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Tracheary elements (TEs) are highly specialized cells that play central roles in the development of vascular plants. TEs function as components of xylem vessels or tracheids to deliver water throughout plant parts and to confer mechanical strength on a plant body. As a result of distinctive cytological features, patterned secondary walls or the loss of the protoplast, a differentiated TE cell is easily recognized, and has long provided a simple analytical model system of plant cell differentiation. Evidence obtained from this simple system indicates, however, that the regulatory mechanisms underlying TE differentiation are quite complicated. Various factors such as plant hormones and unidentified offspring of cell-cell interactions are involved in the induction of TE differentiation. With the help of some signal transduction machinery, such developmental or environmental cues activate the gene expression cascades required for TE wall material synthesis and protoplast digestion. This review covers recent advances in physiological and genetic studies on this paradigm. The detailed mechanisms of the regulation of TE differentiation are discussed, especially analyses using in vitro culture systems for TE differentiation, transgenic plants, or mutants defective in leaf vascular pattern formation that are accelerating the expansion of our knowledge on the process of vascular cell fate specification.

Differentiation into a tracheary element (TE) is a typical example of programmed cell death (PCD) in the developmental processes of vascular plants. In the PCD process the TE degrades its cellular contents and becomes a hollow corpse that serves as a water conduct. Using a zinnia (Zinnia elegans) cell culture we obtained serial observations of single living cells undergoing TE PCD by confocal laser scanning microscopy. Vital staining was performed and the relative fluorescence intensity was measured, revealing that the tonoplast of the swollen vacuole in TEs loses selective permeability of fluorescein just before its physical rupture. After the vacuole ruptured the nucleus was degraded rapidly within 10 to 20 min. No prominent chromatin condensation or nuclear fragmentation occurred in this process. Nucleoids in chloroplasts were also degraded in a similar time course to that of the nucleus. Degradations did not occur in non-TEs forced to rupture the vacuole by probenecid treatment. These results demonstrate that TE differentiation involves a unique type of PCD in which active and rapid nuclear degradation is triggered by vacuole rupture.

Genes that are expressed only in the young zygote are considered to be of great importance in the development of an isogamous green alga, Chlamydomonas reinhardtii. Clones representing the Zys3 gene were isolated from a cDNA library prepared using zygotes at 10 min after fertilization. Sequencing of Zys3 cDNA clones resulted in the isolation of two related molecular species. One of them encoded a protein that contained two kinds of protein-to-protein interaction motifs known as ankyrin repeats and WW domains. The other clone lacked the ankyrin repeats but was otherwise identical. These mRNA species began to accumulate simultaneously in cells beginning 10 min after fertilization, and reached maximum levels at about 4 h, after which time levels decreased markedly. Genomic DNA gel-blot analysis indicated that Zys3 was a single-copy gene. The Zys3 proteins exhibited parallel expression to the Zys3mRNAs at first, appearing 2 h after mating, and reached maximum levels at more than 6 h, but persisted to at least 1 d. Immunocytochemical analysis revealed their localization in the endoplasmic reticulum, which suggests a role in the morphological changes of the endoplasmic reticulum or in the synthesis and transport of proteins to the Golgi apparatus or related vesicles.

Death of tracheary elements which compose vessels and tracheids is a typical example of programmed cell death in plants. Anin vitro system usingZinnia mesophyll cells which differentiate directly into tracheary elements has provided various types of data on the cell death process. In this paper, we will summarize recent results obtained using theZinnia system and discuss the programming of cell death during tracheary element differentiation.

DNA-fluorescence from nuclei and nucleoids in gametes of Ulva pertusa have beenmeasured after staining with 4'-6-diamidino-2-phenylindol. The nuclei emitted 2.2 times as much fluorescence as that from haploid Chlamydomonas reinhardtii, whose nuclei have been reported to contain 7.2 × 1010 daltones (Chiang and Sueoka 1967) and a GC content of 62.1% (Sager and Ishida 1963). The average nucleoid number of U. pertusa from 100 gametes observed was 7.97±2.60 (S.D.). DNA fluorescence of each nucleoid ranged from 0.27 to 8.0 times as much as that of T4 phage, which has been reported to contain 1.1 × 108 daltons of DNA (Freifelder 1970), with a GC content of 36% (Runder et al. 1969). Total nucleoid DNA-fluorescence in a cell of U. pertusa was 22.4 to 32.3 times as much as tht of T4 phage.

Sexually competent cells of a cellular slime mold Dictyostelium discoideum strain NC4, were mixed with fusion-competent cells of either HM1, or WS2162, and mixed cell suspensions were incubated with rotation in the dark. Cells 30min after mixing NC4 and SW2162 contained giant cells and smaller cells. Mitochondria of giant cells were charastenstically distributed to the cell periphery. This trend was more evident in giant cells as nucleus number increased in a cell. At 24hr after mixing, blue fluorescences from cell wall, and dark brown fluorescence in the center of and around squashed structures were eminent, while both fluorescences were not detected in 30min cell. Western blot analysis using rabbit polyclonal antibody against bacterial maltose-binding protein detected a major 40 kD and a minor 43 kD peptides in total protein from cells at 24 and 66 hr after mixing NC4 and HN1 cells, while these bands were not detected in two types of gametes before mixing and cells 30min after mixing.

Polar auxin transport is essential for the formation of continuous vascular strands in the plant body. To understand its mechanism, polar auxin transport inhibitors have often been used. However, the role of auxin in vascular differentiation at the unicellular level has remained elusive. Using a Zinnia elegans cell culture system, in which single mesophyll cells transdifferentiate into tracheary elements (TEs), we demonstrated that auxin transport inhibitors prevented TE differentiation and that high concentrations of 1-naphthaleneacetic acid (NAA) and IAA overcame the repression of TE differentiation. Measurements of NAA accumulation with 3H-labeled NAA in the presence or absence of 1-N-naphthylphthalamic acid (NPA) revealed enhanced NAA accumulation within the cell. In the NPA-treated cells, intracellular free NAA decreased, while its metabolites increased. Therefore, the polar auxin transport inhibitors may prevent auxin efflux and consequently promote NAA accumulation in Zinnia cells. The excess intracellular NAA may also activate NAA metabolism, resulting in a decrease in free NAA levels. This depletion of free NAA may prevent TE differentiation. The decreased auxin activity in NPA-treated cells was confirmed by the fact that the DR5 (a synthetic auxin-inducible promoter)-mediated expression of a reporter protein was suppressed in such cells. Gene expression analysis indicated that NPA suppressed TE differentiation at an early process of transdifferentiation into TEs. Based on these results, the inter-relationship between auxin and vascular cell development at a cellular level is discussed.

A tracheary element (TE) is a typical example of a cell type that undergoes programmed cell death in the developmental processes of vascular plants. The loss of the selective permeability of the tonoplast, which corresponds to tonoplast disintegration, occurred after the cells commenced secondary wall thickening and played a pivotal role in the programmed cell death of TEs in a zinnia (Zinnia elegans L.) cell culture. A search for events specifically associated with the TE vacuole provided an important clue to the understanding of the cell death mechanism. The transport of fluorescein, a fluorescent organic anion, across the tonoplast declined drastically in differentiating TEs. The capacity of the vacuole to accumulate the probe was also impaired. Treatment with probenecid, an inhibitor of organic anion transport, caused rapid cell death of TEs and led to the ultimate disruption of the vacuole even in other types of cultured cells. These changes in vacuolar properties during TE development were suppressed by cycloheximide. Specific mRNA accumulation in cells cultured in a TE differentiation-inductive condition was abolished by probenecid. These results suggest that a change in vacuolar membrane permeability promotes programmed cell death in TEs.

1. To make clear ecologicai characteristics of auto-tetraploid in rice plant, diploid plants of six varieties and the auto-tetraploid ones induced artificially from each of them were used. They were exposed to various environmental conditions, i. e. natural conditions, short day, Ioilg day, high Lem-perature, early sowing, and iate sowing. Gtowth, date of heading, and fertility were investigated to corxipare the tetraploids with the diploids. 2. There was a tendency that tetraploids were. superior to diploids in the elongation of their heiaht from tillering stage to the booting stage. But as fbr the height of plant after he.ding.", the tetraploid were c, .earfy lower than diploids. The cause of this seems to lie in the fact that the d.iploids are very superior to the tetraploids in the length of the first interriode Sust Jender the ear. 3. In bomparison with diploids, the date of heading of the tetraploids was little later or nearly equal in the Japanese late varieties. This tehdency was more clear in Java N0.28. On the contrary Aikoku (middle variety) and P.hiiippine No. 5, were hastened. 4. Between the diploid and tetraploid of Philippine No. 5, there was a difference in photoperiodic resonse. The heading of the tetraploids was earlier than the diploids in aH the other treatments except short day treatment in which the former was later than the latter. Ear formatiori of diploids did not occur under the long day condition but in the tetra-plaids, it was perfectly indifferent to this condition. 5. These-facts will furnish same new valuable data on the problems of adaptation and geographical distribution of polyploid plants.

A theory of Pendellosung fringes due to the incident beam of an unpolarized spherical wave is presented. The agreement with the observations pertaining to the fading of the fringes is very well. The observed fringe distance \(\varLambda\) is given by \begin{aligned} \frac{1}{\varLambda}{=}\frac{1}{2}(1+\cos 2\theta_{B})\frac{1}{\varLambda}_{\bot}, \end{aligned} where θ B the Bragg angle and \(\varLambda_{\bot}\)is the fringe distance for a planepolarized spherical wave, the electric vector of which is perpendicular to the plane of reflection. The positions of maxima and minima of the fringes are interchanged before and after the fading position. These results give the theoretical and experimental bases to the new method of determining crystal structure factors (H. Hattori, H. Kuriyama, T. Katagawa and N. Kato: J. Phys. Soc. Japan 20 (1965) 988).

Structure factors of Si single crystal were measured absolutely by means of Pendellosung fringes, the method being entirely free from the ambiguity of extinction. The causes of slight but systematic discrepancy recongnized in the previous work (N. Kato and A. R. Lang: Acta cryst. 12 (1959) 787) were elucidated. For eliminating the causes of errors, the section pattern was used. The structure factors obtained agree well with Gottlicher et al 's values which were obtained by the usual X-ray method. This implies that the Debye-Waller factor to be used in dynamical diffraction theory should be the same one as the factor adequate to the kinematical theory. The Debye temperature \(\varTheta_{M}\) for X-ray diffraction is determined to be 538°K. at room temperature. Based on the structure factors obtained, it is also concluded that a kind of scattering factor f e of the bonding charge assumed at the middle of the -bond can be represented in the form f e =0.45exp -13(sin θ/λ) 2 .

The ripening-black coloration of rice hulls is controlled by two complementary genes, Ph and Bh. Ph is the phenol reaction gene, and Bh seems to be a gene producing some phenol substance. Most Ph were distributed among indica varieties, while Bh were distributed among japonica varieties.