Impact of two different types of heat stress on chloroplast movement and fluorescence signal of tobacco leaves

Abstract

Although the chloroplast movement can be strongly affected by ambient temperature, the information about chloroplast movement especially related to high temperatures is scarce. For detailed investigation of the effects of heat stress (HS) on tobacco leaves (Nicotiana tabacum L. cv. Samsun), we used two different HS treatments in dark with wide range of elevated temperatures (25-45 degrees C). The leaf segments were either linearly heated in water bath at heating rate of 2 degrees C min(-1) from room temperature up to maximal temperature (T (m)) and then linearly cooled down to 25 degrees C or incubated for 5 min in water bath at the same T (m) followed by 5 min incubation at 25 degrees C (T-jump). The changes in light-induced chloroplast movement caused by the HS pretreatment were detected after the particular heating regime at 25 degrees C using a method of time-dependent collimated transmittance (CT) and compared with the chlorophyll O-J-I-P fluorescence rise (FLR) measurements. The inhibition of chloroplast movement started at about 40 degrees C while the fluorescence parameters responded generally at higher T (m). This difference in sensitivity of CT and FLR was higher for the T-jump than for the linear HS indicating importance of applied heating regime. A possible influence of chloroplast movement on the FLR measurement and a physiological role of the HS-impaired chloroplast movement are discussed.

Chloroplast avoidance movement as a sensitive indicator of relative water content during leaf desiccation in the dark

“…Some studies have shown that during desiccation, the nonchloroplast water is lost faster than so called chloroplast water (McCain et al 1988;Carter and McCain 1993;Ning et al 1994), which means that the water surrounding thylakoid membranes and particularly PSII complex remains unchanged longer than the cytoplasmic medium and cytoplasm in epidermal cells. It is interesting to note that even the high temperature stress, which is relatively homogeneously distributed in leaf tissue, is detected sooner by chloroplast movement than by Chl fluorescence (the O-J-I-P curve; Frolec et al 2010). It is possible that the changes in light-induced chloroplast movement represent an early signal of a general stress situation.…”

“…The T C dependence on time of blue light exposure, the T C (t) curve, reflecting the chloroplast avoidance movement, was characterized by a sigmoidal increasing shape (see Nauš et al 2008, Frolec et al 2010. We used an illumination time of 25 min, which was time necessary to reach the beginning of the T C plateau in control leaves (Fig.…”

“…This method is described in detail in Frolec et al (2010) and Nauš et al (2008). Briefly, the leaves were illuminated from the adaxial side by blue light (Schott KL 2500 LCD cold light source (Schott Glass AG, Mainz, Germany) in combination with blue Schott BG12 glass filter).…”

“…However, few studies have focused on the effect of abiotic stress factors on chloroplast movement. For example, inhibition of chloroplast movement has been reported in the case of heat (Brugnoli and Björkman 1992;Frolec et al 2010) and heavy metal (lead) stress (Samardakiewicz et al 2015). Changes in chloroplast movement and relocation during water-deficit stress have been described by Kondo et al (2004) and Yamada et al (2009).…”

“…Our method (Nauš et al 2008;Frolec et al 2010) is simpler and more straightforward, as we detect the leaf transmittance not in the red region but at the wavelength of minimal transmittance in the blue region (around 436 nm). In other words, a part of the blue light stimulating chloroplast movement is used simultaneously as the measuring light.…”