Rice calli may decelerate its metabolism to adapt hormone free medium

Plant Cell, Tissue and Organ Culture (PCTOC) - This report focuses on the crucial role of lipids and starch metabolism in the growth and ultrastructure of the cell wall (CW) in rice calli....     

Natural variation in the fast phase of chlorophyll a fluorescence induction curve (OJIP) in a global rice minicore panel

Photosynthesis Research - Photosynthesis can be probed through Chlorophyll a fluorescence induction (FI), which provides detailed insight into the electron transfer process in Photosystem II, and...     

Binding of biogenic and synthetic polyamines to β-lactoglobulin

The bindings of biogenic polyamines spermine (spm), spermidine (spmd) and synthetic polyamines 3,7,11,15-tetrazaheptadecane·4HCl (BE-333) and 3,7,11,15,19-pentazahenicosane·5HCl (BE-3333) with β-lactoglobulin (β-LG) were determined in aqueous solution. FTIR, UV-vis, CD and fluorescence spectroscopic methods as well as molecular modeling were used to determine the polyamine binding sites and the effect of polyamine complexation on protein stability and secondary structure. Structural analysis showed that polyamines bind β-LG via both hydrophilic and hydrophobic contacts. Stronger polyamine-protein complexes formed with synthetic polyamines than biogenic polyamines, with overall binding constants of K_spm-β-LG = 3.2(±0.6) × 10⁴ M⁻¹, K_spmd-β-LG = 1.8(±0.5) × 10⁴ M⁻¹, K_BE-333-β-LG = 5.8(±0.3) × 10⁴ M⁻¹ and K_{BE-3333-β-LG} = 6.2(±0.05) × 10⁴ M⁻¹. Molecular modeling showed the participation of several amino acids in the polyamine complexes with the following order of polyamine-protein binding affinity: BE-3333 > BE-333 > spermine > spermidine, which correlates with their positively charged amino group content. Alteration of protein conformation was observed with a reduction of β-sheet from 57% (free protein) to 55-51%, and a major increase of turn structure from 13% (free protein) to ∼21% in the polyamine-β-LG complexes, indicating a partial protein unfolding.     

Functional aspects of the photosynthetic light reactions in heat stressed Arabidopsis deficient in digalactosyl-diacylglycerol

Plants are often submitted, in their natural environment, to various abiotic stresses such as heat stress. However, elevated temperature has a detrimental impact on overall plant growth and development. We have examined the physiological response of the dgd1-2 and dgd1-3 Arabidopsis mutants lacking 30-40% of digalactosyl-diacylglycerol (DGDG) exposed to heat constraint. These mutants, which grow similarly to wild type under normal conditions, were previously reported to be defective in basal thermotolerance as measured by cotyledon development. However their functional properties were not described. Chlorophyll fluorescence measurements and absorbance changes at 820 nm were used to monitor photosystem II (PSII) and PSI activity, respectively. It was observed that both mutants have similar photosystem activities with some differences. The mutants were less able to use near saturation light energy and elicited higher rates of cyclic PSI electron flow compare to wild type. Arabidopsis leaves exposed to short-term (5 min) mild (40 °C) or strong (44 °C) heat treatment have shown a decline in the operating effective quantum yield of PSII and in the proportion of active PSI reaction centers. However, cyclic PSI electron flow was enhanced. The establishment of the energy-dependent non-photochemical quenching of chlorophyll fluorescence was accelerated but its decline under illumination was inhibited. Furthermore, heat stress affected the process implicated in the redistribution of light excitation energy between the photosystems known as the light state transitions. All the effects of heat stress mentioned above were more intense in the mutant leaves with dgd1-3 being even more susceptible. The decreased DGDG content of the thylakoid membranes together with other lipid changes are proposed to influence the thermo-sensitivity of the light reactions of photosynthesis towards heat stress.     

How does iron deficiency disrupt the electron flow in photosystem I of lettuce leaves?

The changes observed photosystem I activity of lettuce plants exposed to iron deficiency were investigated. Photooxidation/reduction kinetics of P700 monitored as ΔA₈₂₀ in the presence and absence of electron transport inhibitors and acceptors demonstrated that deprivation in iron decreased the population of active photo-oxidizable P700. In the complete absence of iron, the addition of plant inhibitors (DCMU and MV) could not recover the full PSI activity owing to the abolition of a part of P700 centers. In leaves with total iron deprivation (0 μM Fe), only 15% of photo-oxidizable P700 remained. In addition, iron deficiency appeared to affect the pool size of NADP⁺ as shown by the decline in the magnitude of the first phase of the photooxidation kinetics of P700 by FR-light. Concomitantly, chlorophyll content gradually declined with the iron concentration added to culture medium. In addition, pronounced changes were found in chlorophyll fluorescence spectra. Also, the global fluorescence intensity was affected. The above changes led to an increased rate of cyclic electron transport around PSI mainly supported by stromal reductants.     

Effect of moderate and high light on photosystem II function in Arabidopsis thaliana depleted in digalactosyl-diacylglycerol

The response of the heat-sensitive dgd1-2 and dgd1-3 Arabidopsis mutants depleted in the galactolipid DGDG to photoinhibition of chloroplasts photosystem II was studied to verify if there is a relationship between heat stress vulnerability due to depletion in DGDG and the susceptibility to photoinhibitory damage. Non-photochemical quenching (NPQ) is known to dissipate excessive absorbed light energy as heat to protect plants against photodamage. The main component of NPQ is dependent of the transthylakoid pH gradient and is modulated by zeaxanthin (Zx) synthesis. These processes together with chlorophyll fluorescence induction were used to characterize the response of the genotypes. The mutants were more sensitive to photoinhibition to a small extent but this was more severe for dgd1-3 especially at high light intensity. It was deduced that DGDG was not a main factor to influence photoinhibition but other lipid components could affect PSII sensitivity towards photoinhibition in relation to the physical properties of the thylakoid membrane. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.