Cytokinin

Plants deploy a finely tuned balance between growth and defence responses for better fitness. Crosstalk between defence signalling hormones such as salicylic acid (SA) and jasmonates (JAs) as well as growth regulators plays a significant role in mediating the trade-off between growth and defence in plants. Here, we specifically discuss how the mutual antagonism between the signalling of auxin and SA impacts on plant growth and defence. Furthermore, the synergism between auxin and JA benefits a class of plant pathogens. JA signalling also poses growth cuts through auxin. We discuss how the effect of cytokinins (CKs) is multifaceted and is effective against a broad range of pathogens in mediating immunity. The synergism between CKs and SA promotes defence against biotrophs. Reciprocally, SA inhibits CK-mediated growth responses. Recent reports show that CKs promote JA responses; however, in a feedback loop, JA suppresses CK responses. We also highlight crosstalk between auxin and CKs ...

The effect of plant growth regulators on in vitro propagation of Fragaria x ananassa Duch. cv. Pharachatan 80 was conducted in sterile conditions. For shoot multiplication, shoot tip were cultured on Murashige and Skoog (MS, 1962) medium for 6 weeks. The results indicated that shoot tips could induce shoots and roots 90%. Then shoot tips were cultured on MS medium supplemented with combination of cytokinin (BAP or Kinetin at 0, 0.1, 0.2 and 0.5 mg /l) and auxin (IBA at 0, 0.05, 0.1 and 0.2 mg/l) for 6 weeks. The results showed that shoot tips cultured on MS medium supplemented with 0.2 mg/l BAP and 0.2 mg/l IBA had the highest number of shoots (1.70 ± 0.82 shoots/explant) and shoots tips that cultured on MS medium supplemented with 0.2 mg/l IBA had the highest number of roots (5.40 ± 4.67 root/explant). From this study, it was found that MS medium supplemented with BAP and IBA gave the best results on shoot and root induction than MS medium supplemented with Kinetin and IBA. For the...

Cotyledons were excised from 7-day-old dark-grown cucumber seedlings and treated with water, benzyladenine (BA), kinetin (K), zeatin (Z), or zeatin riboside (ZR) in dark after endogenous cytokinin depletion. We have compared changes in chitinase (EC. 3.2.1.14) activity induced by these cytokinins. We find that the activities of chitinase and its isoforms increase by approximately 3- to 6-fold following BA, Z, and ZR treatments. Among these treatments, Z was more effective. K was totally ineffective in inducing chitinase activity. Immunoblot analysis suggests that the cytokinin Z-induction of enzyme activity is due to the induction of higher chitinase protein levels and not the activation of existing enzyme. Furthermore, the Z-induced chitinase activity and its protein accumulation were completely inhibited by the protein kinase inhibitor staurosporine, whereas the protein phosphatase inhibitor sodium fluoride was not effective in such inhibitions. Treatment of cotyledons with extemal $CaCl_2$ and calcium ionophore increased the basal chitinase activity by 6- and 5-fold, respectively. Moreover, the effects of staurosporine, sodium fluoride, and $Ca^{2+}$ on Z-induced chitinase activity correlate with their effects on chitinase protein levels. Taken together, our data suggests $Ca^{2+}$ and staurosporine-sensitive protein kinase(s) as components of the cytokinin transduction machinery involving induction of chitinase in cucumber.

The establishment of a micro-propagation protocol for banana (Musa sp.) cv. Sabri, was carried out using meristematic stem cuttings explant. MS medium supplemented with BAP singly or in combination with auxin, IAA and coconut water was used for this purpose. Highest percentage of shoot regeneration (90%) and maximum number of shoots (10) per explant were observed when cultured on MS + 4.0 mg/1 BAP + 2.0 mg/1 IAA + 13% (v/v) coconut water. Best response towards root induction was achieved on half MS medium supplemented with 0.5 mg/1 IBA. The regenerated healthy rooted plantlets were transferred to small plastic pot containing garden soil and compost in a ratio of 2:1. Through this method, complete micro-propagated plantlets were obtained within three months.   DOI: http://dx.doi.org/10.3329/bjsir.v47i2.11444   Bangladesh J. Sci. Ind. Res. 47(2), 143-146, 2012  

In strawberry micropropagation, several challenges must be overcome to obtain quality plants and achieve high survival rate to ex vitro acclimatization. In this study, therefore, a set of protocols were evaluated to optimize explant (meristem) disinfection, in vitro growth (multiplication and rooting), and ex vitro acclimatization of strawberry. The results showed that explants treated with 1.0% NaClO for 5 min had a lower percentage of contamination, and achieved a higher percentage of viability, height, and number of leaves. In vitro growth was favored by the use of 1 mg L−1 zeatin, since it allowed greater seedling growth (number of shoots, seedling height, number of leaves, number of roots and root length), and a higher pre-acclimation rate (100%). In the acclimatization phase, plants grown in a substrate composed of compost + peat combined with 4 g of humic acid achieved better response in morphological and physiological variables. In fact, the results of this study could be us...

This work covers peculiarities of introduction of the hybrid form of hyacinth (Hyacinthus) introduced and spread in Georgia into in-vitro culture and induction of embryogenesis. Aiming to derive the sterile cultures, we matched the sterilizing agent and its exposition. Besides, we used hyacinth bulb peel as an initial explant to derive the embryogenic callus. Aiming induction of callusogenesis and embryogenesis, we tested and researched concurrent exposition to benzylaminopurine and auxins (NAA and IBA) in concentrations correlation of 2:10; 2:15; 2:20. We derived the embryogenic calli and somatic embryoids, developed conditions for maturation of the embryoids and regeneration of the somatic embryos.

The establishment of a micro-propagation protocol for banana (Musa sp.) cv. Sabri, was carried out using meristematic stem cuttings explant. MS medium supplemented with BAP singly or in combination with auxin, IAA and coconut water was used for this purpose. Highest percentage of shoot regeneration (90%) and maximum number of shoots (10) per explant were observed when cultured on MS + 4.0 mg/1 BAP + 2.0 mg/1 IAA + 13 % (v/v) coconut water. Best response towards root induction was achieved on half MS medium supple-mented with 0.5 mg/1 IBA. The regenerated healthy rooted plantlets were transferred to small plastic pot containing garden soil and com-post in a ratio of 2:1. Through this method, complete micro-propagated plantlets were obtained within three months.