Additional far-red light promotes adventitious rooting of doubleroot-cutting grafted watermelon seedlings

Root regeneration is an important factor influencing the healing rate of graft union and the survival of double-root-cutting grafting.To date,little information is available on how to enhance root regeneration of rootstock in grafted watermelon(Citrullus lanatus)seedlings.In this study,the effects of different light treatments on root regeneration were determined.This revealed that addition of far-red light(Fr)could significantly expedite root formation in the rootstock.Moreover,the results of transcriptome analysis revealed that plant hormone pathway and auxinrelated genes were greatly induced by Fr,especially for auxin-response proteins(including CmIAA11,CmIAA17,and CmAUX28),Small auxinup RNA genes(including CmSAUR20 and CmSAUR50)and the auxin efflux transporter(CmPIN3).In addition,the expression of Phytochrome Interacting Factor(PIFs),such as CmPIF1,CmPIF3 and CmPIF7,was remarkably increased by Fr.These genes may act together to activate auxinrelated pathways under Fr treatment.Based on the results of HPLC-MS/MS analysis,the concentrations of different auxin-types in adventitious root were significantly influenced by Fr.Furthermore,the better growth of rootstock root displayed superior vasculature transport activity of the graft union with Fr treatment,which was determined by the acid magenta dyeing experiment.Therefore,all the results suggested that Fr could induce AR formation in rootstocks,which may be associated with the auxin accumulation by regulating the transcriptional level of auxinrelated and PIF genes.The findings of this study demonstrated a practicable way to shorten the healing period of graftings and improve the quality of grafted watermelon seedlings,which will provide a theoretical basis for the speeding development of industrialized seedlings production.

Ultrasound Pulse Emission Spectroscopy Method to Characterize Xylem Conduits in Plant Stems

Although it is well known that plants emit acoustic pulses under drought stress,the exact origin of the waveform of these ultrasound pulses has remained elusive.Here,we present evidence for a correlation between the characteristics of the waveform of these pulses and the dimensions of xylem conduits in plants.Using a model that relates the resonant vibrations of a vessel to its dimension and viscoelasticity,we extract the xylem radi from the waveforms of ultrasound pulses and show that these are correlated and in good agreement with optical microscopy.We demonstrate the versatility of the method by applying it to shoots of ten different vascular plant species.In particular,for Hydrangea quercifolia,we further extract vessel element lengths with our model and compare them with scanning electron cryomicroscopy.The ultrasonic,noninvasive characterization of internal conduit dimensions enables a breakthrough in speed and accuracy in plant phenotyping and stress detection.