In the context of global climate change, drought is one of the major stress factors with negative effect on photosynthesis and plant productivity. Currently, chlorophyll fluorescence parameters are widely used as indicators of plant stress, mainly owing to the rapid, non-destructive and simple measurements this technique allows. However, these parameters have been shown to have limited sensitivity for the monitoring of water deficit as leaf desiccation has relatively small effect on photosystem II photochemistry. In this study, we found that blue light-induced increase in leaf transmittance reflecting chloroplast avoidance movement was much more sensitive to a decrease in relative water content (RWC) than chlorophyll fluorescence parameters in dark-desiccating leaves of tobacco (Nicotiana tabacum L.) and barley (Hordeum vulgare L.). Whereas the inhibition of chloroplast avoidance movement was detectable in leaves even with a small RWC decrease, the chlorophyll fluorescence parameters (F V/F M, V J, Ф PSII, NPQ) changed markedly only when RWC dropped below 70 %. For this reason, we propose light-induced chloroplast avoidance movement as a sensitive indicator of the decrease in leaf RWC. As our measurement of chloroplast movement using collimated transmittance is simple and non-destructive, it may be more suitable in some cases for the detection of plant stresses including water deficit than the conventionally used chlorophyll fluorescence methods.

• Keywords
• Chlorophyll fluorescence, Chloroplast avoidance movement, Desiccation, Relative water content, Transmittance,
• MeSH
• Chlorophyll metabolism   MeSH
• Chloroplasts physiology   radiation effects   MeSH
• Fluorescence MeSH
• Photosynthesis MeSH
• Stress, Physiological MeSH
• Hordeum physiology   radiation effects   MeSH
• Plant Leaves physiology   radiation effects   MeSH
• Droughts MeSH
• Nicotiana physiology   radiation effects   MeSH
• Darkness MeSH
• Water analysis   physiology   MeSH
• Desiccation MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll MeSH
• Water MeSH

Leaf chlorophyll content is an important physiological parameter which can serve as an indicator of nutritional status, plant stress or senescence. Signals proportional to the chlorophyll content can be measured non-destructively with instruments detecting leaf transmittance (e.g., SPAD-502) or reflectance (e.g., showing normalized differential vegetation index, NDVI) in red and near infrared spectral regions. The measurements are based on the assumption that only chlorophylls absorb in the examined red regions. However, there is a question whether accumulation of other pigments (e.g., anthocyanins) could in some cases affect the chlorophyll meter readings. To answer this question, we cultivated tomato plants (Solanum lycopersicum L.) for a long time under low light conditions and then exposed them for several weeks (4 h a day) to high sunlight containing the UV-A spectral region. The senescent leaves of these plants evolved a high relative content of anthocyanins and visually revealed a distinct blue color. The SPAD and NDVI data were collected and the spectra of diffusive transmittance and reflectance of the leaves were measured using an integration sphere. The content of anthocyanins and chlorophylls was measured analytically. Our results show that SPAD and NDVI measurement can be significantly affected by the accumulated anthocyanins in the leaves with relatively high anthocyanin content. To describe theoretically this effect of anthocyanins, concepts of a specific absorbance and a leaf spectral polarity were developed. Corrective procedures of the chlorophyll meter readings for the anthocyanin contribution are suggested both for the transmittance and reflectance mode.

• MeSH
• Algorithms MeSH
• Anthocyanins analysis   metabolism   MeSH
• Models, Chemical MeSH
• Chlorophyll analysis   metabolism   MeSH
• Chloroplasts metabolism   MeSH
• Plant Leaves metabolism   MeSH
• Computer Simulation MeSH
• Solanum lycopersicum chemistry   metabolism   radiation effects   MeSH
• Light MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Anthocyanins MeSH
• Chlorophyll MeSH

Non-destructive assessment of chlorophyll content has recently been widely done by chlorophyll meters based on measurement of leaf transmittance (e.g. the SPAD-502 chlorophyll meter measures the leaf transmittance at 650 and 940 nm). However, the leaf transmittance depends not only on the content of chlorophylls but also on their distribution in leaves. The chlorophyll distribution within leaves is co-determined by chloroplast arrangement in cells that depends on light conditions. When tobacco leaves were exposed to a strong blue light (about 340 μmol of photons m⁻² s⁻¹), a very pronounced increase in the leaf transmittance was observed as chloroplasts migrated from face position (along cell walls perpendicular to the incident light) to side position (along cell walls parallel to the incoming light) and the SPAD reading decreased markedly. This effect was more pronounced in the leaves of young tobacco plants compared with old ones; the difference between SPAD values in face and side position reached even about 35%. It is shown how the chloroplast movement changes a relationship between the SPAD readings and real chlorophyll content. For an elimination of the chloroplast movement effect, it can be recommended to measure the SPAD values in leaves with a defined chloroplasts arrangement.

• MeSH
• Chlorophyll metabolism   MeSH
• Chloroplasts metabolism   MeSH
• Plant Leaves metabolism   MeSH
• Nicotiana metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chlorophyll MeSH

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.

• MeSH
• Chlorophyll chemistry   metabolism   MeSH
• Chloroplasts metabolism   radiation effects   ultrastructure   MeSH
• Fluorescence MeSH
• Photochemistry MeSH
• Photosynthesis physiology   MeSH
• Phototropism physiology   radiation effects   MeSH
• Stress, Physiological physiology   MeSH
• Plant Leaves cytology   metabolism   MeSH
• Cell Movement physiology   radiation effects   MeSH
• Photic Stimulation MeSH
• Light MeSH
• Nicotiana cytology   metabolism   radiation effects   MeSH
• Temperature MeSH
• Hot Temperature adverse effects   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Comparative Study MeSH
• Names of Substances
• Chlorophyll MeSH