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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.

mediated by this enzyme. The activity of SAMDC has been shown to be rate-limiting in this pathway (Slocum

The level of mRNA for S-adenosylmethionine decarboxylase (SAM DC) (EC 4.1.1.50) in leaves of Pharbitis nil exposed to light began to increase affer 15 min exposure, peaked by 45 min and was followed by a rapid decline, suggesting a very rapid light-regulation of the gene expression. These changes of the mRNA level indicate that the photoresponse of SAMDC abundance is regulated primarily at a transcriptional level.

If, following an inductive treatment of 2 d of continuous darkness, shoot apices of Pharbitis nil are cultured 1 d later on White’s medium supplemented with2%sucrose, they cannot form carpels, but they can if they are cultured on 2% glucose. It was hypothesized that the differential effect of these sugars was because of differential expression of carpel-specific genes. Partial cDNA homologues to the Arabidopsis genes, LEAFY (PnLFY), AGAMOUS (PnAG1/2), and CRABS CLAWS (PnCRC1/2)were cloned. PnLFY was expressed in the shoot apex 1 d following the start of induction and remained higher than in non-induced apices for a further 6 d before exhibiting a major peak of expressionon day 7. Peaks of expression of PnAG1 and PnAG2 spanned days 7–11, coinciding with the appearance of stamens and then carpels. The Pharbitis ‘PnCRC2’ showed greatest homology to Arabidopsis YABBY2 (PnYABBY). Its expression peaked on day 8 when the carpels first appeared. ‘PnCRC1’ showed greatest homology to Arabidopsis FILAMENTOUS (PnFIL). Its expression was approximately the same in inductive and non-inductive treatments. Apart from PnFIL these partial cDNAs could be used as markers to test the hypothesis concerning differential effects of sucrose and glucose. Cultured shoot apices from induced plants were sampled at weekly intervals. All four genes were expressed more strongly in the glucose compared with the sucrose treatment, most notably at day 17. A more intensive sampling (days 15–19) indicated that PnLFY and PnYABBY exhibited much higher expression on glucose compared with sucrose, most notably on days 15–16 and days 18–19.

The rates of increase in dry weight, leaf area, and length of hypocotyl plus radicle of mung bean (Vigna radiata L.) and morning glory (Pharbitis nil Chois) all show marked responses to decreasing temperature, although when drawn as Arrhenius plots these responses resemble smooth curves rather than sets of intersecting straight lines. Chilling sensitivity was shown to be dependent on temperature, light intensity, and the previous history of the plant. It is argued on theoretical grounds that changes in membrane lipid mobility would not be expected to cause abrupt changes in the slope of such Arrhenius plots at either the enzyme or whole plant level.

Release of apical dominance can be induced in Pharbitis nil by the inversion of the upper shoot. This promotion of outgrowth of the highest lateral bud adjacent to the bend of the stem appears to be mediated by ethylene inhibition of growth of the inverted main shoot. In the present investigation the existence of a direct correlation between ethylene evolution and the direction of gravistimulus is demonstrated as well as an inverse correlation between ethylene production by the inverted upper shoot and its elongation. An inverse correlation also exists between elongation of the inverted upper shoot and the outgrowth of the highest lateral bud if the lower portion of the shoot (below the bend) is oriented in an upright position. The patent period for shoot-inversion induction of ethylene production is about 2 h. These results support the hypothesis of indirect ethylene control of apical dominance release by retardation of elongation of the inverted shoot.