K. N. Guruprasad

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.

Changes in antioxidant defenses of cucumber cotyledons in response to UV-B and to the free radical generating compound AAPH

Abstract A comparative study has been made on the creation of oxidative stress as well as induction of antioxidant mechanisms in cucumber cotyledons by free radical generating compound 2,2′-azobis (2-amidino propane) dihydrochloride (AAPH) and UV-B radiation. Both AAPH and UV-B enhanced the level of formation of Thiobarbituric acid reacting substances and inhibited the growth of hypocotyl and cotyledons. UV-B enhanced the level of ascorbic acid, an antioxidant in the cotyledons. This response was not induced by AAPH. The level of α-tocopherol was reduced by both, AAPH and UV-B with a temporal difference. Similarities were observed in the induction of antioxidant enzymes in the cotyledons. Activation of antioxidants as well as enzymes by the two factors is discussed.

Intraspecific variations in growth, yield and photosynthesis of sorghum varieties to ambient UV (280–400 nm) radiation

A field study was conducted to investigate the impact of ambient solar UV on the various growth, physiological and yield parameters of four sorghum (Sorghum bicolor L.) varieties-Indore-12, Indore-26, CSV-23 and Indore-27 by excluding either UV-B (<315 nm) or UV-A/B (<400 nm) components of solar spectrum. Exclusion of UV significantly enhanced plant height, area and specific leaf weight of flag leaf, biomass accumulation, yield parameters and harvest index in all the sorghum varieties. Chlorophyll b was significantly enhanced and chlorophyll a increased to a lesser extent, UV-B absorbing substances and chlorophyll a/b ratio were significantly decreased by the exclusion of solar UV. The enhancement in the vegetative growth and yield by UV exclusion might be linked to the remarkable increase in rate of photosynthesis in sorghum varieties. The magnitude of the response was high in I-26 and I-27 as compared to CSV-23 and I-12 after exclusion of solar UV. All the varieties of sorghum had a negative cumulative stress response index (CSRI), the sensitivity of the sorghum varieties was in the following sequence I-12>CSV-23>I-26>I-27. Thus I-27 was the most sensitive and I-12 the least sensitive variety to present level of solar UV radiation. The differences in UV sensitivity identified among sorghum varieties might be useful in breeding programs for increased tolerance to UV-B radiation.

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.

Enhancement in leghemoglobin content of root nodules by exclusion of solar UV-A and UV-B radiation in soybean

The impact of exclusion of solar UV-B (280–320 nm) and UV-A+B (280–400 nm) radiation on the root nodules was studied in soybean(Glycine max var. MACS 330). Soybean plants were grown in the tropical region of Indore (Latitude-22.4°N), India under field conditions in metal cages covered with polyester exclusion filters that specifically cut off UV-B (<320 nm) and UV-A+B (<400 nm) radiation; control plants were grown under ambient solar radiation. Leghemoglobin content was analyzed in the root nodules on the 50th day after emergence of seedlings. Exclusion of UV radiations significantly enhanced the leghemoglobin content in the nodules on fresh weight basis; 25% and 45% higher amount of leghemoglobin were present in the nodules after the exclusion of UV-B and UV-A+B radiation respectively. Analysis by native and SDS-PAGE showed high intense bands of leghemoglobin after the exclusion of UV-A+B as compared to control. Exclusion of UV radiation also enhanced the growth of roots as well as aerial parts of the plants. UV Exclusion increased nodulation by increase in the number and size of nodules. The results are discussed in the light of advantage of exclusion for enhancing protein/nitrogen content in the plants.

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.

Similarities in the biochemical changes between solar UV exclusion and GA application in Amaranthus caudatus

Seedlings of Amaranthus caudatus grown under UV exclusion filters (-UV -B <320nm; -UV -B/A <400nm) in the ambient solar radiation showed an enhancement in growth. This was accompanied by reduction in the synthesis of betacyanin but enhancement in the level of amino acids and proteins. The growth promotion and the accompanying biochemical changes were similar to the external application of GA3 to the seedlings under ambient solar radiation. The results are discussed in the light of similarities between UV exclusion and GA3 application in terms of diversion of amino acid precursors towards enhanced primary metabolism.

International conference ''Photosynthesis in the Global Perspective'' held in honor of Govindjee, November 27-29, 2008, Indore, India

An International conference ‘‘Photosynthesis in the Global perspective’’ was held in Indore, India, during November 27–29, 2008, in honor of Professor Govindjee. The conference provided an opportunity to felicitate him for the numerous significant and outstanding contributions in the field of photosynthesis research (also see Eaton-Rye 2007a, b). His dedication for communicating photosynthesis and his passion for the ‘‘History of Photosynthesis Research’’ has been commendable. He has been already recognized with the first Lifetime Achievement Award of the Rebeiz Foundation for Basic Research (Rebeiz et al. 2007) and with the prestigious 2007 Communication Award of the International Society of Photosynthesis Research (ISPR) (see Blankenship 2007). Just before the conference in Indore, University of Illinois recognized him on October 24, 2008, with an LAS (Liberal Arts and Sciences) Alumni Achievement Award (see http://www.las.illinois.edu/alumni/magazine/articles/2009/ govindjee). Figure 1A shows Govindjee’s photograph with three of his graduate students (George Papageorgiou, Julian Eaton-Rye and Prasanna Mohanty) who actively participated at the Indore Conference. Figure 1B shows a group photograph of Govindjee with many of the participants at the conference. The conference covered all the important aspects of photosynthesis, especially their relationship to global issues. Topics included: photobiology, structure and function of Photosystems I and II, stress responses & adaptive mechanisms, plant productivity, and artificial photosynthesis. Advances in structural and functional aspects of Photosystem II (PS II, the water-plastoquinone oxido-reductase, the only system on Earth that is capable of oxidizing water to molecular oxygen) was at the heart of many talks. This was highly appropriate for this celebration since Govindjee and co-workers were the first to measure the primary photochemistry of PS II, to provide an understanding of the PS II light emission from plants, algae, and cyanobacteria, to provide the theory of thermoluminescence from PS II, and to establish the unique role of bicarbonate/carbonate on the electron acceptor side of PS II. Stress responses of plants and their adaptive strategy to cope with stress was another key issue at the conference. There were 32 talks and about 45 posters, presented by both established and young scientists from about 12 countries (listed alphabetically): Australia, Azerbaijan, Canada, (The) Czech Republic, Finland, Hungary, India, Japan, Korea, New Zealand, Switzerland, UK, and USA. Speakers included (listed alphabetically): Arjun Tiwari, Asako Kawamori, Atipally Reddy, Baishnab Tripathy, Basanti Biswal, Bhumi Nath Tripathy, Debashish Banerji, Eva Mari Aro, Gyozo Garab, Hiroyuki Mino, James Barber, Julian EatonRye, K Padamsree, Kastoori Hingorani, Kumud Mishra, Louis Sherman, M.J. Baig, Michael Seibert, Munna Singh, Norm Huner, Pandit Vidyasagar, Prabhat Kumar Sharma, Prasanna Mohanty, Ralph Gasanov, Renu Khanna-Chopra, Reto Strasser, Shigeru Itoh, Subramanyam Rajagopal, Sujata Mishra, Suvendra Bagchi, Toshi Nagata and Uday Pathre. The guest of honor at the inaugural session was James Barber, President of International Society of Photosynthesis Research (ISPR). Govindjee delivered his inaugural talk Prasanna Mohanty—Formerly Professor of School of Life Science, Jawaharlal Nehru University, New Delhi, India.

Identification of genetically diverse genotypes for photoperiod insensitivity in soybean using RAPD markers

Most of the Indian soybean varieties were found to be highly sensitive to photoperiod, which limits their cultivation in only localized area. Identification of genetically diverse source of photoperiod insensitive would help to broaden the genetic base for this trait. Present study was undertaken with RAPD markers for genetic diversity estimation in 44 accessions of soybean differing in response to photoperiod sensitivity. The selected twenty-five RAPD primers produced a total of 199 amplicons, which generated 89.9 % polymorphism. The number of amplification products ranged from 2 to 13 for different primers. The polymorphism information content ranged from 0.0 for monomorphic loci to 0.5 with an average of 0.289. Genetic diversity between pairs of genotypes was 37.7% with a range of 3.9 to 71.6%. UPGMA cluster analysis placed all the accessions of soybean into four major clusters. No discernable geographical patterns were observed in clustering however; the smaller groups corresponded well with pedigree. Mantel’s test (r = 0.915) indicates very good fit for clustering pattern. Two genotypes, MACS 330 and 111/2/1939 made a very divergent group from other accessions of soybean and highly photoperiod insensitive that may be potential source for broadening the genetic base of soybean for this trait.