Journal of Plant Growth Regulation

The epiphytic habitat is potentially one of the most stressful environments for plants, making the effective developmental control in response to external cues critical for epiphyte survival. Because ethylene mediates several abiotic stresses in plants, here, we have examined the ethylene influence in both shoot and root systems of the epiphytic orchid Catasetum fimbriatum. Under controlled conditions, ethylene production was quantified during an entire growth cycle of C. fimbriatum development in vitro, while treatments modulating either ethylene concentration or perception were carried out over the early growth phase of these plants. After treatments, growth measurements and histological features were studied in both shoot and root tissues. Ethylene production showed a decreasing trend over the period of organ elongation; however, it increased considerably when leaves were shed, and a new axillary bud was initiating. The early exposure of young plants to higher concentrations of ethylene triggered morphogenic responses that included root hair formation instead of velamen, and a combination of inhibitory effects (decreases in both stem enlargement and cellular/organ elongation) and inductive effects (increases in leaf and root formation, bud initiation and cellular thickening) on plant growth, which favored biomass allocation to roots. Conversely, inhibition of ethylene perception over the plant growth phase generally resulted in the opposite morphogenic responses. Our data indicate that periodic variations in ethylene concentration and/or sensitivity seem to modulate several developmental features in shoot and root systems of C. fimbriatum which could have adaptive significance during the growing phase of this epiphytic orchid.

Storage and maintenance of horticultural products in optimal conditions for a reasonable period, once they have been harvested is a technological challenge. Diverse methods are generally used, i.e., low temperature but, in many cases, it may provoke undesirable collateral effects such as softening or promoting pathogens infections, thus causing their deterioration. Nitric oxide (·NO) and hydrogen sulfide (H2S) are compounds generated endogenously by plants with signaling properties that mediate fruit development and ripening. Additionally, when these molecules are applied exogenously, they can provide benefits such as maintaining the quality of horticultural products and even prolonging their shelf-life once they are stored. This review provides a broad perspective of ·NO and H2S metabolism in plant cells and, in addition, different plant models are described of how the exogenous application of either NO or H2S to horticultural products preserves nutritional quality during postharvest storage.

Catharanthus roseus is a great medicinal plant used for treating diseases such as cancer, as it contains different biochemicals including terpenoids. Salinity is a major stress, significantly decreasing the growth and yield of medicinal plants, worldwide. However, to our knowledge, there is not any data on the growth improvement in C. roseus seedling under salinity stress using the priming techniques tested in the presented research. The objective was to investigate the effects of seed priming including hydro- (distilled water), osmo- (KNO3 1%), and hormonal priming (salicylic acid, SA 0.5 mM) on the seedling growth of C. roseus under natural salinity (salt obtained from Qom Lake, Iran) of 0, 2.95, 5.66, 8.13, and 10.66 dSm−1. The treated seeds were grown in Petri dishes and placed in a germinator (25 ± 1 °C) for germination and the growth of seedlings. The plant seedlings were planted in the greenhouse conditions and treated during the V6–V8 growth stage with the salinity treatments (a factorial design on the basis of a completely randomized block design with three replicates) under hydroponics conditions. Different morphological properties of C. roseus including the length and the dry weight of rootlet, plumule, and seedling as well as leaf relative water content (RWC) were measured. The results indicated the alleviating effects of different priming techniques on the growth of C. roseus under natural salt stress. Although the effect of priming was not significant on RWC, salt stress and its interaction with priming significantly affected RWC indicating that the alleviating effect of priming on RWC is a function of salinity level. With increasing the level of salinity, rootlet dry weight increased, which indicates the allocation of more carbon to the roots under stress. It is possible to plant C. roseus in saline fields using the priming techniques tested in this research work.

Induction of defense response in host plants by the Trichoderma spp. has been attributed as one of the major mechanisms leading to inhibition of the pathogenic ingression. The present study sheds light on the mechanisms employed by the Trichoderma isolates, obtained from phyllosphere (BHUF4) and rhizosphere (T16A), to modulate the defense network of chili plant under Colletotrichum truncatum challenge. Plants treated with both the Trichoderma strains exhibited significant accumulation of phenols under C. truncatum challenge with maximum increment recorded for capsaicin (16.1-fold), ferulic acid (5.03-fold), quercetin (5.36-fold), salicylic acid (94.88-fold), and kaempeferol (6.22-fold). Phenol accumulation corresponded to the subsequent defense gene expression pattern. When compared to the pathogen-challenged control plants, enhanced expression of PR1, PIK1, CHI, GLU, Cdef, and SAR genes was recorded in the Trichoderma-treated plants acting as a biocontrol agent (BCA). The results of the present study suggest that to strengthen the defense pathways in the host plant, the mechanisms employed by Trichoderma isolates differ and depend upon their origin and site of application. While phyllospheric Trichoderma isolate (BHUF4) employed the systemic acquired resistance (SAR) pathway, the rhizospheric Trichoderma strain (T16A) used the induced systemic response (ISR) pathway for eliciting the defense response in the host plant under C. truncatum challenge. The study signifies how Trichoderma strains obtained from different origin and when applied at different sites in plant judiciously reprogram the defense network of the host plant to provide robust protection against phytopathogens. In the present case, overall protection is provided to the chili plants against the foliar or underground attack of C. truncatum.

Cytokinin dehydrogenase (CKX) degrades the cytokinin hormone in plants and plays an important role in cytokinin regulatory processes. CKX proteins are encoded by a multigene family with a varying number of members. In this study, 13 maize CKX sequences were collected in which ten transcripts were confirmed by RT-PCR. The tissue- and cytokinin-dependent expression studies indicated that ZmCKX genes exhibit a variety of expression patterns, suggesting diverse functions. Besides 13 maize CKXs, 7 Arabidopsis, 9 poplar, and 11 rice CKX proteins were further used to construct a phylogenetic tree. The CKX members were assigned to six groups, and the intron/exon structures, sequence motifs, and protein properties were conserved within groups. The genome distribution of CKXs supports that segmental duplication contributes to the expansion of the CKX gene family. By quantitative RT–PCR analysis of maize members and digital Northern analysis of Arabidopsis, poplar, and rice members for their tissue expression patterns, highly correlative expression profiles of CKX genes were found among some of the orthologs, whereas different expression manners were found between some of the paralogs. These results suggest functional conservation within each group of the CKX family and provide a clue for transfer of a gene function from one species to the other and further contribute to uncovering the role of CKX genes in planta.

This study investigated whether and how the interaction between abscisic acid (ABA) and ethylene is involved in the regulation of rice (Oryza sativa L.) spikelet sterility when subjected to water stress during meiosis. Two rice cultivars, HA-3 (drought-resistant) and WY-7 (drought-susceptible), were used and subjected to well-watered and water-stressed (WS) treatments during meiosis (15–2 days before heading). Leaf water potentials of both cultivars markedly decreased during the day as a result of the WS treatment, but panicle water potentials remained constant. The percentage of sterile spikelets in WS plants was increased by 49.7% for WJ-7 but only 12.7% for HA-3. ABA, ethylene, and 1-aminocyclopropane-1-carboxylic acid were all enhanced in spikelets by the water stress, but ethylene was enhanced more than ABA in WY-7 when compared with that in HA-3. Spikelet sterility was significantly reduced when ABA or amino-ethoxyvinylglycine, an inhibitor of ethylene synthesis, was applied to the panicles of WS plants at the early meiosis stage. Application of ethephon, an ethylene-releasing agent, or fluridone, an inhibitor of ABA synthesis, had the opposite effect, and sterility was increased. The results suggest that antagonistic interactions between ABA and ethylene may be involved in mediating the effect of water stress on spikelet fertility. A higher ratio of ABA to ethylene would be a physiologic trait of rice adaptation to water stress.