A nitrogen source was needed for the flowering of Lemna gibba L., a long‐day plant, and L. perpusilla Torr., a shortday plant. The level of endogenous amino acids analyzed by an Amino Acid Analyzer, rose during the first few inductive cycles, but was reduced during later stages of the flowering process. Serine and threonine levels increased during the light period and decreased during the dark period in L. perpusilla. Exogenous serine and threonine added to the culture medium at 10−6M increased the rate of flowering by more than 35% over the controls. Cysteine inhibited flowering, while other amino acids had little or no promotive effect on flowering. Serine and threonine increased flowering rate in L. perpusilla only when added during a dark period of the inductive cycle. The addition of amino acids during a light period not followed by a dark period had no effect on flowering.

The Arabidopsis CONSTANS (CO) gene is a key regulator of the long day (LD)-dependent flowering pathway and two CO homologous genes COL1 and COL2 are involved in the regulation of the circadian rhythm. In order to understand the role of CO and COL in short-day plants, a CO homologue, PnCOL1, was isolated and characterized from Japanese morning glory (Pharbitis nil). The deduced PnCOL1 protein of 386 amino acid residues contained two putative zinc finger motifs at the N-terminal region and a conserved CCT domain at the C-terminal region. The deduced amino acid sequence of PnCOL1 was 34% identical to that of PnCO, but 32%, 34%, and 34% identical to those of CO, COL1, and COL2, respectively. Expression of PnCOL1 was barely detected in the cotyledons of plants grown under continuous light (CL), but highly expressed in the cotyledons of plants grown under SD. Expression of PnCOL1 showed a pattern of circadian rhythm as well as daily oscillation. The overexpression of PnCOL1 by a 35S promoter did not overcome the late-flowering phenotype of Arabidopsis co mutants. The results provided in this study suggest that PnCOL1 may have a role in the circadian rhythm in Pharbitis nil.

A PnFL-2 gene is a single copy gene that was isolated from the flower-induced cotyledons of Pharbitis nil. The deduced amino acid sequence of the PnFL-2 includes two functional domains, a single TIFY (ZIM) motif and nuclear localization signal CCT motif. The TIFY family is a novel plant specific gene involved in the regulation of diverse plant specific biological process, such as development and responses to phytochrome, implying that PnFL-2 may play a role in the mechanism of flowering induction. Subcelluar localization analysis confirmed that PnFL-2 is localized in the nucleus. Expression of PnFL-2 was induced during 16h-long inductive night, whereas accumulation of its transcripts significantly abolished by night-break, completely eliminated flowering induction of Pharbitis nil. Accumulation of its induced PnFL-2 transcripts depends on tissue, such as the cotyledons and the leaves. To study its biological functions directly, we have characterized gain of function transgenic over-expression plants for PnFL-2 in Arabidopsis. Transgenic plants that constitutively over-express PnFL-2 displayed slightly early flowering time under the long day condition as compare to those in wild type. These results indicate that PnFL-2 is potentially involved in the regulation of flowering induction in Pharbitis nil.

The dark reaction of the short day plant Lemna perpusilla was investigated. It was found that 3‐phosphoglycerate and pyruvate (10−6M) increased the flowering rate in the presence of nitrates. Pyruvate‐2‐14C was added to the culture solution during two hours of the dark reaction and 14C was incorporated into serine, aspartate and glutamate. It was postulated that pyruvate reacted with a nitrogen source forming an intermediate, possibly aspartate, which was further converted into serine. L. perpusilla failed to flower when the dark period was interrupted with red light and as a result endogenous serine accumulated in a high concentration. The dark reaction of L. perpusilla, in which serine was involved, required (1) oxygen, (2) ATP, (3) moderate temperature, and (4) an enzyme system.

ProteinsPokeweed antiviral proteins (PAPs) become novel therapeutic agents in relation to application in human viral diseases and cancer, as well as potent tools in plant system for defending viral infection. We have studied the expression characteristics of PAPs in pokeweed plants by western blot analysis. PAP-I was constitutively expressed in leaves, stems and roots of the pokeweed plant, while PAP-II was not expressed in roots. The expression of PAP-I1 began in May and then gradually increased with development of the plants. The PAP-II expression was induced and/or stimulated not only by biotic stresses, such as insect pests and viral infection, but also by abiotic stresses, like drought. Interestingly, low-light intensity was found to be more effective than high-light in the expression of both PAP-I and PAP-II. Our results suggest that PAP-II appears to have an additive effect in terms of protection of the plant against pathogens during summer-time when the plant actively grows and is attacked by various pathogens.