Decline In Relative Water Content Research Articles

Autumn cold acclimation and freezing tolerance of three oak species in semi-Mediterranean Zagros forests

Aim of study: To identify and compare the early frost resistance mechanisms in three oak species (Quercus brantii, Quercus libani and Quercus infectoria). Area of study: Zagros forests of Iran. Material and methods: The physiological and biochemical variables such as chlorophyll fluorescence, relative water content (RWC), electrolyte leakage, and osmotic metabolite content, such as proline, glucose, and potassium of three oak species seedlings with varying altitudinal and latitudinal ranges were measured under various treatments, including cold treatments (4°C: control, -20°C (1 hour) and -20°C (2 hours)) and four levels of hardening steps with decreasing temperature and photoperiod. Main results: Results showed that decreasing photoperiod and temperature during cold hardening was associated with decreasing Fv/Fm, ΦPSII and electron transport rate, increasing (NPQ) measured from chlorophyll fluorescence, as well as increasing osmotic metabolite content and decline of RWC, except the glucose content decreased in Q. brantii from lower altitudes and south aspect. On the other hand, Q. libanii, which originates from higher altitudes and north aspect showed the strongest cold-resistance and faster developing cold-acclimation capacity using earlier accumulation of osmotic metabolites, diminishing RWC and subsequently lowest EL compared to the other oak species. Research highlights: The physiological and biochemical responses of oak species differed based on origin and there was a positive relation between osmotic metabolite content, NPQ, altitude, and cold stress resistance. These physiological responses, especially NPQ (as a fast and non-invasive tool) provide a quantitative assessment of the risks associated with autumn freezing in different oak species and ecotypes relevant to conservation and reforestation projects of the Zagros forests under changing climatic conditions.

Do the expected heatwaves pose a threat to lichens?: Linkage between a passive decline in water content in thalli and response to heat stress.

Being poikilohydric, lichens are inherently exposed to alternating desiccation and hydration cycles. They can exhibit extraordinary resistance to extreme temperatures in a dehydrated state but thermal thresholds for hydrated lichens are lower. The ability of the lichen Cetraria aculeata to recovery after high temperature treatment (40°C, 60°C) at different air humidity levels (relative humidity [RH]: <15%, 25%, 50%, 75%, ≅100%) was examined to find a linkage between passive dehydration of the lichen and its physiological resistance to heat stress. The response to heating was determined by measuring parameters related to photosynthesis and respiration after 2- and 24-h recovery. A higher RH level resulted in a slower decline in relative water content (RWC) in hydrated thalli. In turn, the stress resistance of active thalli depended on the ambient humidity and associated RWC reduction. Elevated temperature had a negative impact on bioenergetic processes, but only an unnatural state of permanent full hydration during heat stress resulted in a lethal effect. Hydrated lichen thalli heated at 40°C and 50% relative humidity (RH) tended to be least susceptible to stress-induced damage. Although atypical climatic conditions may lead lichens to lethal thresholds, the actual likelihood of deadly threat to lichens due to heat events per se is debatable.

Thriving under Salinity: Growth, Ecophysiology and Proteomic Insights into the Tolerance Mechanisms of Obligate Halophyte Suaeda fruticosa.

Studies on obligate halophytes combining eco-physiological techniques and proteomic analysis are crucial for understanding salinity tolerance mechanisms but are limited. We thus examined growth, water relations, ion homeostasis, photosynthesis, oxidative stress mitigation and proteomic responses of an obligate halophyte Suaeda fruticosa to increasing salinity under semi-hydroponic culture. Most biomass parameters increased under moderate (300 mmol L-1 of NaCl) salinity, while high (900 mmol L-1 of NaCl) salinity caused some reduction in biomass parameters. Under moderate salinity, plants showed effective osmotic adjustment with concomitant accumulation of Na+ in both roots and leaves. Accumulation of Na+ did not accompany nutrient deficiency, damage to photosynthetic machinery and oxidative damage in plants treated with 300 mmol L-1 of NaCl. Under high salinity, plants showed further decline in sap osmotic potential with higher Na+ accumulation that did not coincide with a decline in relative water content, Fv/Fm, and oxidative damage markers (H2O2 and MDA). There were 22, 54 and 7 proteins in optimal salinity and 29, 46 and 8 proteins in high salinity treatment that were up-regulated, down-regulated or exhibited no change, respectively, as compared to control plants. These data indicate that biomass reduction in S. fruticosa at high salinity might result primarily from increased energetic cost rather than ionic toxicity.

Influence of Drought Stress and Foliar Application of Salicylic Acid on Early Vegetative Stage of Cacao

Cacao (Theobroma cacao L.) is noted to have a low tolerance to drought and is, therefore, not resilient to prolonged dry periods. The study sought to evaluate the morpho-anatomical and physiological responses of two clonal seedlings of cacao BR25 and K9 under drought stress and to explore the potential alleviating effects of salicylic acid (SA) at concentrations of 0.5 and 1.0 mM on the early vegetative stage. Eleven-month-old BR25 and K9 cacao were pre-treated with foliar application of 0.5 and 1.0-mM SA for 2 wk before the onset of drought conditions. Well-watered and drought seedlings with no pre-treatments served as the control. Water was withheld for 20 d, after which rewatering resumed for 3 mo. Results revealed that after 20 d of drought, both clonal varieties experienced a significant decline in relative water content (RWC) and increased ascorbate peroxidase (APX) and catalase activity. Changes in stem diameter were observed after a rewatering period of 3 mo. K9 exhibited a noticeable reduction in root and shoot dry weight and stomatal aperture after 20 d of drought, whereas BR25 showed a decrease in total chlorophyll content and chlorophylls a and b. Furthermore, the results of the study suggest that 0.5-mM SA has the potential to mitigate the drastic effects during drought in BR25 and K9 cacao by improving RWC, stomatal length, and width. On the other hand, 1.0- mM SA has the potential to alleviate the effects of drought experienced earlier on by improving root dry weight and APX activities of the seedlings.

Alteration in physio-chemical properties and gene expression pattern of snapmelon (Cucumis melo var. momordica) genotypes against drought stress

AbstractLack of water at limiting levels results in drought stress, which may have an impact on the various stages of a crop's life cycle. Four different genotypes of snapmelon (Cucumis melo L. var. momordica) responded differently to 0, 7 and 21 d of simulated drought stress. Information was collected on a range of morpho-physiological, biochemical and molecular characteristics. Each genotype had longer roots, though BAM-VR-312 had the longest roots overall. As the severity of the drought grew, the net photosynthetic rate (Pn) and stomatal conductance (Gs) dropped. In BAM-VR-312, a smaller decline in relative water content (RWC) was recorded, despite the fact that drought stress caused a significant fall in RWC. BAM-VR-312 had smaller accumulations of electrolyte leakage, hydrogen peroxide, phenol and malondialdehyde, although proline content was greater. A decrease in photosynthetic pigments was noted, though BAM-VR-312 had the least reduction. Antioxidant enzyme activity increased in BAM-VR-312, as evidenced by records of ascorbate peroxidase, catalase, guaiacol peroxidase, glutathione reductase and superoxide dismutase. Similarly, expression level of their respective genes was recorded highest in BAM-VR-312. Overall, the study clearly identified distinct genotype based on morpho-physiological, biochemical and molecular properties under drought stress and revealed that the genotype BAM-VR-312 had more efficient drought tolerance mechanisms than the other genotypes under the drought stress condition.

Insights into physiological and metabolic modulations instigated by exogenous sodium nitroprusside and spermidine reveals drought tolerance in Helianthus annuus L.

Drought is the most critical climatic factor instigating severe threats to crop production worldwide. As stress ameliorants, exogenous sodium nitroprusside (SNP) or spermidine (Spd) supply has positive responses in alleviating the drought adversities in crops, however, reports regarding their combined effects is still elusive. Here, the protective role of SNP and Spd to confer drought resistance in sunflower (Helianthus annuus L.) through up-regulation of physiological and metabolic processes was investigated. Plants were foliar sprayed with individual or combined SNP (100 μM) or Spd (100 μM). Drought was induced by keeping the soil at 100% (normal) and 60% (drought stress) field capacity levels. Drought exposure caused a marked decline in relative water content (RWC), excised leaf water retention (ELWR), net photosynthesis (PN), transpiration rate (E), stomatal conductance (gs), and sub-stomatal conductance (Ci) with substantial increase in catalase (CAT), superoxide dismutase (SOD), and peroxidase (POX). SNP plus Spd exhibited a considerable increase in CAT, SOD, and POX activities under drought, and helped the plants to retain optimum water status and gas exchange attributes. Similarly, hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents were increased significantly to drought; however, a notable decline was recorded in drought prone plants treated with exogenous SNP plus Spd. Moreover, addition of SNP plus Spd under drought caused a remarkable increase in chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll total (Chl t), carotenoids (Car), and growth traits like shoot length (SL), root length (RL), shoot fresh weight (SFW), shoot dry weight (SDW), root dry weight (RDW). Combined SNP and Spd application could potentially alleviate the drought-induced damages in sunflower through increased water status (8–10%), antioxidant enzymes (17–28%), chlorophyll pigments (14–21%), and growth performance (12–22%) under drought stress.

Potassium application enhances drought tolerance in sesame by mitigating oxidative damage and regulating osmotic adjustment.

Potassium (K) is known for alleviating the negative effects of abiotic stresses on plants. To explore the functions of K in controlling reactive oxygen species (ROS), antioxidant activities, and osmoregulation in sesame under drought stress, a pot experiment was conducted with three K levels (0, 60, and 120kg ha-1, recorded as K0, K1, and K2, respectively) and exposed to well-watered (WW, 75% ± 5% soil relative water content) and drought-stressed (DS, 50% ± 5% soil relative water content) conditions. The results showed that DS stimulated the production of ROS such as increased hydrogen peroxide (H2O2), leading to lipid peroxidation as characterized by higher malondialdehyde (MDA) and, consequently, resulting in the decline in relative water content (RWC) and photosynthetic pigments as compared with WW plants. These adverse effects were exacerbated when drought stress was prolonged. Concurrently, K application alleviated the magnitude of decline in the RWC, chlorophyll a, and chlorophyll b, and plants applied with K exhibited superior growth, with the optimal mitigation observed under K2 treatment. Additionally, DS plants treated with K exhibited lower lipid peroxidation, higher antioxidant activities, and increased osmotic solute accumulation in comparison with plants under K deficiency, which suggested that exogenous K application mitigated the oxidative damages and this was more prominent under K2 treatment. Noteworthily, proline and soluble protein, respectively, dominated in the osmotic regulation at 3 and 6 days of drought stress according to the analysis of the quantitative comparison among different osmotically active solutes. Based on the correlation of the aforementioned traits and the analysis of variance on the interaction effects of drought stress and potassium, we propose that superoxide dismutase (SOD), glutathione reductase (GR), and MDA could be critical indicators in balancing ROS detoxification and reproduction. In summary, our studies suggest that optimized K application keeps a balance between the production of antioxidants and ROS and simultaneously affects osmoregulation to alleviate the damage from drought stress.

Stress-Responsive cis-Regulatory Elements Underline Podophyllotoxin Biosynthesis and Better Performance of Sinopodophyllum hexandrum Under Water Deficit Conditions

Sinopodophyllum hexandrum is an endangered medicinal herb known for its bioactive lignan podophyllotoxin (PTOX), which is used for the preparation of anticancer drugs. In its natural habitat, S. hexandrum is exposed to a multitude of adversities, such as fluctuating temperatures, water deficit, and high UV radiations. Transcriptional regulation of genes, which is regulated by the condition-specific binding of transcriptional factors to precise motifs in the promoter region, underlines responses to an environmental cue. Therefore, analysis of promoter sequences could ascertain the spatio-temporal expression of genes and overall stress responses. Unavailability of genomic information does not permit such analysis in S. hexandrum, especially on regulation of PTOX pathway. Accordingly, this study describes isolation and in silico analysis of 5′-upstream regions of ShPLR (PINORESINOL-LARICIRESINOL REDUCTASE) and ShSLD (SECOISOLARICIRESINOL DEHYDROGENASE), the two key genes of the PTOX biosynthetic pathway. Data showed a range of motifs related to basal transcription, stress-responsive elements, such as those for drought, low temperature, and light, suggesting that the expression of these genes and resulting PTOX accumulation would be affected by, at least, these environmental cues. While the impact of temperature and light on PTOX accumulation is well studied, the effect of water deficit on the physiology of S. hexandrum and PTOX accumulation remains obscure. Given the presence of drought-responsive elements in the promoters of the key genes, the impact of water deficit on growth and development and PTOX accumulation was studied. The results showed decline in relative water content and net photosynthetic rate, and increase in relative electrolyte leakage with stress progression. Plants under stress exhibited a reduction in transpiration rate and chlorophyll content, with a gradual increase in osmoprotectant content. Besides, stressed plants showed an increase in the expression of genes involved in the phenylpropanoid pathway and PTOX biosynthesis, and an increase in PTOX accumulation. Upon re-watering, non-irrigated plants showed a significant improvement in biochemical and physiological parameters. Summarily, our results demonstrated the importance of osmoprotectants during water deficit and the revival capacity of the species from water deficit, wherein PTOX synthesis was also modulated. Moreover, isolated promoter sequences could be employed in genetic transformation to mediate the expression of stress-induced genes in other plant systems.

SEED GERMINATION BEHAVIOUR, SEEDLING GROWTH, MORPHO-PHYSIOLOGICAL AND YIELD ATTRIBUTES OF RICE GROWN IN CADMIUM-ADDED SOIL

An experiment was conducted to investigate the effect of different levels of cadmium (Cd) stress on germination, morphology, physiology and yield of rice. There were five treatments, viz. control (no Cd), 0.5 mM CdCl2, 1 mM CdCl2, 1.5 mM CdCl2 and 2 mM CdCl2, carried out by a randomized complete block design (RCBD) with three replications. Cadmium stress caused a significant reduction of plant height and tillers hill-1 in a dose-dependent manner. The highest decline of relative water content and SPAD value was found at 1.5 mM (11 and 16%) and 2 mM (14 and 19%) Cd stress compared to the control. The number of effective tillers hill-1, filled grains panicle-1, 1000-grain weight, length of panicle, grain yield and straw yield reduced significantly by 44, 32, 15, 24, 37 and 45%, respectively, over the control. Germination and seedling-related parameters were recorded 10 days after germination. The lowest germination percentage (27%), germination index (27%) and seedling vigour index (49%) were observed at the highest level of Cd stress in comparison to the control. Cadmium stress resulted in maximum abnormal seedlings and markedly reduced length of root and shoot as well as their fresh and dry weight. Root shoot ratio showed differential responses to Cd stress. Thus, it can be concluded that a higher level of Cd in soil has a detrimental effect on seed germination, morphology, physiology and yield of rice.

Central role of 70-kDa heat shock protein in adaptation of plants to drought stress

The 70-kDa heat shock proteins (HSP70s) are a conserved class of chaperones that play critical roles during the normal life cycle of plants. HSP70s are particularly involved in the regulation of biotic and abiotic stress responses. In this paper, the potential roles of this protein were investigated. A reverse genetic approach was employed for transient silencing of hsp70 gene in tomato (Solanum lycopersicum L.) to evaluate different growth and physiological parameters under normal conditions and during the response to drought stress. A combined ANOVA (analysis of variance) and HCA (hierarchical clustering analysis) showed that hsp70 silencing led to severe growth retardation and mortality, significant membrane damage and leakage, decline in relative water content, low rate of pigment accumulation, and reduced antioxidant enzyme activity under normal and drought stress conditions. Among the different parameters, proline was the only trait that was unaffected by gene silencing and accumulated by similar amounts to that of nonsilent plants. In conclusion, HSP70 played critical roles in maintaining the cellular homeostasis of plants during adaptation to drought and under normal plant life conditions. It was speculated that proline was, to some extent, involved in improving the loss of protein folding or function resulting from HSP70 deficiency, and played a crucial role in the adaptation of plants on exposure to stress.

Selenium and Salt Interactions in Black Gram (Vigna mungo L): Ion Uptake, Antioxidant Defense System, and Photochemistry Efficiency.

Salinity is a major abiotic stress which limits crop production, especially under rainfed conditions. Selenium (Se), as an important micronutrient, plays a vital role in mitigating detrimental effects of different abiotic stresses. The objective of this research was to examine the effect of Se fertilization on black gram (Vigna mungo) under salt stress. Our results showed that salt stress (100 mM NaCl) in leaves significantly induced oxidative damage and caused a decline in relative water content, chlorophyll (Chl), stomatal conductance (gs), photochemical efficiency (Fv/Fm), sucrose, and reducing sugars. A low dose of Se (1.5 ppm) significantly reduced hydrogen peroxide content, malondialdehyde formation, cell membrane damage, and also improved antioxidative enzyme activities, including superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, and glutathione peroxidase under salt stress. Se-treated plants exhibited higher Chl, gs, Fv/Fm, sucrose, and reducing sugars than untreated plants in response to salt stress. In addition, Se application enhanced Se uptake and reduced Na+ uptake, but Cl− remained unaffected. Our results indicated that a low dose of Se effectively alleviated salt damage via inhibition of Na+ uptake and enhanced antioxidant defense resulting in a significant decrease in oxidative damage, and maintained gaseous exchange and PS II function for sucrose and reducing sugars accumulation in black gram.

Combined Kinetin and Spermidine Treatments Ameliorate Growth and Photosynthetic Inhibition in Vigna angularis by Up-Regulating Antioxidant and Nitrogen Metabolism under Cadmium Stress.

Pot experiments were conducted to investigate the probable beneficial role of the individual as well as combined application of kinetin (50 μM Kn) and spermidine (200 μM Spd) on Vigna angularis under cadmium (Cd) stress. Cd treatment reduced growth by declining the content of chlorophylls and carotenoids, photosynthesis, and gas exchange parameters. Exogenously, Kn and Spd application enhanced the photosynthetic parameters and up-regulated the antioxidant system by improving the activities of antioxidant enzymes and the content of non-enzymatic components. In addition, the application of Kn and Spd resulted in significant improvement in the content of sugars, proline, and glycine betaine, ameliorating the decline in relative water content. Oxidative stress parameters including hydrogen peroxide, superoxide, lipid peroxidation, lipoxygenase activity, and electrolyte leakage increased due to Cd stress; however, the application of Kn and Spd imparted a significant decline in all these parameters. Further, reduced Cd uptake was also observed due to Kn and Spd application. Total phenols and flavonoids also increased due to Kn and Spd treatments under normal as well as Cd stress conditions, which may have further helped with the elimination of reactive oxygen species. Reduction in the activity of nitrate reductase and the content of nitrogen was ameliorated due to the exogenous application of Kn and Spd. Therefore, the exogenous application of Kn and Spd benefited Vigna angularis counteracting the damaging effects of Cd stress by up-regulating the tolerance mechanisms, including antioxidant and osmolyte metabolism.

Effect of Relative Air Humidity and High Temperature on the Physiological and Anatomical Responses of Two Rhododendron Cultivars

The effects of different relative air humidity (RH) levels under high temperature and accompanying vapor pressure deficits (VPDs) on the physiology, photosynthesis, and anatomy of Rhododendron need to be better understood to help in reducing damage to leaves caused by high temperature. In this study, two Rhododendron cultivars were exposed at 45%, 55%, 65%, 75%, and 85% RH to a treatment of constant temperature at 38 °C for 14 days, resulting in a VPD of 3.64, 2.98, 2.32, 1.66, and 0.99 kPa, respectively. The results showed the least reduction of the net photosynthetic rate (Pn) under 75% RH treatment in R. ‘Fen Zhenzhu’ (decreased by 79.8%), and under the 85% RH treatment in R. ‘Zhuangyuan Hong’ (decreased by 75.4%). The decline in relative water content (RWC) was less under the 75% and 85% RH treatments, and electrolyte leakage showed a slight decrease under the 75% RH treatment in the two Rhododendron cultivars. The appearance of the two cultivars under greater RH showed less damage, probably because plants can avoid damage by increasing total chlorophyll content, decreasing stomatal area, stomatal density, and opened stomata ratio, enhancing enzymatic activity and osmoregulation substances, and improving leaf structure. The findings show that greater RH can alleviate damage caused by heat stress and improve thermostability.

Alleviation of chromium toxicity in rice seedling using Phyllanthus emblica aqueous extract in relation to metal uptake and modulation ofantioxidative defense

Chromium is a key metal pollutant of the environment. When present in high concentrations in soil it adversely affects plant growth and productivity. Phyllanthus emblica(P.emblica) aqueous extract contains many natural antioxidants, and it has been widely used in traditional medicine for the treatment of severe oxidative stress-related diseases and disorders. The present study was aimed to investigate the possible role of P.emblica aqueous extract in alleviating Cr toxicity effects in rice (Oryza sativa) seedlings in relation to growth attributes, Cr uptake, production of reactive oxygen species (ROS), lipid peroxidation, and activities of antioxidative enzymes. Rice seedlings were raised for 4–8days in Yoshida nutrient medium in hydroponics containing either 100μM Cr (K2Cr2O7) or Cr+P.emblica aqueous extract. Cr treatment to the seedlings caused decrease in root and shoots length and fresh biomass, decline in relative water content (RWC) and photosynthetic pigments and increase in root membrane permeability. Uptake of Cr was more in roots than in shoots. Increased production of ROS, increase in lipid peroxidation and increased activities of antioxidative enzymes superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) were observed in Cr-treated seedlings as compared to controls. With the addition of aqueous extract of P.emblica(5mgml−1) in the Cr treatment medium, significant alleviation of Cr-induced decline in growth, biomass, photosynthetic pigments, and reduction in Cr-induced elevated activities of antioxidative enzymes in the seedlings was observed. Our results suggest that P.emblica aqueous extract considerably alleviates the effects of Cr in rice seedlings by suppressing Cr uptake, reducing oxidative stress and modulating activities of antioxidative enzymes.

Leaf photosynthetic function duration during yield formation of large-spike wheat in rainfed cropping systems.

Improving photosynthetic capacity significantly affects the yield of wheat (Triticum aestivum L.) in rainfed regions. In this study, the physiological characteristics of eight large-spike wheat lines were compared with a multiple-spike cultivar as a control (CK) in a field over two consecutive seasons: 2010–2012. The tillering peak was 7–21 d after returning green for line 2040, the average rate of decline of relative water content was slower, and the average duration time of photosynthetic rate was longer than CK in vitro. There was a strong linear and positive correlation between photosynthetic rate and root activity at jointing, flowering, and grain-filling stages. In addition, average yields were higher in large-spike lines than CK (multiple-spike cultivar). The results suggest that large-spike lines might have greater water retaining capacity during yield formation under rainfed conditions.

Exogenous application of nitric oxide modulates osmolyte metabolism, antioxidants, enzymes of ascorbate-glutathione cycle and promotes growth under cadmium stress in tomato.

Experiments were carried out to investigate the role of nitric oxide (NO) in ameliorating the negative effects of cadmium stress in tomato seedlings. Plants treated with cadmium (CdCl2, 150μM) showed reduced growth, biomass yield, pigment content, chlorophyll fluorescence, and gas exchange parameters. Exogenous application of NO donor (sodium nitroprusside) with nutrient solution protected chlorophyll pigments, restored chlorophyll fluorescence and gas exchange parameters, and caused significant enhancements in growth and biomass yield. Cadmium triggered the synthesis of proline and glycine betaine; however, application of NO caused further enhancement of their accumulation, reflecting an obvious amelioration of the cadmium-induced decline in relative water content. Activities of the antioxidant enzymes superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, monodehydroascorbate reductase, dehydroascorbate reductase, and other enzymatic activities of ascorbate-glutathione cycle were enhanced following the application of NO, as compared with those in untreated seedlings under control and cadmium stress conditions. NO increased the flavonoid and total phenol content in Cd-stressed tomato plants. Moreover, NO application restricted the uptake of cadmium and enhanced the accumulation of nutrients in different parts of tomato plants. On the basis of the findings of the present study, we propose that NO has a potential role as a growth promoter for tomato under cadmium stress.

In vitro propagation of Gerbera jamesonii Bolus ex Hooker f. in a temporary immersion bioreactor

In the global flower industry, gerbera (Gerbera jamesonii Bolus ex Hooker f.) is ranked within the top 10 cut ornamental flowers. Commercially, micropropagation is more important than seed or vegetative propagation. This study assessed the viability of using a temporary immersion bioreactor (TIB; BIT®) to propagate shoots in vitro. Factors such as immersion frequency (6, 8 and 12 h), additional ventilation (1 min every 2 h) and the length of duration of shoot culture (14, 21, 28 and 35 days) were tested. Immersion every 8 h with additional ventilation produced more shoots with better morphology than the control. The average multiplication rate was 9 shoots/explant across treatments. However, when shoots were immersed every 6 h, shoots had higher fresh and dry weight, but displayed hyperhydricity. No differences in shoots were found when immersion frequency was 8 or 12 h. Additional ventilation (12 min/day) reduced shoot hyperhydricity to 5.24% as compared to the ventilation-free control (31.37%). Shoots receiving additional air supply every 8 h had lower fresh and dry weight with an 89.8% decline in relative water content. The number of shoots/explant increased as culture time increased, 6.7 after 28 days, and 6.1 after 35 days (statistically equal). After 7 and 14 days, shoots were induced to root in the TIB using the same medium but supplemented with IAA. Plantlets were subsequently acclimatized. More than 87% of plantlets survived in a zeolite and sugarcane filter cake (1:1) substrate. This protocol allows for the mass production of gerbera shoots in a simple TIB, with effective rooting and acclimatization. This is the first documented TIB for gerbera.

Distinct growth and physiological responses of Arabidopsis thaliana natural accessions to drought stress and their detection using spectral reflectance and thermal imaging.

Reduced growth and stomatal closure are the two main responses of plants to drought stress. The extent to which these processes are connected and whether different genotypes prefer one over the other remains unclear. To understand the genotype-specific interconnections of these two processes and evaluate potential utilisation of this knowledge for drought tolerance phenotyping, six natural accessions of Arabidopsis thaliana (L.) Heynh. were exposed to drought stress for 10 days. Projected leaf area of rosette, light-saturated CO2 assimilation rate (Amax), relative water content (RWC), leaf temperature (thermal imaging), and spectral reflectance were measured through the course of induced drought stress. Three types of acclimation were identified: (i) growth not affected but Amax significantly reduced, (ii) both growth and Amax significantly reduced, and (iii) growth significantly reduced but only small decrease in Amax. Within the last type, the smallest decline in RWC was evident. These results show that a substantial reduction in leaf area may cause a decline in transpiration that enables maintenance of both RWC and physiological processes. Both non-invasive thermal imaging and spectral reflectance measurements proved reliable tools for tracking drought-induced changes in Amax and RWC across all accessions tested and thus are effective tools for phenotyping stress tolerance.

Changes in antioxidant enzyme activities and gene expression in two muskmelon genotypes under progressive water stress

Responses of two muskmelon (Cucumis melo L.) genotypes (drought tolerant SC-15 and drought susceptible EC-564755) were analyzed at 0, 7, 14, and 21 d of progressive water stress. Although water deficit caused a significant decline in relative water content, the magnitude of reduction was lower in SC-15. Electrolyte leakage, hydrogen peroxide, and malonydialdehyde generation were higher in EC-564755, whereas accumulation of proline was higher in SC-15. Higher activities of antioxidant enzymes, such as catalase, superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase, and higher expression of the respective genes were recorded in SC-15 than in EC-564755. Expressions of DREB2C and DREB3 in SC-15 revealed a fluctuating pattern with down-regulation on days 7 and 21 of water stress, whereas up-regulation was observed on day 14. Concurrently, both genes in EC-564755 showed continuous down-regulation on days 7, 14, and 21 of water stress. Expressions of RD22 and dehydrin recorded on days 7, 14, and 21 were lower in SC-15. The cluster analysis showed that, these two genotypes had a clear distinction in physiological and biochemical properties and gene expressions under water stress and the genotype SC-15 had more efficient osmoprotectant mechanism than genotype EC-564755 under water deficit conditions.

Specific activities and transcript levels of glycolytic enzymes under dehydration in chickpea (Cicer arietinum L.) seedlings

The effect of dehydration on the specific activities and transcript levels of several glycolytic enzymes was determined in two chickpea (Cicer arietinum L.) cultivars- Pusa362 (drought tolerant) and SBD377 (drought sensitive). Dehydration treatment was imposed on 6 days old chickpea seedlings by removing them from pots and keeping them on table top on 3MM Whatman paper at room temperature for 5 h. The stress imposed was judged by determining relative water content (RWC) and proline content. RWC decreased and proline content accumulated after five hours of dehydration treatment. The decline in RWC was higher in SBD377 than in Pusa362, while varietal differences were absent in proline content. With the exception of NADP-glyceraldehyde-3-phospahte dehydrogense, whose activity as well as transcript level showed marginal decrease in both the varieties, dehydration had little effect on all glycolytic enzymes studied.