Salty freshwater macrophytes: the effects of salinization in freshwaters upon non-halophyte aquatic plants.

Salinization is a threat that affects aquatic ecosystems worldwide. As primary producers, freshwater macrophytes are of paramount importance in these ecosystems, however, information regarding the potential impacts of salinization upon these organisms is still scarce. In this review we provide a comprehensive and updated discussion of how freshwater macrophytes deal with salinity increase in freshwaters. We reviewed the salinity tolerance of widespread non-halophyte macrophytes through an overview of salinity tolerance mechanisms, their tolerance classification, and salinity effects at different levels of organization: from individuals to ecosystems. Thus, we demonstrated that widespread macrophytes that inhabit freshwaters display efficient salinity tolerance to salinity levels between 5 and 10 g L-1, and only a few species display tolerance to salinities higher than 10 g L-1. Widespread macrophytes demonstrated salinity tolerance of approximately 5 g L-1. Widespread macrophytes demonstrated salinity tolerance of approximately 5 g L-1. Emergent, floating and submerged species showed no significant difference in salinity tolerance. Salinity stress symptoms in freshwater macrophytes are somewhat similar to those of terrestrial plants and can show up even at slight salinity increases. Salinities higher than 1 g L-1 can negatively affect both physiology and diversity of non-halophyte macrophytes and cause long-term - and not well understood - changes in freshwater ecosystems. Salinization of freshwater ecosystems, among others threats, in combination with climate change, raise concerns about the future ecological status of freshwater ecosystems and the services they can provide.

Phytotoxic effects of plastic pollution in crops: what is the size of the problem?

Plastic pollution is one of the most impactful human interferences in our planet. Fragmentation of plastic leads to nano- and microplastics (NP/MP) formation, which accumulate in agricultural lands, representing an increasing risk for crop production and food safety. It has been shown that MP promote damage in plant tissues by several direct and indirect ways, and that NP can enter the tissues/cells and accumulate in edible organs. Investigation of the phytotoxic effects of NP/MP in plants started only in 2016, with most of the studies performed with crops. Since contradictory results are often observed, it is important to review the literature in order to identify robust effects and their possible mechanisms. In this review, we discuss the potential of NP/MP in damaging crop species, with focus on the physiological changes described in the literature. We also performed scientometrics analyses on research papers in this field during 2016-2021, to reveal the research situation of phytotoxic effects of plastic pollution in crops. Our review is as a starting point to help identify gaps and future directions in this important, emerging field.

Transcriptional plasticity buffers genetic variation in zinc homeostasis.

In roots of Arabidopsis thaliana, Zn can be either loaded into the xylem for translocation to the shoot or stored in vacuoles. Vacuolar storage is achieved through the action of the Zn/Cd transporter HMA3 (Heavy Metal Atpase 3). The Col-0 accession has an HMA3 loss-of-function allele resulting in high shoot Cd, when compared to accession CSHL-5 which has a functional allele and low shoot Cd. Interestingly, both Col-0 and CSHL-5 have similar shoot Zn concentrations. We hypothesize that plants sense changes in cytosolic Zn that are due to variation in HMA3 function, and respond by altering expression of genes related to Zn uptake, transport and compartmentalisation, in order to maintain Zn homeostasis. The expression level of genes known to be involved in Zn homeostasis were quantified in both wild-type Col-0 and Col-0::HMA3CSHL-5 plants transformed with the functional CSHL-5 allele of HMA3. We observed significant positive correlations between expression of HMA3 and of genes known to be involved in Zn homeostasis, including ZIP3, ZIP4, MTP1, and bZIP19. The results support our hypothesis that alteration in the level of function of HMA3 is counterbalanced by the fine regulation of the Zn homeostasis gene network in roots of A. thaliana.

Morpho-anatomical and growth alterations induced by arsenic in Cajanus cajan (L.) DC (Fabaceae).

Arsenic (As) is a toxic element to most organisms. Studies investigating anatomic alterations due to As exposure in plants are scarce but of utmost importance to the establishment of environmental biomonitoring techniques. So, this study aimed to investigate the effects of As on the development and initial root growth in Cajanus cajan (Fabaceae), characterize and quantify the possible damages, evaluate genotoxic effects, and identify structural markers to be used in environmental bioindication. Plants were exposed hydroponically to 0.5, 1.0, 1.5, and 2.0 mg As L(-1), as sodium arsenate. Growth parameters were measured, and in the end of the exposure, root samples were analyzed for qualitative and quantitative anatomical alterations. Arsenic genotoxicity was evaluated through analysis of the mitotic index in the root apex. Compared to the control, As-treated seedlings showed an altered architecture, with significantly decreased root length (due to the lower mitotic index in the apical meristem and reduced elongation of parenchyma cells) with darkened color, and abnormal development of the root cap. A significant increase in vascular cylinder/root diameter ratio was also detected, due to the reduction of the cellular spaces in the cortex. The secondary xylem vessel elements were reduced in diameter and had sinuous walls. The severest damage was visible in the ramification zone, where uncommon division planes of phellogen and cambium cells and disintegration of the parenchyma cells adjacent to lateral roots were observed. The high sensibility of C. cajan to As was confirmed, since it caused severe damages in root growth and anatomy. The main structural markers for As toxicity were the altered root architecture, with the reduction of the elongation zone and increase of ramification zone length, and the root primordia retained within the cortex. Our results show a new approach about As toxicity and indicate that C. cajan is a promising species to be used for bioindication of environmental contamination by As.