Photosynthetica最新文献

In heating experiments with leaves, the temperature at which dark-level F₀ chlorophyll a fluorescence begins to rise, T_crit, is widely used as an indicator of photosystem II thermotolerance. However, little is known about how T_crit correlates with irreversible leaf tissue damage. Young and mature leaves of the tropical tree species Calophyllum inophyllum were heated stepwise from 30 to 55°C, at 1°C min^-1. T_crit was 47°C in young leaves and 49°C in mature leaves. Contrary to the higher T_crit in mature leaves, heating to 55°C elicited greater tissue damage in mature than in young leaves. Young and mature leaves heated to their respective T_crit or T_crit + 2°C exhibited no or little tissue necrosis after 14 d of post-culture. It is concluded that measurements of the temperature-dependent F₀ fluorescence rise underestimate the thermal thresholds above which significant irreversible leaf damage occurs.

Potato tuber greening occurs due to the chlorophyll accumulation upon exposure to light, however, fundamental information on tuber chlorophyll metabolism is lacking. We measured the effect of varying light exposure (0, 48, 96, and 168 h) on chlorophyll concentration and gene expression of enzymes in the chlorophyll metabolic pathway in the potato varieties that differ in greening propensity. Greening was associated with the upregulation of genes involved in chlorophyll biosynthesis, particularly glutamyl-tRNA reductase 1, magnesium-chelatase subunit H, and magnesium-protoporphyrin IX monomethyl ester cyclase, and downregulation of genes involved in chlorophyll cycling and degradation, including chlorophyllide a oxygenase, and pheophorbide a oxygenase. Our findings suggest that relative resistance to tuber greening propensity may be due to a weaker upregulation of chlorophyll biosynthesis genes and weaker downregulation of chlorophyll degradation genes that occurs in susceptible varieties. The association of these biosynthesis and degradation genes with greening susceptibility may provide possible breeding targets for the future development of more greening-resistant varieties.

In 1931, Hans Kautsky discovered not only chlorophyll (Chl) fluorescence induction ("Kautsky effect") in green leaves but also metastable excited oxygen, now known as singlet oxygen, which he showed to act as an intermediate in dye-sensitized photooxidations of organic substances in vitro ("Kautsky mechanism"). While at that time practically nothing was known about the primary reactions of photosynthesis, Kautsky firmly believed that "his" mechanism is also effective in the "Chl-sensitized" conversion of light energy into chemically fixed energy. This erroneous assumption complicated the interpretation of rapid Chl fluorescence induction kinetics, particularly those measured by his student Ulrich Franck in his 1941 dissertation, part of which indicated the existence of two excitonically separated light reactions. This historical note deals with the essence of Kautsky's two discoveries, the scientific environment under which they took place, and the question of why mainstream photosynthesis researchers have largely ignored the ensuing detailed experimental work of Ulrich Franck. The first commented English version of Kautsky and Hirsch (1931) is presented in the Appendix.

I present here the story of my personal and scientific life. I provide information on my parents, my childhood, schooling, education at the Wageningen Agricultural University, and the work for my PhD degree on the action of some herbicides on photosynthesis under the guidance of Professor Evert Christiaan Wassink. After graduation, I obtained a position as a professor. In 1977, I spent a one-year sabbatical with Professor Govindjee at the University of Illinois at Urbana-Champaign, USA. This was the start of a long-time and successful cooperation on the effects of bicarbonate on Photosystem II. The research on the impact of herbicides on photosynthesis was extended in cooperation with Professor Ko Wakabayashi and his co-workers at the Tamagawa University at Machida-shi, Tokyo, Japan. Another topic of my research was the photoinhibition of PSII by too much light; for this, I worked with Professor Christa Critchley at the University of Queensland in Brisbane, Australia. At the end, I list my service in several professional committees.

The following scientific autobiography is presented here as a homage to Professor Kazuo Shibata, who is the one who led me to do research in photosynthesis. He had invited me to Riken (The Institute of Physical and Chemical Research), and had launched the Japan-US Collaboration Project on "The Solar Energy Conversion by Means of Photosynthesis" and had invited many international scientists to Riken. My research, under Shibata, started on using a sensitive method for the determination of chlorophyll b, and of SDS-PAGE for the pigment protein complexes of the two photosystems. After Shibata had passed away at the age of 66, I found post-illumination CO₂ burst from cyanobacterial cell suspensions. This finding led me to study the CO₂-concentrating mechanism (CCM) and the function and structure of NADP(H) dehydrogenase complexes (NDH-I) in cyanobacteria, which were developed after I had moved to Nagoya University, and in several other laboratories in the world after I had retired from Nagoya University.

The effects of deficiency of cryptochrome 1 (CRY1), phytochrome B2 (phyB2) and the photoreceptor signalling DET-1 protein (hp-2 mutant) on photosynthesis and pro-/antioxidant balance in Solanum lycopersicum exposed to high-intensity blue light [HIBL, 72 h, 500/1,000 μmol(photon) m^-2 s^-1] were studied. Noticeable photoinhibition of photosynthesis and PSII was found in all these variants. However, the greatest decrease in photosynthesis and PSII activity was observed in the cry1 mutant. The difference among the other options was less pronounced. This low resistance of the cry1 mutant to HIBL is associated with reduced photosynthetic pigments, phenols, and anthocyanins. It appears that under HIBL, CRY1 and, to a lesser extent, phyB2 are required to maintain photosynthesis and antioxidant defence, mitigating blue light-induced oxidative stress. This study expands our understanding of the defence functions of CRY1 and highlights its importance in adapting the photosynthetic apparatus to HIBL.

High temperatures severely affect plant growth and development leading to major yield losses. These temperatures are expected to increase further due to global warming, with longer and more frequent heat waves. Rhamnolipids (RLs) are known to protect several plants against various pathogens. To date, how RLs act under abiotic stresses is unexplored. In this study, we aimed to investigate whether RLs could modify Arabidopsis thaliana physiology during prolonged heat stress. Measurement of leaf gas exchange and chlorophyll fluorescence showed that heat stress reduces photosynthetic rate through stomatal limitation and reduction of photosystem II yield. Our study reported decreased chlorophyll content and accumulation of soluble sugars and proline in response to heat stress. RLs were shown to have no detrimental effect on photosynthesis and carbohydrate metabolism in all conditions. These results extend the knowledge of plant responses to prolonged heat stress.

Application of hyperspectral reflectance technology to track changes in photosynthetic activity in Atractylodes chinensis (A. chinensis) remains underexplored. This study aimed to investigate the relationship between hyperspectral reflectance and photosynthetic activity in the leaves of A. chinensis in response to a decrease in soil water content. Results demonstrated that the reflectance in both the visible light and near-infrared bands increased in conjunction with reduced soil water content. The derived vegetable indices of photochemical reflection index (PRI) and the pigment-specific simple ratio of chlorophyll b (PSSR_b) gradually decreased. In contrast, the normalized difference in water index (NWI) and water index (WI) increased. Moreover, significant correlations were observed between PRI, PSSR_b, WI, and NWI and photosynthetic activity indices, namely photosynthetic rate and total performance index. Consequently, hyperspectral reflection represents a productive approach for evaluating the influence of water deficit on photosynthetic activity in A. chinensis leaves.

This study aimed to explore the mechanism by which Zn retards Fe toxicity by analyzing the morphological, photosynthetic, and chloroplast physiological parameters of wheat seedlings treated with either single or combined Zn and Fe. Different behavior of the seedlings was observed under untreated and treated conditions. The most discriminating quantitative traits were associated with leaf area, biomass dry mass and fresh mass, net photosynthetic rate, intercellular CO₂ concentration, stomatal conductance, transpiration rate of seedlings, Hill reaction, Mg²⁺-ATPase and Ca²⁺-ATPase activities, malondialdehyde and O₂ ^·- contents, and glutathione reductase, ascorbate peroxidase, peroxidase, and superoxide dismutase activities and their gene expression in the seedling chloroplast. The obtained findings suggest the important function of an appropriate Zn concentration in preventing Fe toxicity. Therefore, a thorough evaluation of the effects of Zn on Fe-stressed plant growth is beneficial for sustainable agriculture.