Physiochemical response of papaya genotypes exposed to low temperature regimes

Susceptibility to low temperature stress is the major threat to papaya cultivation. Here, we studied a low temperature stress tolerance in papaya plant. We have investigated the effect of different low temperature regimes, 28°/18°C (day/night) to 16°/06°C (day/night) with a gradual decrease of 2°C on every two days and one set with direct exposure to the low temperature of 18°/08°C (day/night), called the acclimatized plant, in five diverse papaya genotypes (Pusa Nanha, Red Lady P-7-2, P-7-9, and P-7-14) and cold tolerant wild relative of cultivated papaya genotype (Vasconcellea cundinamarcensis V.M. Badillo) under controlled regulated conditions. It was observed that there were significant variations in the physiological and biochemical parameters like photosynthetic gas exchange parameters, chlorophyll content, fluorescence parameters, relative water content (RWC), membrane stability index (MSI), total sugars content, total soluble proteins content, lipid peroxidation, and proline accumulation in leaf tissues. Maximum stomatal conductance, chlorophyll fluorescence, RWC, MSI, total sugars, total soluble proteins, proline and lowest MDA contents were observed in Vasconcellea cundinamarcensis followed by inbred P-7-9 as compared to other genotypes under low temperature stress. Among all the papaya genotypes, P-7-9 showed more adaptability to low temperature stress and it further give new insights for developing low temperature tolerant papaya genotypes, especially under changing climate situations.

Agrobacterium-Mediated Transfоrmation of Maize with Antisense Suppression of the Proline Dehydrogenase Gene by an In Planta Method.

Aims: The aim of this study was to estimate the efficiency of T-DNA transfer during Agrobacterium-mediated transformation of maize (Zea mays L.) at different temperatures. In addition, the way of T-DNA transfer was studied after application of an Agrobacterium suspension at maize pistil filaments. Study Design: Transgenic maize plants were obtained with an antisense suppressor of the proline dehydrogenase gene (ASPG) by using the binary vector pBi2E. Temperatures of 28-35ºC were used to establish suitable conditions for transformation in planta. Place and Duration of Study: Laboratory of Bioengineering, Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences; between May 2008 and May 2013. Methodology: A. tumefaciens strain LBA4404 (pBi2E), containing the marker gene and the ASPG from Arabidopsis thaliana was used for maize transformation. The presence of T-DNA in the maize genome was detected by PCR. The proline concentration in transgenic hybrids of maize lines was determined colorimetrically. Results: T-DNA carrying the marker genes (nptII, gus) and the ASPG construct was detected in the maize genomes after Agrobacterium-mediated transformation. PCR analysis of total DNA isolated from 409 kanamycin-resistant diploid F1 seedlings revealed T-DNA insertions in the genomes of 30 plants. Expression of the ASPG in the maize genome led to a 4.5-fold increase (P=0.05) in free proline content in the transformed plants. Temperatures above 3ºC blocked the T-DNA transfer. Conclusion: The transfer of the ASPG by Agrobacterium T-DNA into the maize genome was achieved with a frequency of 0.3-2.3% at temperatures not higher than 31ºC. The PCR-positive maize plants had a statistically significant increase in the proline concentration in leaf tissues as compared with the non-transformed control. T-DNA may be transported into the maize egg cell by the growing pollen tube after the pistil filaments are inoculated with an Agrobacterium suspension.

Antioxidant Content and Free Radical Scavenging Activity of Honeys of Apis mellifera of Obudu Cattle Ranch.

Honey is a naturally sweet and viscous fluid produced by honeybees (Apis mellifera) from the nectar of flowers. Proline, free amino acid, tannins, phenols and flavonoids content were determined in eight samples of Obudu cattle ranch honeys. Antioxidant content (ascorbic acid equivalent, quercetin equivalents, tocopherol content) and free radical scavenging activity of Obudu ranch honeys were determined by standard methods. The relationship existing between proline and antioxidant content with free radical scavenging activity was assessed by mathematical modelling using Levenberg Marquardt algorithm. Results of our study showed that Obudu ranch honey was of high quality having comparable total free amino acid, proline, phytochemical and antioxidant content with good quality honeys found elsewhere. α-Tocopherol content was 16.50 ± 1.40 μg/100 g, quercetin equivalent antioxidant content (QEAC) was 9.43 ± 0.9 mg/100 g, ascorbic acid equivalent antioxidant content (AEAC) was 18.56 ± 1.78 mg/100 g, while the mean inhibitory concentration (IC50) of the honey samples against the 2,2-diphenyl-1- picrylhydrazyl (DPPH) radicals (RSA: IC50) was evaluated to be 12.74 ± 0.71mg/ml. Proline content, AEAC, QEAC and α-tocopherol were logistically related (r2 = 0.726, 0.971, 0.960 and 0.888 respectively) to the radical scavenging activity. The results obtained from the present study showed that Obudu ranch honeys were of high quality and possessed antioxidant and free radical scavenging property. Since proline content of the tested honey samples were comparable to proline content of unadulterated honey samples elsewhere, the commercial samples may not be adulterated Results showed that traditional usage of the honey for various medicinal usages may be related to its chemical content and radical scavenging property.

Comparative studies on antioxidant enzyme action and ion accumulation in soybean cultivars under salinity stress.

Plant biomass, antioxidant enzymes activity, ions accumulation and proline level in four soybean cultivars were investigated at different NaCl concentrations (20, 40, 60, 80 and 100 mM) applied to plants 15 days after sowing. There was a significant decrease in plant biomass and soluble protein content with each NaCl treatment. Accumulation of Na+ and Cl– was maximum in roots, followed by the stem and leaves in all the treated cultivars; Pusa 9712 being the top accumulator. On the contrary, K+ and Ca2+ ion concentrations were inhibited in all the treated cultivars. Activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase and glutathione reductase) and proline content increased significantly in all the cultivars with each NaCl treatment. The maximum increase was found in Pusa 9712. However, catalase activity decreased in all the cultivars except in Pusa 9712. On the whole, Pusa 9712 was most efficient in managing protection against salinity stress.