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. and M. Jayakumar ... [et al.].
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. and S. M. J. Nithia, N. Shanthi, G. Kulandaivelu.
Cyamopsis tetragonoloba L. seedlings were subjected to continuous ultraviolet (UV)-B radiation for 18 h and post-irradiated with "white light" (WL) and UV-A enhanced fluorescent radiations. UV-B treatment alone reduced plant growth, pigment content, and photosynthetic activities. Supplementation of UV-A promoted the overall seedling growth and enhanced the synthesis of chlorophyll and carotenoids with a relatively high photosystem 1 activity. Post UV-B irradiation under WL failed to photoreactive the UV-B damage whereas a positive photoregulatory effect of UV-A was noticed in electron transport rates and low temperature fluorescence emission spectra. and K. Lingakumar, G. Kulandaivelu.
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. and K, Balakrishnan, C. Rajendran, G. Kulandaivelu.
In field-grown Cyamopsis seedlings, distinct changes were found in the rates of photosystems (PS) 2 and 1 activities at different time of the day. Maximum PS2 activity was at around 11:00 h and decreased thereafter. On the contrary, PS1 activity continued to increase up to 14:00 h and declined in evening hours. Significant energy transfer from PS2 to PS1 was evident during the morning and evening hours of the day whereas a slow excitation of PS2 and energy transfer was favoured during noon hours. and K. Lingakumar, G. Kulandaivelu.
In greenhouse experiments the efFect of simulated acid rain (mist of H2SO4) treatment on i'*C02 fixation, ribulose-l,5-bisphosphate carboxylase (RuBPC), nitráte reductase (NR) and nitrite reductase (NiR) activities in Vigna sinensis L. and Phaseolus mungo L. was investigated at different pH. Seedlings exposed to acidic mists of pH 5.6, 4.0 and 2.0 for 5 d showed significant reduction in *“*€02 fixation, RuBPC, NiR and especially NR activities. Sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) of crude leaf extracts of RuBPC indicated a significant loss of 55 and 15 kDa polypeptides at pH 2.0 in both the crop plants. The reduction in the RuBPC activity in seedlings grown under acidic mists correlated well with the CO2 fixation. NR activity was affected more than the NiR activity.
The effect of spraying triacontanol (Tria) solution (1 g m'^) on •'*C02 fíxation, ribulose-l,5-bisphosphate carboxylase (RuBPC), nitráte reductase (NR) and photosystem (PS) activities in waterlogged Erythrina variegata Lam. was investigated under field conditions. Seedlings exposed to flooding for 10 d showed a significant reduction in •‘♦CO2 fíxation, and in NR, RuBPC and PS2 activities. Electrophoretic analysis of thylakoid polypeptides indicated a significant loss of 47, 43, 33, 25, 23, 17 and 15 kDa polypeptides in flooded seedlings. However, the application of Tria partially ameliorated the effect of flooding and promoted the above activities. The site of flooding injury was at the oxidation site of PS2 prior to the hydroxylamine donating site and perhaps close or after the diphenylcarbazide donating site. The increase in the RuBPC activity in Tria-treated seedlings under flooding correlated well with the changes in CO2 fíxation rate.
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. and M. Jayakumar ... [et al.].
Chloroplasts isolated from Vigna sinensis L, seedlings grown under cool íluorescent (control chloroplasts) and ultraviolet-B (UV-B)-enhanced íluorescent (UV chloroplasts) radiation, when incubated at 10, 20, 30 and 40 °C, showed large variations in the photosynthetic electron transport reactions. The overall electron transport activity in both control and UV chloroplasts incubated at 40 decreased rapidly. In contrast to this, at 30 the control chloroplasts got inactivated very rapidly during the 30 min of incubation while the UV chloroplasts showed high stability. A similar trend was also noticed at 20 “C. At 10 °C, although the rate of inactivation was slow, UV chloroplasts were more stable than control chloroplasts. A similar trend was noticed in photosystern (PS) 2 activity. In contrast to overall electron transport and PS2 reactions, PS 1 activity showed only marginal changes at all temperatures. The polypeptide profiles of chloroplasts exposed to UV-B iixadiation for 60 min at different temperatures revealed marked decreases in the level of the 23 and 33 kDa polypeptides in control chloroplasts while in UV chloroplasts these polypeptides were highly stable. In addition, UV chloroplasts contained several new polypeptides of both high and low molecular masses. The polypeptide partem indicated that higher photochemical activity of UV chloroplasts over the control chloroplasts could be due to stabilization of PS 2 core complexes by the new polypeptides induced under UV-B enhanced radiation.
Changes in the activity of ribulose 1,5-bisphosphate carboxylase (RuBPC), soluble proteins and l‘*C02 fixation were studied in Vigna sinen.sis L. seedlings grovvn under nonnal and ultraviolet-B (UV-B) enhanced radiations at 10, 20, 30 and 40 ^C. The seedlings grown under nonnal radiation showed a progressive increase in enzyme activity, soluble protein and *‘*C02 fixation with an increase in temperature from 20 to 40 oC, while seedlings grown under UV-B enhanced radiation showed gradual decrease in these parameters with a maximum effect at 20-30 oC, At 40 oC, the inhibition was less. RuBPC activity, soluble protein content and '‘♦CO2 fixation showed parallel increases with increasing period of UV-B treatment at 10 oC, The polypeptide pattem of crude leaf extract showed progressive decrease in the level of 55 and 13 kDa polypeptides with the time of UV-B treatment at 20 and 30 °C. However, no such loss in these polypeptides was observed at 10 oC, and at 40 oC only a marginal loss in the level of 13 kDa polypeptide had occuned.