The regulation of abscisic acid (ABA) biosynthesis is essential for plant responses to drought stress. In this study, we examined the tissue-specific localization of ABA biosynthetic enzymes in turgid and dehydrated Arabidopsis (Arabidopsis thaliana) plants using specific antibodies against 9-cis-epoxycarotenoid dioxygenase 3 (AtNCED3), AtABA2, and Arabidopsis aldehyde oxidase 3 (AAO3). Immunohistochemical analysis revealed that in turgid plants, AtABA2 and AAO3 proteins were localized in vascular parenchyma cells most abundantly at the boundary between xylem and phloem bundles, but the AtNCED3 protein was undetectable in these tissues. In water-stressed plants, AtNCED3 was detected exclusively in the vascular parenchyma cells together with AtABA2 and AAO3. In situ hybridization using the antisense probe for AtNCED3 showed that the drought-induced expression of AtNCED3 was also restricted to the vascular tissues. Expression analysis of laser-microdissected cells revealed that, among nine drought-inducible genes examined, the early induction of most genes was spatially restricted to vascular cells at 1 h and then some spread to mesophyll cells at 3 h. The spatial constraint of AtNCED3 expression in vascular tissues provides a novel insight into plant systemic response to drought stresses.

It is well known that endogenous abscisic acid (ABA) levels increase rapidly in response to drought stress and that this induces stomatal closure. In Arabidopsis thaliana, ABA levels increased rapidly in the leaves and roots when intact wild-type whole plants were exposed to drought stress. However, if the leaves and roots were separated and exposed to drought independently, the ABA level increased only in the leaves. These results suggest that, under our experimental conditions, ABA is synthesized mainly in the leaves in response to drought stress and that some of the ABA accumulated in the leaves is transported to the roots. Tracer experiments using isotope-labeled ABA indicate that the movement of ABA from leaves to roots is activated by water deficit in the roots. We also demonstrate that the endogenous ABA level in the leaves increased only when the leaves themselves were exposed to drought stress, suggesting that leaves play a major role in the production of ABA in response to acute water shortage.

Ultrafast photoinduced phase transition in a spin-Peierls (SP) system of K-tetracyanoquinodimethane (K-TCNQ) was studied by femtosecond (fs) reflection spectroscopy. Photocarriers destabilize the SP phase, resulting in a decrease in molecular dimerization within 400 fs. Such a melting of the SP phase drives three kinds of coherent oscillations. By comparing the oscillations with the Raman bands activated by the dimerization, we show that the oscillation of 20 cm-1 is due to an LO phonon, and it plays an important role for the stabilization of the SP phase.

Bryophyte species growing in areas in which temperatures fall below zero in winter are likely to have tolerance to freezing stress. It is well established in higher plants that freezing tolerance is acquired by exposure to non-freezing low temperatures, accompanied by expression of various genes and increases in levels of the stress hormone abscisic acid (ABA). However, little is known about the physiological changes induced by cold acclimation in non-vascular plants such as bryophytes. We examined the effects of low temperatures on protonema cells of the moss Physcomitrella patens (Hedw.) Bruch and Schimp. The freezing tolerance of protonema cells was clearly increased by incubation at low temperatures ranging from 10 degrees C to 0 degrees C, with maximum tolerance achieved by incubation at 0 degrees C for several days. The enhancement of freezing tolerance by low temperatures occurred in both light and dark conditions and was accompanied by accumulation of several transcripts for late-embryogenesis-abundant (LEA) proteins and boiling-soluble proteins. By de-acclimation, low-temperature-induced expression of these transcripts and proteins, as well as the freezing tolerance, was reduced. Interestingly, endogenous levels of ABA in tissues or that secreted into the culture medium were not specifically increased by low-temperature treatment. Furthermore, removal of ABA from the medium by addition of activated charcoal did not affect low-temperature-induced freezing tolerance of the protonema cells. Our results provide evidence that bryophytes have an ABA-independent cold-signaling pathway leading to expression of stress-related genes and resultant acquisition of freezing tolerance.

Photovoltaic and structural characteristics of Langmuir-Blodgett film photocells have been studied using asymmetrically substituted copper phthalocyanine (asy-CuPc). By polarized-light absorbance measurements, each phthalocyanine molecule was found to be arranged in the film with its ring facing towards the dipping direction. The polarity of photoelectric characteristics showed typical features expected for an organic p-type Schottky diode, while the dark characteristics exhibited a reversed polarity. The maximum short-circuit photocurrent was on the order of 10-8 A/cm2 for 100 µW/cm2 monochromatic light, indicating the superiority of asy-CuPc as a film-forming molecule for photovoltaic LB films.

In this study, we examined the effects of ethylene and abscisic acid (ABA) upon heterophyllous leaf formation of Ludwigia arcuata Walt. Treatment with ethylene gas resulted in the formation of submerged-type leaves on terrestrial shoots of L. arcuata, while treatments with ABA induced the formation of terrestrial-type leaves on submerged shoots. Measurement of the endogenous ethylene concentration of submerged shoots showed that it was higher than that of terrestrial ones. In contrast, the endogenous ABA concentration of terrestrial shoots was higher than that of submerged ones. To clarify interactions of ethylene and ABA, simultaneous additions of these two plant hormones were examined. When L. arcuata plants were treated with these two plant hormones, the effects of ABA dominated that of ethylene, resulting in the formation of terrestrial-type leaves. This suggests that ABA may be located downstream of ethylene in signal transduction chains for forming heterophyllous changes. Further, ethylene treatment induced the reduction of endogenous levels of ABA in tissues of L. arcuata, resulting in the formation of submerged-type leaves. Thus the effects of ethylene and ABA upon heterophyllous leaf formation are discussed in relationship to the cross-talk between signaling pathways of ethylene and ABA.

Langmuir−Blodgett films of mixtures of fatty acids (FA) and a merocyanine dye (DS), bearing one long alkyl chain and one carboxylic group, were prepared at a nitrogen−pure water interface. The films exhibit a distinct and highly anisotropic J-band near 605 nm, even though they do not contain any metallic or ammonium cations. Although an isotropic band was seen in the region of 500−550 nm, the contribution of the J-aggregates was extracted from the observed visible and IR absorption spectra by using the difference in the polarization of the bands. This analysis indicates a change in the electronic structure of DS in the J-aggregates, probably corresponding to intramolecular charge transfer. Furthermore, this analysis also suggests that in this metal-free case, the formation of the J-aggregates is strongly affected by the hydrogen bonding between the carboxylic groups in two DS and that between the carboxylic groups in DS and FA.

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