Seedlings of morning glory (Pharbitis nil) were exposed to blue light-emitting diodes (LEDs) with various peak wavelengths, or mixture lights of blue light and red light to confirm the spectral sensitivity to flowering. Flowering responses to the respective LEDs corresponded to the absorption spectrum of cryptochromes, which is one of blue light receptors. On the other hand, the light qualities consisting of rich blue light had an effective influence on flowering responses. The number of flower buds decreased after being exposed to the red-rich light qualities, a situation under which phytochromes absorb well. From our study, we conclude that cryptochromes, which absorb blue light, effectively act on flowering, whereas phytochromes act on the inhibition of flowering in Pharbitis nil under the normal light/dark cycles.
Seeds of cv. T-340 were sown in the field on 10 March and 9 April 1997. The lateral root (LR) production was progressively intensified in early sown plot (ESP) instead of late (LSP). Plants in the ESP produced roots with small mean weights, diameter and length as compared with those in the LSP. Early-sown seedlings were subjected to low soil temperature conditions, below approximately 12°C during the first growth stage. In a second experiment, seeds of cvs. T-340 and T-396 were sown in 2 experimental plots: a control plot and a high soil temperature plot (HTP). The minimum soil temperatures in the control were often remained below 10°C for about 25 days after sowing, but the temperatures in the HTP kept above 15°C during the growth period. When grown under the control, larger number of thickened LRs was observed in roots of cv. T-340, but roots of cv. T-396 did not exhibit this disorder at any soil temperature plot. In both cvs., hinder root elongation was observed in the control as compared with the HTP. In a third experiment, varietal difference in the occurrence of LR in roots of cvs. Oshin, T-340, T-396 and Tenpou was compared. Although no correlation was observed between the different cvs. and root growth, active meristematic activity was observed in the pericycle region outside the protoxylem in roots of susceptible cvs. Oshin and T-340. Conversely, this meristematic activity remained low in roots of resilient cvs. T-396 and Tenpou. These observations led to the hypothesis that the obstruction of root elongation caused by low soil temperatures (below 12°C) during the first growth period often results in activation of the basal region of the LR meristem in susceptible cvs. prompting LR development. However, in resilient cvs., the LR seldom occur, even when root elongation is inhibited by low soil temperatures that normally decrease the meristematic activity of this region.
The change in cell size with fruit development and the accumulation of sugars in fruits have been investigated independently in many kind of fruits. In this report the relationship between cell size and the kind of sugars accumulated was investigated using Delaware grape berries and melon fruits. The size of cells of grape berries at 65 DAA (days after anthesis) was 144 μm and the sucrose, glucose and fructose content was 13.5 g l-1, 81 g l-1 and 87 g l-1, respectively. On the contrary, the size of cells of melon fruits at 50 DAA was 261 μm and the sucrose, glucose and fructose content was 54 g l-1, 18 g l-1 and 18 g l-1, respectively. It is suggested that glucose and fructose accumulate preferentially in grape berries, which has a large number of smaller cells, but sucrose accumulates preferentially in melon fruit, which has a great number of larger cells.
Gas exchange status is considered to influence tuberous root morphogenesis in sweetpotato (Ipomoea batatas (L.) Lam.). Gas exchange inhibition by using water or applying Vaseline to the young root and the development process of the root were investigated. Water can be considered as a barrier to O2 diffusion since O2 is only slightly soluble in water, while Vaseline can act as a barrier to all types of gases. Effects of hypoxia on root development were also examined. Tuberous roots were not formed in both the Vaseline-coated roots and submerged roots. The area of lignified region in the cross-section of the root increased due to gas exchange inhibition. Similarly, hypoxia inhibited the induction of tuberous root formation in young roots, and depressed the swelling of the roots that were in the process of tuberous root formation. The extent of lignification in roots also increased under hypoxia treatment. The results suggest that the level of O2 is a determinant factor of tuberous root formation in sweetpotato. The induction of tuberous root morphogenesis and the subsequent expansive growth are both inhibited due to O2 deprivation and stress-promoted lignification within the root stele.
Hypericum perforatum L. (St. John's wort) is a traditional medicinal plant that is mainly used for the treatment of neurological disorders and depression. The present study was undertaken to investigate the effects of different light quality, including blue, white, and red light, in combination with two light intensities, 250 and 500 μmol m-2s-1 photosynthetic photon flux (PPF) on the concentrations of medicinally important secondary metabolites in the leaf tissues and growth of H. perforatum plants. The results revealed that growth was greatest in those plants grown under white and red light with 500 μmol m-2s-1 PPF. The hypericin and pseudohypericin contents of the plants grown under red light with 250 μmol m-2s-1 PPF were 1.9 and 1.9 times higher, respectively, than those grown under red light with 500 μmol m-2s-1 PPF. The differences in contents between blue and white light treatment were not significant for plants grown with 250 μmol m-2s-1 PPF. Our result revealed that the contents of medicinally important secondary metabolites in the tissues of H. perforatum plants can be altered by controlling the light environment.
The nutation frequency of Arabidopsis inflorescence stems gradually decreased when cultivated under dark or irradiation of weak white light (<5 μmol m-2s-1). Re-irradiation of white, blue, red and far-red light during dark treatment had different effects on the nutation frequency. The nutation frequency of inflorescence stems increased soon after irradiation with a red light. This quick response in the nutation frequency to red light irradiation was observed in wild-type plant and phyB mutant, but not in either phyA or phyAphyB mutants. These results suggest that the light intensity and the red light photoperception via phytochrome A play important roles in the regulation of circumnutation.
Micropropagation of Tartary buckwheat (Fagopyrum tataricum Gaertn.) plants was examined by the culture of a reproductive organ, seeds in vitro. In initial culture, multiple shoots were induced from a single shoot derived from a 3 week old seedling. Indevidual shoots excised from multiple shoots produced multiple shoots successively at 6 week intervals when cultures were maintained in modified Murashige and Skoog's medium supplemented with 20 μM BAP, 30 g/l sucrose and 1 g/l Gellan Gum in vitro. In some conditions, protrusions were formed and further developed to axillary buds and shoots. One can calculate that about 258 (152,587,890,625) shoots could be propagated from one shoot per year. Plantlets were regenerated by rooting from single shoots in medium containing 1 μM IBA. After acclimatization, almost 100% of regenerated plants were well established in soil. Application of the present micropropagation procedure to multiply inter-specific hybrid plants between common and Tartary buckwheat plant is discussed.