<Details of the projects of Kataoka group>

I. Analyses of photophysiological responses of tip-growing cells.

1)Phototropism of Vaucheria

 The body of Vaucheria is composed of a sparsely branched coenocytic tube of 50-100 オm in diameter. Each apex of the tube shows typical tip-growth. Vaucheria is the very suitable model system of tip-growth, because no cell wall expansion occurs below the hemispherical dome. Vaucheria exhibits positive phototropism when the fluence rate of the unilateral light is moderate; but shows negative phototropism when the fluence rate exceeds a critical value. Such switchover of the sign of phototropism is not seen in most higher plants. Thus, the phototropism of Vaucheria is the most suitable system for the analysis of light vector sensing mechanism. We have found that a bluelight-dependent influx of Ca2+ ion at the cell apex is involved in the regulation of positive and negative phototropsic response. (Kataoka 1988, 1990, 2000; Kataoka and Watanabe1992, 1993, 2000). We are intending to directly confirm the increase in cytoplasmic Ca2+ concentration in teh apical cytoplasm and elucidate the role of high Ca2+ in regulation of local increase/decrease of exocytosis.

2)Photomorphogenesis of Vaucheria.

 When a narrow region of the coenocytic alga, Vaucheria is irradiated with bluelight of moderate intensity, one or more bulge(s) is induced from the center of the irradiated region 4 - 5 h after the onset of BL (Kataoka 1975, Takahashiet al. 2001). The bulge then grows to a branch.
 Chloroplasts immediately start to accumulate into the BL-region. The accumulation of chloroplasts, which almost completes within 60 min. is necessary, but insufficient by itself for the branch induction. Instead, accumulation of nuclei, which starts 30-40 min after the onset of BL is indispensable. No nuclear division is induced.
 Nuclear accumulation is synchronized with disorientation and degradation of microtubule (MT) bundles, which originally run parallel to the cell axis. Gathering nuclei, not by nuclear division is a very unique way of forming a new shape which none of multicellular plants can adopt. None but coenocytes can gather nuclei from adjacent regions!
 A long (50-60 µm) MT bundle extends from the head of every nucleus. An additional short MT bundle(s) extends backward. Centrosome (including centrioles) serves as an MTOC. The frontal MT bundles pulled nuclei in longitudinal direction. Motility of the nucleus-MT complex and its control mechanism are investigated.

   And recently we are finding that a novel bZIP-LOV bluelight receptor molecule for the bluelight-induced branching, using the RNAi-knock down experiments (see main page).

 Other coenocytic algae, such as Caulerpa and Bryopsis are also used for the study of bluelight-induced photo-cytomorphogenesis.

The recent paper on this subject (Takahashi et al 2001) can be seen in


 Also, For further detail, go to
Phototropism and photomorphogenesis of Vaucheria.


II. Biology of coenocytes, esp. Vaucheria and Bryopsis.

 Most eukaryotic cells are, no matter whether they are unicellular organisms or composing a multicellular organism, uninuclear cells having only one nucleus in a cell. There are, however, various types of coenocytic cells among various phylogenical groups. Coenocytic cell is the cell in which many nuclei are involved within a single protoplasmic continuum. The cause of the multinucleation appears to be the lost of cytokinesis that follows nuclear division in ordinary uninuclear cells. The true cause, the origin and ecological advantages of being a coenocytic cell are, however, still not known.
 In the bluelight-induced branching (see I-b), Vaucheria adopt an alternative principle for the cytomorphogenesis, i. e., Vaucheria gathers nuclei from adjacent dark region to the bluelight-irradiated region without waiting next mitotic phase (Takahashi et al. 2001) . None of uninuclear cells can adopt this principle!
On the other hand, this unique principle may indicate an important possibility: the morphogenesis of plants do require a high nuclear density in a restriced region, but do not require the cell division it self. As demonstrated previously in fern protonemata and in our present study, the nuclear control reaches only short distance upon cytomorphogenesis. Namely, even in a uninuclear cell the nucleus may have to move to and reside for a while the presumptive site of deformation.
 There could not be so wide gap between uninuclear- and coenocytic cells, if we think of symplasts of a monocot hypocotyl, for example. A symplast can be regarded as a pack of discoidal coenocytes, since indivisual cells of a symplast are only radially connected with each other through plasmodesmata,
 Study of coenocytes is thus very interesting and significant when man asks following questions: how are informations exchanged between individual nuclei, is there hierarchies between nuclei, why cytokinesis does not follow nuclear division... It may give hints to develop multi-CPU computers...

 For further detail go to Biology of Coenocytes

III. Phylogenetical relationship between green plants and yellow plants (Stramenopiles) in response to osmotic and ionic regulation.

 Yellow plants (Chromista, Stramenopiles) are very large phyrum including diatoms, brown algae, Xanthophyceae and Oomycetes. They are thought to be evolved from an ancestral nonphotosyntehtic oomycetous eucaryote and second endosymbiot eucaryotes relatating to red algae. That is their origins of chloroplasts are not procaryotic cyanobacterium but eucaryote.
  Thus, staramepiles are phylogenetically completely different from green plants which include land plants.
  Fresh water Vaucheria has an ability to regulate its osmotic and turgor pressure by taking up ions when it is subjected to hyperosmotic stress. Surprisingly, however, Vaucheria suck up more sulfate ions than Cl and nitrate ions, while most green algae exclusively use Cl- , and only slightly suck up sulfate ions.
  We have also found that some marine brown algae (Deamarestia spp. and some of Dictyotales algae) accumulate high concentration (as high as 400 mM) of sulfuric acid (H2SO4). Related species of Dictyotales which do not accumulate sulfuric acid also accumulate same amount of sulfate ion (SO42-). They accumulate equivalent concentration of K or Na rather than H+ (Sasaki et al. 1999, 2001).
  We are proposing a hypothesis that this remarkable difference in the ion species used for osmo/turgor regulation may be an important key which divide green plants and yellow plants. To examin this ypothesis, we are starting comparative phyological and phylogenetical studies of osmo/turgor regulation mechanism of many green and yellow plants.