G. Kulandaivelu

Impacts of Ambient Solar UV (280-400 nm) Radiation on Three Tropical Legumes

Tropical regions receive the highest level of global solar ultraviolet (UV) radiation especially UV-B (280-320 nm). The average daily dose of the UV-B radiation in Madurai, South India (10°N) is 10 kJ m-2. This is approximately 50% more than the average daily UV-B radiation in many European countries. A field study was conducted using selective filters to remove either the UV-B (< 320 nm) or UV-B/A (<400 nm) of the solar spectrum, and the effects were followed inCyamopsis tetragonoloba, Vigna mungo, andVigna radiata to determine their sensitivity to UV. When compared to ambient radiation, exclusion of solar UV-B increased the seedling height, leaf area, fresh weight and dry weight and the crop yield by 50% in the case ofCyamopsis, and the extent of such increase was slightly less under UV-B/A exclusion. InV. mungo a significant reduction was seen in solar UV excluded plants whileV. radiata was found to be unaffected.

Exclusion of solar UV-B (280–315 nm) radiation on vegetative growth and photosynthetic activities in Vigna unguiculata L.

Abstract The impact of solar radiation with and without UV-B component was studied in a tropical legume Vigna unguiculata L. The average level of ambient UV-B was 10 kJ m−2 day−1. Exclusion of solar UV-B increased the seedling height, leaf area and fresh weight. On a unit fresh weight basis, a 50% increase in total chlorophyll and 47% decrease in flavonoids was noticed after 20 days of growth. Decrease in flavonoid content in UV-B filtered seedlings indicates the plant responsiveness to minimal UV-B radiation existing inside the filter cage. UV-B exclusion during the early phase of seedling growth also promoted photosynthetic activities, measured as O2 evolution or fluorescence transients. Such an enhancement in activity was attributed to modification in thylakoid organization under UV-B exclusion.

Differential responses of iron, magnesium, and zinc deficiency on pigment composition, nutrient content, and photosynthetic activity in tropical fruit crops.

Fe, Mn, and Zn affected the chlorophyll (Chl) content whereas Fe deficiency caused larger reduction of total chlorophyll content than Mg and Zn deficiencies. Mg deficient mango had a higher Chl a/b ratio than the respective healthy plants. The foliar contents of Fe, Zn, and Mg in the deficient leaves were lower than the critical level. Nutrient deficiency significantly affected the Fv/Fm ratios as observed from the Chl fluorescence induction curves. Fe deficiency resulted in larger reduction of variable fluorescence than Mg and Zn deficiency.

Influence of increased solar UV-B radiation on magnesium deficient cowpea seedlings : Changes in growth and foliar constituents

Abstract The influence of increased solar UV-B radiation (UV-B IS ) equivalent to 20% ozone depletion at Madurai (10°N, India) on growth and various foliar components of Mg-sufficient (Mg S 0.65 mM MgSO 4 ) and Mg-deficient (Mg d 0.02 mM MgSO 4 ) cowpea ( Vigna unguiculata L. Walp cv. Pusa-152) was examined after 20 days of stress imposition in the field. The combination of Mg d and UV-B IS stimulated stem elongation as compared with either stresses imposed independently, while such inductive influence was not manifested in leaf growth. Both stresses, when imposed independently or jointly, produced an increase or decrease in photosynthetic and non-photosynthetic pigment levels to various extents. Concentrations of some macro and microelements in shoot and leaves (both primary and trifoliate) suggest that Mg d -mediated physiological nutritional imbalance was minimized when both Mg d and UV-B IS were given simultaneously.

Effect of low doses of UV-A and UV-B radiation on photosynthetic activities inPhaseolus mungo L.

The effect of low doses of UV-A (320–400 nm) and UV-B (280–320 nm) radiation on photosynthetic activities inPhaseolus mungo L. was investigated under field condition. Supplementation of UV-A enhanced the synthesis of chlorophyll and carotenoids than the UV-B supplemented plants. Significant increase was seen in the concentration of UV-B absorbing compounds of UV-B treated plants. Increase of PS 2 activity in UV-A treated plants was seen. Changes in photosynthetic activity were measured in terms of PS 2 mediated O2 evolution and Chl a fluorescence.

INFLUENCE OF UV B SUPPLEMENTAL RADIATION ON GROWTH AND PIGMENT CONTENT IN SUAEDA MARITIMA L.

In a field experiment with a mangrove species Suaeda maritima L. grown under ambient and supplementary UV-B radiation corresponding to 20 % ozone depletion, changes in growth and contents of photosynthetic and UV-absorbing pigments were determined. Supplemental UV-B irradiation for 9 d significantly reduced the growth and concentration of photosynthetic pigments. However, anthocyanin and flavonoid contents were significantly increased in UV-treated plants and which could be reduce the UV-B penetration and damage to the underlying tissues.

Induced UV-B resistance against photosynthesis damage by adaptive mutagenesis in Synechococcus PCC 7942

Abstract Photosynthetic electron transfer was studied in thylakoids isolated from wild type, UV-B and UV-C adapted cells of Synechococcus . When thylakoids were irradiated with UV-B for 60 min, a drastic decrease in the rate of PSII electron transport chain (H 2 O→BQ) had occurred in wild type cells. The UV adapted cells showed greater resistance to UV-B radiation. In contrast to this, wild type cells were highly sensitive to UV-B irradiation. The artificial electron donors DPC and NH 2 OH restored the PSII activity markedly in the wild type cells. It shows that the UV-B treatment inactivates the donor side of PS II. The marked loss of PS II activity was confirmed by the immunological studies showing the content of the D1 protein of PSII reaction center and of 33 kDa of water splitting complex was diminished significantly in UV treated wild type cells where as marginal loss or enhanced synthesis of these proteins was evident in adapted cells.

Changes in Pigment Composition and Photosynthetic Activity of Aquatic Fern (Azolla Microphylla Kaulf.) Exposed to Low Doses of UV-C (254 nm) Radiation

Changes in the content of pigments and rate of photosynthesis in Azolla microphylla Kaulf. fronds were measured during growth under solar and ultraviolet-C (UV-C) supplemented solar radiation. Maximum content of total chlorophyll (Chl) was observed on the 13th day (termination of the experiment) of treatment in both control and treated plants. The treated plants had significantly lower total Chl and carotenoid contents than the control plants during the 1st day of growth. After the 4th day of exposure to UV-C supplemented solar radiation, the Chl and carotenoids accumulation increased in treated plants, so that the pigment concentration in the treated fronds was nearer to the control values after the 13th day of treatment. Significant increase in UV absorbing pigments, anthocyanins, and flavonoids was observed at the 13th day of treatment. In spite of the roughly similar photosynthetic pigment concentration, the photosynthetic activity measured as the rate of electron transport at photosystem 2 was only 65 % of the control values after 13 d of UV-C exposure.

Different responses to UV-B enhanced solar radiation in radish and carrot

Radish (Raphanus sativus L.) and carrot (Daucus carota L.), plants with underground storage organs grown in the field, were exposed to either ambient (UVA) or 20 % UV-B (UVE) enhanced solar radiation till their root yield stage. In radish, UVE produced a significant increase in shoot and root fresh mass (FM), increase in the contents of chlorophyll, carotenoids, flavonoids, and total proteins per unit FM, Hill reaction rate, and root yield. In contrast, carrot responded negatively to UVE showing a loss in the above parameters.

Effects of Enhanced Ultraviolet-B (280-320 nm) Radiation on Growth and Photosynthetic Activities in Aquatic Fern Azolla Microphylla Kaulf

The effects of enhanced UV-B radiation on growth and photosynthetic activities were investigated in fronds of the aquatic fern Azolla microphylla Kaulf. The fronds were exposed to UV-B radiation intermittently once in 3 d during 12 d. Biomass and relative growth rate of UV-B treated Azolla plants and the heterocyst frequency of the UV-B treated symbiont decreased resulting in an increase in doubling time over the control. The doubling time was 3.08 d for control and 3.35 d for UV-B irradiated plants. Chl and carotenoid contents per unit fresh mass and photosystem 2 (PS2) activity also decreased under UV-B treatment. Measurements of photosynthetic activity in terms of fluorescence kinetics and PS2 mediated O2 evolution showed that the aquatic fern Azolla is sensitive to UV-B damage.