The AtCRK5 Protein Kinase Is Required to Maintain the ROS NO Balance Affecting the PIN2-Mediated Root Gravitropic Response in Arabidopsis

The Arabidopsis AtCRK5 protein kinase is involved in the establishment of the proper auxin gradient in many developmental processes. Among others, the Atcrk5-1 mutant was reported to exhibit a delayed gravitropic response via compromised PIN2-mediated auxin transport at the root tip. Here, we report that this phenotype correlates with lower superoxide anion (O-2(center dot-)) and hydrogen peroxide (H2O2) levels but a higher nitric oxide (NO) content in the mutant root tips in comparison to the wild type (AtCol-0). The oxidative stress inducer paraquat (PQ) triggering formation of O-2(center dot-) (and consequently, H2O2) was able to rescue the gravitropic response of Atcrk5-1 roots. The direct application of H2O2 had the same effect. Under gravistimulation, correct auxin distribution was restored (at least partially) by PQ or H2O2 treatment in the mutant root tips. In agreement, the redistribution of the PIN2 auxin efflux carrier was similar in the gravistimulated PQ-treated mutant and untreated wild type roots. It was also found that PQ-treatment decreased the endogenous NO level at the root tip to normal levels. Furthermore, the mutant phenotype could be reverted by direct manipulation of the endogenous NO level using an NO scavenger (cPTIO). The potential involvement of AtCRK5 protein kinase in the control of auxin-ROS-NO-PIN2-auxin regulatory loop is discussed

CRK5 Protein Kinase Contributes to the Progression of Embryogenesis of Arabidopsis thaliana

The fine tuning of hormone (e.g., auxin and gibberellin) levels and hormone signaling is required for maintaining normal embryogenesis. Embryo polarity, for example, is ensured by the directional movement of auxin that is controlled by various types of auxin transporters. Here, we present pieces of evidence for the auxin-gibberellic acid (GA) hormonal crosstalk during embryo development and the regulatory role of the Arabidopsis thaliana Calcium-Dependent Protein Kinase-Related Kinase 5 (AtCRK5) in this regard. It is pointed out that the embryogenesis of the Atcrk5-1 mutant is delayed in comparison to the wild type. This delay is accompanied with a decrease in the levels of GA and auxin, as well as the abundance of the polar auxin transport (PAT) proteins PIN1, PIN4, and PIN7 in the mutant embryos. We have previously showed that AtCRK5 can regulate the PIN2 and PIN3 proteins either directly by phosphorylation or indirectly affecting the GA level during the root gravitropic and hypocotyl hook bending responses. In this manuscript, we provide evidence that the AtCRK5 protein kinase can in vitro phosphorylate the hydrophilic loops of additional PIN proteins that are important for embryogenesis. We propose that AtCRK5 can govern embryo development in Arabidopsis through the fine tuning of auxin-GA level and the accumulation of certain polar auxin transport proteins

EMBRYOLOGICAL CHARACTERS TO STUDY THE JUSTICIA-RUNGIA COMPLEX (ACANTHACEAE)

Family Acanthaceae is characterized by very diverse plants whose taxonomic position is debated. Therefore, study of various macroscopic and microscopic characters had been used for studying the relatedness of the various taxa. Embryological characters are considered as one of the most stable characters. Justicia–Rungia Complex is one of the intriguing complexes present in family Acanthaceae. Justicia is basically a Linnaean Genus which included Rungia also. But later Rungia was separated from Justicia by Nees. Another offshoot of Justicia has been the formation of new genus Rostellularia which is also the creation of Nees. Due to this the Rungia is sometime confused as Justicia and some time it is considered as Rostellularia. In the present investigation embryological data is used to study the Justicia–Rungia Complex. The plants studied in present investigation are Justicia procumbens, Rungia repens, Haplanthus verticillata and Blepharis repens. The embryological study using UPGMA clearly indicates a very close similarity between Justicia procumbens and Rungia repens