The functional role of the photosynthetic apparatus in the recovery of Brassica napus plants from pre-emergent metazachlor exposure

Using Glyphosate on Guarana Seedlings in the Amazon

The seed yield of guarana (Paullinia cupana H.B.K. var. sorbilis) is affected by weeds. Management is difficult for Amazon farmers and ranchers, owing to the hot and humid climate prevailing in the region, which makes mechanical control inefficient and leads farmers to the decision to use herbicides. Herbicide damage to this species is unknown. The objective of this study was to evaluate glyphosate damage to the development and quality of guarana seedlings. The treatments consisted of glyphosate doses at concentrations of 0, 126, 252, 540, 1080, 2160 and 3240 g a.e. ha^-1 and were evaluated for 60 days, in two applications. Analyses were performed for biometrics, seedling development, anthracnose and Injury characteristics. Glyphosate caused symptoms of Injury in all doses applied, but lower doses did not interfere with seedling growth and development. There was a correlation between anthracnose severity and increased glyphosate dose. When applied correctly, glyphosate can be an integrated weed management tool for use in guarana crops.

Chloroacetanilides inhibit photosynthesis and disrupt the thylakoid membranes of the dinoflagellate Prorocentrum minimum as revealed with metazachlor treatment

The chloroacetanilides are among the most commonly used herbicides worldwide, which contaminate aquatic environments and affect aquatic phototrophs. Their sub-lethal toxicity has been evaluated using freshwater algae; however, the modes of cellular toxicity and levels of toxicity to marine organisms are not fully understood. In the present study, we assessed the cellular and molecular effects of chloroacetanilides on marine phototrophs using the dinoflagellate Prorocentrum minimum and the herbicide metazachlor (MZC). The MZC treatment led to a considerable reduction in cell number and pigment, and the EC₅₀ of MZC was calculated to be 0.647 mg/L. The photosynthetic parameters, Fv/Fm and chlorophyll fluorescence significantly decreased with MZC exposure time in a dose-dependent manner. In addition, MZC significantly induced photosynthesis genes, including PmpsbA, PmpsaA, and PmatpB, and the antioxidant PmGST, but not PmKatG. These findings were well matched to reactive oxygen species (ROS) production in MZC-treated cells. Interestingly, we observed inflated vacuoles, undivided chloroplasts, and breakdown of thylakoid membranes in MZC-treated cells. These results support the hypothesis that MZC severely damages chloroplasts, resulting in dysfunction of the dinoflagellate photosynthesis and possibly marine phototrophs in the environment.

The Influence of Herbicide Underdosage on the Composition and Diversity of Weeds in Oilseed Rape (Brassica napus L. var. oleifera D.C.) Mediterranean Fields

Weed flora is considered harmful for crop growth and yield, but it is fundamental for preserving biodiversity in agroecosystems. Two three-year trials were conducted in Italy (two different sites) to assess the effect of six herbicide treatments on the weed flora structure of an oilseed rape crop. We applied metazachlor during the pre-emergence stage at 25%, 50%, 75%, and 100% of the labelled dose (M25, M50, M75, M100); trifluralin (during the first growing season); post-emergence treatment (PE); and a weedy control (W). Species richness, and diversity indices were used to characterize weed flora composition and to evaluate the effect of herbicide treatments on the considered variables. Results highlighted that the weed community is characterized by a higher diversity in underdosed than in M100 treated plots. Raphanus raphanistrum and Sinapis arvensis were the most common species in M75 and M100 treatments in both sites, while more weed species were detected in underdosed treatments and in weedy plots. The highest Shannon index values were observed in the underdosed treatments. In general, only a slightly similar trend was observed between sites, weed abundance and diversity being positively affected both by low-input herbicide management and by environmental factors (e.g., pedoclimatic situation and previous crop).

Histological, Physiological, and Comparative Proteomic Analyses Provide Insights into Leaf Rolling in Brassica napus

Moderate leaf rolling is important in ideotype breeding, as it improves photosynthetic efficiency and therefore increases crop yields. To understand the regulatory network of leaf rolling in Brassica napus, a down-curved leaf mutant ( Bndcl1) has been investigated. Physiological analyses indicated that the chlorophyll contents and antioxidant enzyme activities were remarkably increased and the photosynthetic performance was significantly improved in Bndcl1. Consistent with these findings, 943 differentially accumulated proteins (DAPs) were identified in the Bndcl1 mutant and its wild-type plants using iTRAQ-based comparative proteomic analyses. Enrichment analysis of proteins with higher abundance in Bndcl1 revealed that the functional category "photosynthesis" was significantly overrepresented. Moreover, proteins associated with oxidative stress response and photosystem II repairing were also up-accumulated in Bndcl1, which might help the mutant to sustain the photosynthetic efficiency under unfavorable conditions. Histological observation showed that the mutant displayed defects in adaxial-abaxial patterning. Important DAPs associated with leaf polarity establishment were detected in Bndcl1, including ribosomal proteins, proteins involved in post-transcriptional gene silencing, and proteins related to brassinosteroid. Together, our findings may help clarify the mechanisms underlying leaf rolling and its physiological effects on plants and may facilitate ideotype breeding in Brassica napus.