Gibberellic Acid and Jasmonic Acid Improve Salt Tolerance in Summer Squash by Modulating Some Physiological Parameters Symptomatic for Oxidative Stress and Mineral Nutrition.

Gibberellic acid (GA) and jasmonic acid (JA) are considered to be endogenous regulators that play a vital role in regulating plant responses to stress conditions. This study investigated the ameliorative role of GA, JA, and the GA + JA mixture in mitigating the detrimental effect of salinity on the summer squash plant. In order to explore the physiological mechanisms of salt stress alleviation carried out by exogenous GA and JA, seed priming with 1.5 mM GA, 0.005 mM JA, and their mixture was performed; then the germinated summer squash seedlings were exposed to 50 mM NaCl. The results showed that a 50 mM NaCl treatment significantly reduced shoot and root fresh and dry weight, water content (%), the concentration of carotenoid (Car), nucleic acids, K+, and Mg++, the K+/Na+ ratio, and the activity of catalase (CAT) and ascorbate peroxidase (APX), while it increased the concentration of proline, thiobarbituric acid reactive substances (TBARS), Na+, and Cl- in summer squash plants, when compared with the control. However, seed priming with GA, JA and the GA + JA mixture significantly improved summer squash salt tolerance by reducing the concentration of Na+ and Cl-, TBARS, and the Chl a/b ratio and by increasing the activity of superoxide dismutase, CAT, and APX, the quantities of K+ and Mg++, the K+/Na+ ratio, and the quantities of RNA, DNA, chlorophyll b, and Car, which, in turn, ameliorated the growth of salinized plants. These findings suggest that GA and JA are able to efficiently defend summer squash plants from salinity destruction by adjusting nutrient uptake and increasing the activity of antioxidant enzymes in order to decrease reactive oxygen species accumulation due to salinity stress; these findings offer a practical intervention for summer squash cultivation in salt-affected soils. Synergistic effects of the GA and JA combination were not clearly observed, and JA alleviated most of the studied traits associated with salinity stress induced in summer squash more efficiently than GA or the GA + JA mixture.

Foliar Sprayed Green Zinc Oxide Nanoparticles Mitigate Drought-Induced Oxidative Stress in Tomato.

This study explored the effectiveness of green zinc oxide nanoparticles (ZnO-NPs) foliar spray on tomato growth and oxidative stress relief under drought conditions. Tomato plant subjected to four water regimes (100, 75, 50, and 25% FC), and in the same while seedlings were sprayed with 25, 50, and 100 mg/L green ZnO-NPs. The results showed that tomato growth parameters reduced significantly by increasing drought stress levels, while ZnO-NPs enhanced plant growth under all studied drought levels. Out of three ZnO-NPs concentrations tested, 25 and 50 mg/L ZnO-NPs proved to be the optimum treatments for alleviating drought stress. They increased shoot and root biomass compared to untreated controls. Application of 25 and 50 mg/L ZnO-NPs enhanced shoot dry weight by about 2-2.5-fold, respectively, under severe drought conditions (25%) compared to ZnO-NPs untreated plants. The application of 25 and 50 mg/L green ZnO-NPs decreased the drought-induced oxidative stress as indicated by the reduction in malondialdehyde and hydrogen peroxide concentrations compared to untreated controls. While 100 mg/L ZnO-NPs further increased oxidative stress. The beneficial effects of ZnO-NPs were evident in the plants' defensive state, in which the concentration of ascorbic acid, free phenols, and the activity of superoxide dismutase, catalase, and ascorbate peroxidase were maintained at higher levels compared to NPs-untreated plants. At severe drought conditions, 25 mg/L ZnO-NPs induced SOD, CAT, and APX activity by about 3.99-, 3.23-, and 2.82-fold of their corresponding controls, respectively. Likewise, at 25% FC, SOD, CAT, and APX activity increased with 50 mg/L ZnO-NPs by about 4.58-, 3.57-, and 3.25-fold consecutively compared with their respective controls. Therefore, foliar use of green ZnO-NPs at lower concentrations might be suggested as an efficient way for enhancing tomato tolerance to drought stress.

Jasmonates mediate plant defense responses to Spodoptera exigua herbivory in tomato and maize foliage.

Plants evolve diverse strategies to cope with herbivorous insects, in which the lipid-derived phytohormone jasmonic acid (JA) plays a crucial role. This study was conducted to investigate the differential responses of tomato and maize plants to Spodoptera exiguaherbivory and to clarify the role played by JA, methyl-jasmonate (MeJA) and jasmonoyl-L-isoleucine (JA-L-Ile) in their defense responses. JA, MeJA and JA-L-Ile were quantified using HPLC-MS/MS. The results showed that maize plant was more tolerant toS. exiguaherbivory than tomato. Spodopteraexigua attack induced JA, MeJA, and JA-L-Ile to high levels after 2 h of infestation in both test plants. Then, all studied JAsconcentration decreased gradually by increasing infestation time up to 1 week. JA concentration in infested maize was much higher than that in infested tomato leaves. However, MeJA concentration in infested tomato leaves was higher than that in maize. In control plants, JA was not recorded, while MeJA was recorded in comparable values both in tomato and maize. Our results showed that JA plays the main role in increasing defense responses to S. exigua infestation in the studied plants as a direct signaling molecule; however, MeJA could play an indirect role by inducing JA accumulation. JA-L-Ile indicated a less efficient role in defense responses to S. exigua attack in both test plants where its level is much lower than JA and MeJA.

Stepwise response of MeJA-induced genes and pathways in leaves of C. roseus.

Catharanthus roseus is a perennial herb known for the production of important terpenoid indole alkaloids (TIAs) in addition to a variety of phenolic compounds. The goal of the present work was to detect the prolonged effects of MeJA (6 uM) treatment across time (up to 24 days) in order to detect the stepwise response of MeJA-induced genes and pathways in leaves of C. rouses. Prolonged exposure of plants to MeJA (6 uM) treatment for different time points (6, 12 and 24 days) indicated that genes in the indole alkaloid biosynthesis pathway and upstream pathways were triggered earlier (e.g., 6 days) than those in the anthocyanin biosynthesis pathway and its upstream pathways (e.g., 12 days). Three enzymes, e.g., T16H, OMT, and D4H, in the six-step vindoline biosynthesis and two enzymes, e.g., TDC and STR, acting consecutively in the conversion of tryptophan to strictosidine, were activated after 6 days of MeJA treatment. Two other key enzymes, e.g., TRP and CYP72A1, acting concurrently upstream of the TIA biosynthesis pathway were upregulated after 6 days. The genes encoding TDC and STR might concurrently act as a master switch of the TIA pathway towards the production of the indole alkaloids. On the other hand, we speculate that the gene encoding PAL enzyme also acts as the master switch of phenylpropanoid biosynthesis and the downstream flavonoid biosynthesis and anthocyanin biosynthesis pathways towards the production of several phenolic compounds. PAL and the downstream enzymes were activated 12 days after treatment. Cluster analysis confirmed the concordant activities of the flower- and silique-specific bHLH25 transcription factor and the key enzyme in the TIA biosynthesis pathway, e.g., STR. Due to the stepwise response of the two sets of pathways, we speculate that enzymes activated earlier likely make TIA biosynthesis pathway a more favourable target in C. roseus than anthocyanin biosynthesis pathway.

Physiological parameters of salt tolerance during germination and seedling growth of Sorghum bicolor cultivars of the same subtropical origin.

Salt-tolerant ecotypes (or cultivars, varieties, etc.) of different plant species have been long known to evolve in nature. In the past few years, plant breeders have made significant achievements regarding salt tolerance in a number of potential crops using artificial selection. The aim of this work was to evaluate and screening of the natural sea water (Red sea) tolerance of 7 Saudi local (Baish, Jazan; 17.388086, 42.524070) cultivars of sorghum (Sorghum bicolor L., Moench; Poaceae) with respect to the performance of some physiological parameters such as germination, shoot and root development which could be recommended to local farmers and plant breeders. The shoot growth of the studied sorghum cultivars were significantly affected by the exposure to sea water. Root growth was different among cultivars even when treated with normal water. The cultivar C3 (mix white and red seeds) was observed as more salt tolerant and cultivar C4 (whitish seeds) was more salt sensitive on the basis of the germination-ability and shoot development. Cultivar C3 was also observed to produce better seeds compared with the other cultivars. Results of this experiment can be useful to the local sorghum growing farmers or as a genetic resource for the development of sorghum cultivars with improved germination under salt stress.

Whole mitochondrial and plastid genome SNP analysis of nine date palm cultivars reveals plastid heteroplasmy and close phylogenetic relationships among cultivars.

Date palm is a very important crop in western Asia and northern Africa, and it is the oldest domesticated fruit tree with archaeological records dating back 5000 years. The huge economic value of this crop has generated considerable interest in breeding programs to enhance production of dates. One of the major limitations of these efforts is the uncertainty regarding the number of date palm cultivars, which are currently based on fruit shape, size, color, and taste. Whole mitochondrial and plastid genome sequences were utilized to examine single nucleotide polymorphisms (SNPs) of date palms to evaluate the efficacy of this approach for molecular characterization of cultivars. Mitochondrial and plastid genomes of nine Saudi Arabian cultivars were sequenced. For each species about 60 million 100 bp paired-end reads were generated from total genomic DNA using the Illumina HiSeq 2000 platform. For each cultivar, sequences were aligned separately to the published date palm plastid and mitochondrial reference genomes, and SNPs were identified. The results identified cultivar-specific SNPs for eight of the nine cultivars. Two previous SNP analyses of mitochondrial and plastid genomes identified substantial intra-cultivar ( = intra-varietal) polymorphisms in organellar genomes but these studies did not properly take into account the fact that nearly half of the plastid genome has been integrated into the mitochondrial genome. Filtering all sequencing reads that mapped to both organellar genomes nearly eliminated mitochondrial heteroplasmy but all plastid SNPs remained heteroplasmic. This investigation provides valuable insights into how to deal with interorganellar DNA transfer in performing SNP analyses from total genomic DNA. The results confirm recent suggestions that plastid heteroplasmy is much more common than previously thought. Finally, low levels of sequence variation in plastid and mitochondrial genomes argue for using nuclear SNPs for molecular characterization of date palm cultivars.

Characterization of ten date palm (Phoenix dactylifera L.) cultivars from Saudi Arabia using AFLP and ISSR markers.

Date palm is the most economically important plant in the Middle East due to its nutritionally valuable fruit. The development of accurate DNA fingerprints to characterize cultivars and the detection of genetic diversity are of great value for breeding programs. The present study explores the usefulness of ISSR and AFLP molecular markers to detect relationships among 10 date palm (Phoenix dactylifera L.) cultivars from Saudi Arabia. Thirteen ISSR primers and six AFLP primer combinations were examined. The level of polymorphism among cultivars for ISSRs ranged from 20% to 100% with an average of 85%. Polymorphism levels for AFLPs ranged from 63% to 84% with an average of 76%. The total number of cultivar-specific markers was 241, 208 of which were generated from AFLP analysis. AJWA cultivar had the highest number of cultivar-specific ISSR markers, whereas DEK, PER, SUK-Q, SHA and MOS-H cultivars had the lowest. RAB and SHA cultivars had the most and least AFLP cultivar-specific markers, respectively. The highest pairwise similarity indices for ISSRs, AFLPs and combined markers were 84% between DEK (female) and PER (female), 81% between SUK-Q (male) and RAB (male), and 80% between SUK-Q (male) and RAB (male), respectively. The lowest similarity indices were 65% between TAB (female) and SUK-Q (male), 67% between SUK-A (female) and SUK-Q (male), and 67% between SUK-A (female) and SUK-Q (male). Cultivars of the same sex had higher pairwise similarities than those between cultivars of different sex. The Neighbor-Joining (NJ) tree generated from the ISSR dataset was not well resolved and bootstrap support for resolved nodes in the tree was low. AFLP and combined data generated completely resolved trees with high levels of bootstrap support. In conclusion, AFLP and ISSR approaches enabled discrimination among 10 date palm cultivars of from Saudi Arabia, which will provide valuable information for future improvement of this important crop.