The present experiment aims to clarify the roles of 65 kDa microtubule-associated protein-1 (MAP65-1) and basic proline-rich protein1 (BPP1), which are involved in the maintenance of transverse microtubule orientation, in gravity resistance, using green fluorescent protein (GFP)-expressing Arabidopsis lines. Hypergravity at 300 G inhibited elongation growth and promoted lateral expansion of epidermal cells in the subapical region of hypocotyls in GFP-MAP65-1 line expressing by native promoter and BPP1-GFP line expressing by a constitutive cauliflower mosaic virus 35S promoter. In BPP1-GFP line, hypergravity showed smaller effects on modification of growth anisotropy than wild type. Also, hypergravity induced reorientation of cortical microtubules from transverse to longitudinal directions in both lines. However, in BPP1-GFP line, hypergravity showed smaller effects on reorientation of cortical microtubules. When the expression levels of MAP65-1 were determined by analyzing GFP fluorescence in hypocotyls of GFP-MAP65-1 line, hypergravity decreased the levels of MAP65-1 in the subapical region, where hypergravity modified growth anisotropy and orientation of cortical microtubules. These results indicate that the regulation of levels of MAP65-1 and BPP1 is involved in the hypergravity-induced reorientation of cortical microtubules, which may lead to modification of growth anisotropy, thereby developing a tough body against the gravitational force in Arabidopsis hypocotyls

How microgravity in space influences plant cell growth is an important issue for plant cell biology as well as space biology. We investigated the role of cortical microtubules in the stimulation of elongation growth in Arabidopsis (Arabidopsis thaliana) hypocotyls under microgravity conditions with the Resist Tubule space experiment. The epidermal cells in the lower half of the hypocotyls of wild-type Columbia were longer in microgravity than at on-orbit 1 g, which precipitated an increase in the entire hypocotyl length. In the apical region, cortical microtubules adjacent to the outer tangential wall were predominantly transverse to the long axis of the cell, whereas longitudinal microtubules were predominant in the basal region. In the 9th to 12th epidermal cells (1 to 3 mm) from the tip, where the modification of microtubule orientation from transverse to longitudinal directions (reorientation) occurred, cells with transverse microtubules increased, whereas those with longitudinal microtubules decreased in microgravity, and the average angle with respect to the transverse cell axis decreased, indicating that the reorientation was suppressed in microgravity. The expression of tubulin genes was suppressed in microgravity. These results suggest that under microgravity conditions, the expression of genes related to microtubule formation was downregulated, which may cause the suppression of microtubule reorientation from transverse to longitudinal directions, thereby stimulating cell elongation in Arabidopsis hypocotyls.

Enhancement of cardiac differentiation is critical to stem cell transplantation therapy for severe ischemic heart disease. The aim of this study was to investigate whether several derivatives of tryptanthrin (1), extracted from the medicinal plant Polygonum tinctorium, induce the differentiation of P19CL6 mouse embryonal carcinoma cells into beating cardiomyocyte-like cells. P19CL6 cells were cultured in α-MEM supplemented with 10% FBS including a test compound or vehicle. Drug-induced differentiation was assessed by measuring the number of beating and nonbeating aggregates and the area of beating aggregates, and the expression of genes involved in cardiac differentiation was evaluated by real-time PCR. A 1 μM concentration of 8-methyltryptanthrin (2) induced the differentiation of P19CL6 cells into cardiomyocyte-like cells to a significantly greater degree than 1% dimethyl sulfoxide (DMSO), a conventional differentiation inducer of P19CL6 cells. Furthermore, 2 strongly increased both the number and the area of spontaneously beating aggregates in comparison with DMSO. Two distinct genes of the calcium channel family, Cav1.2 and Cav3.1, underlying cardiac automaticity were significantly expressed in the presence of 2. Gap junction genes GJA1 and GJA5 contributing to the synchronized contraction of the myocardium were also induced significantly by 2. These results suggest that 2 successfully differentiated P19CL6 cells into spontaneously beating cardiomyocyte-like cells by activating the gene expression of pacemaker channels and gap junctions.

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