Deferral of senescence and abscission by chemical inhibition of ethylene synthesis and action in bean explants

Effect of nano silver and silver nitrate on seed yield of (Ocimum basilicum L.)

Background

The aim of this study was to evaluate the effect of nano silver and silver nitrate on yield of seed in basil plant. The study was carried out in a randomized block design with three replications.

Results

Four levels of either silver nitrate (0, 100, 200 and 300 ppm) or nano silver (0, 20, 40, and 60 ppm) were sprayed on basil plant at seed growth stage. The results showed that there was no significant difference between 100 ppm of silver nitrate and 60 ppm concentration of nano silver on the shoot silver concentration. However, increasing the concentration of silver nitrate from 100 to 300 ppm caused a decrease in seed yield. In contrast, a raise in the concentration of nano silver from 20 to 60 ppm has led to an improvement in the seed yield. Additionally, the lowest amount of seed yield was found with control plants.

Conclusions

Finally, with increasing level of silver nitrate, the polyphenol compound content was raised but the enhancing level of nano silver resulting in the reduction of these components. In conclusion, nano silver can be used instead of other compounds of silver.

An early ethylene up-regulated gene encoding a calmodulin-binding protein involved in plant senescence and death

35S-Labeled calmodulin (CaM) was used to screen a tobacco anther cDNA library. A positive clone (NtER1) with high homology to an early ethylene-up-regulated gene (ER66) in tomato, and an Arabidopsis homolog was isolated and characterized. Based on the helical wheel projection, a 25-mer peptide corresponding to the predicted CaM-binding region of NtER1 (amino acids 796-820) was synthesized. The gel-mobility shift assay showed that the peptide formed a stable complex with CaM only in the presence of Ca(2+). CaM binds to NtER1 with high affinity (K(d) approximately 12 nm) in a calcium-dependent manner. Tobacco flowers at different stages of development were treated with ethylene or with 1-methylcyclopropene for 2 h before treating with ethylene. Northern analysis showed that the NtER1 was rapidly induced after 15 min of exposure to ethylene. However, the 2-h 1-methylcyclopropene treatment totally blocked NtER1 expression in flowers at all stages of development, suggesting that NtER1 is an early ethylene-up-regulated gene. The senescing leaves and petals had significantly increased NtER1 induction as compared with young leaves and petals, implying that NtER1 is developmentally regulated and acts as a trigger for senescence and death. This is the first documented evidence for the involvement of Ca(2+)/CaM-mediated signaling in ethylene action.

Bean abscission cellulase : characterization of a cDNA clone and regulation of gene expression by ethylene and auxin

The physiology and anatomy of abscission has been studied in considerable detail; however, information on the regulation of gene expression in abscission has been limited because of a lack of probes for specific genes. We have identified and sequenced a 595 nucleotide bean (Phaseolus vulgaris cv Red Kidney) abscission cellulase cDNA clone (pBACl). The bean cellulase cDNA has extensive nucleic and amino acid sequence identity with the avocado cellulase cDNA pAV363. The 2.0 kilobase bean mRNA complementary to pBACl codes for a polypeptide of approximately 51 kilodalton (shown by hybrid-selection followed by in vitro translation). Bean cellulase antiserum is shown to immunoprecipitate a 51 kilodalton polypeptide from the in vitro translation products of abscission zone poly(A)(+) RNA. Ethylene initiates bean leaf abscission and tissue-specific expression of cellulase mRNA. If ethylene treatment of bean explants was discontinued after 31 h and then 2,5-norbornadiene given to inhibit responses resulting from endogenously synthesized ethylene, polysomal cellulase mRNA hybridizing to pBACl decreased. Thus, ethylene is required not only to initiate abscission and cellulase gene expression but also to maintain continued accumulation of cellulase mRNA. Explants treated with auxin 4 hours prior to a 48 hour treatment with ethylene showed no substantial accumulation of RNA hybridizing to pBACl or expression of cellulase activity.