Kaolin Application Modulates Grapevine Photochemistry and Defence Responses in Distinct Mediterranean-Type Climate Vineyards

At a local scale, kaolin particle-film technology is considered a short-term adaptation strategy to mitigate the adverse effects of global warming on viticulture. This study aims to evaluate kaolin application effects on photochemistry and related defence responses of Touriga Franca (TF) and Touriga Nacional (TN) grapevines planted at two Portuguese winegrowing regions (Douro and Alentejo) over two summer seasons (2017 and 2018). For this purpose, chlorophyll a fluorescence transient analysis, leaf temperature, foliar metabolites, and the expression of genes related to heat stress (VvHSP70) and stress tolerance (VvWRKY18) were analysed. Kaolin application had an inhibitory effect on VvHSP70 expression, reinforcing its protective role against heat stress. However, VvWRKY18 gene expression and foliar metabolites accumulation revealed lower gene expression in TN-treated leaves and higher in TF at Alentejo, while lipid peroxidation levels decreased in both treated varieties and regions. The positive kaolin effect on the performance index parameter (PIABS) increased at ripening, mainly in TN, suggesting that stress responses can differ among varieties, depending on the initial acclimation to kaolin treatment. Moreover, changes on chlorophyll fluorescence transient analysis were more pronounced at the Douro site in 2017, indicating higher stress severity and impacts at this site, which boosted kaolin efficiency in alleviating summer stress. Under applied contexts, kaolin application can be considered a promising practice to minimise summer stress impacts in grapevines grown in Mediterranean-like climate regions.

Effects of Bacterial Leaf Blight on Photosynthesis and Chlorophyll a Fluorescence in Susceptible and Resistant Rice Cultivars

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae is a serious disease affecting rice. Understanding of the effects of this disease on photosynthesis and chlorophyll (Chl) a fluorescence is important in rice management. We studied the effect of BLB on enzyme activities, photosynthetic rate (Pn) and Chl a fluorescence transient in susceptible Neiwuyou 8015 and resistant Shenzhou 98 rice cultivars. BLB had a negative effect on rice net photosynthesis (Pn) and stomatal conductance (Gs). Superoxide dismutase (SOD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL) activities, malondialdehyde (MDA) contents were increased while Chl content was decreased, indicating that rice photosynthetic functions were damaged by BLB. The effect of BLB on photosynthesis was greater in susceptible rice than in resistant rice. A significant difference of Chl a fluorescence transient curves was observed between BLB treatments and healthy ones. Parameters measured in transient rice Chl a fluorescence showed the photosynthetic reaction center was inactive after BLB. These findings will help in evaluating rice resistance and may be useful for rice disease management. © 2021 Friends Science Publishers

Chlorophyll a Fluorescence Transient and 2-Dimensional Electrophoresis Analyses Reveal Response Characteristics of Photosynthesis to Heat Stress in Malus. ‘Prairifire’

Flowering crabapples are a series of precious ornamental woody plants. However, their growth and development are inhibited in the subtropical regions due to the weak photosynthesis under high-temperature environment in the summer. Chlorophyll a fluorescence transient and 2-dimensional electrophoresis (2-DE) analyses were conducted to investigate the response characteristics of photosynthesis under simulated 38 °C heat stress in leaves of Malus. ‘Prairifire’, a spring-red leaf cultivar of flowering crabapple with strong thermal adaptability. In the present study, the net photosynthetic rate (Pn) was significantly decreased during the heat shock process, which showed a similar trend to the stomatal conductance (Gs), indicating a sensitive stomatal behavior to heat stress. Moreover, an efficient reaction center in photosystem II (PSII), and a functionally intact oxygen-evolving complex (OEC) conferred strong photosynthetic adaptability under heat stress. The higher level of transketolase (TK) under 48-h heat shock treatment was considered a protective mechanism of photosynthetic apparatus. However, heat stress inhibited the functions of light harvesting complex II (LHCII), electron transport in PSII, and the levels of key enzymes in the Calvin cycle, which were considered as the reasons causing an increase in the proportion of non-stomatal restrictions.

Morphophysiological responses of Billbergia zebrina Lindl. (Bromeliaceae) in function of types and concentrations of carbohydrates during conventional in vitro culture

When propagated in vitro, explants receive all the nutrients needed for their growth, including carbohydrates, from the culture medium. However, it is not well understood how the type and concentration of carbohydrates can affect the functioning of the photosynthetic apparatus (particularly photosystem II) of these plants. The aim was to assess the morphophysiological responses of Billbergia zebrina plants in function of sources and concentrations of carbohydrates during in vitro culture. Side shoots of plants previously established in vitro were individualized and transferred to a culture medium containing fructose, glucose or sucrose in four concentrations (0, 15, 30 or 45 g L−1). After growth for 55 days, the chlorophyll a fluorescence transient, leaf anatomy and growth were analyzed. The concentration and type of carbohydrate employed during in vitro culture did not decrease the photosynthetic apparatus performance. However, concentrations above 30 g L−1 led to anatomical modifications, revealing some degree of stress suffered by the plants. When grown in concentrations of 15 and 30 g L−1, irrespective of the carbohydrate used, the plants presented greater stomatal density. The supplementation of the culture medium with monosaccharides caused alterations in the development of the xylem vessels, such as increased number and diameter, allowing adjustment to the microenvironmental conditions. The in vitro conditions influenced the photosynthetic and anatomical responses of plants. The concentration interval from 15 to 30 g L−1 sucrose had a better effect by not causing large changes in the performance of the photosynthetic apparatus and anatomy of plants.

The impact of reporter kinetics on the interpretation of data gathered with fluorescent reporters

Fluorescent reporters of biological functions are used to monitor biochemical events and signals in cells and tissue. For neurobiology, these have been particularly useful for monitoring signals in the brains of behaving animals. In order to enhance signal-to-noise, fluorescent reporters typically have kinetics that are slower than that of the underlying biological process. This low-pass filtering by the reporter renders the fluorescence transient a leaking integrated version of the biological signal. Here I discuss the effects that low-pass filtering, or more precisely of integrating by convolving with an exponentially decaying kernel, has on the interpretation of the relationship between the reporter fluorescence transient and the events that underlie it. Unfortunately, when the biological events being monitored are impulse-like, such as the firing of an action potential or the release of neurotransmitter, filtering greatly reduces the maximum correlation coefficient that can be found between the events and the fluorescence signal. This can erroneously support the conclusion that the fluorescence transient and the biological signal that it reports are only weakly related. Furthermore, when examining the encoding of behavioral state variables by nervous system, filtering by the reporter kinetics will favor the interpretation that fluorescence transients encode integrals of measured variables as opposed to the variables themselves. For these reasons, it is necessary to take into account the filtering effects of the indicator by deconvolving with the convolution kernel and recovering the underlying biological events before making conclusions about what is encoded in the signals emitted by fluorescent reporters.