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Date palm (Phoenix dactylifera) seeds were exposed to different copper (Cu) solutions to examine plant stress responses. Low Cu concentrations (0.02 and 0.2 mM) caused an increase of seed germination, whereas higher Cu amounts (2 mM) significantly inhibited seed germination, delayed hypocotyl elongation, increased seedling mortality, and reduced the germination index by more than 90%. Metal-related toxicity symptoms appeared after 15 d of 2 mM of Cu exposure. Biochemical activities such as amylase activity and redox balance elements were examined to study the relationship between external Cu amount and internal plant response. The present study showed that amylolytic activity was dose- and time-dependent. Likewise, H2 O2 production increased after exposure to Cu, which was correlated with thiobarbituric acid reactive substance (TBARS) accumulation. Furthermore at low Cu concentrations, superoxide dismutase (SOD) and catalase (CAT) activities increased, suggesting that date palm seed stimulated its metal homeostasis networks. However, the highest cupric ion amounts increased cell oxidant accumulation and reduced enzyme production. Gene expression level measures of P. dactylifera phytochelatin synthase (Pdpcs) and P. dactylifera metallothionein (Pdmt) encoding genes have been carried out to investigate the implication of PdPCS and PdMT proteins in Cu homeostasis and/or its sequestration. Phoenix dactylifera metallothionein induction reached a peak after 30 d of exposure to 0.2 mM of Cu. However, it was down-regulated in plants exposed to higher Cu concentrations. In the same conditions, Pdpcs was overexpressed during 1 mo of exposure before it decreased thereafter. These observations provide a new insight into date palm cell response to Cu, a metal that can be toxic but that is also an essential element. Environ Toxicol Chem 2018;37:797-806. © 2017 SETAC.

Reverse transcription polymerase chain reaction (RT-PCR) was used for the detection of Hop stunt viroid (HSVd) and Citrus exocortis viroid (CEVd) in nucleic acid extracts of infected fig leaf tissues. RT-PCR results were confirmed by cDNA sequencing. This is the first report of CEVd and HSVd infecting fig in Tunisia. Alignments and phylogenetic analysis classify the HSVd Tunisian isolates in the plum-type group. CEVd Tunisian isolates are very closely related to the CEVd tomato hybrid callus isolate and to CEVd Gynura isolate from the USA.

Reverse transcription polymerase chain reaction (RT-PCR) was used for the detection of Citrus exocortis viroid (CEVd) in total nucleic acids from infected citrus indicator hosts or directly from field trees. Grapevine yellow speckle viroid-1 (GYSVd-1) and Australian grapevine viroid (AGVd) were also detected by this technique in total nucleic acids from infected grapevine plants. Three protocols for nucleic acid extraction were tested: a phenol-based method, a protocol using a commercial reagent (Trizol) and a method in which extraction with a high-salt buffer was combined with partial purification using non-ionic cellulose. The third protocol, coupled to RT-PCR, seems to be the most suitable, allowing detection of the three viroids in Tunisian citrus and grapevine samples. This method should be used in a testing programme to produce certified viroid-free planting material.