Shantha Nagarajan

Effect on germination and early growth characteristics in sunflower (Helianthus annuus) seeds exposed to static magnetic field.

Seeds of sunflower (Helianthus annuus) were exposed in batches to static magnetic fields of strength from 0 to 250mT in steps of 50mT for 1-4h in steps of 1h. Treatment of sunflower seeds in these magnetic fields increased the speed of germination, seedling length and seedling dry weight under laboratory germination tests. Of the various treatments, 50 and 200mT for 2h yielded the peak performance. Exposure of seeds to magnetic fields improved seed coat membrane integrity and reduced the cellular leakage and electrical conductivity. Treated seeds planted in soil resulted in statistically higher seedling dry weight, root length, root surface area and root volume in 1-month-old seedlings. In germinating seeds, enzyme activities of alpha-amylase, dehydrogenase and protease were significantly higher in treated seeds in contrast to controls. The higher enzyme activity in magnetic-field-treated sunflower seeds could be triggering the fast germination and early vigor of seedlings.

Exposure of Seeds to Static Magnetic Field Enhances Germination and Early Growth Characteristics in Chickpea (Cicer arietinum L.)

Seeds of chickpea (Cicer arietinum L.) were exposed in batches to static magnetic fields of strength from 0 to 250 mT in steps of 50 mT for 1-4 h in steps of 1 h for all fields. Results showed that magnetic field application enhanced seed performance in terms of laboratory germination, speed of germination, seedling length and seedling dry weight significantly compared to unexposed control. However, the response varied with field strength and duration of exposure without any particular trend. Among the various combinations of field strength and duration, 50 mT for 2 h, 100 mT for 1 h and 150 mT for 2 h exposures gave best results. Exposure of seeds to these three magnetic fields improved seed coat membrane integrity as it reduced the electrical conductivity of seed leachate. In soil, seeds exposed to these three treatments produced significantly increased seedling dry weights of 1-month-old plants. The root characteristics of the plants showed dramatic increase in root length, root surface area and root volume. The improved functional root parameters suggest that magnetically treated chickpea seeds may perform better under rainfed (un-irrigated) conditions where there is a restrictive soil moisture regime.

Biochemical and biophysical changes associated with magnetopriming in germinating cucumber seeds.

Seeds of cucumber were exposed to static magnetic field strength from 100 to 250 mT for 1, 2 or 3 h. Germination-percentage, rate of germination, length of seedling and dry weight increased by 18.5, 49, 34 and 33% respectively in magnetoprimed seeds compared to unexposed seeds. Among different magnetic field doses, 200 mT for 1 h showed significant effect on germination parameters and hence selected for studying changes in water uptake, (1)H transverse relaxation time (T(2)), hydrolytic enzymes, reactive oxygen species and antioxidant enzyme system in germinating seeds. Water uptake and T(2) values were significantly higher in treated seeds during imbibition. The activities of hydrolytic enzymes, amylase and protease were greater than the untreated controls by 51% and 13% respectively. Superoxide radicals also enhanced by 40% and hydrogen peroxide by 8% in magnetically exposed seeds. In magetoprimed seeds, increased activities of antioxidant enzymes, superoxide dismutase (8%), catalase (83%) and glutathione reductase (77%) over control was recorded. We report that magnetopriming of dry seeds can be effectively used as a pre-sowing treatment for seed invigoration in cucumber. Unlike other priming treatments seed is not required to be dehydrated after priming, allowing easy storage.

High temperature index--for field evaluation of heat tolerance in wheat varieties

High temperature (> 30 °C) at the time of grain filling is one of the major constraints in increasing productivity of wheat in tropical countries like India. Hence, wheat genotypes from national and international sources are regularly evaluated for tolerance to high temperature stress. Generally, genotypes are tested across space and time under field conditions by manipulation of date of sowing or choosing sites, which are featured by high temperature at grain filling (“hot spots”). Under such conditions, magnitude of heat stress determines accuracy of evaluation and selection of genotypes. Mean ambient temperatures during the day, month or crop season are often used to quantify the magnitude of heat stress. These temperature parameters, however, fail to account for changes in diurnal amplitude. As a consequence, actual duration of high temperature stress to which the crop is exposed to remains elusive. An attempt is made here to derive a thermal index to quantify heat stress under field conditions, taking into consideration the diurnal thermal amplitude. A mathematical equation is derived to quantify high temperature stress by integrating both the temperature and the duration. High temperature index (HTI) developed on the basis of this equation is compared with other thermal indices such as heat degree-days and mean temperatures. The index was found to be highly efficient in differentiating two crop environments. Further, HTI was used to quantify the magnitude of heat stress to which 12 advanced wheat (Triticum aestivum) genotypes were exposed during two crop seasons. This index along with grain yield loss during hot season is used to identify genotypes performing better by tolerating the high temperature or by escaping from it.

Characterisation of germinating and non-germinating wheat seeds by nuclear magnetic resonance (NMR) spectroscopy

Experiments were conducted to characterise the changes, especially of water status in germinating and non-germinating wheat seeds by nuclear magnetic resonance (NMR) spectroscopy. NMR relaxation time (T2) measurements showed tri-phasic or bi-phasic characteristics during different stages of hydration, depending on the seeds ability to germinate. Component analysis of T2 data revealed the existence of only two components, bound and bulk water, in dry seeds. In contrast, both the germinating and non-germinating wheat seeds had a three-component water proton system (bound, bulk and free water) in phase I of hydration. During the lag phase (phase II) of hydration, bulk water component of non-germinating seeds disappeared completely, resulting in a two component water proton system. Nevertheless, the three component water proton system was observed in the germinating seeds in phase II. Following phase II, rapid hydration (phase III) was observed in germinating seeds only. Water protons were re-organised and there were increases in bulk and free water but decreases in bound water concomitantly. Comparison of the physical state of water in these seeds by NMR spectroscopy with that of tissue leachate conductivity measurement suggests that the seed membrane system was affected more evidently in non-germinating seeds, leading to the disorganised cell structure. The present study provides evidence that the reorganisation of physical state of water in germinating wheat seeds during hydration is essential for its subsequent event of germination.

Characterization of germinating and non-viable soybean seeds by nuclear magnetic resonance (NMR) spectroscopy

The changes in water status of germinating and non-viable soybean ( Glycine max L. Merr.) seeds were characterized by nuclear magnetic resonance (NMR) spectroscopy. There were distinct changes in water status between viable and non-viable soybean seeds. In dry seeds, there were only two components, bound and bulk water, as revealed by component analysis of NMR (T 2 ) data. On the contrary, a three-component water proton system (bound, bulk and free water) was observed in both germinating and non-viable soybeans during Phase I of hydration. The bulk water component of non-viable seeds disappeared completely during the lag phase (Phase II) of hydration, resulting in a two-component water proton system. In contrast, the three-component water proton system in Phase II was observed in the germinating seeds. Rapid hydration (Phase III), following Phase II, was observed in germinating soybean seeds only. Due to reorganization of water protons, there was a concomitant increase in bulk and free water, but a decrease in bound water. The physical state of water in these seeds (analysed by NMR spectroscopy) and the measurements of tissue leachate conductivity suggest that non-viable soybean seeds were more affected by the disorganized cell structure in the seed membrane system. The present study also provides evidence that physical reorganization of water is essential in germinating soybean seeds during hydration.

Characterisation of Soybean and Wheat Seeds by Nuclear Magnetic Resonance Spectroscopy

The effects of equilibration under different air relative humidities (RH, 1 – 90 %) and temperatures (35 and 45 °C) on soybean (Glycine max) and wheat (Triticum aestivum) seeds were studied using different techniques. Seed moisture content, electrical conductivity (EC) of seed leachate and per cent seed germination were measured following standard procedures, and compared with nuclear magnetic resonance spin-spin relaxation time (T2) measurements. Moisture contents of soybean and wheat seeds, following the reverse sigmoidal trend, were greater at 35 than at 45 °C at any particular RH. Changes in T2 were related to the changes in germination percentage and leachate EC of both soybean and wheat seeds. Equilibrating soybean seeds at RH ≤ 11 % decreased germination percentage with corresponding decrease in T2. On the contrary, EC of seed leachate increased. In wheat seeds equilibrated at 45 °C, T2 was maximal at RH 5.5 %. T2 declined in seeds equilibrated at high RH (> 80 %) together with low germination percentage.

Pre-sowing static magnetic field treatment for improving water and radiation use efficiency in chickpea (Cicer arietinum L.) under soil moisture stress.

Soil moisture stress during pod filling is a major constraint in production of chickpea (Cicer arietinum L.), a fundamentally dry land crop. We investigated effect of pre-sowing seed priming with static magnetic field (SMF) on alleviation of stress through improvement in radiation and water use efficiencies. Experiments were conducted under greenhouse and open field conditions with desi and kabuli genotypes. Seeds exposed to SMF (strength: 100 mT, exposure: 1 h) led to increase in root volume and surface area by 70% and 65%, respectively. This enabled the crop to utilize 60% higher moisture during the active growth period (78-118 days after sowing), when soil moisture became limiting. Both genotypes from treated seeds had better water utilization, biomass, and radiation use efficiencies (17%, 40%, and 26% over control). Seed pre-treatment with SMF could, therefore, be a viable option for chickpea to alleviate soil moisture stress in arid and semi-arid regions, helping in augmenting its production. It could be a viable option to improve growth and yield of chickpea under deficit soil moisture condition, as the selection and breeding program takes a decade before a tolerant variety is released. Bioelectromagnetics. 37:400-408, 2016.

Role of sugars and proteins in development of desiccation tolerance in fresh and shade-dried onion seeds

In a 2-year field study, the umbels of open-pollinated onion cv. ‘Pusa Red’ were tagged on the day of anthesis and were sampled at different intervals until harvest maturity. Each umbel was cut in half and bulked with others in the respective replication. Seeds were immediately taken from half of the umbels for analysis of seed water content, leachate conductivity, seed capsule chlorophyll, seed dry weight and seed germination. They were also subjected to rapid desiccation to identify the stage at which desiccation tolerance occurred. The remaining umbel halves were shade dried and subjected to the same quality analyses except chlorophyll content. With seed maturation, there were rapid declines in chlorophyll content, leachate conductivity and seed water content, whereas seed dry weight and germination increased. In fresh seeds, maximum germination occurred around 50 days after anthesis, when physiological maturity and maximum seed weight were attained. In shade-dried seed, maximum germination occurred at 42 days after anthesis. This coincided with drastic reductions in seed capsule chlorophyll, leachate conductivity and seed water content in fresh seeds. At this stage, reducing sugar concentration declined and non-reducing sugar concentration increased many fold in shade-dried seeds. SDS-PAGE analysis of the heat-stable proteins extracted from the seeds also showed prominent bands in the lower molecular weight region at 42 DAA. Therefore, the shade-dried seeds attained membrane stability at 42 DAA. In cases of adverse weather conditions or disease attack, seed umbels can be harvested as early as 42 DAA and shade dried without compromising seed germination. Desiccation tolerance in fresh onion seeds occurred around 46 DAA and was a gradual event.