Microwave treatment of eight seconds protects cells of Isatis indigotica from enhanced UV-B radiation lesions.

To determine the role of microwaves in the stress resistance of plants to enhanced ultraviolet-B (UV-B) radiation, Isatis indigotica Fort. seeds were subjected to microwave radiation for 8 s (wavelength 125 mm, power density 1.26 mW mm(-2), 2450 MHz). Afterwards they were cultivated in plastic pots in an artificial-glass greenhouse maintained at 25 degrees C, 70% relative humidity, and 400 micromol mol(-1) CO2, under visible-light conditions of 1500 micromol m(-2) s(-1) for 8 h day(-1). When the seedlings were 10 days old, they were subjected to 10.08 kJ m(-2) UV-B (PAR: 220 micromol m(-2) s(-1)) radiation for 8 days. Changes in a number of physiological and biochemical characteristics and in the thermal decomposition enthalpy of biomass were measured and used as indicators of the protective capacity of microwave radiation in this experiment. Our results revealed that microwave pretreatment of seeds enhanced UV-B stress resistance in the seedlings by decreasing the concentration of malondialdehyde (MDA) and increasing the concentration of ascorbic acid (AsA) and UV-B-absorbing compounds, increasing the activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), and increasing the energy accumulation of photosynthesis. All these results suggest that microwave radiation enhances plant metabolism and results in increased UV-B stress resistance. This is the first investigation reporting the use of microwave pretreatment to protect the cells of Isatis indigotica from UV-B-induced lesions.

Light quality influences indigo precursors production and seed germination in Isatis tinctoria L. and Isatis indigotica Fort.

Isatis tinctoria L. and Isatis indigotica Fort. are biennial herbaceous plants belonging to the family of Cruciferae that are used as a source of natural indigo and show several morphological and genetic differences. Production of indigo (indigotin) precursors, indican (indoxyl beta-D glucoside) and isatan B (indoxyl ketogluconate), together with seed germination ability were compared in Isatis tinctoria and Isatis indigotica grown under six different light conditions (darkness, white, red, far red, blue, yellow light) at 25 degrees C. Light quality influenced both germination and production of indigo precursors in the two Isatis species. Different responsiveness to far red and blue light was observed. Indeed, a detrimental effect on germination by blue and far red light was found in I. tinctoria only. Different amounts of isatan B were produced under red and far red light in the two Isatis species. In I. tinctoria, the level of main indigo precursor isatan B was maximal under red light and minimal under far red light. Whereas in I. indigotica far red light promoted a large accumulation of isatan B. The photon fluence rate dependency for white and yellow light responses showed that the accumulation of indigo precursors was differently influenced in the two Isatis species. In particular, both white and yellow light enhanced above 40 micromol m(-2) s(-1) the production of isatan B in I. indigotica while only white light showed a photon fluence dependency in I. tinctoria. These results suggest a different role played by the labile and stable phytochrome species (phyA and phyB) in the isatan B production in I. tinctoria and I. indigotica. I. indigotica, whose germination percentage was not influenced by light quality, demonstrated higher germination capability compared with I. tinctoria. In fact, I. tinctoria showed high frequency of germination in darkness and under light sources that establish high phytochrome photoequilibrium (red, white and yellow light). Germination in I. tinctoria was negatively affected by far red and blue light. I. indigotica seeds appear to be indifferent to canopy-like light (far red). Our results provide further insights on the distinct behaviour of I. tinctoria and I. indigotica that belong to two different genetic clusters and different original environments.

Response of antioxidant defense system to laser radiation apical meristem of Isatis indigotica seedlings exposed to UV-B.

To determine the response of antioxidant defense system to laser radiation apical meristem of Isatis indigotica seedlings, Isatis indigotica seedlings were subjected to UV-B radiation (10.08 kJ m(-2)) for 8 h day(-1) for 8 days (PAR, 220 micromol m(-2) s(-1)) and then exposed to He-Ne laser radiation (633 nm; 5.23 mW mm(-2); beam diameter: 1.5 mm) for 5 min each day without ambient light radiation. Changes in free radical elimination systems were measured, the results indicate that: (1) UV-B radiation enhanced the concentration of Malondialdahyde (MDA) and decreased the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in seedlings compared with the control. The concentration of MDA was decreased and the activities of SOD, CAT and POD were increased when seedlings were subjected to elevated UV-B damage followed by laser; (2) the concentration of UV absorbing compounds and proline were increased progressively with UV-B irradiation, laser irradiation and He-Ne laser irradiation plus UV-B irradiation compared with the control. These results suggest that laser radiation has an active function in repairing UV-B-induced lesions in seedlings.