Sunita Kataria

Impact of increasing Ultraviolet-B (UV-B) radiation on photosynthetic processes.

Increased UV-B radiation on the earths surface due to depletion of stratospheric ozone layer is one of the changes of current climate-change pattern. The deleterious effects of UV-B radiation on photosynthesis and photosynthetic productivity of plants are reviewed. Perusal of relevant literature reveals that UV-B radiation inflicts damage to the photosynthetic apparatus of green plants at multiple sites. The sites of damage include oxygen evolving complex, D1/D2 reaction center proteins and other components on the donor and acceptor sides of PS II. The radiation inactivates light harvesting complex II and alters gene expression for synthesis of PS II reaction center proteins. Mn cluster of water oxidation complex is the most important primary target of UV-B stress whereas D1 and D2 proteins, quinone molecules and cytochrome b are the subsequent targets of UV-B. In addition, photosynthetic carbon reduction is also sensitive to UV-B radiation which has a direct effect on the activity and content of Rubisco. Some indirect effects of UV-B radiation include changes in photosynthetic pigments, stomatal conductance and leaf and canopy morphology. The failure of protective mechanisms makes PS II further vulnerable to the UV-B radiation. Reactive oxygen species are involved in UV-B induced responses in plants, both as signaling and damaging agents. Exclusion of ambient UV components under field conditions results in the enhancement of the rate of photosynthesis, PS II efficiency and subsequently increases the biomass accumulation and crop yield. It is concluded that predicted future increase in UV-B irradiation will have significant impact on the photosynthetic efficiency and the productivity of higher plants.

Enhancement of growth, photosynthetic performance and yield by exclusion of ambient UV components in C3 and C4 plants

A field experiment was conducted under tropical climate for assessing the effect of ambient UV-B and UV-A by exclusion of UV components on the growth, photosynthetic performance and yield of C3 (cotton, wheat) and C4 (amaranthus, sorghum) plants. The plants were grown in specially designed UV exclusion chambers, wrapped with filters that excluded UV-B (<315nm), UV-A+B (<400nm), transmitted all the UV (280-400nm) or without filters. All the four plant species responded to UV exclusion by a significant increase in plant height, leaf area, leaf biomass, total biomass accumulation and yield. Measurements of the chlorophyll, chlorophyll fluorescence parameters, gas exchange parameters and the activity of Ribulose-1,5-bisphosphate carboxylase (Rubisco) by fixation of (14)CO2 indicated a direct relationship between enhanced rate of photosynthesis and yield of the plants. Quantum yield of electron transport was enhanced by the exclusion of UV indicating better utilization of PAR assimilation and enhancement in reducing power in all the four plant species. Exclusion of UV-B in particular significantly enhanced the net photosynthetic rate, stomatal conductance and activity of Rubisco. Additional fixation of carbon due to exclusion of ambient UV-B was channeled towards yield as there was a decrease in the level of UV-B absorbing substances and an increase in soluble proteins in all the four plant species. The magnitude of the promotion in all the parameters studied was higher in dicots (cotton, amaranthus) compared to monocots (wheat, sorghum) after UV exclusion. The results indicated a suppressive action of ambient UV-B on growth and photosynthesis; dicots were more sensitive than monocots in this suppression while no great difference in sensitivity was found between C3 and C4 plants. Experiments indicated the suppressive action of ambient UV on carbon fixation and yield of C3 and C4 plants. Exclusion of solar UV-B will have agricultural benefits in both C3 and C4 plants under tropical climate.

Intraspecific variation in sensitivity to ambient ultraviolet-B radiation in growth and yield characteristics of eight soybean cultivars grown under field conditions

The present study was conducted with eight cultivars of soybean (Glycine max) to determine the effect of exclusion of solar UV-B on the vegetative growth (plant height, leaf area, no. of nodes), UV absorbing compounds (implicated in UV protection) and crop yield (No. of pods and seed weight) and to determine the cultivar difference in their sensitivity to ambient UV-B. Exclusion of solar UV-B enhanced the vegetative growth and yield of all the soybean cultivars. The results showed a significant inverse association between the enhancement in vegetative growth and number of pods among the cultivars tested, indicating differences in the carbon partitioning amongst the cultivars by the way of exclusion of solar UV-B. NRC-7, Pusa-24 and JS-335 showed maximum promotion in vegetative growth and less enhancement in crop yield after solar UV-B exclusion. Kalitur, JS71-05, Hardee, PK-472 and PK-1029 showed improved performance both in terms of number of pods/plant and seed weight after solar UV-B exclusion. An enhancement in the crop yield by exclusion of solar UV-B indicated poor response of the cultivar to the ambient solar UV-B; these cultivars would be more suitable at latitudes, which received less UV-B. According to UV-SI, sensitivity of eight Indian soybean cultivars to ambient level of UV-B (280-320 nm) radiation had the following descending order; PK-472 > JS-335 > Hardee > Kalitur > JS71-05 > Pusa-24 > NRC-7 > PK-1029. These findings suggest the way to select the best-suited cultivar for particular latitude.

Static magnetic field treatment of seeds improves carbon and nitrogen metabolism under salinity stress in soybean

The effectiveness of magnetopriming was assessed for alleviation of salt-induced adverse effects on soybean growth. Soybean seeds were pre-treated with static magnetic field (SMF) of 200 mT for 1 h to evaluate the effect of magnetopriming on growth, carbon and nitrogen metabolism, and yield of soybean plants under different salinity levels (0, 25, and 50 mM NaCl). The adverse effect of NaCl-induced salt stress was found on growth, yield, and various physiological attributes of soybeans. Results indicate that SMF pre-treatment significantly increased plant growth attributes, number of root nodules, nodules, fresh weight, biomass accumulation, and photosynthetic performance under both non-saline and saline conditions as compared to untreated seeds. Polyphasic chlorophyll a fluorescence (OJIP) transients from magnetically treated plants gave a higher fluorescence yield at J-I-P phase. Nitrate reductase activity, PIABS , photosynthetic pigments, and net rate of photosynthesis were also higher in plants that emerged from SMF pre-treated seeds as compared to untreated seeds. Leghemoglobin content and hemechrome content in root nodules were also increased by SMF pre-treatment. Thus pre-sowing exposure of seeds to SMF enhanced carbon and nitrogen metabolism and improved the yield of soybeans in terms of number of pods, number of seeds, and seed weight under saline as well as non-saline conditions. Consequently, SMF pre-treatment effectively mitigated adverse effects of NaCl on soybeans. It indicates that magnetopriming of dry soybean seeds can be effectively used as a pre-sowing treatment for alleviating salinity stress. Bioelectromagnetics. 37:455-470, 2016.

Antioxidant defense response of fenugreek to solar UV

ABSTRACT In the tropics, solar UV-B background level is often high and can affect growth and development of vegetables. Fenugreek (Trigonella foenum-graecum L.), which is not native to India, may be detrimentally affected by solar ultraviolet (UV). This UV radiation-impacting plants can affect defense system by activating, or elevating, antioxidant enzymes. The study was undertaken to determine physiological and defensive responses of fenugreek to solar UV from 280 to 400 nm. The UV-B and UV-B+A were excluded with appropriate filters to assess effects of UV-B radiation under field conditions. Plants were grown in iron mesh cages covered with filters to specifically exclude UV-B (280–315 nm) or UV-B+A (280–400 nm) solar radiation. Control plants were grown under polyethylene filters transmissible to solar UV. Exclusion of solar UV enhanced plant height, leaf area, and fresh and dry weight of plants compared to the control. Exclusion of UV-B and UV-B+A decreased levels of antioxidants ascorbic acid (ASA), malondialdehyde, and activities of the antioxidant enzymes superoxide dismutase, ASA peroxidase, and guaiacol peroxidase in leaves compared to the control. There was a reduction in UV absorbing substances (UAS) after solar UV exclusion. The overall decrease in levels of antioxidants and antioxidant enzymes by solar UV exclusion demonstrates that ambient UV components exert detrimental effects and can potentially reduce growth and yield of fenugreek. Reduced amount of UAS and antioxidant enzymes in UV-excluded plants indicates that plants do not have to divert metabolic energy in detoxification of reactive oxygen species (ROS) produced due to exposure to solar UV. The metabolic energy required for scavenging these ROS was efficiently utilized toward maintaining growth of plants and improved the crop yield under exclusion of ambient UV conditions.

Involvement of nitric oxide in enhanced germination and seedling growth of magnetoprimed maize seeds

ABSTRACT Nitric oxide (NO) is a highly reactive gaseous free radical, which in plants was found to stimulate seed germination and ending of dormancy. Experiments were conducted to study the effect of NO inhibitors sodium tungstate (ST) and Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME), NADPH oxidase inhibitor diphenyleneiodonium (DPI) and NO donor sodium nitroprusside (SNP) on untreated and magnetoprimed maize (Zea mays var: GSF-2) seeds. Treatment of maize seeds with these inhibitors inhibited germination related parameters like seedling length, fresh weight, dry weight and vigour indices and α-amylase activity of maize seeds under laboratory conditions, whereas NO donor (SNP) promoted all these parameters. Among 3 different inhibitors used ST was most effective and showed an inhibition in seedling length of 67% and 71% at 1 mM concentration for untreated (UT) and magnetically treated (MT) seeds respectively. Data presented here indicate the involvement of nitric oxide in enhanced germination and seedling growth of magnetoprimed maize seeds. ROS are continuosly produced by the cells of germinating seeds and play a positive role in germination of magnetoprimed maize seeds. ROS inhibitor (DPI) inhibited seedling length by 34% and 40% for control and MT seeds respectively. α-amylase activity was also inhibited by all the 3 inhibitors used. It is concluded that NO inhibitors and ROS inhibitor inhibited magnetic field induced promotion of seedling parameters and α- amylase activity of maize seeds.