Physio-biochemical Responses of In Vitro Cooking Banana Musa paradisiaca cv Lang towards Pseudo Induced Drought Stress by Polyethylene Glycol (PEG)

Musa paradisiaca cv Lang belongs to cooking banana group, and it has high potential to be used in banana chips production. Like other cultivars, M. paradisiaca cv Lang is susceptible towards water shortage, therefore affecting banana growth and productivity. In this study, to mimic the drought condition, pseudo-drought stress was given to in vitro Lang banana seedlings by adding polyethylene glycol (PEG). Overall, decrement of roots length and chlorophyll (Chl) content was displayed by the seedlings exposed to 1%, 2%, 3%, 4%, and 5% (w/v) of PEG after three weeks of exposure. The proline content, total soluble protein content, and antioxidant capacity in leaf and roots, however, countered differently towards different levels of drought. Proline content showed the highest in leaf of 2% (w/v) PEG-treated seedling (12.66±0.38 µmoles/g) while the total soluble protein content showed the highest in roots of 5% (w/v) of PEG-treated seedling (30.65±1.07 mg/g FW). Antioxidant capacity of stressed seedlings revealed the catalase (CAT), guaiacol peroxidase (POD), and ascorbate peroxidase (APX) activities were the highest in the leaf of 1% (w/v) (10.69±5.06 µmol/min/mg), 4% (w/v), (0.079±0.03 µmol/min/mg), and 5% (w/v) (9.11±8.47 µmol/min/mg) of PEG- treated seedlings, respectively. Meanwhile, the highest CAT, POD, and APX activities in the roots were determined in 3% (w/v) (0.49±0.04 µmol/min/mg), 2% (w/v) (0.03±0.02 µmol/min/mg), and 3% (w/v) (16.69±0.5 µmol/min/mg) of PEG-treated seedlings, respectively. These data show that PEG can be a priming agent to induce defense system at seedling stage of banana, which could enhance their survivability during ex vitro acclimatization.

Salinity stress affects growth and physiology of mulberry (Morus sp.)

Mulberry (Morus sp.) plant is used to feed silkworms, and the leaves contain compounds with medicinal properties of secondary metabolites. However, the content of these compounds tends to increase under stress conditions, for instance, salt stress. This study, therefore, aimed to determine the accessions of mulberry with tolerance for salt stress. The stem cuttings of seven accessions from 5 regions, Bogor, Pati, Situbondo, Bali, and Gowa, were planted following a factorial randomized block design with 3 replications. Subsequently, the first factor using the accessions, and the second factor using NaCl solution (0.0%, 0.2%, 0.3%, and 0.4% concentrations) were performed. The variables observed were growth (leaves number, plant height, and shoots number), photosynthesis rate, total chlorophyll, and proline content. The results showed that the M6 accession exhibited tolerance under high salt stress, based on the leaves number, plant height, shoot number, photosynthesis rate, and proline content. Furthermore, an increase in salt concentration was discovered to cause a decrease in growth, photosynthesis rate, and total chlorophyll content. Also, proline accumulation stimulated by high salt stress possibly plays an important role in salinity tolerance.

Physiological Response and Proteomics Analysis of Reaumuria soongorica Under Salt Stress

Soil salinity can severely restrict plant growth. Yet Reaumuria soongorica can tolerate salinity well. However, large-scale proteomic studies of this plant’s salinity response have yet to reported. Here, R. soongorica seedlings (4 months old) were used in an experiment where NaCl solutions simulated levels of soil salinity stress. The fresh weight, root/shoot ratio, leaf relative conductivity, proline content, and total leaf area of R. soongorica under CK (0 mM NaCl), low (200 mM NaCl), and high (500 mM NaCl) salt stress were determined. The results showed that the proline content of leaves was negatively correlated with salt concentration. With greater salinity, the plant fresh weight, root/shoot ratio, and total leaf area increased initially but then decreased, and vice-versa for the relative electrical conductivity of leaves. Using iTRAQ proteomic sequencing, 47, 177, 136 differentially expressed proteins (DEPs) were identified in low-salt vs. CK, high-salt vs. control, and high-salt vs. low-salt comparisons, respectively. A total of 72 DEPs were further screened from the groups, of which, 34 DEPs increased and 38 DEPs decreased in abundance. These DEPs are mainly involved in translation, ribosomal structure, and biogenesis. Finally, 21 key DEPs (SCORE value ≥ 60 point) were identified as potential targets for salt tolerance of R. soongolica. By comparing the protein structure of treated vs. CK leaves under salt stress, we revealed the key candidate genes underpinning R. soongolica’s salt tolerance ability. This works provides fresh insight into its physiological adaptation strategy and molecular regulatory network, and a molecular basis enhancing breeding, under salt stress conditions.

Phospholipase Dα1 Acts as a Negative Regulator of High Mg2+-Induced Leaf Senescence in Arabidopsis

Magnesium (Mg2+) is a macronutrient involved in essential cellular processes. Its deficiency or excess is a stress factor for plants, seriously affecting their growth and development and therefore, its accurate regulation is essential. Recently, we discovered that phospholipase Dα1 (PLDα1) activity is vital in the stress response to high-magnesium conditions in Arabidopsis roots. This study shows that PLDα1 acts as a negative regulator of high-Mg2+-induced leaf senescence in Arabidopsis. The level of phosphatidic acid produced by PLDα1 and the amount of PLDα1 in the leaves increase in plants treated with high Mg2+. A knockout mutant of PLDα1 (pldα1-1), exhibits premature leaf senescence under high-Mg2+ conditions. In pldα1-1 plants, higher accumulation of abscisic and jasmonic acid (JA) and impaired magnesium, potassium and phosphate homeostasis were observed under high-Mg2+ conditions. High Mg2+ also led to an increase of starch and proline content in Arabidopsis plants. While the starch content was higher in pldα1-1 plants, proline content was significantly lower in pldα1-1 compared with wild type plants. Our results show that PLDα1 is essential for Arabidopsis plants to cope with the pleiotropic effects of high-Mg2+ stress and delay the leaf senescence.

Rice MYB transcription factor OsMYB1R1 negatively regulates drought resistance

MYB transcription factors have been demonstrated to play an important role in plant growth, development and abiotic stresses. This study isolated a rice MYB gene, OsMYB1R1 (Os04g0583900), and functionally characterized its role in tolerance to drought stress by generating transgenic rice plants with overexpressing (OE) and RNA interference (RNAi) OsMYB1R1 . Expression of OsMYB1R1 was down-regulated by drought stress. The tissue-specific expression analysis indicated that OsMYB1R1 was expressed at high level in panicle, but relatively low in the other parts of rice. No difference in germination rate among OsMYB1R1- OE, RNAi and wild-type (WT) seeds under mannitol treatments. No differences in phenotypes, physiological indicators and agronomic traits among WT, OE and RNAi plants were observed under normal grown conditions. Under drought stress, the RNAi plants were more tolerant to drought stress and higher survival rate after re-watering than WT plants, whereas, the overexpressing plants have found just the opposite. The OsMYB1R1 -OE plants exhibited increased relative electrical conductivity (REC), increased malondialdehyde (MDA) content, and decreased proline content compared with the wild type, whereas lower REC and MDA content and higher proline content were found in the RNAi plants. These results suggest that OsMYB1R1 functions as a negative regulator in response to drought stresses, and may be used as a candidate gene for molecular breeding of drought-tolerant crop varieties.

Morpho-physiological and phytochemical responses of basil (Ocimum basilicum L.) to toxic heavy metal cadmium

Cadmium (Cd) is a particularly noteworthy metal that may change the secondary metabolism efficacy of pharmaceutical valuable plants. This study aimed to explore the influence of Cd (0, 25, 75, 100, and 150 µM) on the morpho-physiological traits, mineral contents, essential oil composition, and morphology of secretory glands in basil (Ocimum basilicum L.). The exposure to Cd reduced significantly shoot and root dry weight, shoot and root lengths, total chlorophyll, number, and length of secretory gland compared to control plants, while increased peroxidase activity, proline content, and number of stomata. Essential oil compositions were varied in the Cd-treated plants in a dose-dependent manner. The main compounds of the essential oil were Estragole followed by Linalool and Geranial which the highest percentages were observed in the plants treated with Cd 150 µM. The Cd-treated plants exhibited reductions in calcium (Ca) and iron (Fe) concentrations in both leaves and roots. Cd contents in roots and shoots progressively enhanced with increasing Cd concentrations In general, basil showed good tolerance to Cd stress, so that 50% reduction in shoot dry weight occurred in above 100 μm treatments, which can be related to physiological reactions such as increased antioxidant activity, proline content, number of leaves stomata, and changes in other morpho-physiological factors.

Some Biological Aspects and Proline Metabolism Genes as Influenced by Polyethylene Glycol and Salicylic Aacid in Two Wheat Cultivars

The aim of this work was to study the response of two wheat cultivars with different drought tolerance to PEG (-0.4 Mpa) and SA (0.5 mM). Data of seed germination and seedling growth indicated that Misr-2 cultivar was more drought tolerant than Gemmeiza-12. Under non- stress conditions, Misr-2 had higher values of pigments, soluble sugars (Glu, Fru and Suc) and activities of antioxidant enzymes (CAT, APOX, GPOX and SOD) but lower values of proline than those of Gemmeiza-12. The cultivar with a higher proline content (Gemmeiza-12) compared to the other cultivar had a higher expression of proline synthesizing gene (P5CS) but lower expression of proline degrading genes (PDH and P5CDH). Under drought conditions, the drought-sensitive (Gemmeiza-12) needed more osmoregulators and antioxidants than drought-tolerant cultivar (Misr-2) to minimize the negative effects of water and associated oxidative stresses. Therefore, soluble sugars, proline content and anti-oxidation enzymes were higher in Gemmeiza-12 than Misr-2. Also, under drought stress, up-regulation of P5CS and down-regulation of PDH and P5CDH in Gemmeiza-12 were higher than Misr-2. While treatment of the stressed plants with SA up-regulated P5CS gene in both cultivars, down-regulation of PDH and P5CDH in Gemmeiza-12 was clearer than Misr-2.

Effect of Vacuum Impregnation with Sucrose and Plant Growth Hormones to Mitigate the Chilling Injury in Spinach Leaves

Vacuum impregnation (VI) has been immensely used in modifying the physicochemical properties, nutritional values and sensory attributes of fruits and vegetables. However, the metabolic consequences of the plant tissue upon impregnation have not been profoundly explored although shelf life is strongly dependent on this factor. In this study, spinach leaves were impregnated with salicylic acid (SA), γ-aminobutyric acid (GABA) and sucrose to improve its quality and storage ability by reducing the chilling injury through the improvement of proline content. The spinach leaves were stored at 4 °C for 7 days and were analyzed at 12 h interval. Upon 1 day of impregnation, the proline content in GABA, sucrose and SA impregnated leaves was increased by 240%, 153% and 103%, respectively, while in non-impregnated leaves, the proline content was decreased by 23.8%. The chlorophyll content of GABA impregnated leaves exhibited the lowest reduction (49%) followed by sucrose (55%) and SA (57%); meanwhile, non-impregnated leaves reduced 80% of chlorophyll content at the end of storage. Sensory evaluation showed that GABA, sucrose and SA impregnated leaves respectively, obtained higher score in terms of freshness, color, texture and overall appearance as compared to non-impregnated leaves.

Growth response of diploid and tetraploid taro (Colocasia esculenta (L.) Schott) shoot culture to drought stress using polyethylene glycol

Taro genetic improvement through polyploidy induction is expected to be tolerant to abiotic stress. Several studies have shown that polyploidy plants have a higher adaptability to dry environments. In vitro selection technique for evaluation of plant tolerance to drought stress can be done by applying polyethylene glycol (PEG) as a selection agent. The aim of the research was to investigate the growth response of diploid and tetraploid taro shoot culture to drought stress using PEG. The experiment was conducted using a completely randomized design with two factors. The first factor was the concentration of PEG at 0, 5, 10, 15 and 20%. The second factor was Bentul taro clones which were 1 diploid clone and 2 tetraploid clones (clones 4.6.3 and 5.4.4). PEG was added to liquid MS medium containing 2 mg/l BAP. Observations of growth variables were carried out every week until the six weeks of culture. Fresh and dry weights, mortality percentage and proline content were determined at six weeks of culture. The results showed that the addition of PEG in liquid medium significantly affected the number of leaves, petiole length, number of roots, fresh and dry weights, as well as shoot mortality percentage. Differences in clones significantly affected the number of leaves, fresh and dry weights. The two factors tested (PEG and clones), gave an interaction on the number of leaves, fresh and dry weights. The proline content in all diploid and tetraploid clones showed an increase with increasing PEG concentration. The LC50 value in diploid clones was 9.82%, in tetraploid clones 4.6.3 and 5.4.4 were 14.14 and 15.45%, respectively. The results showed that PEG at 10% and 15% could be used for in vitro selection to drought stress both for diploid and tetraploid taro.

Effect of Humic and Salicylic Acids Foliar Application in The Chemical Content of Papaya Seedlings

The experiment was carried out on Papaya seedlings (2 months old) to determine the effect of humic acid (HA) and Salicylic acid (SA) on seedlings growth under local environmental conditions of in a private orchard in Diyala governorate. Humic acid (HA) sprayed at 4 concentrations (0, 1, 2 and 3%), whereas Salicylic acid (SA) was used at three concentrations (0, 200 and 400 mg.L-1). The results showed that spraying with the high concentrations of both acids gave the best results in most studied traits, in addition these treatments decreased significantly leaves proline content.