Elicitation-Based Modulation of Shelf Life in Fruits: Physiological and Molecular Insights

The process of ripening involves physiological and biochemical events that become a concern during postharvest storage.We have documented different approaches for the preservation and maintenance of fruit quality during the postharvest period that are biocompatible and fully safe for consumption.Chemical residues that sustain sensory characteristics,such as color,flavor,aroma,and texture,are considered.In fruit ripening,both physical and chemical elicitors are described that regulate ethylene biosynthesis or its signaling for gene expression.The key regulatory enzymes,such as ACC synthase and ACC oxidase,for ethylene biosynthesis,are important for both climacteric and non-climacteric fruits.Anti-oxidizing genes that retain sensory characteristics are concerns in this respect.Chemical elicitors,including chitosan,polyamine,phenolics,lipopolysaccharide,silver derivatives,and nanocomposites,are described.Gas pressure,light wavelengths,relative humidity,cooling,and other environmental factors are important for improved postharvest storage.These elicitors maintain redox status by inhibiting the generation of reactive oxygen species(ROS)or their lysis.Growth regulators,including abscisic acid,auxin,brassinosteroids,jasmonic acid,and salicylic acid,are important for the regulation of ripening.Mechanical injuries,ionic imbalances,temperature variations,and tissue dehydration can occur irrespective of ripening cate-gories.The use of synthetic physiochemically active compounds is discussed in terms of physiological,metabolic,cellular,and molecular functions.Ethylene-induced autocatalytic processes,antioxidant cascades,epigenetic regulation,and homeodomain gene expression are discussed.Sugar–acid metabolism,dissolution of the cell wall,and direct or indirect production of secondary metabolites related to postharvest storage are mentioned regarding chilling storage.Elicitors and agrochemicals that trigger plant defense to increase secondary metabolite production are discussed for reducing fruit senescence during postharvest storage.

Physio-Biochemical and Genetic Exploration for Submergence Tolerance in Rice (<i>Oryza sativa</i>L.) Landraces with Special References to <i>Sub</i>1 Loci

In the present study a group of four indigenous and less popular rice genotypes (Meghi, Panibhasha, Jabra and Sholey) reported by growers as submergence tolerant lines from flood prone areas of south Bengal were explored through study of nodal anatomy, physio-biochemical screening under submergence and genotyping with submergence tolerance linked rice microsatellite loci (RM loci). To identify the different allelic forms of different Sub1 compnents (Sub1A, Sub1B and Sub1C) among the studied lines, the genomic DNA of individual genotypes was amplified with three ethylene response factor like genes from Sub1 loci, located on rice chromosome 9. From the different physio-biochemical experiments performed in this investigation, it has been shown that Meghi and Jabra are the two probable potent genotypes which share common properties of both submergence tolerant and deep water nature whereas rest two genotypes (Sholey and Panibhasha) behave like typical deep water rice. The submergence tolerance property of Meghi was also confirmed from submergence tolerance linked SSR based genotyping by sharing with FR13A for some common alleles as reflected in fingerprint derived dendrogram. The rest of the genotypes shared a number of alleles and were included in a separate cluster. The common behaviour of Meghi and FR13A under submergence was also confirmed from genetic study of Sub1 loci through sharing of some common alleles for three Sub1 components (Sub1A, Sub1B and Sub1C loci). One SSR loci (RM 285) was identified as a potent molecular marker for submergence tolerance breeding programme involving these two selected rice lines (Meghi and Jabra) as donor plant through marker assisted selection.

Assessment of Some Biomarkers under Submergence Stress in Some Rice Cultivars Varying in Responses

Three rice varieties, significantly differed in their ability, when subjected to submergence have been studied in relation to physiological attributes. On account of oxidative stress, MDA content and carbonyl content were measured. The MDA content was maximally decreased in FR13A and minimally decreased in Swarna irrespective of shoots and roots. A higher increase in carbonyl content was found in Swarna followed by FR13A and Swarna Sub1A in both shoots and roots. The activity of antioxidant moieties like total phenolics content and flavonoid content were more increased under submergence than that in air except for Swarna. FR13A showed maximum increase in Phenolics and flavonoid content in both shoots and roots when subjected to submergence. A sharp increase in guaiacol peroxidase and glutathione reductase characterized the plants’ response to sub-mergence irrespective of varieties. The expression of Guaiacol peroxidase was increased in FR13A followed by Swarna Sub1A and Swarna. Glutathione reductase was measured in terms of oxidation of NADP(H) and both FR13A and Swarna Sub1A recorded maximum oxidation than Swarna under submergence. With regards to isozymic variation plants were differed to the intensities of poly-peptide, however not in numbers and may be suggestive for concomitant gene expression to sub-mergence. The analysis clarification for possible biomarkers with regards to cellular responses of rice plants under submergence has been anticipated.

Impeded Carbohydrate Metabolism in Rice Plants under Submergence Stress

The detrimental effects of submergence on physiological performances of some rice varieties with special references to carbohydrate metabolisms and their allied enzymes during post-flowering stages have been documented and clarified in the present investigation. It was found that photosynthetic rate and concomitant translocation of sugars into the panicles were both related to the yield. The detrimental effects of the complete submergence were recorded in generation of sucrose, starch, sucrose phosphate synthase and phosphorylase activity in the developing panicles of the plants as compared to those under normal or control （i.e. non-submerged） condition. The accumulation of starch was significantly lower in plants under submergence and that was correlated with ADP-glucose pyrophosphorylase activity. Photosynthetic rate was most affected under submergence in varying days of post-flowering and was also related to the down regulation of Ribulose bisphosphate carboxylase activity. However, under normal or control condition, there recorded a steady maintenance of photosynthetic rate at the post-flowering stages and significantly higher values of Ribulose bisphosphate carboxylase activity. Still, photosynthetic rate of the plants under both control and submerged conditions had hardly any significant correlation with sugar accumulation and other enzymes of carbohydrate metabolism like invertase with grain yield. Finally, plants under submergence suffered significant loss of yield by poor grain filling which was related to impeded carbohydrate metabolism in the tissues. It is evident that loss of yield under submergence is attributed both by lower sink size or sink capacity （number of panicles, in this case） as well as subdued carbohydrate metabolism in plants and its subsequent partitioning into the grains.

2,4-D Hyper Accumulation Induced Cellular Responses of Azolla pinnata R. Br. to Sustain Herbicidal Stress

In the present experiment with ongoing concentration(0µM,100µM,250µM,500µM and 1000µM)of 2,4-D,the responses of Azolla pinnata R.Br.was evaluated based on cellular functions.Initially,plants were significantly tolerated up to 1000µM of 2,4-D with its survival.This was accompanied by a steady decline of indole acetic acid(IAA)concentration in tissues with 78.8%over the control.Membrane bound H^(+)-ATPase activity was over expressed within a range of 1.14 to 1.25 folds with activator(KCl)and decreased within a range of 57.3 to 74.6%in response to inhibitor(Vanadate)application.With regards to IAA metabolism,plants recorded a linear increase with wall bound oxidase activity up to maximum concentration of 2,4-D.The variations were more moderated when wall bound IAA-oxidase recorded a linear increase proportionate to the 2,4-D concentrations.This was more extended with the presence of different isoforms of IAA-oxidase which was much more pronounced with distinct polymorphisms of expressed proteins,however,not independent to the 2,4-D concentrations.Polyamines like spermine,spermidine and putrescine(spm,spd and put)were not consistent in concentration with the dosages of 2,4-D.Besides these,plants were induced to apoplastic NAD(P)H oxidase activity maximally by 1.6 folds under 500µM 2,4-D over control.Still,putrescine responded more or less consistently and recorded maximally 11.9 folds at 500µM 2,4-D as compared to the control.NAD(P)H oxidase activity recorded maximally 1.6 folds against control and remain consistent throughout the concentrations of 2,4-D.GPX along with APX were more linear in responses through the concentration of 2,4-D except CAT as compared to control.On enzymatic antioxidative activity,peroxidases(GPX and APX)were overexpresed in a similar manner except for catalase with a non-significant rise.In stabilization of cellular redox,glutathione reductase attended maximum value by 2.45 folds at 1000µM evidenced with significant variations in protein polymorphism.The sensitivity of 2,4-D also appeared in Azolla with a maximum loss of nucleic acids as documented by the comet assay.Moreover,the Azolla might have some DNA damage protective activity as evident using frond extract with plasmid nick assay.Therefore,Azolla plants with its cellular responses is evident to sustain against the 2,4-D herbicidal stress and may be granted in bio remediation process for the contaminated soil.

Physio-Biochemical and Microsatellite Based Profiling of Lowland Rice (<i>Oryza sativa</i>L.) Landraces for Osmotic Stress Tolerance

Global climate changes accelerate a wide range of abiotic stresses leading to a series of physiological, biochemical and molecular changes that adversely affect the growth and productivity of rice (Oryza sativa L.). In this background, there is limited knowledge and profiling reports of lowland, less popular rice landraces in relation to their osmotic stress tolerance. Laboratory mediated physiological and biochemical screening for a selected set of 20 lowland rice landraces was done in induced drought and salinity stress conditions. Varietal genetic diversity and inter-relatedness were assessed by using osmotic stress tolerance linked forty-five rice microsatellite markers. For representing the allelic diversity of the studied microsatellite loci across the selected genotypes, a microsatellite panel was constructed and PIC values of all used microsatellite markers were calculated. The obtained database can be used for varietal identification, characterization and genetic information in relation to osmotic stress tolerance.

Preliminary Variations in Physiological Modules When <i>sub</i>1<i>A</i>QTL Is under Soil-Moisture Deficit Stress

The present investigation embodies with some distinct physiological responses of rice seedlings bearing sub1A allele when cultured under soil moisture deficit condition. In order to estimate the extent of variation of sub1A allele in cv. Swarna Sub1, few specific responses were recorded. Ongoing days (2, 4 and 8) of water stress, rice seedlings were mostly concerned with regulation of root growth through 1.24%, 4.10% and 8.96% as compared to control. When relative growth rate (RGR) of the biomass was considered, it recorded a significant down regulation maximum by 27.27% over non-stressed plants. The light absorbing capacity of foliages in terms of leaf mass ratio (15.62%) and specific leaf weight (8.45%) was also curtailed under stress contiguously with total dry matter accumulation. For light harnessing mechanism, the contributing pigments were most significantly (p ≤ 0.05) affected with maximum variation for chlorophyll (31.29%), lycopene (79.31%) and carotenoids (55.31%) over control. NAR was strikingly differed by 32.72% under water stress in average. To support the water stress related depletion of moisture tension, plants recorded RWC with a ranges of 6.62% to 21.57% under stress than control. In balance of cellular dehydration rice seedlings were recorded 6.72% loss of proline, but up-regulated the release of free amino acids by 1.35 fold. In expression of generic potential for sub1A allele, the growth inhibition even under water deficit was evident from carbohydrate depletion by 10.93%, 11.42% and 24.35% through days of treatments. This was supported by depletion of apoplastic and cellular invertase activities by 90.90% and 72.91%. The possibility for sub1A in tolerance of deficit water status in rice culture has been discussed in more details.

Cadmium Accumulation in <i>Marsilea minuta</i>Linn. and Its Antioxidative Responses

The present study was carried out to investigate the extent of cadmium (Cd) accumulation with its possible impact on physiological and biochemical basis of heavy metal tolerance in Marsilea minuta Linn. Cd salt (0 μM, 50 μM and 100 μM) was allowed to absorb by the plants for prolong days in hydroponic culture and a significant deterioration of the plant biomass was recorded. However, roots absorbed more metals than the leaves. Plants recorded a significant rise of superoxide (O-2) and hydrogen peroxide (H2O2). A noticeable amount of protein oxidation and lipid peroxidation were in proportionate to Cd accumulation. Anthocyanin and flavonoid content were decreased as compared to control condition. Superoxide dismutase (SOD), guaiacol peroxidase (GPX) and glutathione reductase (GR) contributed their antioxidative functions according to the Cd doses. The expression of GR was also evident from its activity staining in gel. So, it may suggest that antioxidative enzymes are up regulated and likely to be responsible for tolerance to Cd induced oxidative stress in Marsilea minuta Linn.

Responses of <i>Marsilea minuta</i>L. to Cadmium Stress and Assessment of Some Oxidative Biomarkers

In a hydroponic based experiment, the Cd toxicity is monitored with some cellular responses of Marsilea plant. Initially, plants were grown under varying concentrations (0, 50, 100 and 200 μM of Cd) of cadmium (Cd) with supplementation of 2 mM spermidine (Spd). The oxidative stress developed by Cd overaccumulation was measured with fall in Relative Growth Rate (RGR) by 27.11% to 59.83% growth reduction over control under varying Cd treatments. The retrieval of RGR was recovered by 1.59 folds as compared to the highest concentration of Cd (200 μM) when plants were fed with Spd. A concomitant degradation of chlorophyll was recorded in dose-dependant manner, however, the retrieval was not much pronounced with Spd. On the contrary, the non-oxidant thiol had borne more clarity with ongoing Cd concentration and appeared to be 40.51% increase maximally for GSH: GSSG at the highest concentration of Cd. Spd has minimized the ratio by 27.4%. The recovery of osmotic turgidity was indexed with a sharp rise in glycine betaine by 3.86 folds maximum at the highest concentration of Cd over control which declined by 30.9% with Spd. Another cellular response of treated plants was more evident from their isozymic profiles with regard to superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX). The intensity of protein expression was significantly variable but not in band numbers as evident from Cd treated plants. In vitro enzyme assay of catalase showed as declining trend within the limit of 33.13% to 43.22% which was reported by 1.45 folds when Spd was applied. Therefore, from the present study, the cellular responses of Marsilea plant which showed compatibility for their expression with Cd toxicity could be hypothesized as a case of bioindication.