Suppression of Cdc27B expression induces plant defence responses

Non-host resistance is the most general form of disease resistance in plants because it is effective against most phytopathogens. The importance of hypersensitive responses (HRs) in non-host resistance of Nicotiana species to the oomycete Phytophthora is clear. INF1 elicitin, an elicitor obtained from the late-blight pathogen Phytophthora infestans , is sufficient to induce a typical HR in Nicotiana species. The molecular mechanisms that underlie the non-host resistance component of plant defence responses have been investigated using differential-display polymerase chain reaction (PCR) in a model HR system between INF1 elicitin and tobacco BY-2 cells. Differential-display PCR has revealed that Cdc27B is down-regulated in tobacco BY-2 cells after treatment with INF1 elicitin. Cdc27B is one of 13 essential components of the anaphase-promoting complex or cyclosome (APC/C)-type E3 ubiquitin ligase complex in yeast. This APC/C-type E3 ubiquitin ligase complex regulates G2-to-M phase transition of the cell cycle by proteolytic degradation. In this study, we investigated the roles of this gene, NbCdc27B , in plant defence responses using virus-induced gene silencing. Suppression of NbCdc27B in Nicotiana benthamiana plants induced defence responses and a gain of resistance to Colletotrichum lagenarium fungus. Elicitin-induced hypersensitive cell death (HCD) was inhibited mildly in plants silenced with tobacco rattle virus::Cdc27B. Cdc27B could manage the signalling pathways of plant defence responses as a negative regulator without HCD.     

Anticomplementary Activity of Antitumour Polysaccharides

THE polysaccharides obtained from some basidiomycetes, Pleurotus ostreatus (Jacq. ex Fr.) Quel.¹, Flammulina velutipes (Curt, ex Fr.) Sing.², Lentinus edodes (Berk.) Sing.^2–4, Polia cocos, Wolf (Bukuryo)⁵ and Schizophyllum commune Fr.⁷, strongly inhibit the growth of sarcoma 180 and their anti-tumour activity is host-mediated^8,9.     

Ion gradients in xylem exudate and guttation fluid related to tissue ion levels along primary leaves of barley

The concentration of ions in plant cells and tissues is an essential factor in determining physiological function. In the present study, we established that concentration gradients of mobile ions exist in both xylem exudates and tissues within a barley (Hordeum vulgare) primary leaf. For K⁺ and NO₃^?, ion concentrations generally decreased from the leaf base to the tip in both xylem exudates and tissues. Ion gradients were also found for Pi and Cl^? in the xylem. The hydathode strongly absorbed Pi and re‐translocated it to the rest of the plant, whereas Cl^? was extruded. The ion concentration gradients developed early during leaf growth, increased as the tissue aged and remained under both high and low transpiration conditions. Measurement of the expression profiles of Pi, K⁺ and NO₃^? transporters along the longitudinal axis of the leaf revealed that some transporters are more expressed at the hydathode, but for most transporters, there was no significant variation along the leaf. The mechanisms by which longitudinal ion gradients develop in leaves and their physiological functions are discussed.     

Initiation of Sperm Motility Induced by Cyclic AMP in Hamster and Boar

When the plasma membrane of hamster and boar spermatozoa was extraced by treatment with Triton X-100 and the demembranated spermatozoa were transferred to a reactivating medium containing only ATP, axonemes were initially immotile, and then gradually became motile. Under these experimental conditions, the cAMP content in the reactivating medium increased soon. This suggests that cAMP is synthesized from ATP by adenylate cyclase involved in incompletely removed or solubilized residual sperm membrane and that the autosynthesized cAMP causes the delay in motility initiation. This delayed initiation of motility did not occur when phosphodiesterase was added to the reactivating medium and the phosphodiesterase-dependent quiescent sperm became motile instantaneously at any time when excess cAMP was supplemented. Furthermore, demembranated sperm which were diluted in the reactivating medium containing ATP and cAMP, immediately became motile. cAMP levels in the cell increased during the initiation of sperm motility in both species. These results suggest that cAMP is the real factor indispensable for the initiation of sperm motility at ejaculation in mammals.     

Differential Expressions of Two Types of Alkaline Phosphatase during Developmental Growth of Embryoid Bodies of Mouse Teratocarcinoma OTT-6050 In Vitro

Ascites teratocarcinoma OTT-6050 is a totipotent tumor line producing indefinitely the simple type of embry-oid bodies (EBs). In culture with fetal calf serum (FCS) in Eagle's minimal essential medium (MEM), these EBs show developmental growth, only in which some differentiative events result. EBs also show this developmental growth in MEM supplemented with two fractions of FCS separated with a Amicon PM 10 membrane, i.e. a low molecular weight Fraction L (mol. wt. less than 10,000) and a high molecular weight Fraction H (mol. wt. more than 10,000). Fraction H is necessary for the survival of EBs in vitro. Fraction L enhances the uptake of ³H-thymidine into EB cells with increase in the Vmax , but no change in the K m. On culture of EBs with both Fractions, a marked bimodal increase in alkaline phosphatase (ALPase) activity is seen on day 1–2 and 4, resulting from the differential expressions of two electrophoretically distinct ALPases (Bands I and II). The differential expressions of ALPase are also observed cytochemically, one activity being on the inner cells and the other on the surrounding cells of EBs. From the cytochemical similarity of ALPase activity to that of normal mouse embryos, Band I ALPase is inferred to be the epiblast (developmentally totipotent stem cell)-type and Band II ALPase to be the distal (parietal) endoderm-type.     

VACUOLATION OF EXPLANTED AND IMPLANTED NOTOCHORDS OF AMPHIBIA

Processes of vacuolation were investigated with the explanted and implanted rudiments of amphibian notochord. Explanted notochords generally underwent vacuolation when they were surrounded by other differentiating tissues. In the absence of these tissues, they were not only unable to vacuolate but also unable to survive. When the notochords were implanted into the ventral mass of yolk granules of neurula, they showed no vacuolation and died within a few days if they were alone and not surrounded by other differentiating tissues. These facts suggest that the presence of other differentiating tissues surrounding the notochord is a requisite for the notochord to vacuolate. Further, the fact that in explanted notochords, vacuolation was frequently interrupted and was left unfinished when the surrounding tissues were scarce, suggests that the quantity of the surrounding tissues is important in promoting vacuolation. Interruption of the vacuolation occurs in the explanted notochord at any stage from the beginning to the end of the process. Therefore, almost all the stages of vacuolation were observed in these notochords. Very frequently, different parts of a single notochord presented different stages of vacuolation. All these stages were essentially the same as those found in the normal notochord. From these results, it emerges that although vacuolation of the explanted and implanted notochords is carried out with the same process as in the normal intact one, it is accomplished only when they are surrounded by a sufficient quantity of other differentiating tissues.     

Optical Recording of the Pacemaking Activity of a Congenital Double-heart in an Early Chick Embryo

A congenital double-hearted chick embryo was found among 16,171 embryos, which was at the 11 somite stage of development. The pacemaking activity of its double heart was monitored simultaneously from 9 different regions by optical methods. The right and left half hearts were tubular, and in both, spontaneous rhythmical action potentials and beating were detected, and differences were detected in their rhythms. Action potentials were also monitored in a malformed embryonic heart formed by partial fusion of the primordia. The results are discussed in relation to genesis of intrinsic pacemaking activity in cardiac primordia and to a spatial gradient of rhythmicity in the early stages of cardiogenesis.