aldehyde dehydrogenases (ALDHs) are a group of enzymes catalyzing the conversion of aldehydes to the corresponding acids. In mammals and yeasts, at least two isozymes of ALDH are known to be involved in ethanol metabolism (cytosolic ALDHl and mitochondrial ALDH2). Although mitochondrial ALDH isozymes have previously been identified in several plants, such as maize and tobacco, it is unclear whether cytosolic ALDH isozymes also exist in plants. In this study, we identified and characterized a cDNA clone encoding aldehyde dehydrogenase (ALDHIa) from rice (Oryza. saliva L. cv. Nipponbare). The open reading frame of this clone did not contain a typical mitochondrial targeting signal. Analysis of the subcellular localization of ALDHIa using green fluorescent protein (GFP) suggested that ALDHIa is a cytosolic enzyme rather than a mitochondrial enzyme. A genomic Southern hybridization indicated that sequences homologous to the ALDHIa gene are present in at least two regions of the rice genome. Amplification by RT-PCR showed that ALDH1a is expressed strongly in roots, but not in leaves, of rice seedlings, suggesting that ALDHIa functions in roots.

It is known that alcoholic fermentation is important for survival of plants under anaerobic conditions. Acetaldehyde, one of the intermediates of alcoholic fermentation, is not only reduced by alcohol dehydrogenase but also can be oxidized by aldehyde dehydrogenase (ALDH). To determine whether ALDH plays a role in anaerobic metabolism in rice {Oryza sativa L. cv Nipponbare}, we characterized a cDNA clone encoding mitochondrial ALDH from rice (Aldh2a). Analysis of sub-cellular localization of ALDH2a protein using green fluorescent protein and an in vitro ALDH assay using protein extracts from Escherichia coli cells that overexpressed ALDH2a indicated that ALDH2a functions in the oxidation of acetaldehyde in mitochondria. A Southern-blot analysis indicated that mitochondrial ALDH is encoded by at least two genes in rice. We found that the Aldh2a mRNA was present at high levels in leaves of dark-grown seedlings, mature leaf sheaths, and panicles. It is interesting that expression of the rice Aldh2a gene, unlike the expression of the tobacco (Nicotiana tabacum) Aldh2a gene, was induced in rice seedlings by submergence. Experiments with ruthenium red, which is a blocker of Ca2+ Pfluxes in rice as well as maize (Zea mays), suggest that the induction of expression of Adh1 and Pdc1 by low oxygen stress is regulated by elevation of the cytosolic Ca2+ P level. However, the induction of Aldh2a gene expression may not be controlled by the cytosolic Ca2+ P level elevation. A possible involvement of ALDH2a in the submergence tolerance of rice is discussed.