Paclitaxel and Caffeine-Taurine, New Colchicine Alternatives for Chromosomes Doubling in Maize Haploid Breeding.

The doubled haploid (DH) technology is employed worldwide in various crop-breeding programs, especially maize. Still, restoring tassel fertility is measured as one of the major restrictive factors in producing DH lines. Colchicine, nitrous oxide, oryzalin, and amiprophosmethyl are common chromosome-doubling agents that aid in developing viable diploids (2n) from sterile haploids (n). Although colchicine is the most widely used polyploidy-inducing agent, it is highly toxic to mammals and plants. Therefore, there is a dire need to explore natural, non-toxic, or low-toxic cheaper and accessible substitutes with a higher survival and fertility rate. To the best of our knowledge, the advanced usage of human anticancer drugs "Paclitaxel (PTX)" and "Caffeine-Taurine (CAF-T)" for in vivo maize haploids doubling is being disclosed for the first time. These two antimitotic and antimicrotubular agents (PTX and CAF-T) were assessed under various treatment conditions compared to colchicine. As a result, the maximum actual doubling rates (ADR) for PTX versus colchicine in maize haploid seedlings were 42.1% (400 M, 16 h treatment) versus 31.9% (0.5 mM, 24 h treatment), respectively. In addition, the ADR in maize haploid seeds were CAF-T 20.0% (caffeine 2 g/L + taurine 12 g/L, 16 h), PTX 19.9% (100 µM, 24 h treatment), and colchicine 26.0% (2.0 mM, 8 h treatment). Moreover, the morphological and physiological by-effects in haploid plants by PTX were significantly lower than colchicine. Hence, PTX and CAF-T are better alternatives than the widely used traditional colchicine to improve chromosome-doubling in maize crop.

Involvement of throm box aneA2 and tyrosine kinase in the synergistic interaction of platelet activating factor and calcium ionophore A23187 in human platelet aggregation

The present study was carried out to examine the mechanisms of the synergistic interaction of PAF and A23187 mediated platelet aggregation. We found that platelet aggregation mediated by subthreshold concentrations of PAF (5 nM) and A23187 (1 micrometer) was inhibited by PAF receptor blocker (WEB 2086, IC50=0.65 micrometer) and calcium channel blockers, diltiazem (IC50=13 micrometer) and verapamil (IC50=18 micrometer). Pretreatment of platelets with PAF and A23187 induced rise in intracellular calcium and this effect was also blocked by verapamil. While examining the role of the down stream signaling pathways, we found that platelet aggregation induced by the co-addition of PAF and A23187 was also inhibited by low concentrations of phospholipase C (PLC) inhibitor (U73122; IC50 = 10 micrometer), a cyclooxygenase inhibitor (indomethacin; IC50=0.2 micrometer) and inhibitor of TLCK, herbimycin A with IC50 value of 5 micrometer. The effect was also inhibited by a specific TXA2 receptor antagonist, SQ 29548 with very low IC50 value of 0.05 micrometer. However, the inhibitors of MAP kinase, PD98059 and protein kinase C, chelerythrine had no effect on PAF and A23187-induced platelet aggregation. These data suggest that the synergism between PAF and A23187 in platelet aggregation involves activation of thromboxane and tyrosine kinase pathways.

Synergistic interaction of adrenaline and histamine in human platelet aggregation is mediated through activation of phospholipase, map kinase and cyclo-oxygenase pathways.

This study was conducted to examine the mechanism(s) of synergistic interaction of histamine- and adrenaline-mediated human platelet aggregation. We found that platelet aggregation mediated by subthreshold concentrations of histamine (1-4 microm) plus adrenaline (0.5-2 microm) is inhibited by both an alpha(2)-adrenoceptor blocker (yohimbine) and a histamine (H1) receptor antagonist (diphenhydramine). In examining the role of the downstream signalling pathway, we found that such an interaction is inhibited by the calcium channel blockers verapamil and diltiazem. However, platelet aggregation by adrenaline plus histamine was inhibited by very low concentrations of the phospholipase C (PLC) inhibitor, U73122 (IC(50)= 1.2 microm), the MEK inhibitor, PD98059 (IC(50)= 1.1 microm) and the cyclo-oxygenase (COX) inhibitor, indomethacin (IC(50)= 7 microm). However the inhibition of receptor tyrosine kinase, protein kinase C and phosphatidylinositol 3-kinase by genistien, chelerythrine and wortmannin, respectively, had no significant effect on aggregation. Similarly the nitric oxide donor (SNAP) had no effect on this synergism. These data suggest that the synergistic effect of histamine and adrenaline during human platelet aggregation is receptor mediated and involves activation of PLC, COX and MAP kinase signalling pathways.