Quantification of stress adaptation by laser-induced fluorescence spectroscopy of plants exposed to engine exhaust emission and drought

Transcriptome-based identification and validation of reference genes for corm growth stages, different tissues, and drought stress in Taro (Colocasia esculenta)

Taro is a widely utilized starch resource plant. It is essential to quantify the expression levels of functional genes associated with taro growth using real-time quantitative polymerase chain reaction (RT-qPCR). However, to obtain reliable RT-qPCR results, appropriate reference genes (RGs) are required for data normalization. In this study, we screened seven novel candidate RGs using transcriptome datasets from taro, encompassing data from growth corms and various tissues. The expression stability of these seven new RGs, along with the commonly used RGs Actin, EF1-α, and β-tubulin, was assessed using Delta Ct, BestKeeper, geNorm, and NormFinder algorithms. Furthermore, we conducted a comprehensive analysis using the RefFinder program and validated the results using the target gene, CeAGPL1. The findings revealed that ACY-1 and PIA2 were the optimal multiple RGs for normalization during corm growth, while COX10 and Armc8 were suitable for samples including various types of tissues. Furthermore, we found three RGs, Armc8, COX10 and CCX4L, were the optimal RGs for drought stress. This study assessed the suitability of RGs in taro for the first time. The identified RGs provide valuable resources for studying corm growth, diverse tissues, and drought stress. This study contributes to the advancement of our understanding of the underlying mechanisms that govern the growth of taro.

Effects of periodic drought with severe exhaust exposure on particle retention capacity and physiological responses of Photinia × fraseri Dress

Urban plants are regarded as an effective agent to control particulate matter (PM) pollution by absorbing PM. Repeated PM and drought stress in urban areas often cause morphological and physiological damage to plants, resulting in lower ecological benefits. Nevertheless, knowledge in PM retention capability, morphology and physiology of plants under repeated stress and cross stress has been barely available. In order to investigate changes in these aspects under repeated stress, we applied periodic drought with severe exhaust exposure on Photinia × fraseri Dress (a common urban tree species with strong PM retention ability). The study was carried out in a six-period scenario, with a duration of 10 days for each period: initial value (R0), initial stress period (S1), initial recovery period (R1) second stress period (S2), second recovery period (R2) and final stress period (S3). The results are as follows: In terms of periodic factor, PM retention of tail gas stress group (P) and cross stress group (PD) in S2 decreased by 10.00 μg/cm² and 12.60 μg/cm² respectively compared with those during S1 (p > 0.05). During S3, the total amount of PM on leaf surface in both P and PD demonstrated a significant decrease (p < 0.05). The retention capacity of P. fraseri may be dramatically limited under multi-period stress. In this experiment, we attribute the decrease of PM retention to the morphological changes (shedding of mature leaves, smaller leaf area and thinner wax layer) and physiological responses (an increase in gas exchange) under multi-period stress. In terms of cross-stress factor, the total retained PM on leaf surface in PD was higher than that in P, especially during S3, and the interaction between drought and PM reached a significant level (p < 0.01, η² = 0.808), which indicated that drought reduced the loss of dust under PM stress. Changes in morphology and gas exchange indicated that the mechanisms for the high dust retention rate on the leaf surface of PD group varied in the three stress periods. In addition, except the chlorophyll relative value, the alleviated accumulation of MDA and intense production of soluble sugar with PD showed favorable responses to disturbance compared with those in P under the repeated stress. Therefore, we infer that, under multi-period stress of drought and tail gas, P. fraseri may better maintain PM retention ability and resistance than under single stress.

Dynamics of particle retention and physiology in Euonymus japonicus Thunb. var. aurea-marginatus Hort. with severe exhaust exposure under continuous drought

Frequent drought events and particulate matter pollution from vehicular exhaust seriously affect urban plant growth and provisioning of ecological services. Yet, how plants respond physiologically and morphologically to these two combined stressors remains unknown. Here, we assessed particle retention dynamics and plant morphology and physiology of Euonymus japonicus Thunb. var. aurea-marginatus Hort. under continuous drought with severe exhaust exposure. Our results showed that continuous drought insignificantly lowered particle retention in each of three size fractions by 1.02 μg·cm^-2 on average in the first 28 days, but significantly lowered total particle retention by 35.75 μg·cm^-2 on the 35th day. We observed evident changes in morphology, leaf mass per area (LMA), pigments, gas exchange in all stressed plants. Compared with single stress, combined drought and pollution caused earlier yellowing and shedding of old leaves, significantly lowered LMA by 1.21 mg·cm^-2, caused a greater decline in pigments and net photosynthetic rate (P_n). Large particles may mainly explain pigment reduction, lower weekly LMA increases, and stomatal restriction, while coarse particles may be the main drivers of the decline in P_n. Continuous drought mediated the influence of all three particle sizes on some parameters, such as weakening the impact of total particles on LMA, strengthening the impact of fine particles on photosynthesis. Our findings suggest that drought accelerates the physiological responses of plants to exhaust pollution. Under controlled severe exhaust pollution conditions, the optimal time to maintain high particle retention during continuous drought without decline in physiological conditions for E. japonicus var. aurea-marginatus was 14 days. Some additional interventions after 14 days (it could be postponed appropriately under field conditions) may help ensure healthy growth of plants and retention of particulate matter.

Drought-induced modifications of photosynthetic electron transport in intact leaves: analysis and use of neural networks as a tool for a rapid non-invasive estimation

Water deficit is one of the most important environmental factors limiting sustainable crop yields and it requires a reliable tool for fast and precise quantification. In this work we use simultaneously recorded signals of photoinduced prompt fluorescence (PF) and delayed fluorescence (DF) as well as modulated reflection (MR) of light at 820nm for analysis of the changes in the photosynthetic activity in detached bean leaves during drying. Depending on the severity of the water deficit we identify different changes in the primary photosynthetic processes. When the relative water content (RWC) is decreased to 60% there is a parallel decrease in the ratio between the rate of excitation trapping in the Photosystem (PS) II reaction center and the rate of reoxidation of reduced PSII acceptors. A further decrease of RWC to 20% suppresses the electron transfer from the reduced plastoquinone pool to the PSI reaction center. At RWC below values 15%, the reoxidation of the photoreduced primary quinone acceptor of PSII, Q(A)(-), is inhibited and at less than 5%, the primary photochemical reactions in PSI and II are inactivated. Using the collected sets of PF, DF and MR signals, we construct and train an artificial neural network, capable of recognizing the RWC in a series of "unknown" samples with a correlation between calculated and gravimetrically determined RWC values of about R(2)≈0.98. Our results demonstrate that this is a reliable method for determination of RWC in detached leaves and after further development it could be used for quantifying of drought stress of crop plants in situ. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Development, photosynthetic activity and habitat selection of the clonal plant Fragaria vesca growing in copper-polluted soil

The ability of clonal systems to spread by ramet production may expose the clone to spatial heterogeneity. This study explored the physiological and morphological responses in the clonal plant Fragaria vesca L. growing in homogeneous (Cu-contaminated or uncontaminated) or in heterogeneous environments with patches of contrasting quality (Cu-contaminated or uncontaminated). We also investigated the potential of this species to selectively establish ramets within a heterogeneous environment. In heterogeneous environments, plants expanded ramets randomly, but selectively established ramets in the favourable patches. We discuss whether the selective establishment of ramets is a consequence of direct suppression of plant growth due to copper toxicity. The assimilate demand from offspring ramets in unfavourable environments increased the chlorophyll content and photosynthetic efficiency of parents by a feedback regulation process. Integration ameliorated the effects of copper on the photochemical efficiency of the offspring ramets. We did not observe integration costs, in terms of total biomass, for parents supporting ramets in Cu-contaminated environments, although we did detect costs in terms of ramet production. Parents with offspring ramets in Cu-contaminated environments produced 25 times more reproductive biomass than parents with offspring ramets in uncontaminated environments. We interpret this as a strategy for escaping from stressful environments. In this study, we extend the concept of physiological integration in clonal plants to include photochemical responses.