Changes in chloroplast ultrastructure, specific and phenomenological energy flux, and proline content in the Dracocephalum kotschyi plants during acclimation to combined UVB radiation and high light stress

High light (HL) and enhanced ultraviolet-B (UVB) radiation are major abiotic constraints affecting plant growth worldwide. We studied the effect of HL and UVB on chloroplast ultrastructure, specific and phenomenological energy flux, and proline content in low and high-altitude Dracocephalum kotschyi plants. Plants were treated with two levels of light intensity, including ۴۰۰ and high light (HL, ۸۰۰ µmol m-۲ s-۱), as well as with two levels of ultraviolet-B irradiation (control, UVB, ۱۵ and ۳۰ kJ m-۲ d-۱) for a further ۱۰ days. We observed that the exposure of high-altitude plants to combined stress (HL+UVB) caused an increase in proline content; however, after exposure of low-altitude plants to stress combination, proline content decreased significantly. Based on present results, trapped energy flux (TRO/CSm) and electron transport flux (ETO/CSm) decreased with UVB۱۵+HL because active reaction centers (RCs) are converted into inactive or closed RCs consequently decreasing the trapping efficiency and electron transport from PSII. Interestingly, in high-altitude plants exposed to UVB۳۰+HL, the ratio of total dissipation to the number of active RCs (DIO/RC) is not very influenced, due to the effective utilization of energy by the active RCs. Ultrastructural analyses of chloroplasts revealed an accumulation of plastoglobules only in high-altitude plants leaves under control conditions. In both low and high-altitude plants, UVB۳۰ alone and combined UVB۳۰+HL treatments caused a significant increase in starch granules in chloroplasts, and those chloroplasts tended to be round, especially in high-altitude plants. Thus, significant variation in chloroplast ultrastructure, specific and phenomenological energy flux, and proline content exists between low and high-altitude Dracocephalum kotschyi plants, which is apparently due to their altitudinal distributions.

کلیدواژه ها:

Altitudinal gradient ، Starch granules ، Trapping efficiency ، UVB radiation ، Altitudinal gradient ، Starch granules ، Trapping efficiency ، UVB radiation