The impact of mechanical stress on anatomy, morphology, and gene expression in Urtica dioica L.

MAIN CONCLUSION: Mechanical stress induces distinct anatomical, molecular, and morphological changes in Urtica dioica, affecting trichome development, gene expression, and leaf morphology under controlled conditions The experiments were performed on common nettle, a widely known plant characterized by high variability of leaf morphology and responsiveness to mechanical touch. A specially constructed experimental device was used to study the impact of mechanical stress on Urtica dioica plants under strictly controlled parameters of the mechanical stimulus (touching) and environment in the growth chamber. The general anatomical structure of the plants that were touched was similar to that of control plants, but the shape of the internodes' cross section was different. Stress-treated plants showed a distinct four-ribbed structure. However, as the internodes progressed, the shape gradually approached a rectangular form. The epidermis of control plants included stinging, glandular and simple setulose trichomes, but plants that were touched had no stinging trichomes, and setulose trichomes accumulated more callose. Cell wall lignification occurred in the older internodes of the control plants compared to stress-treated ones. Gene analysis revealed upregulation of the expression of the UdTCH1 gene in touched plants compared to control plants. Conversely, the expression of UdERF4 and UdTCH4 was downregulated in stressed plants. These data indicate that the nettle's response to mechanical stress reaches the level of regulatory networks of gene expression. Image analysis revealed reduced leaf area, increased asymmetry and altered contours in touched leaves, especially in advanced growth stages, compared to control plants. Our results indicate that mechanical stress triggers various anatomical, molecular, and morphological changes in nettle; however, further interdisciplinary research is needed to better understand the underlying physiological mechanisms.

K+ and Cl- channels/transporters independently fine-tune photosynthesis in plants.

In variable light environments, plants adjust light use in photosynthetic electron transport and photoprotective dissipation in the thylakoid membrane. In this respect, roles of the K+/H+ antiporter KEA3, the Cl- channel/transporter CLCe and the voltage-dependent Cl- channel VCCN1 have been unraveled in Arabidopsis thaliana. Here we report that they independently adjust photosynthesis on the basis of analyses using single and higher order loss-of-function mutants. In short experiments of photosynthetic response on transition from dark to low light, we reveal a sequential functioning of VCCN1 and CLCe in the activation of photoprotection and of KEA3 in its downregulation to a low steady state while adjusting the electron transport. On transition from low to high light, VCCN1 accelerates the activation of photoprotection, whereas KEA3 slows it down on transition from high to low light. Based on parallel electrochromic band shift measurements, the mechanism behind is that VCCN1 builds up a pH gradient across the thylakoid membrane, whereas KEA3 dissipates this gradient, which affects photoprotection. CLCe regulates photosynthesis by a pH-independent mechanism likely involving Cl- homeostasis. Nevertheless, all genotypes grow well in alternating high and low light. Taken together, the three studied ion channels/transporters function independently in adjusting photosynthesis to the light environment.

Expression Analysis of PIN Genes in Root Tips and Nodules of Lotus japonicus.

Auxins are postulated to be one of the pivotal factors in nodulation. However, their transporters in Lotus japonicus, the model species for the study of the development of determinate-type root nodules, have been scarcely described so far, and thus their role in nodulation has remained unknown. Our research is the first focusing on polar auxin transporters in L. japonicus. We analyzed and compared expression of PINs in 20 days post rhizobial inoculation (dpi) and 54 dpi root nodules of L. japonicus by real-time quantitative polymerase chain reaction (qPCR) along with the histochemical ß-glucuronidase (GUS) reporter gene assay in transgenic hairy roots. The results indicate that LjPINs are essential during root nodule development since they are predominantly expressed in the primordia and young, developing nodules. However, along with differentiation, expression levels of several PINs decreased and occurred particularly in the nodule vascular bundles, especially in connection with the root's stele. Moreover, our study demonstrated the importance of both polar auxin transport and auxin intracellular homeostasis during L. japonicus root nodule development and differentiation.