Arbuscular mycorrhizal fungi enhance the copper tolerance of Tagetes patula through the sorption and barrier mechanisms of intraradical hyphae.

Arbuscular mycorrhizal fungi (AMF) are widespread soil fungi that can form endosymbiotic structures with the root systems of most plants and can improve the tolerance of host plants to heavy metals. In the present study, we investigated the effects of AMF (Glomus coronatum) inoculation on the tolerance of Tagetes patula L. to Cu. Almost all of the non-mycorrhizal plants exposed to 100 µM Cu died after 3 d, whereas phytotoxicity was only observed in mycorrhizal plants that were exposed to Cu concentrations greater than 100 µM. Analysing the dynamic accumulation of Cu indicated that, after 7 d of Cu exposure, less Cu was absorbed or accumulated by mycorrhizal plants than by control plants, and significantly less Cu was translocated to the shoots. Meanwhile, analysing the root morphology, the integrity of the root plasma membranes, the photosynthesis rate, and the content of essential elements of plants growing in cultures with 50 µM Cu revealed that AMF inoculation markedly alleviated the toxic effects of Cu stress on root system activity, photosynthesis rate, and mineral nutrient accumulation. In addition, to understand the Cu allocation, an energy spectrum analysis of Cu content at the transverse section of root tips was conducted and subsequently provided direct evidence that intraradical hyphae at the root endodermis could selectively immobilise large amounts of Cu. Indeed, the sorption and barrier mechanisms of AMF hyphae reduce Cu toxicity in the roots of T. patula and eventually enhance the plants' Cu tolerance.

Nitric oxide and hydrogen peroxide alleviate drought stress in marigold explants and promote its adventitious root development.

Drought stress is one of the most important environmental factors that regulates plant growth and development. In this study, we examined the effects of nitric oxide (NO) and hydrogen peroxide (H(2)O(2)) on adventitious rooting in marigold (Tagetes erecta L.) under drought stress. The results showed that the promoting effect of NO or H(2)O(2) on rooting under drought stress was dose-dependent, with a maximal biological response at 10 µM NO donor sodium nitroprusside (SNP) or 600 µM H(2)O(2). Results also indicated that endogenous NO and H(2)O(2) may play crucial roles in rooting under drought conditions, and H(2)O(2) may be involved in rooting promoted by NO under drought stress. NO or H(2)O(2) treatment attenuated the destruction of mesophyll cells ultrastructure by drought stress. Similarly, NO or H(2)O(2) increased leaf chlorophyll content, chlorophyll fluorescence parameters (Fv/Fm, ΦPS II and qP), and hypocotyls soluble carbohydrate and protein content, while decreasing starch content. Results suggest that the protection of mesophyll cells ultrastructure by NO or H(2)O(2) under drought conditions improves the photosynthetic performance of leaves and alleviates the negative effects of drought on carbohydrate and nitrogen accumulation in explants, thereby adventitious rooting being promoted.

Carotenogenic gene expression and ultrastructural changes during development in marigold.

Marigold (Tagetes erecta) flowers are a good source of carotenoids and can be used as a model studies on pigmentation during flower development. They show different levels of pigmentation caused by lutein. Here we describe the expression of several genes in the carotenoid biosynthetic pathway: phytoene synthase (Psy), phytoene desaturase (Pds), lycopene beta-cyclase (Lcy-b) and lycopene epsilon-cyclase (Lcy-e). cDNA inserts from isolated clones were 1376-1916bp long. The predicted amino acid sequences showed from 66 to 100% homology with other reported sequences (NCBI gene bank). Northern blot analyses of three varieties of marigold showed that most gene transcripts were expressed during flower development. The ultrastructural changes that occurred during plastid differentiation in flower morphogenesis were analyzed, and pigment accumulation among varieties was evaluated. The pigment deposition in specific structures (lipidic vesicles) during flower development was demonstrated.