Prabhat Kumar Sharma

Photochemical and biochemical changes in wheat seedlings exposed to supplementary ultraviolet-B radiation

Abstract The effect of UV-B radiation (312 nm; 1 mW cm −2 ) was studied on net photosynthesis, chlorophyll fluorescence and changes in flavonoid and carotenoid contents in wheat seedlings. Control plants (without UV-B treatment but identical light and temperature regime as for UV-B treatment) and UV-B treated plants were grown in two separate growth chambers for 15 days. The supplementary UV-B radiation caused a significant decrease in net photosynthesis which was much greater than could be explained by limitation of stomatal conductance. Initial fluorescence ( F o ), F v / F m and photochemical quenching ( q P ) and non-photochemical quenching ( q N ) of chlorophyll fluorescence did not change due to 5 days of UV-B treatment, but longer treatment (up to 15 days) increased F o while decreasing the F v / F m ratio. q P and q N also decreased after 15 days of UV-B exposure. Changes in UV-B absorbing phenolic compounds such as flavonol (kaempferol), caumarin and anthocyanin were observed, whereas cinnamic acid was only synthesised after 4 days of UV-B treatment. No zeaxanthin formation was observed while neoxanthin showed a decrease in longer UV-B treatment. Violaxanthin showed an increase in early treatment but decreased after 15 days of UV-B exposure. Our results suggest two types of damage, one within 4–5 days of UV-B exposure and another with longer than 5 days exposure.

High-light–induced Changes on Photosynthesis, Pigments, Sugars, Lipids and Antioxidant Enzymes in Freshwater (Nostoc spongiaeforme) and Marine (Phormidium corium) Cyanobacteria

Abstract We studied the effects of high-light exposure (500 μmol m−2 s−1 of photosynthetic active radiation) on the cyanobacteria Nostoc spongiaeforme Agardh, a fresh-water alga, and Phormidium corium Agardh (Gomont), a marine alga, with respect to photosynthesis, pigments, sugar content, lipid peroxidation, fatty acids composition, antioxidant enzymes activity and DNA. It was seen that the ratio of variable fluorescence (Fv) to maximum fluorescence (Fm), which is indicative of photosynthetic efficiency, decreased because of the light treatment. The damage to photosynthesis occurred in the antenna system and the photosynthetic II reaction center. Photobleaching of photosynthetic pigments was also observed. High-light treatment also resulted in decreased sugar content, which was probably due to the effect on photosynthesis. Peroxidation of membrane lipids, indicating oxidative damage to lipids and a high level of unsaturation in the cell membrane, was also observed. The activity of antioxidant enzyme superoxide dismutase and ascorbate peroxidase was increased, probably as a result of oxidative damage observed in the form of lipid peroxidation. Quantitative decreases in phospholipid and glycolipid levels were also observed. The level of unsaturated fatty acids in total lipids and glycolipids remained unchanged in both species; however, the level of saturated fatty acids decreased, which slightly changed the ratio in favor of unsaturated fatty acids. Degradation of DNA was also observed in both species. There was a transient plateau 2–4 h after exposure to high-light treatment in the Fv/Fm ratio and in levels of phycobilisome pigments, sugars and antioxidant enzymes after an initial decrease 1 h after the treatment. These findings may indicate a period of partial adaptation to high light that is due to the efficiency of protective processes operational in the two species, which subsequently failed after a longer exposure duration of 4–6 h.

Arbuscular mycorrhizal status and root phosphatase activities in vegetative Carica papaya L. varieties

The arbuscular mycorrhizal (AM) status and root phosphatase activities were studied in four vegetative Carica papaya L. varieties viz., CO-1, CO-2, Honey Dew and Washington. Standard techniques were used to ascertain information on spore density and species diversity of AM fungi. Although in case of estimation of root colonization and root phosphatase activities, the existing methods were slightly modified. Root colonization and spore density of AM fungi along with root phosphatase (acid and alkaline) activities varied significantly in four papaya varieties. The present study recorded higher acid root phosphatase activity when compared with alkaline root phosphatase activity under P-deficient, acidic soil conditions. The present study revealed that the root colonization of AM fungi influenced acid root phosphatase activity positively and significantly under P-deficient, acidic soil conditions. A total of 11 species of AM fungi belonging to five genera viz., Acaulospora, Dentiscutata, Gigaspora, Glomus and Racocetra were recovered from the rhizosphere of four papaya varieties.

Pigment, fatty acid and extracellular enzyme analysis of a fungal strain Thelebolus microsporus from Larsemann Hills, Antarctica

A cold-tolerant fungal strain Thelebolus microsporus was investigated for the first time for its pigment and fatty acid production. High-performance liquid chromatography analysis confirmed the presence of carotenoid pigment. Gas chromatography observations showed the presence of major fatty acids: myristic acid (14:0), palmitic acid (16:0), stearic acid (18:0), heptadecanoic acid (17:0), linolenic acid (18:3) and linoleic acid (18:2). Of these, linolenic acid, a polyunsaturated fatty acid, was present in substantial quantity, suggesting that it may have a role in adapting the fungus to low Antarctic temperatures by modulating membrane fluidity. The commercial application of linolenic acid is as a food supplement for humans suffering from eczema, cardiovascular disease and diabetic neuropathy. Another fatty acid, linoleic acid, a precursor of 1-octen-3-ol, is the principal aromatic compound in most fungi and has also been documented in this strain. Screening of the fungal culture for extracellular enzyme activity for amylase, protease, lipase, chitinase and cellulase was carried out. The isolate showed maximum α-amylase activity at 20°C, suggesting effective applications as a detergent additive, in textile processing and in the food industry.

Symbiotic interactions between arbuscular mycorrhizal (AM) fungi and male papaya plants: its status, role and implications.

Experiments were conducted to study the arbuscular mycorrhizal (AM) status and its role in P-uptake through assay of root phosphatases activities in four varieties of male Carica papaya L. viz. CO-1, CO-2, Honey Dew and Washington during flowering stages. In the present study, mean total root colonization of AM fungi recorded peak increase in flowering stage-II while mean root phosphatase (acid and alkaline) activities recorded peak increase in flowering stage-I. Unlike root colonization and root phosphatase activities, spore density did not exhibit any definite patterns and recorded a narrow range of fluctuation during different flowering stages of male C. papaya. The study brought out the fact that root colonization and spore density of AM fungi along with root phosphatase activities varied significantly within the four varieties of male C. papaya plants during each flowering stage. The study also recorded consistently higher acid root phosphatase activity than alkaline root phosphatase activity under P-deficient, acidic soil conditions during all flowering stages of male C. papaya plants. Studies revealed that the root colonization of AM fungi influenced root phosphatase activities (acid and alkaline) positively and significantly during all flowering stages of male C. papaya plants. A total of twelve species of AM fungi belonging to five genera viz. Acaulospora, Dentiscutata, Gigaspora, Glomus, and Racocetra were recovered from the rhizosphere of male C. papaya plants.

Effect of NaCl and Exogenously Supplied ABA on Xanthophyll Cycle Pigments and Energy Dissipation in Rice Plants Under High Light Stress

In The Present Study Rice (Oryza Sativa L. Cv. Jyothi) Plants Grown In The Shade And Direct Sunlight Were Subjected To Salt Stress (100 Mm) Or Fed With Aba (10 Mm) Through Roots To Investigate Their Influence On The Light-Dependent Z Formation And Energy Dissipation. Plants (Both -Nacl/+Nacl And -Aba/+Aba) Were Then Treated With High Light By Exposing Them To Direct Sunlight (1,200– 2,200 μMol M-2 S-1 Pfd). Leaf Samples Were Collected For Chlorophyll Fluorescence Measurements, Pigment And Aba Analysis At Different Intervals During The Exposure. Results Show Plants Subjected To Salinity And High Light Stress Showed An Increase In The Endogenous Aba Level While Z Was Absent. Fv/Fm And Qn Remained More Or Less Same In Plants Grown With Nacl And Photoinhibited And Plants Grown Without Nacl And Photoinhibited. Neoxanthin (Nx) Content Were Much Higher In Salt Grown Plants But Declined Initially After Onset Of Sun Light Treatment But Increased After Longer Duration Of The Exposure. When Plants Were Grown With Exogenously Supplied Aba And Subsequently Exposed To Sunlight Most Of The V Was Made Available For Conversion To Z And This Was Correlated With Higher Level Of Qn And Better Photoprotection.